|
So it's about the time of year where I'm allowed to buy one piece of test gear and I'm thinking I want a bench meter with higher resolution. The best I've got so far is the Tek 2465BDM which has a 20,000 count 0.03% accuracy DMM. It's however a little out of cal and I just don't want to spend the cash to get it back in perfect spec. It's also a bit crazy to have a scope running just to use the DMM. This brings me to the 3478A. While I could technically afford to buy a new 120,000 count DMM I just can't justify the cost for the hobby type work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy on say ebay?
The problem I have with the meter on my Tek is that you have to run the entire cal for each measurement type, If you start with DC you have to go all the way up the range from millivolts up to several hundred volts. As we all know it's easy to get a precision calibrated low voltage references such as a DMM check board, it's another thing to get 500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be calibrated or have a calibration transfer standard meter that's above the specs of the 3478A? In other words if all you have is just a few standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision resistors and an op-amp to generate other reference voltages with any degree of accuracy? Also has anyone found a good source of say 500 volts 60 Hz AC? The right audio amp and a sig gen can get you some of the other odd cal standards. High voltage DC is just so much easier to obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The 54111D is still running great. My thanks again for everyone who helped me fix the ROM's.
Jeff
|
Jeff,
I have a 3478A and I have calibrated it by hand but it has been a while. I
*think* it is possible to just calibrate one range at a time but I'd have to
look at the manual. When I did the calibration, I was trying to 'harvest'
the CAL data and lost it so I had to do a complete calibration.
For my day to day bench work, I use a Fluke 8050A. They are usually
available very cheap and are quite reliable. I have never calibrated one
though, even though the process is described in the manual.
If you get the 3478A, I would send it out for calibration and make it your
'house transfer standard'. IIRC, though, it's maximum range is 300 Volts so
might not be a great meter for 'general purpose' trouble shooting but good
around most old HP equipment.
For most AC work, the usual frequency used for calibration is 1 KHz, not 60
Hz. You might want to take a look at a Fluke 5100B. Very interesting piece
of cal gear. Volts, current, AC and DC, and resistance. Big and heavy
though.
Good luck and Merry Christmas.
Joe
toggle quoted message
Show quoted text
-----Original Message-----
From: hp_agilent_equipment@...
[mailto:hp_agilent_equipment@...] On Behalf Of Jeff Machesky
Sent: Tuesday, December 18, 2012 8:25 AM
To: hp_agilent_equipment@...
Subject: [hp_agilent_equipment] HP 3478A general questions
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
|
My experience is that an HP 3478A won't need to be calibrated unless
the battery dies.
As has been mentioned many times, the weak spots are the LCD display
and the 300V input limit.
|
Joe:?
?
What are your thoughts on the HP 745A for AC calibrations.? It has a 1K and a 10K range.
?
I have two of them, ...one working, one needs the optical thermistor in the clipper circuit.
?
Thanks, ...-Don
?
?
?
===============================
?
?
?
?
?
?
?
From: J. L. Joe:Trantham <jltran@...>
To: hp_agilent_equipment@...
Sent: Tuesday, December 18, 2012 9:30 AM
Subject: RE: [hp_agilent_equipment] HP 3478A general questions
?
Jeff,
I have a 3478A and I have calibrated it by hand but it has been a while. I
*think* it is possible to just calibrate one range at a time but I'd have to
look at the manual. When I did the calibration, I was trying to 'harvest'
the CAL data and lost it so I had to do a complete calibration.
For my day to day bench work, I use a Fluke 8050A. They are usually
available very cheap and are quite reliable. I have never calibrated one
though, even though the process is described in the manual.
If you get the 3478A, I would send it out for calibration and make it your
'house transfer standard'. IIRC, though, it's maximum range is 300 Volts so
might not be a great meter for 'general purpose' trouble shooting but good
around most old HP equipment.
For most AC work, the usual frequency used for calibration is 1 KHz, not 60
Hz. You might want to take a look at a Fluke 5100B. Very interesting piece
of cal gear. Volts, current, AC and DC, and resistance. Big and heavy
though.
Good luck and Merry Christmas.
Joe
-----Original Message-----
From: mailto:hp_agilent_equipment%40yahoogroups.com
[mailto:mailto:hp_agilent_equipment%40yahoogroups.com] On Behalf Of Jeff Machesky
Sent: Tuesday, December 18, 2012 8:25 AM
To: mailto:hp_agilent_equipment%40yahoogroups.com
Subject: [hp_agilent_equipment] HP 3478A general questions
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]
|
The 3478A is a nice meter, but bear in mind that it is 300V max.
It is accurate, stable, and works smoothly. It is easily controlled
over HPIB.
In its deficiency corner, is the 300V max,and a non back lit LCD that
tends to get lost in the shadows.
I have never needed to calibrate mine, but I am pretty sure that you
need to complete the calibration of all steps before you leave a
particular function, say DCV, or ACV, or Ohms....
The calibration procedure takes a measurement of a known standard
on a particular range, and creates an offset that it used when it
calculates the voltage to display. The 30mv standard only calibrates
the offset for the 30mv range. The 3V standard, the 3V range...
You shouldn't have to pay more than about $100 for a working calibrated
3478A. Tucker has them for sale periodically.
9 times out of 10, a voltage measured by a scope's trace is good enough.
Did I mention that the 3478A only measures up to 300V?
-Chuck Harris
Jeff Machesky wrote:
toggle quoted message
Show quoted text
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
------------------------------------
Yahoo! Groups Links
|
Thanks Chuck, sounds like the cal routine is the same as the Tek 2465BDM DMM function which technically is high enough resolution for 99.9% of my needs. I guess I'm just a bit of a stickler for that absolute precision. I have an If I could afford an 8 1/2 digit meter I would get one kind of mentality. Their of course is a practical side that says don't waste a ton of money for an extra digit or two. The 3478A appears to be a good choice.
What's sending one of these off to get NIST traceable calibrated normally run ?
If I were to buy new I was looking at the U3402A. Buying new gives me that nice cal sheet that satisfies my need for accuracy. Whole lot of difference in price however.
Thanks,
Jeff
toggle quoted message
Show quoted text
On 12/18/2012 8:54 AM, Chuck Harris wrote:
The 3478A is a nice meter, but bear in mind that it is 300V max.
It is accurate, stable, and works smoothly. It is easily controlled
over HPIB.
In its deficiency corner, is the 300V max,and a non back lit LCD that
tends to get lost in the shadows.
I have never needed to calibrate mine, but I am pretty sure that you
need to complete the calibration of all steps before you leave a
particular function, say DCV, or ACV, or Ohms....
The calibration procedure takes a measurement of a known standard
on a particular range, and creates an offset that it used when it
calculates the voltage to display. The 30mv standard only calibrates
the offset for the 30mv range. The 3V standard, the 3V range...
You shouldn't have to pay more than about $100 for a working calibrated
3478A. Tucker has them for sale periodically.
9 times out of 10, a voltage measured by a scope's trace is good enough.
Did I mention that the 3478A only measures up to 300V?
-Chuck Harris
Jeff Machesky wrote:
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
------------------------------------
Yahoo! Groups Links
|
Hi:
Be careful to read the specs for the ranges you are interested in.
AFAICR the display is showing a digit or two more than the accuracy.
Have Fun,
Brooke Clarke
hp_agilent_equipment@... wrote:
toggle quoted message
Show quoted text
HP 3478A general questions
|
Thanks Brooke, that part I'm aware of. I actually made up a spreadsheet that I can plug in rated accuracies and quickly see how many digits I can trust a meter to have absolute accuracy at a given value. It's shown me that you really have to get a meter with incredible accuracy to get in to those lower digits. Sometimes however it's just nice to see the delta of the value vs the absolute value.
A project on my plate at the moment is a 5.5 amp 0-18 volt linear supply. It drifted from 5.000 volts to 5.001 volts over night. It would have been nice to see a few extra digits to see how it was relating to temperature changes in a more real time fashion.
Thanks,
Jeff
toggle quoted message
Show quoted text
On 12/18/2012 10:23 AM, Brooke Clarke wrote:
Hi:
Be careful to read the specs for the ranges you are interested in.
AFAICR the display is showing a digit or two more than the accuracy.
Have Fun,
Brooke Clarke
hp_agilent_equipment@... <mailto:hp_agilent_equipment%40yahoogroups.com> wrote:
HP 3478A general questions
|
Hi Jeff,
I don't know what calibration would cost, but I would think around
$140 would be enough for a 3478A... it is so easy to do.
One of the world's best bargains in a highly stable, and accurate
bench dmm is the HP3456A. It is 6-1/2 digits, and qualifies as a
transfer standard for DC. It is AC, DC and Ohms, and has a max
voltage of 1KV. Typically they can be found for $100 on the bay,
though most of mine have been given to me. Get the newer model that
has no fan, but has a visible to3 pack transistor on the back panel.
-Chuck Harris
Jeff Machesky wrote:
toggle quoted message
Show quoted text
Thanks Chuck, sounds like the cal routine is the same as the Tek
2465BDM DMM function which technically is high enough resolution for
99.9% of my needs. I guess I'm just a bit of a stickler for that
absolute precision. I have an If I could afford an 8 1/2 digit meter I
would get one kind of mentality. Their of course is a practical side
that says don't waste a ton of money for an extra digit or two. The
3478A appears to be a good choice.
What's sending one of these off to get NIST traceable calibrated
normally run ?
If I were to buy new I was looking at the U3402A. Buying new gives me
that nice cal sheet that satisfies my need for accuracy. Whole lot of
difference in price however.
Thanks,
Jeff
On 12/18/2012 8:54 AM, Chuck Harris wrote:
The 3478A is a nice meter, but bear in mind that it is 300V max.
It is accurate, stable, and works smoothly. It is easily controlled
over HPIB.
In its deficiency corner, is the 300V max,and a non back lit LCD that
tends to get lost in the shadows.
I have never needed to calibrate mine, but I am pretty sure that you
need to complete the calibration of all steps before you leave a
particular function, say DCV, or ACV, or Ohms....
The calibration procedure takes a measurement of a known standard
on a particular range, and creates an offset that it used when it
calculates the voltage to display. The 30mv standard only calibrates
the offset for the 30mv range. The 3V standard, the 3V range...
You shouldn't have to pay more than about $100 for a working calibrated
3478A. Tucker has them for sale periodically.
9 times out of 10, a voltage measured by a scope's trace is good enough.
Did I mention that the 3478A only measures up to 300V?
-Chuck Harris
Jeff Machesky wrote:
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
------------------------------------
Yahoo! Groups Links
------------------------------------
Yahoo! Groups Links
|
Thanks Chuck, I was looking at those a few days ago. Good to hear they are worth obtaining. I don't at all need the accuracy, but it would be nice to have. I tend to take on projects of a widely varying nature. From DC-DC supplies to ORP sensors. The resolution would be nice if nothing else.
Thanks,
Jeff
toggle quoted message
Show quoted text
On 12/18/2012 10:52 AM, Chuck Harris wrote:
Hi Jeff,
I don't know what calibration would cost, but I would think around
$140 would be enough for a 3478A... it is so easy to do.
One of the world's best bargains in a highly stable, and accurate
bench dmm is the HP3456A. It is 6-1/2 digits, and qualifies as a
transfer standard for DC. It is AC, DC and Ohms, and has a max
voltage of 1KV. Typically they can be found for $100 on the bay,
though most of mine have been given to me. Get the newer model that
has no fan, but has a visible to3 pack transistor on the back panel.
-Chuck Harris
Jeff Machesky wrote:
Thanks Chuck, sounds like the cal routine is the same as the Tek
2465BDM DMM function which technically is high enough resolution for
99.9% of my needs. I guess I'm just a bit of a stickler for that
absolute precision. I have an If I could afford an 8 1/2 digit meter I
would get one kind of mentality. Their of course is a practical side
that says don't waste a ton of money for an extra digit or two. The
3478A appears to be a good choice.
What's sending one of these off to get NIST traceable calibrated
normally run ?
If I were to buy new I was looking at the U3402A. Buying new gives me
that nice cal sheet that satisfies my need for accuracy. Whole lot of
difference in price however.
Thanks,
Jeff
On 12/18/2012 8:54 AM, Chuck Harris wrote:
The 3478A is a nice meter, but bear in mind that it is 300V max.
It is accurate, stable, and works smoothly. It is easily controlled
over HPIB.
In its deficiency corner, is the 300V max,and a non back lit LCD that
tends to get lost in the shadows.
I have never needed to calibrate mine, but I am pretty sure that you
need to complete the calibration of all steps before you leave a
particular function, say DCV, or ACV, or Ohms....
The calibration procedure takes a measurement of a known standard
on a particular range, and creates an offset that it used when it
calculates the voltage to display. The 30mv standard only calibrates
the offset for the 30mv range. The 3V standard, the 3V range...
You shouldn't have to pay more than about $100 for a working calibrated
3478A. Tucker has them for sale periodically.
9 times out of 10, a voltage measured by a scope's trace is good
enough.
Did I mention that the 3478A only measures up to 300V?
-Chuck Harris
Jeff Machesky wrote:
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to
run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing
to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
------------------------------------
Yahoo! Groups Links
------------------------------------
Yahoo! Groups Links
|
Just some food for thought and criticism. Let's say all you can get is a 2.5 or 5.0 volt precision reference. You could in theory use the high resolution of your 5 1/2 or 6 1/2 + digit meter to trim resistors to get precision divider ratios. Even if your meter was not in cal the ratio would still be accurate. So for each calibration range you could divide down your reference or source as needed to match your precision reference. I think this method would get most of us well in the ballpark. It would require a whole lot of patience however and I'm sure would become less accurate at the higher voltages. Perhaps even use a very low offset op-amp to buffer your readings. Once voltage is accurate you could check resistance ranges with a small amount of precision resistors and again trim the other half of a voltage divider until your voltage equates to a value that matches your desired resistance.
So one uncalibrated meter plus one high precision voltage reference and a bit of patience and a good calculator and you can get a fairly close cal. Well in theory at least.
Any thoughts ?
Jeff
toggle quoted message
Show quoted text
On 12/18/2012 8:54 AM, Chuck Harris wrote:
The 3478A is a nice meter, but bear in mind that it is 300V max.
It is accurate, stable, and works smoothly. It is easily controlled
over HPIB.
In its deficiency corner, is the 300V max,and a non back lit LCD that
tends to get lost in the shadows.
I have never needed to calibrate mine, but I am pretty sure that you
need to complete the calibration of all steps before you leave a
particular function, say DCV, or ACV, or Ohms....
The calibration procedure takes a measurement of a known standard
on a particular range, and creates an offset that it used when it
calculates the voltage to display. The 30mv standard only calibrates
the offset for the 30mv range. The 3V standard, the 3V range...
You shouldn't have to pay more than about $100 for a working calibrated
3478A. Tucker has them for sale periodically.
9 times out of 10, a voltage measured by a scope's trace is good enough.
Did I mention that the 3478A only measures up to 300V?
-Chuck Harris
Jeff Machesky wrote:
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
------------------------------------
Yahoo! Groups Links
|
Don,
I am not at all familiar with the HP 745A other than looking at one listed on theBay.
I got involved in calibrating my 3478A on the AC scales and used an HP 3458A calibrated by Agilent as a ¡®transfer standard¡¯ by using a 3326A feeding 50 ohm coax to a 50 ohm termination read by the 3458A then using that same connection to the 3478A and entering the reading on the 3458A to the 3478A. It seemed to have worked in that the meter passes SELF CAL and seems to read accurately. However, I have not had the time to go through a complete ¡®installation¡¯ measurement sequence.
I have since acquired the Fluke 5100B and a couple of Fluke 5200A¡¯s. These beasts can do the job. One of the 5200A¡¯s works and the other has had some ¡®problems¡¯, charred resistors, dead transistors, etc. I am still in the process of resurrecting it.
The 5100B is quite a nice instrument. It displays 4 ? digits (IIRC, maybe 5 ?, it¡¯s late and I am not in the shop) but is fairly stable and I can use the 3458A as a ¡®transfer standard¡¯ to calibrate higher resolution meters. Once/if I get to retire, I am thinking about opening ¡®Trantham¡¯s Calibration Lab¡¯ for non NIST traceable calibration services to experimenters who would like to have a calibration of their ¡®hobbyist¡¯ equipment. It¡¯s fun and keeps me entertained. However, I have a long way to go and I¡¯m slow. I need to do a lot more reading about calibration practices and, likely, build some sort of ¡®environmental chamber¡¯ to house the instruments being used in the calibration process, likely a 3458A and the DUT. This will require accurate measurement and control of temperature and humidity (I live in FL). My thought, so far, is some sort of two or three shelf ¡®box¡¯ that would accommodate several instruments while, at the same time, having connected ducting and electrical connections to accommodate the required environmental inputs, sensors, control connections, power, lighting, etc. Clearly a ¡®work in progress¡¯, currently in the ¡®concept¡¯ stage.
However, the project will ward off Alzheimer¡¯s.
Joe
From: hp_agilent_equipment@... [mailto:hp_agilent_equipment@...] On Behalf Of Don Lewis
Sent: Tuesday, December 18, 2012 9:44 AM
To: hp_agilent_equipment@...
Subject: Re: [hp_agilent_equipment] HP 3478A general questions
Joe:
What are your thoughts on the HP 745A for AC calibrations. It has a 1K and a 10K range.
I have two of them, ...one working, one needs the optical thermistor in the clipper circuit.
Thanks, ...-Don
===============================
From: J. L. Joe:Trantham <jltran@... <mailto:jltran%40att.net> >
To: hp_agilent_equipment@... <mailto:hp_agilent_equipment%40yahoogroups.com>
Sent: Tuesday, December 18, 2012 9:30 AM
Subject: RE: [hp_agilent_equipment] HP 3478A general questions
Jeff,
I have a 3478A and I have calibrated it by hand but it has been a while. I
*think* it is possible to just calibrate one range at a time but I'd have to
look at the manual. When I did the calibration, I was trying to 'harvest'
the CAL data and lost it so I had to do a complete calibration.
For my day to day bench work, I use a Fluke 8050A. They are usually
available very cheap and are quite reliable. I have never calibrated one
though, even though the process is described in the manual.
If you get the 3478A, I would send it out for calibration and make it your
'house transfer standard'. IIRC, though, it's maximum range is 300 Volts so
might not be a great meter for 'general purpose' trouble shooting but good
around most old HP equipment.
For most AC work, the usual frequency used for calibration is 1 KHz, not 60
Hz. You might want to take a look at a Fluke 5100B. Very interesting piece
of cal gear. Volts, current, AC and DC, and resistance. Big and heavy
though.
Good luck and Merry Christmas.
Joe
-----Original Message-----
From: mailto:hp_agilent_equipment%40yahoogroups.com
[mailto:mailto:hp_agilent_equipment%40yahoogroups.com] On Behalf Of Jeff Machesky
Sent: Tuesday, December 18, 2012 8:25 AM
To: mailto:hp_agilent_equipment%40yahoogroups.com
Subject: [hp_agilent_equipment] HP 3478A general questions
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]
|
Jeff, Agilent still does CAL on the 3478A for $204.22 per their website. I have dealt with Agilent on a number of instruments I have sent in for calibration and highly recommend their services. It would probably be worth it to have a ¡®standard¡¯ for your shop. You might also want to take a look at Fluke. Their 289 or 8846A DMM¡¯s might be well worth looking at if you are in the under $1000 range. They handle up to 1 KV. The 289 is a handheld and the 8846A is a bench model. I have seen the 8846A go for under $1K on theBay. I have been very impressed by the stability of Fluke meters, my 8050A¡¯s being the best example. I bought an 8050A new in 1976 and it is perfect to this day. Very inexpensive, usually, on theBay. In the 8 ? digit realm, I am familiar with HP/Agilent 3458A and the Solartron (Ametek) 7081. I have both, both having been calibrated by their respective companies, and both do a great job. The 3458A also reads current. Another option is a Solartron 7061. It is lower resolution but also reads current. Solartron¡¯s only disadvantage is their use of a special connector for test leads (I have all the part numbers if you need them), they require a Calibration Key to turn a switch on the front panel to perform the calibration (I have a key and can send you a duplicate if needed, very easy to calibrate using a serial connection and a terminal program on a computer), and the fact that Ametek is in England and it takes a while to ship the meter (7081 is my only experience with this) there for calibration. However, the 7081 is very stable though a bit slow in reading to maximum resolution, unlike the 3458A. I have seen the 7081¡¯s under $400 and the 7061¡¯s under $150 on theBay, though you don¡¯t know what you are getting until you are able to ¡®install¡¯ it with appropriate mesurements. Good luck. Joe From: hp_agilent_equipment@... [mailto:hp_agilent_equipment@...] On Behalf Of Jeff Machesky Sent: Tuesday, December 18, 2012 10:13 AM To: hp_agilent_equipment@... Subject: Re: [hp_agilent_equipment] HP 3478A general questions Thanks Chuck, sounds like the cal routine is the same as the Tek 2465BDM DMM function which technically is high enough resolution for 99.9% of my needs. I guess I'm just a bit of a stickler for that absolute precision. I have an If I could afford an 8 1/2 digit meter I would get one kind of mentality. Their of course is a practical side that says don't waste a ton of money for an extra digit or two. The 3478A appears to be a good choice. What's sending one of these off to get NIST traceable calibrated normally run ? If I were to buy new I was looking at the U3402A. Buying new gives me that nice cal sheet that satisfies my need for accuracy. Whole lot of difference in price however. Thanks, Jeff On 12/18/2012 8:54 AM, Chuck Harris wrote:
The 3478A is a nice meter, but bear in mind that it is 300V max.
It is accurate, stable, and works smoothly. It is easily controlled
over HPIB.
In its deficiency corner, is the 300V max,and a non back lit LCD that
tends to get lost in the shadows.
I have never needed to calibrate mine, but I am pretty sure that you
need to complete the calibration of all steps before you leave a
particular function, say DCV, or ACV, or Ohms....
The calibration procedure takes a measurement of a known standard
on a particular range, and creates an offset that it used when it
calculates the voltage to display. The 30mv standard only calibrates
the offset for the 30mv range. The 3V standard, the 3V range...
You shouldn't have to pay more than about $100 for a working calibrated
3478A. Tucker has them for sale periodically.
9 times out of 10, a voltage measured by a scope's trace is good enough.
Did I mention that the 3478A only measures up to 300V?
-Chuck Harris
Jeff Machesky wrote:
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
------------------------------------
Yahoo! Groups Links
[Non-text portions of this message have been removed]
|
Thanks Joe, some good options by the sounds of it. I'm eyeballing the 3456A's now, they appear to be fairly accurate and in a good price range. In the end I'm more interested in the resolution then the absolute accuracy. The problem with the 3456A's is the size. I already have a 54111D to contend with. Then again the 3456 wouldn't be a daily device so maybe I can have it in a bit more out of the way location.
Thanks,
Jeff
toggle quoted message
Show quoted text
On 12/18/2012 8:56 PM, J. L. Trantham wrote:
Jeff,
Agilent still does CAL on the 3478A for $204.22 per their website. I have dealt with Agilent on a number of instruments I have sent in for calibration and highly recommend their services.
It would probably be worth it to have a ¡®standard¡¯ for your shop.
You might also want to take a look at Fluke. Their 289 or 8846A DMM¡¯s might be well worth looking at if you are in the under $1000 range. They handle up to 1 KV. The 289 is a handheld and the 8846A is a bench model. I have seen the 8846A go for under $1K on theBay. I have been very impressed by the stability of Fluke meters, my 8050A¡¯s being the best example. I bought an 8050A new in 1976 and it is perfect to this day. Very inexpensive, usually, on theBay.
In the 8 ? digit realm, I am familiar with HP/Agilent 3458A and the Solartron (Ametek) 7081. I have both, both having been calibrated by their respective companies, and both do a great job. The 3458A also reads current. Another option is a Solartron 7061. It is lower resolution but also reads current. Solartron¡¯s only disadvantage is their use of a special connector for test leads (I have all the part numbers if you need them), they require a Calibration Key to turn a switch on the front panel to perform the calibration (I have a key and can send you a duplicate if needed, very easy to calibrate using a serial connection and a terminal program on a computer), and the fact that Ametek is in England and it takes a while to ship the meter (7081 is my only experience with this) there for calibration.
However, the 7081 is very stable though a bit slow in reading to maximum resolution, unlike the 3458A.
I have seen the 7081¡¯s under $400 and the 7061¡¯s under $150 on theBay, though you don¡¯t know what you are getting until you are able to ¡®install¡¯ it with appropriate mesurements.
Good luck.
Joe
From: hp_agilent_equipment@... <mailto:hp_agilent_equipment%40yahoogroups.com> [mailto:hp_agilent_equipment@... <mailto:hp_agilent_equipment%40yahoogroups.com>] On Behalf Of Jeff Machesky
Sent: Tuesday, December 18, 2012 10:13 AM
To: hp_agilent_equipment@... <mailto:hp_agilent_equipment%40yahoogroups.com>
Subject: Re: [hp_agilent_equipment] HP 3478A general questions
Thanks Chuck, sounds like the cal routine is the same as the Tek
2465BDM DMM function which technically is high enough resolution for
99.9% of my needs. I guess I'm just a bit of a stickler for that
absolute precision. I have an If I could afford an 8 1/2 digit meter I
would get one kind of mentality. Their of course is a practical side
that says don't waste a ton of money for an extra digit or two. The
3478A appears to be a good choice.
What's sending one of these off to get NIST traceable calibrated
normally run ?
If I were to buy new I was looking at the U3402A. Buying new gives me
that nice cal sheet that satisfies my need for accuracy. Whole lot of
difference in price however.
Thanks,
Jeff
On 12/18/2012 8:54 AM, Chuck Harris wrote:
The 3478A is a nice meter, but bear in mind that it is 300V max.
It is accurate, stable, and works smoothly. It is easily controlled
over HPIB.
In its deficiency corner, is the 300V max,and a non back lit LCD that
tends to get lost in the shadows.
I have never needed to calibrate mine, but I am pretty sure that you
need to complete the calibration of all steps before you leave a
particular function, say DCV, or ACV, or Ohms....
The calibration procedure takes a measurement of a known standard
on a particular range, and creates an offset that it used when it
calculates the voltage to display. The 30mv standard only calibrates
the offset for the 30mv range. The 3V standard, the 3V range...
You shouldn't have to pay more than about $100 for a working calibrated
3478A. Tucker has them for sale periodically.
9 times out of 10, a voltage measured by a scope's trace is good enough.
Did I mention that the 3478A only measures up to 300V?
-Chuck Harris
Jeff Machesky wrote:
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to
run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing
to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
------------------------------------
Yahoo! Groups Links
|
Found the hole in my own idea so I thought I would post it just in case someone attempts it.
The problem is the "uncalibrated" meter is going to have different amounts of error in different resistance ranges. So measuring the divider resistors will result in an error percentage not less then the differential between two ranges used to measure the resistors. That's not to say a calibrated meter wouldn't work to create the references but at that point you may as well just measure the voltages. Ohhh well. Sorry for the wasted posts.
Jeff
toggle quoted message
Show quoted text
On 12/18/2012 8:14 PM, Jeff Machesky wrote:
Just some food for thought and criticism. Let's say all you can get is
a 2.5 or 5.0 volt precision reference. You could in theory use the
high resolution of your 5 1/2 or 6 1/2 + digit meter to trim resistors
to get precision divider ratios. Even if your meter was not in cal the
ratio would still be accurate. So for each calibration range you could
divide down your reference or source as needed to match your precision
reference. I think this method would get most of us well in the
ballpark. It would require a whole lot of patience however and I'm
sure would become less accurate at the higher voltages. Perhaps even
use a very low offset op-amp to buffer your readings. Once voltage is
accurate you could check resistance ranges with a small amount of
precision resistors and again trim the other half of a voltage divider
until your voltage equates to a value that matches your desired resistance.
So one uncalibrated meter plus one high precision voltage reference and
a bit of patience and a good calculator and you can get a fairly close
cal. Well in theory at least.
Any thoughts ?
Jeff
On 12/18/2012 8:54 AM, Chuck Harris wrote:
The 3478A is a nice meter, but bear in mind that it is 300V max.
It is accurate, stable, and works smoothly. It is easily controlled
over HPIB.
In its deficiency corner, is the 300V max,and a non back lit LCD that
tends to get lost in the shadows.
I have never needed to calibrate mine, but I am pretty sure that you
need to complete the calibration of all steps before you leave a
particular function, say DCV, or ACV, or Ohms....
The calibration procedure takes a measurement of a known standard
on a particular range, and creates an offset that it used when it
calculates the voltage to display. The 30mv standard only calibrates
the offset for the 30mv range. The 3V standard, the 3V range...
You shouldn't have to pay more than about $100 for a working calibrated
3478A. Tucker has them for sale periodically.
9 times out of 10, a voltage measured by a scope's trace is good enough.
Did I mention that the 3478A only measures up to 300V?
-Chuck Harris
Jeff Machesky wrote:
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to
run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing
to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
------------------------------------
Yahoo! Groups Links
|
Jeff,
You can still make the idea work by using multiple resistors of the same value. You can make a 10:1 divider by using, say, 10 each 10K resistors; all can be checked on the same resistance scale. You need to correct for any loading by the meter input, of course, but the input impedance of the 3478A is very high on the 3V and lower DC ranges.
--John Gord
toggle quoted message
Show quoted text
--- In hp_agilent_equipment@..., Jeff Machesky <jeff@...> wrote:
Found the hole in my own idea so I thought I would post it just in case
someone attempts it.
The problem is the "uncalibrated" meter is going to have different
amounts of error in different resistance ranges. So measuring the
divider resistors will result in an error percentage not less then the
differential between two ranges used to measure the resistors. That's
not to say a calibrated meter wouldn't work to create the references but
at that point you may as well just measure the voltages. Ohhh well.
Sorry for the wasted posts.
Jeff
On 12/18/2012 8:14 PM, Jeff Machesky wrote:
Just some food for thought and criticism. Let's say all you can get is
a 2.5 or 5.0 volt precision reference. You could in theory use the
high resolution of your 5 1/2 or 6 1/2 + digit meter to trim resistors
to get precision divider ratios. Even if your meter was not in cal the
ratio would still be accurate. So for each calibration range you could
divide down your reference or source as needed to match your precision
reference. I think this method would get most of us well in the
ballpark. It would require a whole lot of patience however and I'm
sure would become less accurate at the higher voltages. Perhaps even
use a very low offset op-amp to buffer your readings. Once voltage is
accurate you could check resistance ranges with a small amount of
precision resistors and again trim the other half of a voltage divider
until your voltage equates to a value that matches your desired
resistance.
So one uncalibrated meter plus one high precision voltage reference and
a bit of patience and a good calculator and you can get a fairly close
cal. Well in theory at least.
Any thoughts ?
Jeff
On 12/18/2012 8:54 AM, Chuck Harris wrote:
The 3478A is a nice meter, but bear in mind that it is 300V max.
It is accurate, stable, and works smoothly. It is easily controlled
over HPIB.
In its deficiency corner, is the 300V max,and a non back lit LCD that
tends to get lost in the shadows.
I have never needed to calibrate mine, but I am pretty sure that you
need to complete the calibration of all steps before you leave a
particular function, say DCV, or ACV, or Ohms....
The calibration procedure takes a measurement of a known standard
on a particular range, and creates an offset that it used when it
calculates the voltage to display. The 30mv standard only calibrates
the offset for the 30mv range. The 3V standard, the 3V range...
You shouldn't have to pay more than about $100 for a working calibrated
3478A. Tucker has them for sale periodically.
9 times out of 10, a voltage measured by a scope's trace is good enough.
Did I mention that the 3478A only measures up to 300V?
-Chuck Harris
Jeff Machesky wrote:
So it's about the time of year where I'm allowed to buy one piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which has a
20,000 count 0.03% accuracy DMM. It's however a little out of cal and
I just don't want to spend the cash to get it back in perfect spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford to buy a
new 120,000 count DMM I just can't justify the cost for the hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to
run the
entire cal for each measurement type, If you start with DC you have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing
to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it off to be
calibrated or have a calibration transfer standard meter that's above
the specs of the 3478A? In other words if all you have is just a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some precision
resistors and an op-amp to generate other reference voltages with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you some of
the other odd cal standards. High voltage DC is just so much easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone who helped
me fix the ROM's.
Jeff
------------------------------------
Yahoo! Groups Links
|
John, awesome idea. So just build the higher resistance side of the divider with resistors that were all measured from the same range that the low side will be on. That's a great idea. The sum of that would then just plug in to the normal divider formulas to compute the other missing resistor. Once the computed value is known a resistor would be trimmed until the reading on the meter equals the value of the missing resistor. In the end you would have a divider with a ratio that has precision as good as the highest resolution of the meter you used to build it. The meter loading could be added to the formula during computation for the resistor the voltage reading will be taken from. I've made up an excel sheet that I can just plug in my precision reference voltage, the needed test voltage,the value of one resistor and the meter load. It then gives me the missing resistor value. A second part of the same sheet lets me plug in the values I'm getting to see how far off in percentage it'll be.
I think this idea would work really well for what it is. I suspect with a little patience 0.01% could be achieved. Beyond that would require a higher resolution meter and a lot more time. Perhaps with a 6 1/2 digit meter 0.001% could be done. At the very least it's a nice sanity check exercise. Of course any results are only as good as the precision of the reference used. I think for my needs getting even 0.01% would be just fine. It would be better then most of what I would buy brand new in the price range of the used gear.
Thanks,
Jeff
toggle quoted message
Show quoted text
On 12/19/2012 12:21 AM, johncharlesgord wrote:
Jeff,
You can still make the idea work by using multiple resistors of the same value. You can make a 10:1 divider by using, say, 10 each 10K resistors; all can be checked on the same resistance scale. You need to correct for any loading by the meter input, of course, but the input impedance of the 3478A is very high on the 3V and lower DC ranges.
--John Gord
--- In hp_agilent_equipment@... <mailto:hp_agilent_equipment%40yahoogroups.com>, Jeff Machesky <jeff@...> wrote:
Found the hole in my own idea so I thought I would post it just in case
someone attempts it.
The problem is the "uncalibrated" meter is going to have different
amounts of error in different resistance ranges. So measuring the
divider resistors will result in an error percentage not less then the
differential between two ranges used to measure the resistors. That's
not to say a calibrated meter wouldn't work to create the references
but
at that point you may as well just measure the voltages. Ohhh well.
Sorry for the wasted posts.
Jeff
On 12/18/2012 8:14 PM, Jeff Machesky wrote:
Just some food for thought and criticism. Let's say all you can get is
a 2.5 or 5.0 volt precision reference. You could in theory use the
high resolution of your 5 1/2 or 6 1/2 + digit meter to trim resistors
to get precision divider ratios. Even if your meter was not in cal the
ratio would still be accurate. So for each calibration range you could
divide down your reference or source as needed to match your precision
reference. I think this method would get most of us well in the
ballpark. It would require a whole lot of patience however and I'm
sure would become less accurate at the higher voltages. Perhaps even
use a very low offset op-amp to buffer your readings. Once voltage is
accurate you could check resistance ranges with a small amount of
precision resistors and again trim the other half of a voltage divider
until your voltage equates to a value that matches your desired
resistance.
So one uncalibrated meter plus one high precision voltage
reference and
a bit of patience and a good calculator and you can get a fairly close
cal. Well in theory at least.
Any thoughts ?
Jeff
On 12/18/2012 8:54 AM, Chuck Harris wrote:
The 3478A is a nice meter, but bear in mind that it is 300V max.
It is accurate, stable, and works smoothly. It is easily controlled
over HPIB.
In its deficiency corner, is the 300V max,and a non back lit LCD
that
tends to get lost in the shadows.
I have never needed to calibrate mine, but I am pretty sure that you
need to complete the calibration of all steps before you leave a
particular function, say DCV, or ACV, or Ohms....
The calibration procedure takes a measurement of a known standard
on a particular range, and creates an offset that it used when it
calculates the voltage to display. The 30mv standard only calibrates
the offset for the 30mv range. The 3V standard, the 3V range...
You shouldn't have to pay more than about $100 for a working
calibrated
3478A. Tucker has them for sale periodically.
9 times out of 10, a voltage measured by a scope's trace is good
enough.
Did I mention that the 3478A only measures up to 300V?
-Chuck Harris
Jeff Machesky wrote:
So it's about the time of year where I'm allowed to buy one
piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which
has a
20,000 count 0.03% accuracy DMM. It's however a little out of
cal and
I just don't want to spend the cash to get it back in perfect
spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford
to buy a
new 120,000 count DMM I just can't justify the cost for the
hobby type
work that I do. Plus I love working with the older gear and saving money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly
clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I
would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to
run the
entire cal for each measurement type, If you start with DC you
have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing
to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it
off to be
calibrated or have a calibration transfer standard meter
that's above
the specs of the 3478A? In other words if all you have is just
a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some
precision
resistors and an op-amp to generate other reference voltages
with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you
some of
the other odd cal standards. High voltage DC is just so much
easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone
who helped
me fix the ROM's.
Jeff
------------------------------------
Yahoo! Groups Links
|
Another solution that can usually be found for little money are:
For DCV: Dekaviders which can take you out to 6 or more digits with precision when used with a single voltage standard voltage source.
For ACV: Gertsch Ratio Transformers which have a similar precision for ACV when used with a single voltage standard.
I got one of mine for near free and the other on ebay for less than $50 IIRC.
I believe some of the Fluke Differential Meters and Standards may use a similar system, but I have not investigated that though.
Steve, KJ5RV
Jeff Machesky wrote:
toggle quoted message
Show quoted text
John, awesome idea. So just build the higher resistance side of the divider with resistors that were all measured from the same range that the low side will be on. That's a great idea. The sum of that would then just plug in to the normal divider formulas to compute the other missing resistor. Once the computed value is known a resistor would be trimmed until the reading on the meter equals the value of the missing resistor. In the end you would have a divider with a ratio that has precision as good as the highest resolution of the meter you used to build it. The meter loading could be added to the formula during computation for the resistor the voltage reading will be taken from. I've made up an excel sheet that I can just plug in my precision reference voltage, the needed test voltage,the value of one resistor and the meter load. It then gives me the missing resistor value. A second part of the same sheet lets me plug in the values I'm getting to see how far off in percentage it'll be.
I think this idea would work really well for what it is. I suspect with a little patience 0.01% could be achieved. Beyond that would require a higher resolution meter and a lot more time. Perhaps with a 6 1/2 digit meter 0.001% could be done. At the very least it's a nice sanity check exercise. Of course any results are only as good as the precision of the reference used. I think for my needs getting even 0.01% would be just fine. It would be better then most of what I would buy brand new in the price range of the used gear.
Thanks,
Jeff
On 12/19/2012 12:21 AM, johncharlesgord wrote:
Jeff,
You can still make the idea work by using multiple resistors of the same value. You can make a 10:1 divider by using, say, 10 each 10K resistors; all can be checked on the same resistance scale. You need to correct for any loading by the meter input, of course, but the input impedance of the 3478A is very high on the 3V and lower DC ranges.
--John Gord
--- In hp_agilent_equipment@... <mailto:hp_agilent_equipment%40yahoogroups.com>, Jeff Machesky <jeff@...> wrote:
Found the hole in my own idea so I thought I would post it just in case
someone attempts it.
The problem is the "uncalibrated" meter is going to have different
amounts of error in different resistance ranges. So measuring the
divider resistors will result in an error percentage not less then the
differential between two ranges used to measure the resistors. That's
not to say a calibrated meter wouldn't work to create the references but
at that point you may as well just measure the voltages. Ohhh well.
Sorry for the wasted posts.
Jeff
On 12/18/2012 8:14 PM, Jeff Machesky wrote:
Just some food for thought and criticism. Let's say all you can get is
a 2.5 or 5.0 volt precision reference. You could in theory use the
high resolution of your 5 1/2 or 6 1/2 + digit meter to trim resistors
to get precision divider ratios. Even if your meter was not in cal the
ratio would still be accurate. So for each calibration range you could
divide down your reference or source as needed to match your precision
reference. I think this method would get most of us well in the
ballpark. It would require a whole lot of patience however and I'm
sure would become less accurate at the higher voltages. Perhaps even
use a very low offset op-amp to buffer your readings. Once voltage is
accurate you could check resistance ranges with a small amount of
precision resistors and again trim the other half of a voltage divider
until your voltage equates to a value that matches your desired
resistance.
So one uncalibrated meter plus one high precision voltage reference and
a bit of patience and a good calculator and you can get a fairly close
cal. Well in theory at least.
Any thoughts ?
Jeff
On 12/18/2012 8:54 AM, Chuck Harris wrote:
The 3478A is a nice meter, but bear in mind that it is 300V max.
It is accurate, stable, and works smoothly. It is easily controlled
over HPIB.
In its deficiency corner, is the 300V max,and a non back lit LCD
that
tends to get lost in the shadows.
I have never needed to calibrate mine, but I am pretty sure that you
need to complete the calibration of all steps before you leave a
particular function, say DCV, or ACV, or Ohms....
The calibration procedure takes a measurement of a known standard
on a particular range, and creates an offset that it used when it
calculates the voltage to display. The 30mv standard only calibrates
the offset for the 30mv range. The 3V standard, the 3V range...
You shouldn't have to pay more than about $100 for a working
calibrated
3478A. Tucker has them for sale periodically.
9 times out of 10, a voltage measured by a scope's trace is good
enough.
Did I mention that the 3478A only measures up to 300V?
-Chuck Harris
Jeff Machesky wrote:
So it's about the time of year where I'm allowed to buy one
piece of
test gear and I'm thinking I want a bench meter with higher
resolution. The best I've got so far is the Tek 2465BDM which
has a
20,000 count 0.03% accuracy DMM. It's however a little out of
cal and
I just don't want to spend the cash to get it back in perfect
spec.
It's also a bit crazy to have a scope running just to use the DMM.
This brings me to the 3478A. While I could technically afford
to buy a
new 120,000 count DMM I just can't justify the cost for the
hobby type
work that I do. Plus I love working with the older gear and saving
money.
Couple quick questions about the 3478A:
Can one range be calibrated at a time? This is not highly
clear in the
service manual. Can I calibrate just the 3V range for example?
Are they reliable, or will I have to fix up most of what I
would buy
on say ebay?
The problem I have with the meter on my Tek is that you have to
run the
entire cal for each measurement type, If you start with DC you
have to
go all the way up the range from millivolts up to several hundred
volts. As we all know it's easy to get a precision calibrated low
voltage references such as a DMM check board, it's another thing
to get
500 volts or higher reference at the spec of the meter.
So is this really a meter to buy if your willing to send it
off to be
calibrated or have a calibration transfer standard meter
that's above
the specs of the 3478A? In other words if all you have is just
a few
standards are you wasting your time?
Has anyone had any luck using a precision reference, some
precision
resistors and an op-amp to generate other reference voltages
with any
degree of accuracy? Also has anyone found a good source of say 500
volts 60 Hz AC? The right audio amp and a sig gen can get you
some of
the other odd cal standards. High voltage DC is just so much
easier to
obtain then a nice high voltage sine wave.
Sorry for the random questions, and thanks for any replies. The
54111D is still running great. My thanks again for everyone
who helped
me fix the ROM's.
Jeff
------------------------------------
Yahoo! Groups Links
------------------------------------
Yahoo! Groups Links
|
On Tue, Dec 18, 2012 at 11:21 PM, johncharlesgord <johngord@...>wrote: **
Jeff,
You can still make the idea work by using multiple resistors of the same
value. You can make a 10:1 divider by using, say, 10 each 10K resistors;
all can be checked on the same resistance scale. You need to correct for
any loading by the meter input, of course, but the input impedance of the
3478A is very high on the 3V and lower DC ranges.
Another way of doing a 10:1 divider: You need to match three equal value resistors and a trimpot is used for fine tuning by measuring two equal voltages so you would always be on the same range of the meter you are using for tuning. Orin.
|
Orin, this is exactly what I was looking for. I think I'll pick up a voltage standard from voltagestandard.com and use this method to at the very least test some of my gear. Excellent info.
Thanks,
Jeff
toggle quoted message
Show quoted text
On 12/19/2012 10:35 AM, Orin Eman wrote:
On Tue, Dec 18, 2012 at 11:21 PM, johncharlesgord <johngord@... <mailto:johngord%40verizon.net>>wrote:
**
Jeff,
You can still make the idea work by using multiple resistors of the same
value. You can make a 10:1 divider by using, say, 10 each 10K resistors;
all can be checked on the same resistance scale. You need to correct for
any loading by the meter input, of course, but the input impedance of the
3478A is very high on the 3V and lower DC ranges.
Another way of doing a 10:1 divider:
You need to match three equal value resistors and a trimpot is used for
fine tuning by measuring two equal voltages so you would always be on the
same range of the meter you are using for tuning.
Orin.
|
