Author Topic: GW Instek GDM-8251A DMM Calibration  (Read 7291 times)

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Offline Jester

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GW Instek GDM-8251A DMM Calibration
« on: January 11, 2017, 03:48:30 pm »
I picked this up for $100

Basic test looks like everything is working, except calibration is not within tolerance.

I found the calibration procedure that relies on a calibration key (readily available), calibration software "GDM8255ATE" and a Fluke 5720A or equivalent calibrator.

Has anyone ever calibrated one of these and any insight as to if it can be calibrated manually?

 

Offline gnavigator1007

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #1 on: January 11, 2017, 07:48:45 pm »
Sorry no. I ended up with 2 of these, but haven't really used them beyond some quick checks to see them working. Let me know if you do end up needing to borrow a cal key or cd.
 

Offline Jester

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #2 on: January 13, 2017, 05:20:42 pm »
Update,

I contacted Instek, and the tech support engineer sent me the manual calibration procedure. The calibration key is $10 (on order), so if all goes as expected this might be a pretty good deal, the display is excellent and I like the 2nd display function that defaults to range.

Happy camper
« Last Edit: January 17, 2017, 01:48:09 am by Jester »
 
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Offline BloodyCactus

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #3 on: January 13, 2017, 06:19:50 pm »
nice. I like my 8251, its a good bench meter for my uses. I have the cal key that came in the box with it. Just dont have a handy Fluke 5720A laying around :P Can you make the calibration pdf available?

cheers!
-- Aussie living in the USA --
 

Offline mtdoc

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #4 on: January 16, 2017, 07:26:51 pm »
Can you make the calibration pdf available?

Yes, please do!  :)
 
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Offline JXL

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #5 on: January 22, 2017, 03:40:45 am »
Bought 2 and they arrived today.  One barely met specs at 100mV, 1V, and 10V.  The other was out of spec.  Used the CAL doc from Jester to adjust both of them.  BTW, the CAL key is just a short from USB plug pin-1 to pin-4.
 
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Offline mtdoc

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #6 on: January 22, 2017, 04:02:48 am »
Bought 2 and they arrived today.  One barely met specs at 100mV, 1V, and 10V.  The other was out of spec.

Mine arrived today as well. I lucked out and it is in pristine condition. Looks new. I haven't checked every range but a quick check with my DMM Check Plus shows the measured values for DCV, ACV, DCI, ACI, resistance, and frequency to be within spec.

Quote
Used the CAL doc from Jester to adjust both of them.
Yes, thanks Jester  :-+  What did you use to generate your calibration signals?  The recommended Fluke 5725A/5720A calibrators are $30K + on ebay! If I needed to I could generate the requisite DC signals, current and resistance but not the high voltage/high current AC signals.

Quote
BTW, the CAL key is just a short from USB plug pin-1 to pin-4.
  Really! Good to know.
 

Offline JXL

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #7 on: January 22, 2017, 07:21:21 am »
Used the CAL doc from Jester to adjust both of them.
Yes, thanks Jester  :-+  What did you use to generate your calibration signals?  The recommended Fluke 5725A/5720A calibrators are $30K + on ebay! If I needed to I could generate the requisite DC signals, current and resistance but not the high voltage/high current AC signals.

I use my adjustable voltage reference (and a borrowed Fluke 8505A) to generate the DC calibration voltages up to 10V.  I checked DCI (up to 10mA range) with the voltage reference through a calibrated resistor decade box and they are right on the money.  The Resistance measurements up to 1Mohm range also check out with the resistor decade box.  That takes care of 99% of my use cases.  One of these days I'll build a HV reference to adjust the 100V range, so that will take care of 99.999% of my use cases.

 

Offline lmester

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #8 on: January 22, 2017, 08:49:33 am »
Bought 2 and they arrived today.  One barely met specs at 100mV, 1V, and 10V.  The other was out of spec.  Used the CAL doc from Jester to adjust both of them.  BTW, the CAL key is just a short from USB plug pin-1 to pin-4.

My meter firmware is current, It's cal is good. My meter came without the cal key. I was debating buying a cal key just in case I needed it later.

Has this been verified? A USB connector with a jumper from pin 1 to pin 4

If so, I won't be paying $10 for a USB connector with a jumper wire installed!
 

Offline coromonadalix

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #9 on: January 26, 2017, 03:45:07 am »
ME too   is the usb cal is only a short between pin 1 and 4 ???   are they normally the 5v and ground ??
 

Offline Housedad

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #10 on: January 26, 2017, 08:54:20 am »
I see the procedures indicated in the PDF.   Am I to understand that a precision calibrator is needed to send a signal that the DMM relates as the standard for that particular code key range? 

« Last Edit: January 26, 2017, 10:09:06 am by Housedad »
At least I'm still older than my test equipment
 

Offline coromonadalix

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #11 on: January 27, 2017, 12:58:20 am »
now i understand  with an other thread

There's two usb ports at the back, there is one named usb cal ... ,  you have to put the usb calibration key ONLY in that usb port  NOT the other "normal" one.

The usb calibration key is only a short wire between the pin 1 and 4 ..   what a strange dangerous ways to calibrate a bench dmm ... i don't know what happen if you plug it in the wrong usb port ??

I hope it is short protected.
 

Offline JXL

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #12 on: January 27, 2017, 02:07:09 am »
The 5V on the CAL USB port is through a ~1k pull-up.  Instead of a short use a 100ohm resistor between USB pin-1 and pin-4.  So if you accidentally plug it in a real USB port, you just draw ~50mA.  Actually anything below 1k works, but 100ohm pulls it to a solid Vil level.
 
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Offline branjb

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #13 on: February 10, 2017, 04:26:46 am »
I got one of the GW Instek GDM-8251A on ebay via the ITT auction and it reads ~300mV higher than its source.  Does anyone have any insight into how you can calibrate it without a Fluke 5720A?

Is it as simple as following the manual steps in the PDF above, and for each CAL code, putting the requisite signal on the input? (ie, to calibrate for 10V, select CAL code 15, and put 10V on the V input?)

« Last Edit: February 10, 2017, 04:43:51 am by branjb »
 

Offline JXL

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #14 on: February 10, 2017, 06:45:01 am »
I got one of the GW Instek GDM-8251A on ebay via the ITT auction and it reads ~300mV higher than its source.  Does anyone have any insight into how you can calibrate it without a Fluke 5720A?

Is it as simple as following the manual steps in the PDF above, and for each CAL code, putting the requisite signal on the input? (ie, to calibrate for 10V, select CAL code 15, and put 10V on the V input?)



300mV is way off!
Yes, just put 10V on the inputs for CAL code 15, but you should calibrate CAL code 11 (0V) first.
 

Offline branjb

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #15 on: February 11, 2017, 12:59:46 am »
Calibrated and it works great.  Pretty impressed for a $100 DMM, thanks ITT!
 

Offline Housedad

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #16 on: February 11, 2017, 06:42:30 am »
I think I lucked out.   I ordered and received a battery powered AD588BQ voltage reference from China (yeah, I know)  Anyway, it came with a supposed readout from a Agilent 34401a.  ( whoopy doo  a measurement that may or not be calibrated)   They showed a measurement of 10.00039 and 5.00057.

Going by the AD588 Datasheet,  It should not be any more than +/- 1mv off of 10v and 5v.    I hooked up the +15v and -15v to the board from my power supply  (Instek GDP-3303s) and let the AD588BQ  and DMM's warmup for two hours and  checked the voltages.   Meters set to slow mode.  Using standard Probemaster 8008 leads 60" long. 

unit 1:

AD588   5v:     4.9999v
AD588 10v:     9.9993v


Unit 2:

AD588   5v:     4.9999v
AD588 10v:     9.9990v

I know this is only a relative comparison with nothing verifiable, but even given the GDM-8251 tolerance of .012% +5, I'm pretty happy with it. 

edit:  I had originaly mistyped the name of the chip as AD855BQ  when it is actually a AD588BQ reference chip.  Sorry for the confusion it may have caused anyone.
« Last Edit: March 30, 2017, 08:11:42 pm by Housedad »
At least I'm still older than my test equipment
 

Offline h_p

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #17 on: May 03, 2017, 03:04:25 pm »
I just picked up this meter from the ITT auction on eBay. It appears mine is also off by about 300mv. Would any of you folks in the USA be willing to calibrate mine for me? I'd pay for round trip shipping and your time. Thanks!

Also my meter is at firmware version 2.3. Where did you find info on what the latest firmware is? I saw that a new version was released this year. I'm going to try and install that as well.
 

Offline coromonadalix

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #18 on: May 03, 2017, 08:17:28 pm »
The latest seems to be : GDM8251A_V230_7DA400_991130.hex  available  on their website ...

v 2.3 firmware file on EEvblog
https://www.eevblog.com/forum/testgear/gwinstek-gdm-8251a-firmware-file-request/?action=dlattach;attach=300958
« Last Edit: February 16, 2019, 01:57:21 pm by coromonadalix »
 

Offline h_p

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #19 on: May 03, 2017, 09:03:19 pm »
I couldn't find that but I contacted them and they said my unit is running the current firmware.
 

Offline analog8484

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #20 on: February 16, 2019, 08:46:24 am »

I just got one of these and I am trying to calibrate it following the instructions in this thread.   However, I am not sure it's working correctly.  I put in 10V reference voltage and started to run "CAL 15" calibration and tried to save then the "*" appeared and it's supposed to blink when done but it's been over an hour and it's still not blinking.   Is this normal?  Should I wait?  Any help would be appreciated.

 

Offline coromonadalix

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #21 on: February 16, 2019, 02:00:32 pm »
Ask gw Instek for the procedures, maybe you have to do something first like an zero calibration etc ... if you skip a step  maybe the meter doesn't calibrate properly ??


I had a meter who had to do the zero/shorted input before anything else ... if not,  nothing was stored ?
« Last Edit: February 17, 2019, 05:27:05 am by coromonadalix »
 

Offline analog8484

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #22 on: February 17, 2019, 12:27:00 am »


It turns out the instructions in the manual is incorrect.  The "*" appears solid when calibration is saved instead of blinking.   I am satisfied now the meter is calibrated to ~100uv accuracy at 10V scale.
 

Offline coromonadalix

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Re: GW Instek GDM-8251A DMM Calibration
« Reply #23 on: February 17, 2019, 02:29:09 am »
Ohhhhhhh   thks

https://www.eevblog.com/forum/testgear/gw-instek-gdm-8251a-dmm-calibration/?action=dlattach;attach=285658


never saw this link, even when it poped into my eyes  loll  sorry    glad it worked for you   :-+
 


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