EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: jacksradio on May 19, 2016, 01:59:46 am
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I am looking for advice on purchasing a bench DMM. I would like one with 4 wire resistance measurement capability, however, I have a very modest budget. I am open to all brands as long as they are accurate, reliable, repairable and have 4 wire. Thanks.
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... however, I have a very modest budget.
How much money is "a very modest budget" ?
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Siglent SDM3055
http://www.siglentamerica.com/pdxx.aspx?id=176&T=2&tid=37 (http://www.siglentamerica.com/pdxx.aspx?id=176&T=2&tid=37)
https://www.eevblog.com/forum/testgear/siglent-new-bench-dmm-sdm3055/ (https://www.eevblog.com/forum/testgear/siglent-new-bench-dmm-sdm3055/)
If you're not interested in the development and bug fixes just check the last few pages. ;)
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... however, I have a very modest budget.
How much money is "a very modest budget" ?
150USD
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... however, I have a very modest budget.
How much money is "a very modest budget" ?
150USD
Used hp 3478a, good meter and should be in the ball park price wise on the usual auction site.
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Siglent SDM3055
http://www.siglentamerica.com/pdxx.aspx?id=176&T=2&tid=37 (http://www.siglentamerica.com/pdxx.aspx?id=176&T=2&tid=37)
https://www.eevblog.com/forum/testgear/siglent-new-bench-dmm-sdm3055/ (https://www.eevblog.com/forum/testgear/siglent-new-bench-dmm-sdm3055/)
If you're not interested in the development and bug fixes just check the last few pages. ;)
That sure looks like a very nice DMM, but not in the budget right now... :'(
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150USD
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Used hp 3478a, good meter and should be in the ball park price wise on the usual auction site.
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I have looked at those but there was a post here on the forum that said if they are not repairable....something about the display being unobtainium. Although I wonder just how often a display goes bad.
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I have looked at those but there was a post here on the forum that said if they are not repairable....something about the display being unobtainium. Although I wonder just how often a display goes bad.
They are unobtainium, but that's not a real reason to avoid them. Buy one with a working display and use it carefully.
Alternatives to consider:
Keithley 199 (5.5 digits, LED display, fits your price point but rarer than the 3478A)
Keithley 196 (6.5 digits, LED display, need to get lucky on pricing)
Fluke 8840/8842a (5.5 digits, VFD display that goes dim with age, might be missing AC, fits your price point)
BK Precision / GW Instek / Array 5.5 digit bench multimeters (typically VFD displays, modern connectivity, need to get lucky on pricing)
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... however, I have a very modest budget.
How much money is "a very modest budget" ?
150USD
Yep, you can find one with a recent cal sticker (within a year) for around 100 if youre patient from those those vendors who deal mostly in analytic/lab/test gear (I'm guessing primarily stocked from university auctions). There are a few BIN's on ebay if you're in the States for 150ish, though I think the listing I was looking at earlier was just with 2 standard probes. You can find 34401's for under 200 with the VFD fault if 5.5 digits isn't good enough for you, but really, like nidlaX said, a used hp 3478a, good meter and should be in the ball park price wise on the usual auction site. You're going to be waiting for ages on a 196 at that pricepoint. You can DIY a meter for under $100[1]. I built one for fun, although I only had an additional 6.5 to compare it against (and that was cal'd against my uni's reference transfer ~5ish yrs ago) - either they're floating in the same direction, at the same rate as a function of a time in sync or it's holding its own.
[1] https://www.youtube.com/watch?v=wxCW3pbvRi8 (https://www.youtube.com/watch?v=wxCW3pbvRi8)
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If you are planning low resistance measurement (below 100 ohm or so where the +-0.5 ohm test lead resistance of two wire measurement is to much for accurate readings) you could also build yourself a constant current source and measure the voltage drop on the unknown resistor.
I did a simple one with a lm317 a resistor and a trimmer set to output 10mA powered from 4 AA batteries, can be done
for 10 euro or 10 bucks or so including a housing, stability is surprisingly good but could always be calibrated against your meter .
Together with my reliable metrawatt ma5d (bought mine second hand 30 euro..) 5 digit meter on millivolt range I can measure from 30ohms down to 0.001 ohm.
Also save some of the budget to get nice leads and grippers.
Just as an idea.
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Alternatively, if you want to go a bit more precise than an LM317, try Maxim AN-106 and substitute your own choice of semiconductors:
http://www.wentztech.com/radio/resources/Projects/AN106.pdf (http://www.wentztech.com/radio/resources/Projects/AN106.pdf)
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I second the recommendation for the Keithley 199. It is a very nice 5.5 digit meter with True RMS AC measurements. I have two, both with the 8 channel scanner function, which can be more handy than you'd think. I use these nearly every time I am at the bench. The 199 is all through-hole construction with no special ASICs (the ADC is built from standard analog switches, op-amps, etc.), and a service manual with complete schematics is freely downloadable. Calibration/adjustment is easy and can be done on any single range or function as needed, you just need a suitable known reference to measure.
The biggest drawback of the HP 3478A is the LCD display. I absolutely despise LCD displays(*) on bench gear. They are good for handheld stuff because they are readable in sunlight and use virtually no power. For bench gear, neither of those positives actually counts for anything, and because they are inferior in every other way to LED or VFD displays, they are highly undesirable. One wonders why HP decided to use them in the first place, but it was a short-lived decision in any case.
The Keithley 2000 or 2015 is an alternative that you might find near your budget if you are lucky. These are 6.5 digit meters with VFD display. The 2015 adds audio noise and distortion measurements, but these were designed for the telecom industry and don't cut it for Hi-Fi measurements. Nonetheless, the 2015 is common enough on the used market that the extra feature doesn't really cost extra. These are less well known than the venerable HP 34401A, so they sell for much less despite being very comparable instruments.
(* I'm referring to old-school passive reflective black-on-grey type LCDs here, not big bright colour TFT LCDs ... those can be fantastic when done right).
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Thank you all who replied and shared insight and opinion. I have decided to wait and save up more funds towards my purchase of a bench DMM.
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Thank you all who replied and shared insight and opinion. I have decided to wait and save up more funds towards my purchase of a bench DMM.
In that case HP34401A can be had for under US$350
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+1 for the Keithley 199. And they provide an extra digit of resolution out of the GPIB interface.
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Thank you all who replied and shared insight and opinion. I have decided to wait and save up more funds towards my purchase of a bench DMM.
In that case HP34401A can be had for under US$350
Any major differences between an HP 34401a and a Keithley 2000? I have found both in that price range.
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Any major differences between an HP 34401a and a Keithley 2000? I have found both in that price range.
I wouldn't quibble over the difference there, either one is a great meter. Both are industry standard stalwarts.
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Any major differences between an HP 34401a and a Keithley 2000? I have found both in that price range.
I wouldn't quibble over the difference there, either one is a great meter. Both are industry standard stalwarts.
Yes, in looking at the multimeter spreadsheet, they both seem comparable. Just as a question, why do a majority of bench DMMs seem to not measure AC or offer as an option or am I misinterpreting the spreadsheet when it indicates "no AC"?
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Why is the 4 wire resistance measurement important? And what kind of accuracy is required?
There is not much sense in throwing old boat anchors at the OP without this information. For example: there are cheap LCR meters out there (less then $100 new from Ebay) which do a really fine job measuring resistances in the tens of milli-Ohm range with 0.5% accuracy.
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HP 3455/56, will do everything you could need. No size constraints, right..
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I was about to recommend looking at the old Fluke 45s, but it seems they still hold their price somewhat. >=$200 on eBay apparently.
Not bad for a 30 year old model.. :)
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Yes, in looking at the multimeter spreadsheet, they both seem comparable. Just as a question, why do a majority of bench DMMs seem to not measure AC or offer as an option or am I misinterpreting the spreadsheet when it indicates "no AC"?
Are you looking at the "AC+DC" column? That doesn't mean "no AC".
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I was about to recommend looking at the old Fluke 45s, but it seems they still hold their price somewhat. >=$200 on eBay apparently.
In the US, they are about $100. You have to watch out for dim VFDs though.
Not bad for a 30 year old model.. :)
I don't think so... the manual I have is dated 1999, and they were in production for a long time.
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Not bad for a 30 year old model.. :)
I don't think so... the manual I have is dated 1999, and they were in production for a long time.
This one is dated 1989: http://www.ece.ubc.ca/~eng-services/files/manuals/Man_DMM_fluke45.pdf (http://www.ece.ubc.ca/~eng-services/files/manuals/Man_DMM_fluke45.pdf)
The model is about 30 years old, but yea, they were in production for a long while. I doubt the pair I have here are 30 years old, considering that the VFD is as bright as ever.
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Any major differences between an HP 34401a and a Keithley 2000? I have found both in that price range.
I wouldn't quibble over the difference there, either one is a great meter. Both are industry standard stalwarts.
Yes, in looking at the multimeter spreadsheet, they both seem comparable. Just as a question, why do a majority of bench DMMs seem to not measure AC or offer as an option or am I misinterpreting the spreadsheet when it indicates "no AC"?
AC+DC is a special measurement which gives the RMS value of a waveform having both AC and DC (offset) components.
Most bench meters do AC, but not all. For some (especially very high end) it is an option. But when a bench meter does AC measurements, it is usually much better than handhelds. Many handhelds will have a AC accuracy of about +-1% full scale. I have bench meters with +-0.015% AC accuracy, better than the DC accuracy of most handhelds, which is quite a feat. The bandwidth of bench meters is usually much greater than that of handhelds as well.
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I know above first wanted $$ but seems this seller had 29 of these and with a warranty
KEITHLEY-2015
http://www.ebay.com/itm/KEITHLEY-2015-6-1-2-Digit-THD-Audio-MultiMeter-fully-tested-w-warranty-/371582307445?hash=item5684080c75:g:2IsAAOSwSdZWfBdP (http://www.ebay.com/itm/KEITHLEY-2015-6-1-2-Digit-THD-Audio-MultiMeter-fully-tested-w-warranty-/371582307445?hash=item5684080c75:g:2IsAAOSwSdZWfBdP)
$370
Might save a lot of headaches
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Why is the 4 wire resistance measurement important? And what kind of accuracy is required?
There is not much sense in throwing old boat anchors at the OP without this information. For example: there are cheap LCR meters out there (less then $100 new from Ebay) which do a really fine job measuring resistances in the tens of milli-Ohm range with 0.5% accuracy.
Those old 56(a's?, the rack-mount ones) were tanks. It's not like he's out there advocating tube Knight VTVM's or Heathkit scopes from the 50s. Those are still decent bits of kit today.
Where can you get LCR meters for 100$ new (other than those all in one chinese bare-boards all in one testers)? I'd rather pay a few (hundred) dollars extra for a company I can complain to.
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I got this simple LCR meter a couple of years ago:
http://www.ebay.com/itm/LCR-Auto-Digital-Electric-Bridge-Resistance-Capacitance-Inductance-accuracy-0-3-/272181658335 (http://www.ebay.com/itm/LCR-Auto-Digital-Electric-Bridge-Resistance-Capacitance-Inductance-accuracy-0-3-/272181658335)
I also bought an old HP/Yokogawa 4.5 digit LCR meter boat anchor but the little box just kicked the sh*t out of it (especially on the low resistance measurements) so the boat anchor got lifted and moved on to a new owner.