Author Topic: Bench Multimeters  (Read 25418 times)

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Offline ngkee22

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Bench Multimeters
« on: July 20, 2010, 01:41:52 pm »
I have been looking through Ebay on a good bench multimeter.  I prefer the HP 34401A meters and there seem to be plenty of them for sale.  I found a Fluke 8846A the other day, used, for $600 but got to it to late to get it.  They seem like good meters so I started looking for other Fluke bench meters.  I came across a Fluke 8842A bench meter on ebay that looks nice and will probably do what I want.  It is only 5 1/2 digits instead of the 6 1/2 I was looking for, but I think it will work fine.

I wanted to know if anyone else has had any expereince with this model, 8842A, or any other fluke bench meter and what your thoughts were.  

Also, feel free to suggest any other models that you feel are good for their value.
 

alm

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Re: Bench Multimeters
« Reply #1 on: July 20, 2010, 01:58:50 pm »
I have written a few posts about alternatives from Keithley and HP on this forum, should be easy to find if you use the search function. The more recent instruments like HP 34401A and Keithley 2000 tend to cost quite a lot more than the older instrument. The basic voltage/resistance measurement is usually similar, but they do offer extra features like diode test, continuity and frequency. In my opinion the Fluke 8840/8842 is usually overpriced, alternatives from HP and Keithley are often sold for about half the $200 or so that a Fluke 8840/8842 tends to fetch, and keep in mind that some essential features (AC and GPIB?) were optional on the 8840/8842. The VFD is nice as long as it's not dim from being left on 24/7 for years, but in my opinion LED displays are pretty close, I'm not a big fan of LCD for mains-powered applications though, especially without backlight. Some older full-rack instruments (eg. HP 3456A/3457A) can also be a good deal, but are a lot larger and more expensive to ship. If you want to interface these meters with a computer, you need GPIB. RS-232 came later.
 

Offline slburris

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Re: Bench Multimeters
« Reply #2 on: July 20, 2010, 02:06:49 pm »
If you don't mind a boat anchor, the Fluke 8505A (a nice 6.5 digit meter) usually
sells on Ebay for < $100.  I have one (and a Fluke 8502A) and love them.  But
if space is at a premium, stay away.

Scott
 

Offline Rhythmtech

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Re: Bench Multimeters
« Reply #3 on: July 20, 2010, 09:04:08 pm »
I would evaluate what you want from the meter before picking one out based on price. You'll find that holding out for the one that does exactly what you want will be far easier to live with in the long run. Depending on how much you can spend too, it might be wise to look into refurbished meters instead of ebay, you'll usually get a guarantee and a warranty with a refurb that you may not get with an ebay  unit. 

The HP 34401A is a favorite of mine it has high accuracy, PC interface usually RS-232 or GPIB, is very configurable for different averaging, capture rates, and is fairly rugged for its capabilities.
 

Offline rf-loop

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Re: Bench Multimeters
« Reply #4 on: July 21, 2010, 08:48:25 am »
I have HP3456A and 3457A.  Some time ago I also have 34401A (some weeks for testing)

3457A have more functions. Good statistic and other functions, more than 3456A but 3456A have better short time stability and maybe less noise.


34401A is nearly same accuracy but surprice it is not very good. 3456A is better if look stability. Specially short time stability. 3456A is only transfer standard quality (in 2ppm class) if look these three meters.

34401A display go very easy bad (short ageing and it is bad). It is terrible look after quite short time use. Display digits/segments have very soon lot of brightness variations. (but spare part is not very expensive)

In elder equipments also inside voltage referenge have good ageing and many times they drift less. New machines need ageing becouse first 1-2khrs with new equipment have most terrible ageing drift.

3456A is very good equipment if look stability and accuracy and value for money specially if look good value for voltage measurements. (but of course before buy need littlebit look that equipment is good working kondition and nobody have "adjust and repair" it. Most of peoples do not know how to handle these equipments inside. (also if they are electronic "professionals")


If want get accurate measurements with these equipments need also know how to do accurate measurements. There are many things what need care... not only thermal emf with test leads.

Also 3457A is good   but specially  if use long averaging and/or slowest mode. (also it can 7 1/2 digits but not directly) It is more "noisy" than 3456A. This noise is looks random and it can clean with averaging but in this case measurements go slow.

34401A is nice small and many functions but after testing I can not see any better accuracy.. I can see only more bad accuracy.

One interesting point...

I have test my 3457A with one month old cal.certified 3458A super meter (cal specially fine adjusted and then certified). For comparing check Voltage source was Fluke DCV calibrator. I test only DCV becouse no good ACV and Current source. Most bad error was 10ppm and my 3457A have more than 10 years old calibration and all errors was so that errors are between -10ppm and +5ppm. It was very amazing. (but it was of course only in this one time and I can not know how it is if I test agen after moving and different temperature and so on). Also make some test with good and specially accurate Resistance calibration "standards". (Example: reference was labeled  100.00345 Ohm and 3457A show 100,004 Ohm. Ref module  1,00002 Ohm and HP show 0,99917 Ohm.) maybe need do calibration some day.

After this compare in home I compare my 3457A and 3456A. 3456A looks same kind of error (maybe less error) and also this cal is very old and uncnown date (but sure more than 10-15 years old cal)

This time I have not anymore this 34401A for compare. (I put this  out becouse I do not trust this kind of plastic "cheap" stuffs.)

For best DCV accuracy value for money I recommend 3456A if it is in good original condition. (if someone have "repair and adjust" it... do not touch. Also this term "refurbished" is very flexible term.... many times it do not mean anything. Also I have buy from US some equipmets with "calibrated" term in ebay.  may be there is some read and write problem and guy did not know what this word meaning.

Good source (ebay or other seller) can also well explain unit condition and exactly tell how it have checked. If can not... do not buy. Do not buy if seller can not make enough testings! (most time "can not know how to test" is simple lie. )

GPIB (HP-IB) -- USB module is one solution for PC use.










« Last Edit: July 21, 2010, 09:23:25 am by rf-loop »
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alm

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Re: Bench Multimeters
« Reply #5 on: July 21, 2010, 10:05:38 am »
3457A have more functions. Good statistic and other functions, more than 3456A but 3456A have better short time stability and maybe less noise.
The 3456A is actually also better in long-term stability, when the 3457A was introduced, they released improved specs for the 3456A, because the long-term data for the LM199/299/399 voltage reference was better than expected (it's hard to get accurate long-term data when you just introduced a product). There was some talk about this in the HP Journal article about the introduction of the 3457A, and the (abbreviated) specs are in the 1987 catalog. I believe the 3458A was introduced just two years later, not sure if this had anything to do with the (lack of) success of the 3457A. The accuracy of the 3456A is slightly better than the 3457A, it was also more expensive (the 3455A was even more expensive, probably only bought by customers who didn't want to change their procedures/software). Of course, the stability of individual units will vary, this is just the 3-sigma value or something like that.

The HP 3457A display sucks in my opinion, it's not an improvement over the LED display. Not sure why HP liked those LCD displays, probably because they're better at displaying text. The 3457A does have more features (eg. digital filter), better resolution via GPIB, and current measurement, and is a lot smaller and lighter.
 

Offline rf-loop

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Re: Bench Multimeters
« Reply #6 on: July 21, 2010, 10:57:24 am »


The 3456A is actually also better in long-term stability, when the 3457A was introduced, they released improved specs for the 3456A, because the long-term data for the LM199/299/399 voltage reference was better than expected (it's hard to get accurate long-term data when you just introduced a product).

Thank you this information. It confirm littlebit more what I have seen in my home "lab" but becouse I have not enough long time (comparable) data I can not say more than only short time stability.

I hope I can find this HP Journal article and these improved specs. (do you have any link for this?)


The HP 3457A display sucks in my opinion, it's not an improvement over the LED display. Not sure why HP liked those LCD displays, probably because they're better at displaying text. The 3457A does have more features (eg. digital filter), better resolution via GPIB, and current measurement, and is a lot smaller and lighter.

Fully agree this.  Maybe LCD is cheaper for production. Good LED display is exellent but expensive with selected components. (brightness).

Also better resolution can find from keyboard. (reading registers value) Or also with very short time averaging with NPLC 10 or 100 in use. (I am not sure but maybe mean calculation use whole resolution) But this method is also of course slow. (but accurate measurements can not do fast... so it is not big problem)

New 34401A display is also nice but this happyness do not last long time...
(my counter HP53131A have same problem but I have modified it so that I can shut off display if counter need keep on many weeks  continuously)

« Last Edit: July 21, 2010, 11:15:01 am by rf-loop »
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Offline saturation

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Re: Bench Multimeters
« Reply #7 on: July 21, 2010, 11:32:52 am »
Thanks for the historical perspective on the stability of these DVM.  I have a 3456A too, acquired mostly on its long term historical reputation and my need for a very accurate Vdc meter, but its good to hear your viewpoints on it, especially the experiential ones.

Best Wishes,

 Saturation
 

alm

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Re: Bench Multimeters
« Reply #8 on: July 21, 2010, 12:05:46 pm »
Apologies to ngkee22 for the slightly off-topic posts, but it is related to the pro/cons of various bench meters. If you would state some requirements or preferences, we might be able to give you more focused recommendations.

Thank you this information. It confirm littlebit more what I have seen in my home "lab" but becouse I have not enough long time (comparable) data I can not say more than only short time stability.

I hope I can find this HP Journal article and these improved specs. (do you have any link for this?)
You also need a very clean source for comparing them, and ideally a calibrated reference meter to confirm which one is more accurate. Repeating the experiment a year later (at the same temperature and with proper warm-up) with a DCV calibrator and in-cal 3458A would be a good way, the 3458A tolerance (especially if it was calibrated within the last 90 days) should be just low enough to verify the 3457A/3456A. Of course your 3457A might be better than your 3456A, since there's no rule against being better than specs. As you wrote, drift after many years of use is likely to be less than initial drift (although they did age the references to get rid of the worst part). Calibration would probably be more expensive for the 3456A, since it has a bunch of trimmers as opposed to electronic calibration (I think the 3457A is either fully or mostly electronic).

1987 catalog (warning, ~40MB PDF). I think it only contains 90 days specs for ACV and resistance, I haven't found the complete updated specs. The HP Journal issue is February 1986, specifically the long-term stability section that starts on page 18, although the complete article is probably a good read if you're interested in the technology behind these meters. HP used to be pretty good about publishing technical details back then. The HP Journal issue for the 3456A is April 1981.

Also better resolution can find from keyboard. (reading registers value) Or also with very short time averaging with NPLC 10 or 100 in use. (I am not sure but maybe mean calculation use whole resolution) But this method is also of course slow. (but accurate measurements can not do fast... so it is not big problem)
I wasn't aware that you could get the 7.5 digits of resolution via the front-panel, I believe the extra digit is real, but probably not accurate enough for them to fully specify it. Not sure if averaging is the same, I don't think so. But I might be wrong, I've never used a 3457A for any length of time.

New 34401A display is also nice but this happyness do not last long time...
(my counter HP53131A have same problem but I have modified it so that I can shut off display if counter need keep on many weeks  continuously)
I thought that VFD aging was mainly an issue when leaving it on for years, typical hobby use can hardly make a dent in that. The VFD equipment that I have seems to have OK brightness, no obvious issues, and was acquired used so it may have been abused in the past. I would like manufacturers to add a 'disable display' feature, especially for computer controlled measurements.
 

Offline ngkee22

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Re: Bench Multimeters
« Reply #9 on: July 21, 2010, 12:20:57 pm »
Don't worry about getting off topic.  That is what these posts are for.  We all get to share our knowledge to help one another.

I don't really have any specific specs or requirements that I am looking for just yet.  Most of the circuits I designed in college used low voltage, so I was mainly wanting to get a good accurate multimeter that would read into the micovolts range with some precision.  I used a HP 34401A in college, but was looking for alternative ideas and other perspectives.

Here are the models I am considering right now.  I have bee going over the specs of each trying to compare them.  I have these listed, because these are the ones that seem the better deals.
NEW:
Rigol DM3062, DM3061, DM3058
Instek GDM-8255A
Fluke 8808A

USED:
HP/Agilent 34401A
Fluke 8845A, 8846A, 8842A
 

Offline rf-loop

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Re: Bench Multimeters
« Reply #10 on: July 21, 2010, 12:53:16 pm »
OT

alm: Thank you these links related to HP.

My comment for VFD display was related to surplus equipment. If buy new for "home use" it is not problem. Some surplus equipments have been long time in professional use and many times they have lot of hours and there can see many times this problem.

Yes 3457A last "hidden" digit is not enough good for direct use.

After averaging and short time follow up it may give more information about short time drift trend. (mean, min, max give always 8 digits to display)

------------------
more OT: Just now I am using it for develop some simple DCV 10V transfer standard so that I can "pic-up" accurate 10V from "lab".
(reference chip and around components are all in tightly temperature controlled small oven (just like good OCXO but low temp)) I hope (try) get trusted +-1ppm or better for short time (I give "hands up" for +-0.1ppm). Noise is one problem but noise is also random... so not very big problem. But random "jumps" are more problematic.




« Last Edit: July 21, 2010, 01:12:52 pm by rf-loop »
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alm

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Re: Bench Multimeters
« Reply #11 on: July 21, 2010, 03:35:59 pm »
more OT: Just now I am using it for develop some simple DCV 10V transfer standard so that I can "pic-up" accurate 10V from "lab".
(reference chip and around components are all in tightly temperature controlled small oven (just like good OCXO but low temp)) I hope (try) get trusted +-1ppm or better for short time (I give "hands up" for +-0.1ppm). Noise is one problem but noise is also random... so not very big problem. But random "jumps" are more problematic.

The LM 199/299/399 (discontinued) was used in lots of bench meters, it's a stable zener (voltage is something like 6.9V) with an internal heater that keeps it at a constant (high) temperature (like an OCXO), so the tempco is very good. It's still available on ebay. The LTZ1000 is newer, very expensive, and needs more supporting circuitry. I believe the noise perfomance is pretty variable, some devices are good, some not so good. This doesn't take care of the tempco of any dividers or amplifiers. I would age them for a few weeks or so to skip the initial drift, according to the HP Journal article, they aged them for two months (and probably selected them for drift). There's also someone selling HP 3458A reference assemblies for something like $85, he does age them for a number of hours. Not sure how easy it would be to use these.

Rigol DM3062, DM3061, DM3058
Instek GDM-8255A
These are pretty unknown brands, it's hard to find any information about their quality and stability. Last time I looked, the Rigol bench meters were pretty close in price to the similar specced Agilent meters, in that case I'd choose Agilent.

Fluke 8808A
HP/Agilent 34401A
Fluke 8845A, 8846A, 8842A
I've heard some complaints about the split 2x4 wire bana jacks on the recent Fluke meters (8808A/8845A/8846A), they don't appear to survive very long (in professional environments). Apart from that, the 8845A/8846A are probably fine meters, with modern features like ethernet and USB (on the 8846A). The 8808A looks cheaper, only RS-232 for communication seems limited (no GPIB, ethernet or USB), and not great accuracy for a 5.5 digit meter.

The 34401A is a fine and popular meter, older than those Flukes (late eighties/early nineties?) and still in production. Tends to be more expensive used than many other bench meters.

The 8842A is significantly older than the other Flukes you list, from the eighties I think. It's quite close to the 8840A, I think the difference is better stability. AC and GPIB were optional. I described some alternative options from the same era here. My favorite candidates (price/performance) would probably be the Keithley 196/199 (nice LED display), but all others on that list would also make fine bench meters. Note that a bench meter usually does DCV, ACV (sometimes optional), resistance (often also 4-wire), and often DC/AC current. Other features like frequency or continuity on bench meters are more recent developments. With used equipment, a lot depends on what you can get for a good price.

I paid €75 shipped and $25+shipping for two Keithley 199 meters (the former with returns allowed, the latter with some cosmetic damage like cracked display filter from a trusted source), so for me these were good deals, and $300-$400 for a used 34401A seems pretty steep. But I wouldn't pay $110 + shipping for one old as-is that looks like a bomb went off in that room, or $200 for one that looks good but is sold as-is, so based on what's currently on Ebay, I might choose something else. These Keithley meters have nice large LED displays, but the model 199 has weird current ranges (3A or 30mA, but the HP 3468/3478 only have 3A), and the max. voltage is 300V. This 300V limit was common for meters from that time, the same applies to the HP 3457A, 3468A, 3468B, 3478A and various other Keithley meters. The accuracy of the Keithley 199 is quite good for 5.5 digit, 90ppm 1 year basic DC voltage, significantly better than the HP 3468A or Fluke 8808A, quite close to the 6.5 digit model 196 actually.

Are you also considering the full-rack (as opposed to half-rack) instruments? They can be better value, eg. HP 3456A for $150 (random ebay find), similar accuracy and resolution to the 34401A, but larger and less features. The equivalent Fluke offerings (850x) are also fine, but keep in mind that almost everything was optional, so get one with the right options. The best accuracy is always in full rack instruments, even now (eg. Fluke 8508A). Until the 34401A, most half-rack bench meters were limited to 5.5 digits.
 

Offline ngkee22

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Re: Bench Multimeters
« Reply #12 on: July 22, 2010, 12:52:18 pm »
What does everyone think about these meters.  These are the one's I have been considering the most.

Rigol DM3062, DM3061, DM3058
Instek GDM-8255A
 

Offline jahonen

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Re: Bench Multimeters
« Reply #13 on: July 22, 2010, 01:28:34 pm »
I thought that VFD aging was mainly an issue when leaving it on for years, typical hobby use can hardly make a dent in that. The VFD equipment that I have seems to have OK brightness, no obvious issues, and was acquired used so it may have been abused in the past. I would like manufacturers to add a 'disable display' feature, especially for computer controlled measurements.

I think there is a DISPLAY OFF command accessible via GPIB/serial/whatever, at least on 34401A.

Regards,
Janne
 

alm

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Re: Bench Multimeters
« Reply #14 on: July 22, 2010, 02:24:02 pm »
Rigol DM3062, DM3061, DM3058
Instek GDM-8255A
Why consider brands unknown to the bench DMM world over new well-know brands (Fluke 8808A, Agilent 34405A) or used meters from well known brands (plenty of info about them above)? I don't see the advantage, it's not like they're a lot cheaper or perform better. Rigol/Instek scopes are a lot cheaper than Agilent/Tek/Lecroy scopes, but not so with meters. I'm not aware of anyone who has experience with these, but I'd love to hear them. I would be worried to buy from a company who doesn't appear to know the difference between precision and accuracy (Rigol in the DM-30xx manual). How is the support? Do they support SCPI and do they document it fully, like Fluke/Agilent tend to do? Do they make schematics and calibration procedure available? Fluke and Agilent don't publish schematics for their newest meters, which is bad (they do for the 34401A), but they at least publish the full calibration procedure and module level service information. Can your average calibration lab calibrate them? I'm assure they will have no problem with any recent Agilent/Fluke meter (except high-end ones like the 8508A). My research into Rigol function generators showed that documentation, support and software tended to be poor, but I've never looked into their DMM's (I don't see the point).

I think there is a DISPLAY OFF command accessible via GPIB/serial/whatever, at least on 34401A.
You're correct for HP/Agilent equipment, although Keithley uses :DISPLAY:ENABLE OFF for some reason. Thanks for the hint! Too bad Tektronix doesn't support something similar for my DSO.
« Last Edit: July 22, 2010, 04:19:24 pm by alm »
 

Offline saturation

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Re: Bench Multimeters
« Reply #15 on: July 23, 2010, 01:17:31 am »
It would be good to compare the new price of these, tequipment.net has all those highlighted in red.  The low is $630 for the Chinese brand and a high of $750 for the Fluke.  However, the better model Instek and Rigol are within $50 of the Fluke.  You may be able to email Evan at tequipment to bargain down further.  I would be hesitant to select an Instek or Rigol with such a small difference in prices for a new bench DMM.  The 8808A is from the Fluke China factory and the Agilent is from Malaysia. 


Rigol DM3062, DM3061, DM3058
Instek GDM-8255A

Why consider brands unknown to the bench DMM world over new well-know brands (Fluke 8808A, Agilent 34405A) or
Best Wishes,

 Saturation
 

Offline allanw

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Re: Bench Multimeters
« Reply #16 on: July 23, 2010, 04:42:57 am »
Have you considered an HP 3468a or 3478a? They're only $50-$80 on eBay and I really like mine despite the poor display.
 

Offline ngkee22

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Re: Bench Multimeters
« Reply #17 on: July 25, 2010, 02:38:34 am »
After a few people suggested Keithely, I looked into their latest product lines.  As far as I can see, the company looks like a good reputable company.

Right now, the 2100 would meet all of my requirements and the 2000 would too, but it is a little more expensive than I would want to pay right now.  I may find the 2000 model used for a good price though.  I did, however, find the 2100 model for $550 new.  That seems like a good deal, but since I am not familiar with the brand, I thought I would see what everyone thought.

This is the company that has them for $550.
http://www.ntecusa.com/unitDetails.cfm?modelID=40453

Please leave your thoughts on these two models.

Thanks for all the advice.


 

Offline EEVblog

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Re: Bench Multimeters
« Reply #18 on: July 25, 2010, 11:11:42 am »
Sadly, the latest Keithley meters have a horrible reputation. Been plenty of talk about them on the sci.electronics.design forum.

Dave.
 

alm

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Re: Bench Multimeters
« Reply #19 on: July 25, 2010, 02:49:31 pm »
Yes, the Keithley 2100 appears to be crappy Chinese re-brand. The model 2000 is a real Keithley design, and does not have these issues. I think it's also more expensive than the 2100 (new).
 


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