replace dc calibration potentiometer on ut61e  - Page 1
Forum section: electronics / testgear

author: Drhappyness
author_rank: Newbie
timestamp: June 30, 2013, 09:38:49 am
content: hiI ordered ut61e from Franky still do not get it. Once I get it first thing i want to replace the dc volt calibration potentiometer to improve accuracyI wonder if anybody did it already and what value/type of potentiometer i need to buy.i do have reference devices to calibrate it.

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 30, 2013, 10:31:58 am
content: heyI got one for free from the Uni-T distributor in here , I've opened it up and found dogy SMD cap , apart of that I saw the DCV pot , 202 marked , hence 2K 10 pot I guess ,please don't you dear buying that stupide 10 Turn pot of ebay , they are fake and cheap and drift A-lot !do yourself a big favor and buy Burns , that will doPs , I've trimmed the meter to be spot on ( that stupid trimmer response like shit ) but anything higher then 30V it has few digit's out , hence I suspect the ADC or the reference or any other design aspect ,so please don't aspect to fluke 87-V alike performance .as low end "main" meter it should do , but aspect the worse in specs .

author: mariush
author_rank: Super Contributor
timestamp: June 30, 2013, 11:14:24 am
content: I would say don't bother replacing it.Don't even try to "calibrate" it if you don't have some quality reference.Adjusting your meter to show a value identical to another meter is just stupid, because they both may show incorrect value (each multimeter has a +/- something PLUS a few counts of error)The UT61E is in particular quite sensitive to temperature, Martin (mjlorton on youtube) reviewed it quite thoroughly and noticed you can adjust it to show exactly what you want and then when you close the case and let the temperature inside stabilize for let's say 30minutes-1hour you will see it drift a few counts (which is not an issue since the accuracy is 0.1% + 2 counts on DC voltage, more on others).

author: Drhappyness
author_rank: Newbie
timestamp: June 30, 2013, 11:36:18 am
content: eevblogfanOf course Bourns only, in my current projects I am interested in sub 30V range.I saw on teardown pictures trimpod code is x202 code 202 is for 200R no?mariushI am not expect fluke accuracy but I as far as I familiar with low cost china trimpods even moving/shaking it can change it's settings.I am own calibrated hp3478 also just bought from ebay chinese voltage reference Martin reviewed recently, so I think I will be able to calibrate it fine.thanks for your help!

author: eevblogfan
author_rank: Frequent Contributor
timestamp: June 30, 2013, 11:44:26 am
content: Yes I am sure it's 2K potplease see what Mariush said , he is correct , that stupid meter will vary a-Lot with temp ,cheers

author: Drhappyness
author_rank: Newbie
timestamp: June 30, 2013, 12:18:27 pm
content: HiI think to go with Vishay trimpods, for example - 70ppm and relatively cheap:http://il.mouser.com/ProductDetail/Vishay-Sfernice/T93YA202KT20/?qs=sGAEpiMZZMvygUB3GLcD7gTIXvDhNlCg4Q4LUoTH3xs%3dHope it will improve reliability and temperature coefficient of the meter.thanks for help!

author: SeanB
author_rank: Super Contributor
timestamp: June 30, 2013, 12:36:32 pm
content: You would probably be better off replacing the internal reference with an external one. When you do that you get rid of a lot of the self heating from the die, and get a more stable reference. As well unsolder the pot and measure it, then replace with a set of fixed resistors and a lower value pot, so that the effects of drift of the pot are reduced a lot. Makes for a very small adjustment range, but then drift of the pot and noise are so much lower in absolute value.

author: Drhappyness
author_rank: Newbie
timestamp: June 30, 2013, 01:54:14 pm
content: will be enough to replace 10 turn pot with 20+ turn vishay one ?

author: SeanB
author_rank: Super Contributor
timestamp: June 30, 2013, 03:08:52 pm
content: Probably will be a lot better than the existing one.