Cheapest calibration option for DVM - Page 1
Forum section: electronics / testgear

author: davorin
author_rank: Unknown
timestamp: June 28, 2014, 09:09:53 pm
content: Is there a way someone can build an own simple calibration device for calibrating voltage meters?Like using two different metals with an acid fluid to generate a well defined constant voltage?

author: acbern
author_rank: Frequent Contributor
timestamp: June 28, 2014, 09:27:02 pm
content: you should define first what absolute and what long term stability and temp. you need. easiest is a bandgap based voltage reference, depending on your answers there are then different options.secondly, you need to define what volatges you calibrate. even if you have a dmm that does artifact calibration (it calibrates itself based on only one voltage) you then need to verify the defined tolerance is met in all ranges. for that you need to have high and low cal. voltages. typically, this is done by generating a vailable voltage and using a precision self-cailbrating voltage divider. then you can refer all the voltages to the one bandgap reference.and then you also need to define of you want to also calibrate ac-voltages. if so, it gets more complicated but is doable in principle.

author: Andreas
author_rank: Super Contributor
timestamp: June 28, 2014, 09:30:53 pm
content: Quote from: davorin on June 28, 2014, 09:09:53 pmLook for "weston cell" if you want to do it from scratch.But those are not RoHS conform. (containing mercury).And need the proper temperature and some weeks settling time.And you should never let current flowing in or out so you will need a voltage divider and a null voltmeter.So you might get it easier with a ISL21009BFB or a MAX6350 @25 degrees C.Also you will find some calibrated references from the bay (looking for AD584 references).or from here:http://shop.voltagestandard.com/or here:http://www.gellerlabs.com/Voltage%20References.htm(sold out at the time).with best regardsAndreas

author: Wytnucls
author_rank: Super Contributor
timestamp: June 28, 2014, 09:34:12 pm
content: No easy chemical solution:http://www.nist.gov/calibrations/upload/mn84.pdf

author: davorin
author_rank: Unknown
timestamp: June 28, 2014, 09:39:45 pm
content: Interesting read....Well basically I would like to have voltage reference for my 3456A DVMs...the Maxim solution might be worth looking at it.Dunno if a stable voltage can be derived from a frequency like from a GPSDO....but then again...where does a satellite gets its time base from...Is it broadcasted from earth with reference to sea level?Seen an interesting documentation where to atomic clocks have been synchronized an one of them has been put on a plane for few hours....When the plane landed, the atomic clock was few femto seconds or something like that behind (o;Is there a technical paper where all the sources of reference materials are mentioned?I just know that in electronic everything comes down to V, A and seconds....

author: jpb
author_rank: Super Contributor
timestamp: June 28, 2014, 09:59:54 pm
content: Quote from: davorin on June 28, 2014, 09:39:45 pmThe Josephson junction (as in the standard Volt definition) is a voltage to frequency conversion that uses the Cesium frequency standard:http://en.wikipedia.org/wiki/Volt#Josephson_junction_definitionUnfortunately it also involves very low temperatures, superconductivity and microwave frequencies which makes it rather difficult to build for the average home hobbyist!

author: Lightages
author_rank: Unknown
timestamp: June 28, 2014, 10:06:31 pm
content: Geller Labs has shut down, so no chance of getting anything from him. I have purchased a DMM Check and PentaRefs from voltagestandard.com. That is probably your best bet for getting what you need except for maybe the accuracy you need.The problem is that different manufacturers have different voltages for doing calibrations of their DMMs. Some will require their special software to put the meter into calibration mode, some will need special key presses, some will need trim pots tweaked, and some will need some combination the these methods. Having one voltage is not going to do much good. Calibrating 3456As with any home brew stuff is not going to work. You need a voltage accuracy a magnitude better than what you want to calibrate. The cheapest option will probably be for you to send one of them out for cal and tweak the other to match with some voltage source.