Voltage Ref help??? - Page 1
Forum section: electronics / general

author: TorqueRanger
author_rank: Frequent Contributor
timestamp: July 21, 2015, 10:34:21 pm
content: I was looking at different voltage reference to check my dmm and was thinking about building one maybe .. But anyways do you guys recommend going with 1 precision voltage reference or multi values and is it worth while to add Current reference tooThanks

author: Rick Law
author_rank: Super Contributor
timestamp: July 23, 2015, 03:19:18 am
content: How about VoltageStandard.com?DMM Check Plushas 1mA current standard and 5V AC/DC voltage standard, 4 standard resisters, frequency, etc.Also, aPentaRefat 5 buyer-selected voltages.A bit more than the Chinese made references, but what I like about VoltageStandard is that you can send it back to recalibrate against their 8digit DMM.Doug also provides very good service as many in this forum will atest.

author: eas
author_rank: Frequent Contributor
timestamp: July 30, 2015, 11:37:44 pm
content: What DMM? How many digits/counts? What readings/ranges?For $16 you can get an AD588 based reference off ebay that will give your +5 and +10v to +-5mv more or less, and will come with a reading from HP34401 (of unknown calibration) that gives the actual voltage down to 10uV, and which is probably accurate to at lest 100uV. Tempco for the chip according to analog devices is better than 3ppm/C and long term drift is 15ppm for the first 1000 hours. For power you have to provide 15V AC, or +-15VDC.For a bit more you can get an AD584 reference in a plexi case with a rechargeable lithium ion battery that gives +2.5, +5, +7.5 & +10v. Initial accuracy is worse, but they'll come with actual readings from a HP34401 with the same caveats given above. Long term drift is worse too, I think.For less than $30, you can still get a kit with the Geller reference, but it won't be trimmed/calibrated, so you start with the basic accuracy of the AD587 +10v reference, which is roughly similar to the numbers I gave above for the AD588.For $45, you can get the DMMCheck referenced above, which gives DC+5 along with a 1mA DC current source and some resistors. You'll get the actual values measured to 5 digits on a traceably calibrated DMM, and for the cost of round-trip postage you can get it recalibrate for the first two years after purchase. They also sell higher precision refs and a DMM-Check+ that adds AC outputs.If you want to build your own, it probably wouldn't be a bad idea to start by pricing out small quantities of the AD588, AD587 or the Vref used by the DMM check.As for which you should get? I can't help you. I have two different AD584 references, a AD588 board, a DMMCheck+, four bare AD588BQs, a kit for the Geller Reference, and some obsolete temperature compensated zener diodes that I'm going to play with. I also have 5 different 6.5 digit DMMs that I've been logging readings from over the past few days so I can both better describe the operating characteristics of my $16 AD588, and so I can decide if it really matters which DMMs I keep and which I sell.My advice, turn and run, now. Never doubt your DMM, never question it, unless it gives you readings that are completely absurd. If you do otherwise, you'll be on a long steep road to madness. I'm just scratching the surface. Look at the gear some people have accumulated. The time they spend to fix and verify it, the expense of getting it calibrated regularly. Most will die before they reach the end of the road, but for those that do, thatend is a dark, almost impossibly coldone.