Used multimeter buyer's guide

[JenniferG]

Thinking about just getting this one.  It's $8 and the AD584L.  They also measure with a 6 digit calibrated multimeter, at all four voltages: 2.5, 5, 7.5 & 10V.  And they share their results on the bottom on a label.  All you have to do is dial in your meter to match their numbers.

http://www.ebay.com/itm/AD584-4-Channel-2-5v-7-5v-5v-10v-High-Precision-Voltage-Reference-Module-AD584L-/221866626734

[retiredcaps]

It's $8 and the AD584L.

Regarding all these cheap references on ebay, see this thread

https://www.eevblog.com/forum/testgear/dt9939-calibration/

In particular, my comment

"The AD584-M itself might be a decent reference, but if sellers are just cutting and pasting/writing down the same values on each unit, the numbers are worthless."

https://www.eevblog.com/forum/metrology/are-cheap-ad584-units-worth-it/

[usagi]

I have a voltage reference (Hao Qi Xin) which has served me well. (Courtesy Franky Tong)

i agree, these are great precision references. well built and handy.

[kultakala]

The following products have been discontinued:
Vref5-002
DMMCheck
DMMCheck Plus

Oops, didnt know that yet!

So, i was really lucky, got my DMMCheck Plus last week from Doug.
Probably one of the last batch

[Wytnucls]

I've had mine for over 2 years. Haven't noticed much drift, if any at all.

Today's picture:

[JenniferG]

The Instek GDM-8251A you mentioned is so tempting.  I see one in like new condition on ebay for $120 shipped.

http://www.ebay.com/itm/GW-Instek-120-000-Counts-Dual-Display-Multimeter-GDM-8251A-/291980567514

Title says "seller refurbished", so I suppose I should question the seller and ask if that means it has a fresh calibration. How do these compare to the HP bench meters in the $100-300 range?

[WaveyDipole]

Shame this wasn't on eBay UK! I might have saved a few quid/bucks. I've just purchased a HP3478A. It was clean and tidy and also described as calibrated. The photo showed a comparison with a calibrated 6.5 digit DMM. It was listed at 175GBP, but since offers were invited, I made an offer of 150GBP which was accepted, so cost to me was 165GBP shipped. Not at the cheapest end but still within the price bracket in the opening post.

The Instek listing seems to be a liquidation sale of multiple units so I would guess that they are probably being sold 'as is' or with basic power on checks performed, but but there is no harm asking the seller about the calibration. In any case its open to offers, so if you are thinking of purchasing it may be worth putting in an offer of $20-$30 below the asking price and see what happens?

Sorry but I can't comment on Instek vs HP as I have not had the opportunity to compare.

[EEVblog]

The Instek GDM-8251A you mentioned is so tempting.  I see one in like new condition on ebay for $120 shipped.

http://www.ebay.com/itm/GW-Instek-120-000-Counts-Dual-Display-Multimeter-GDM-8251A-/291980567514

US$110 each seems like a bargain. GW Instek make decent gear. Not Keysight/Fluke/Keithley level of course, but decent.

[EEVblog]

Thinking about just getting this one.  It's $8 and the AD584L.  They also measure with a 6 digit calibrated multimeter, at all four voltages: 2.5, 5, 7.5 & 10V.  And they share their results on the bottom on a label.  All you have to do is dial in your meter to match their numbers.

Beware, not all meters can be calibration adjusted that easily. They might need specific voltages and all ranges done, not just individual.

[JenniferG]

Shame this wasn't on eBay UK! I might have saved a few quid/bucks. I've just purchased a HP3478A. It was clean and tidy and also described as calibrated. The photo showed a comparison with a calibrated 6.5 digit DMM. It was listed at 175GBP, but since offers were invited, I made an offer of 150GBP which was accepted, so cost to me was 165GBP shipped. Not at the cheapest end but still within the price bracket in the opening post.

The Instek listing seems to be a liquidation sale of multiple units so I would guess that they are probably being sold 'as is' or with basic power on checks performed, but but there is no harm asking the seller about the calibration. In any case its open to offers, so if you are thinking of purchasing it may be worth putting in an offer of $20-$30 below the asking price and see what happens?

Sorry but I can't comment on Instek vs HP as I have not had the opportunity to compare.

Seems like you got an excellent deal on that HP meter, especially since it has been calibrated and looks clean   Good score!   Regarding the calibration of these "refurbished" meters this guy is selling, I did ask, and he replied "nope".

[JenniferG]

Thinking about just getting this one.  It's $8 and the AD584L.  They also measure with a 6 digit calibrated multimeter, at all four voltages: 2.5, 5, 7.5 & 10V.  And they share their results on the bottom on a label.  All you have to do is dial in your meter to match their numbers.

Beware, not all meters can be calibration adjusted that easily. They might need specific voltages and all ranges done, not just individual.

Thanks. I should of known it wouldn't be simple!  In fact, I am looking at the owners manual for the Fluke 8050A meter I am getting in a few days.  Looking at the calibration section.  To calibrate DC voltage measurements, it requires it to be calibrated in four stages.  You need to supply it a different voltage value each stage, adjusting 1 of four resisters each stage. 

From the instruction manual:

4-44 DC Calibration
4-45 Use the following procedure to perform a DC Calibration:
1. Connect the DMM Calibrator to the 8050A as follows:  H1 to the V/kohm/s input connector and LO to the COMMON input connector.
2. Select the DC V function on the 8050A
3. Turn on the DMM Calibrator
4. For each step in Table 4-8, select the range shown, and adjust the DMM Calibrator for the required 8050A voltage input level, then adjust the indicated component to the display limits.

Table 4-8 DC Calibration:
Step 1: Range 2V, Voltage INput: +1.9000V, Adjust R11, Display Limits: +1.9000 exactly
Step 2: Range 200mv, Voltage Input: +190.00 mv, Adjust R12, Display Limits: +190.00 exactly
Step 3: Range 200v, Voltage Input: +190.00v, Adjust R5, Display Limits: +190.00 exactly
Step 4: Range 1000v dc, Voltage Input: 1000.0v, Adjust R6, Display Limits: +1000.0 exactly

[iainwhite]

It's been a very useful device and it's too bad he is discontinuing it.

He is still selling the 'Pentaref'  which is voltage only (your choice of 5 specific voltages).  You would need other options for current and resistance.  Maybe buy some nice Vishay resistors from Digikey...

[WaveyDipole]

Seems like you got an excellent deal on that HP meter, especially since it has been calibrated and looks clean   Good score!   Regarding the calibration of these "refurbished" meters this guy is selling, I did ask, and he replied "nope".

Yes, as suspected. If it is in good working order then you also seem to have yourself a very good deal on that Fluke 8050 as well. Flukes keep their calibration pretty well so hopefully it will be pretty accurate.

[JenniferG]

Seems like you got an excellent deal on that HP meter, especially since it has been calibrated and looks clean   Good score!   Regarding the calibration of these "refurbished" meters this guy is selling, I did ask, and he replied "nope".

Yes, as suspected. If it is in good working order then you also seem to have yourself a very good deal on that Fluke 8050 as well. Flukes keep their calibration pretty well so hopefully it will be pretty accurate.

We'll see. I am going to take it down to my local electronics shop.  I am a friend of the guy who owns it and he knows pretty much everything about electronics.  He builds a lot of projects and showcases them in the store.  I am sure he has a large digit well calibrated meter there for comparison, and would help me out.  I suppose if I bought a few Vishay resistors from him there he'd record the values he reads from them as well for me -- then I can mount them to a pcb and slap a label on the bottom with the exact values, (to use as a reference).

[mtdoc]

The Instek GDM-8251A you mentioned is so tempting.  I see one in like new condition on ebay for $120 shipped.

http://www.ebay.com/itm/GW-Instek-120-000-Counts-Dual-Display-Multimeter-GDM-8251A-/291980567514

Title says "seller refurbished", so I suppose I should question the seller and ask if that means it has a fresh calibration. How do these compare to the HP bench meters in the $100-300 range?

In case you hadn't seen them, there are several recent threads on this meter. Several of us have purchased them.  Thanks to the recent ITT bankruptcy there are a bunch of them selling at bargain prices on eBay.  They have some nice features like dual display and the ability to display both voltage and current measurements (interleaved) at the same time.  They are easy to calibrate - see this thread or other recent threads (just do a search).

[JenniferG]

In case you hadn't seen them, there are several recent threads on this meter. Several of us have purchased them.  Thanks to the recent ITT bankruptcy there are a bunch of them selling at bargain prices on eBay.  They have some nice features like dual display and the ability to display both voltage and current measurements (interleaved) at the same time.  They are easy to calibrate - see this thread or other recent threads (just do a search).

Nice to know it can be calibrated with just a 10v reference source.  Now I really want one, after reading the calibration instructions for my less expensive 8050A.

It's interesting, many people are buying these meters recently, yet I don't see any youtube reviews nor teardowns.  I guess they'll be popping up soon

[Mr.B]

IIRC it was ~$ 70, but its redeeming feature was it contained a # of standards; voltage, resistance and frequency....
Mr B will put us right on just what it had. 

Yes it was about USD70 shipped.
It has:
10VDC
1mA
1K, 10K, 100K

The DMMCheck 'Plus' version had ACV, ACmA and frequency.
It was a bit more expensive and I chose the cheaper option at the time.

I also have one of the cheap USD20 units out of China that has DCV only, but switchable between 2.5, 5, 7.5 and 10.
It is very good for the price.

[bitseeker]

Regarding the GDM-8251A:

You can check out the insides at
https://www.eevblog.com/forum/testgear/inside-a-gwinstek-gdm-8251a-bench-multimeter/

ACV/DCV auto-ranging issue (dynamic range limitation) on 8251A and 8255A
https://www.eevblog.com/forum/testgear/got-my-gdm-8251-from-ebay-today-one-question/

How to calibrate it
https://www.eevblog.com/forum/testgear/gw-instek-gdm-8251a-dmm-calibration/

Warning: Make sure to put the CAL key in the CAL port, not the USB port. They look identical and the key will fit into either port. However, inserting the CAL key into the USB port will short the power pin to ground.

[usagi]

Topic: Keithley 196 System DMM Teardown
Topic: My Keithley 196 is on its way... (Here she is, lots of pictures)

[JenniferG]

I still need to get another multimeter, a 5.5 digit one.  I am torn between HP 3478A, Kiethley 199, Fluke 8840A and Instek 8251A.

I have the Fluke 8050A and that's it.  So whatever would be complement that one.  All four I mentioned above are about same price.

Hrm, this 6.5 Keithley 196 is only $224 free shipping.  Looks good in photo and said to be working, pulled from lab.

http://www.ebay.com/itm/KEITHLEY-196-System-DMM-Digital-Multimeter-WORKS-GREAT-/232254934100

EDIT: gah now I'm considering the 34401a

[Awesome14]

There is also a Fluke 8842A, which is better in some ways than the 8840A. But if I had the choice of the 8840A w/ AC and GPIB or the 8842A without, I'd take the 8840A. Also conspicuously absent from the OP is the Fluke 8846A, which is a nice meter, but a bit pricey.

[tautech]

I still need to get another multimeter, a 5.5 digit one.

Is a new SDM3055 outside of your budget ?
http://siglentamerica.com/pdxx.aspx?id=176&T=2&tid=37

Or next month there will be a SDM3065X available.

[JenniferG]

Yeah looking for something $100 to $250 max I guess.

Was looking at the specs for 8251A at 5.5 digits .. 10 readings per second for DCV.  Is that pretty slow?

[helius]

10 readings per second is faster than you can think, so it's no problem at all when looking at the display (if the display were to update too fast, the least digits would blur together). The situation when you want faster readings is when you're logging to a computer and can use all the data you can get. Most of the 5.5 digit meters also have smoothing/filtering options to average readings together.

[guenthert]

The HP 3456a has a generous set of 2W and 4W resistance measurement ranges (up to 1GOhm!), so I'd think it should be listed as VOM, not 'mostly voltage only'.  It's notable (other than for it's size (*)),  for its statistics functions, the user interface (no menus, all buttons), the linearity of its ADC, and the fact that it is calibrated using (externally accessible) potentiometers (no calibration data can be lost due to bad battery or NVRAM chips).  Back when, it was used as transfer standard and for calibration of lesser DMM (e.g. the HP3478a).

I think it's a (nowadays) cheap entry into volt nut territory -- the 3458a for those who can't afford/justify a 3458a. 


http://www.rlscientific.com/documenti/HP3456A.pdf


*)  Positively in the boat anchor class.  Don't underestimate the depth of the chassis.  You might need a bigger shelf.