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:
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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
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