Ross, I have a Tek 2465BDM sitting on top of the non vent part of the 54111D. As much as I would love to, it sounds like I shouldn't put a 3456A under all of that. The vents on top of the 54111D stop about 8 inches back. Hmm, running out of room. I may have to opt for something smaller. It almost appears that everything HP branded was BIG. The newer Agilent stuff of course is smaller these days..but so is everything. I plan on running the 54111D into the ground. I still use it where needed, the 2465B gets most of the work however. Just can't beat that analog response, well at least without taking out a loan. The 54111D comes in handy when I need to see the details or freeze something in place, but of course I'm stating what everyone here already knows.
Thanks,
Jeff
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On 12/22/2012 7:16 PM, Ross Wellington wrote:
Hi,
I have 2 HP3456A and I really like them.
The HP3456A is a shallow chassis. The HP54111 is about 4 inches longer (part
of that is the rear feet).
I have stacked alot of weight ontop of mine with no trouble. The HP54111
does weigh 59 lbs though...
Ross
-----Original Message-----
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: Saturday, December 22, 2012 6:03 PM
To: hp_agilent_equipment@... <mailto:hp_agilent_equipment%40yahoogroups.com>
Subject: Re: [hp_agilent_equipment] HP 3456a was Re: HP 3478A general
questions
Wow, thanks for all the info. This will help me make up my mind as to the
direction I go. The boss lady has said no purchases until after x-mas. So
I'm doing my research while I wait. Think I can put the 54111D on top of one
of these without crushing it :)
Thanks,
Jeff
On 12/22/2012 10:17 AM, marvgozum wrote:
The 3456a was the most accurate in the HP fleet when introduced in
1981. The model line was 345x, so in its heritage was the 3455, 3457,
and finally the ersatz standard DMM today, introduced in ~1989, the
3458. HP introduced a high accuracy ADC method, multislope II, with
3456a, you'll see marked change in posted accuracy versus the 3455a.
The 3458a further improves that technique. In summary, if you're
looking for accuracy these series of DMMs are one to shoot for.
There are pros and cons to the discontinued models, 56a and 57a. For
example, The 56a is as good as the 57a in DCV at 1 year ppm, while the
57a is 10x more stable in 1yr as a ohmmeter. The 57a uses all close
case calibration and has more unobtanium in its parts list, versus the
56a, which was the last to use all pots based calibration. The basic
57a reads only to 300Vrms maximum, but also has a current mode.
As for prices, the low end is similar on both, about $50 without
shipping, but on the high end with calibration, the 56a runs to $300
while 57a about $700.
The 3478a was a general purpose working meter, ~10x less accurate in
DCV than the 3456a.
As mentioned earlier you can use a resistor network; dekaviders or KV
bridges in DC, to generate other DC voltages needed to check ranges,
but maintaining stability in the reference enough to check the meter's
accuracy, is the challenge. Its enough a whole new forum discusses
this issue alone, volt-nuts@... <mailto:volt-nuts%40febo.com>
<mailto:volt-nuts%40febo.com>. A
similar problem exists for AC.
To calibrate a meter to realize its best accuracy requires grasping
key concepts in metrology. A simplest approach is to take your DMM and
compare its readings against a known good DMM. The reference DMM
should ideally be 4x to 10x more accurate than the DUT. This is the
concept of TUR, test uncertainty ratio. When making comparisons, say
voltages, the test volt must be stable and precise enough during the
transfer, for example if you are checking the 1V range between DMMs,
you need to generate a 1V voltage stable to 1uV resolution or less,
1.000 000 VDC. Without a high level of thoroughness and stability,
your 6.5 digit DMM will have increasing uncertainty as you get to
its LSD.
On the low end of the range, special conditions apply that are fully
covered in Keithley's low level measurement handbook, and these need
to be controlled once dealing with uV, mohms, and uA adjustments.
Lastly, one has to decide if the effort described in volt nuts is
worth it, or should one just take your DUT to the calibrator
periodically for $100-$150 to insure your 6.5 digit DMM is as good as
you expect it to be.
--- In hp_agilent_equipment@...
<mailto:hp_agilent_equipment%40yahoogroups.com>
<mailto:hp_agilent_equipment%40yahoogroups.com>, Jeff Machesky
<jeff@...> 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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