Options for a 5.5 digit bench DMM ?

[Geoff_S]

I think I need to bite the bullet and get a bench meter with at least 5.5 digits.  I'm trying to troubleshoot some analog parts of an data acquisition system involving low level signals (~10-20 uV) and my Fluke 87V handheld just can't give me enough precision.  I've looked around and come up with a few options:
- 2nd-hand older DMM (eg HP 3478A, about $150-200)
- new, lower-end chinese DMM (eg Rigol DM3058E $500)
- new Keithley 2110 ($650)
- refurb Fluke 8808 ($650)

I'm a bit leery about buying an old unit - not so much about the lack of calibration and absolute accuracy; I just don't want to take the risk that it doesn't work reliably.

On paper the Rigol looks like a pretty even match to the Fluke 8808 and Keithley 2110.  I've read many of the threads here on the Rigol and while it doesn't get rave reviews, nor does it get bad reviews.  In practical terms is there much to recommend it over the other options ?  Any other DMM's in that price range that I could consider ?

[mtdoc]

The GW Instek GDM-8251As from the ITT auction on eBay right now are  bargain.

There's been a few threads here about them.

[Cerebus]

I'm trying to troubleshoot some analog parts of an data acquisition system involving low level signals (~10-20 uV) and my Fluke 87V handheld just can't give me enough precision.

Carefully read the data sheet of anything you're looking at as that 10-20 uV may be off the bottom of the range. That is, on some 5¹/₂ digit meters the highest resolution is 10 uV. The HP 3478 is 100nV so that'd be fine and I don't know the others you've listed off the top of my head.

With the price ranges you've quoted you could look for a 6¹/₂ digit HP 34401A as well.

I'm a bit leery about buying an old unit - not so much about the lack of calibration and absolute accuracy; I just don't want to take the risk that it doesn't work reliably.

Swings and roundabouts. Some individual older meters will be flaky because of age, some will instead be nicely bedded in and settled with most of the intrinsic long term drift having happened a long time ago.

[tautech]

The new 6.5 digit SDM3065X will be out next week if you can wait for the reviews.

Otherwise if 5 1/2 digits are enough SDM3055 @ US$ 469 could be a good option for you.
Basic functionality should be the same between these units and I'll be checking them against each other when I have a 3065X in a week or so.

[Geoff_S]

Thanks for all of the quick replies and helpful suggestions/comments ! 

The Siglent SDM3065X is probably more than I'd ideally want to spend, but I'll keep it in mind.

I had seen the Instek GDM-8251A's on ebay but the seller doesn't ship internationally   I have found a few 2nd hand HP's/Flukes though - just trying to make the decision whether to buy new or not...

[technogeeky]

There are lots of good answers to this question, and my favorite 5.5 digit DMM probably isn't one of them, but only because you want the smallest range.

The Keithley 197 is only $25-$100 and is 220,000 counts. I think that's considerably better than the GW Instek meter on ebay, but that's also guaranteed to work. But the bottom range is 200 mV with 1uV precision, which probably won't be be the leading meter here.

For the price, though, it's *very* hard to beat. I know Keithley also made nanovoltmeters during this time period, but I think they are still relatively expensive.

[mtdoc]

Another used option to consider is the Fluke 8842a.  They can be found on eBay for under $200 - sometimes much less - though not all of them have the AC option.

Shipping internationally is sometimes an issue I guess. Bummer.

[pigrew]

Another concern is the input impedance of the meter. The  GDM-8251A is only 10Mohm. Depending on the circuit being probed, higher input impedance may be needed. The 3478A, 34401A, and Keithley 196, 197 all provide >1Gohm input impedances.

If you buy the 3478A, it needs its input filter capacitors and battery replaced. The 34401A shouldn't need any sort of maintenance.

Addendum: my major deciding factor of new vs. old is if you want USB communications. If not, go for a 6.5 digit used DMM which will get you down to 100 nV resolution. Below that, you'd need to start looking for electrometers.

[technogeeky]

Another concern is the input impedance of the meter. The GDM-8251A is 10Mohm, and the Keithley 197 is 1Mohm. Depending on the circuit being probed, higher input impedance may be needed. The 3478A, 34401A, and Keithley 196 all provide >1Gohm input impedances.

If you buy the 3478A, it needs its input filter capacitors and battery replaced. The 34401A shouldn't need any sort of maintenance.

Addendum: my major deciding factor of new vs. old is if you want USB communications. If not, go for a 6.5 digit used DMM which will get you down to 100 nV resolution. Below that, you'd need to start looking for electrometers.

The 197 is 10M, 11M, or >1G Ohm, and is >1G Ohm on the appropriate ranges.

[pigrew]

The 197 is 10M, 11M, or >1G Ohm, and is >1G Ohm on the appropriate ranges.

My mistake. I just edited my earlier post. I was reading the AC volts specification by mistake.

[LaurentR]

I'd seriously look at a used 34401A. They are plentiful used, so you can pick the seller, state, age and calibration that fit you requirements. And they are bulletproof and very stable so you generally don't need to worry about being let down.

They also boots with 5.5 digits so you can pretend it's only 5.5 

[Geoff_S]

I'd seriously look at a used 34401A. They are plentiful used, so you can pick the seller, state, age and calibration that fit you requirements. And they are bulletproof and very stable so you generally don't need to worry about being let down.

They also boots with 5.5 digits so you can pretend it's only 5.5 

If I lived in the States, I'd buy a used 34401A in a heart beat   The availability of 2nd-hand bench DMM's here in Australia is very, very limited unfortunately.  Having said that, I've come across an old 8440 which might be ok.

[nctnico]

I had seen the Instek GDM-8251A's on ebay but the seller doesn't ship internationally

I'm sure they do! Last time I looked there are sellers which ship internationally. Otherwise just ask because the other sellers used to offer international shipping.

[CustomEngineerer]

The GW Instek GDM-8251As from the ITT auction on eBay right now are  bargain.

There's been a few threads here about them.

Fully agree. I picked one up for $100 even though I didn't really need one, and have really enjoyed using it. Even though it was used it was in very good condition, with only a minor scuff on the front rubber protector that wiped right off. All functionality seems to be working correctly.

[chipss]

KEITHLEY 2015 6-1/2 Digit, about $370 on ebay, sig gen, and thd, seems many here have liked them, and was a fit for me,
just throwing this one out there.

EDIT, i can not recommend this at all, I got a rock, unit in bad shape, had issues as well, sent back and do not recommend it.

[MatteoX]

34401A, suggested by many here, is a decent DMM with a resonable price especially now because it is out of production. 

But the OP wants to measure low uV signals and this is where 34401 has problems. This multimeter is not suitable for measuring small ac signals, say anything smaller than 400uV ac. For details see e.g. Joe Geller's analysis at http://www.gellerlabs.com/34401a%20ac%20zero.htm

[Cerebus]

34401A, suggested by many here, is a decent DMM with a resonable price especially now because it is out of production. 

But the OP wants to measure low uV signals and this is where 34401 has problems. This multimeter is not suitable for measuring small ac signals, say anything smaller than 400uV ac. For details see e.g. Joe Geller's analysis at http://www.gellerlabs.com/34401a%20ac%20zero.htm

To be clear, almost any 'true rms' meter that uses one of the classic AC rms chips will have this problem at the low end of every AC range, around the bottom 5%. Obviously you can avoid the bottom 5% some of the time by switching ranges (as long as the ranges have some overlap, and most meters do) but you can't on the lowest range. So, it's not just HP. This doesn't affect meters that use sampling techniques to calculate rms voltage such as the HP 3458 and some of the newer HP 344xx meters.

[usagi]

I think I need to bite the bullet and get a bench meter with at least 5.5 digits.  I'm trying to troubleshoot some analog parts of an data acquisition system involving low level signals (~10-20 uV) and my Fluke 87V handheld just can't give me enough precision.  I've looked around and come up with a few options:
- 2nd-hand older DMM (eg HP 3478A, about $150-200)
- new, lower-end chinese DMM (eg Rigol DM3058E $500)
- new Keithley 2110 ($650)
- refurb Fluke 8808 ($650)

I'm a bit leery about buying an old unit - not so much about the lack of calibration and absolute accuracy; I just don't want to take the risk that it doesn't work reliably.

On paper the Rigol looks like a pretty even match to the Fluke 8808 and Keithley 2110.  I've read many of the threads here on the Rigol and while it doesn't get rave reviews, nor does it get bad reviews.  In practical terms is there much to recommend it over the other options ?  Any other DMM's in that price range that I could consider ?

from my used multimeter buyer's guide:

GW Instek GDM-8251A. 5.5 digits. this ebay seller has tons for $109/ea. Probably the best bang for the buck right now. Try a 'make offer' around $90.
Keithley 2015 THD. 6.5 digits. this ebay seller has tons for $349.95/ea. An unbelievable deal for a fantastic meter. You will want to replace the electrolytics if you pick one up.
Agilent 34401a. 6.5 digits. Can take a while but you can occasionally pick one up for just under $400 on ebay.

[Jester]

The 8251 at close to $100 is a bargain. I have several 34401's (great meter) but they typically cost x3 what you can get a good 8251 for at the moment. If I needed another meter I would jump all over a good bench DMM for $100.

[HighVoltage]

For precision low AC voltage measurements, look for a used Agilent 34410A that is much more stable in the range that you want to measure. If you are lucky, you can pick one up for less that what the 34401A usually goes for.

[Geoff_S]

I've temporarily rented a Keysight 34461A (quite nice wish I could justify buying one outright), but still plan on getting a decent DMM to continue this work over the coming weeks.  Currently I've narrowed things down to either:
- Agilent 34401A: around $350-400
- GW Instek GDM-8251A: around $100

Other than my immediate troubleshooting task, I don't think I'll really be needing the precision of the Agilent very often, and hence the Instek is tempting.  But I find it hard to go past the solid reputation of the Agilents.  Does anyone have comments on the long-term stability of the Instek GDM-8251A ?  And how noisy is the fan in it ??

The 8251 at close to $100 is a bargain. I have several 34401's (great meter) but they typically cost x3 what you can get a good 8251 for at the moment. If I needed another meter I would jump all over a good bench DMM for $100.

Would you get the 8251 as your FIRST bench DMM though ?

For precision low AC voltage measurements, look for a used Agilent 34410A that is much more stable in the range that you want to measure.

I haven't had much luck finding 33410A's in the price range I'm looking at now, and I'm more interested in DC signals rather than AC.  I'll keep it on the short list though

[Vgkid]

For precision low AC voltage measurements, look for a used Agilent 34410A that is much more stable in the range that you want to measure. If you are lucky, you can pick one up for less that what the 34401A usually goes for.

I have rarely seen an hp 34410a on ebay, they generally go for 2-3 times what an 34401 goes for.

[Jester]

If there is a fan in my 8251 it's either very quiet or not working, I have not opened mine (shame on me).

[Geoff_S]

If there is a fan in my 8251 it's either very quiet or not working, I have not opened mine (shame on me).

I might be mistaken.  On a 8251 teardown thread somewhere here on EEVBlog, there was a picture showing a circular opening on the left hand side which I assumed was for a fan.  Perhaps just passive ventilation instead then ?

[EEVblog]

FYI
One of the lower cost brands is going to release a new 6.5 digit meter shortly.
I don't have details though.