homemade DMM CALI check  - Page 1
Forum section: electronics / beginners

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: December 20, 2012, 04:06:56 pm
content: I picked up a used Fluke 77 Series II and I was seeing if someone built anything so you can check the DMM Cali without a reference ... I have basic equipment and that's about it ... I know about the DMMCheck but wanted to see if anyone built anything cheaper

author: SeanB
author_rank: Super Contributor
timestamp: December 20, 2012, 04:09:11 pm
content: I bought an AD581kh and used it. Cheapest one with good accuracy at RS in a package you can actually see and solder to.

author: quarks
author_rank: Frequent Contributor
timestamp: December 20, 2012, 04:54:35 pm
content: I can highly recommend Joe Gellers products (seewww.gellerlabs.com). I have the SVR and I am very happy with it. You can even buy only his board for very little money and build your own reference. I can confirm that the SVR is very accurate. For example it agrees with my calibrated Tek DMM 4050 and with my best DC calibrator Valhalla 2701C within less than 5 ppm!!! That is amazing for this little money.

author: Jeff1946
author_rank: Regular Contributor
timestamp: December 20, 2012, 05:19:40 pm
content: You can buy 0.1% tolerance resistors for about $0.30 from Mouser. Would give you a quick check on meter performance. Maybe get 3 10k ones to assure resistor isn't defective. If they all measure the same, you could put 3 in series across a 9v battery and verify linearity. I assume meter has about 10M input resistance so it will slightly affect reading since 10k/10M is 1/1000 which is resistor tolerance.

author: Unknown
author_rank: Unknown
timestamp: December 20, 2012, 09:31:03 pm
content: The interesting part about the Geller / Voltagestandard products is not that they stuck a reference IC on a PCB, but that they calibrated it with a very accurate bench DMM. For a calibrator, the focus is usually on stability, not initial accuracy. A reference IC might drift less than 0.01% in a year, but the initial accuracy may be only 5%. So you need an accurate DMM to figure out the actual value. Testing all voltage references to be within 0.01 % would be extremely expensive for the manufacturer. Even the very expensive heated zener references (eg. LM399, LTZ1000) are only specified to be 7V ish, +/- 5% or so.

author: PA4TIM
author_rank: Super Contributor
timestamp: December 31, 2012, 12:26:03 am
content: For a Fluke 77 a simple reference will do. You do not need uV stability and precision. Most references are guaranteed to some value. Just find one that meets the resolution of your meter as much as possible. And if it is aged enough find someone with a calibrated meter and check your reference.I have a 77-III, i found it about 15 years ago on a dirt-road in the rain. Used it around 10 years only in my garage, its yellow protector was totally black. It was in my toolbox while driving oldtimers without any holster other then the yellow protector.And upto today it is still spot on. Never adjusted it in all those years. I tested it a few weeks ago again while doing some calibrations. And in all those years I had to change the batteries twice and soon i think for the 3rd time. I have to recharge my agilent allmost every week ( but I use that more often)

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: December 31, 2012, 01:11:18 pm
content: My plan was to make a cheap reference board ... But I have no way of checking because I have a cheap craftsman and now a fluke which needs to be check ...I am not sure how accurate this process will be but it's the best I got ...For AC I just plugged both of my meters in the wall and compared both readings... But the best I could was to power up my cheap power supply and check the readings between the craftsman,fluke,and the display on the supply ,which where spot on with each other....Next I went through my old parts and found a couple 1% resistors and I know they are not the best but it's all I got for now ...I hooked my meters up to the resistors and found them to be spot on too yah for me lol .... I am not sure how to check the diode setting and the amps setting can't be check right now because the fuses are blow and are being order for replacement ...

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: January 17, 2013, 02:45:17 pm
content: Is it possible to build a DDM reference with a prototype board with any kind of accuracy??Also can you build a reference without calibrating it and will this accurate?

author: Amarbir[Lynx-India]
author_rank: Frequent Contributor
timestamp: January 17, 2013, 02:57:06 pm
content: Quote from: TorqueRanger on January 17, 2013, 02:45:17 pmWell,here is a company called voltage standard that makes low cost stuff for this work .Please check the same

author: Matje
author_rank: Regular Contributor
timestamp: January 17, 2013, 10:48:53 pm
content: Quote from: TorqueRanger on January 17, 2013, 02:45:17 pmYes, depending on your definition of accuracy.Quote from: TorqueRanger on January 17, 2013, 02:45:17 pmTo a degree.Use e.g. a LT1021C for 5 or 10 Volts and it will have initial tolerance of about 0.05%, plus aging of course.Good enough for checking out many (most?) handheld DMMs.