UT58C calibration manual/procedure - Page 1
Forum section: electronics / testgear

author: calin
author_rank: Regular Contributor
timestamp: July 01, 2013, 09:26:50 pm
content: I have an UT58C meter around and is in need of some calibration. That was my first multimeter ... and I still like it even if now I have some serious tools on my bench.I managed blindly to identify some of the pots from where the thing can be calibrated and I got VDC calibration OK. I mean is tracking a 5 1/2 Fluke down to last digit. Also resistance is kind of there too very close to matching the Fluke that has a 4 wire (did not tweak that one yet) . So fsar not bad for a 35$ or 60? i don't remember how much it was when I got itInstead of doing it blindly, twist this pot, then that pot see if values change etc I wold like to have/follow the proper procedure. So does anyone have or knows the proper sequence for "calibrating" an UT58C ? if not I-ll drop a mail to UNI-t maybe they are good to share the info ....

author: Lightages
author_rank: Unknown
timestamp: July 01, 2013, 10:27:23 pm
content: I have schematics for a UT58A and a UT58E, but no UT58C. Open up your meter and see what IC they are using and then maybe I can see which of the schematics will be closest.

author: calin
author_rank: Regular Contributor
timestamp: July 01, 2013, 11:47:31 pm
content: UGH .. chipset used one big blobpicture of boad attached . Nothing on the other side ...

author: Lightages
author_rank: Unknown
timestamp: July 02, 2013, 04:13:06 am
content: OK, then it is the venerable 7106 multimeter chip. It says so right on the board. The UT58A uses this chip too.It appears that VR1 is for the main DC adjustment. VR2 is for AC. VR3 I am not sure yet but it looks like it has to do with capacitance. VR4 for current. VR5 for capacitance.Of course I could be wrong.

author: calin
author_rank: Regular Contributor
timestamp: July 02, 2013, 05:21:14 am
content: Thanks, this definitely helps . The adjustment pots are on the other side and they seem to match with the schematic. UT58C has one more for Hz ... I managed to get the thing calibrated for the 20Khz range but I can't seem to hit it on the 2khz one .. wrong pot probably. Resistance seems OK, capacitance so so ... I really don't care that much but I will cal that too to match my 87V. DC after "calibration" is bang on.I also sent a mail to UNI-T just for kickers to see if they answer.

author: Alana
author_rank: Frequent Contributor
timestamp: July 02, 2013, 07:15:03 am
content: What voltage reference you used for this cal? Bench supply and compare with fluke?Any ideas on home made voltage standard that would hold its parameters longer than my meters?

author: calin
author_rank: Regular Contributor
timestamp: July 02, 2013, 07:46:45 am
content: To answer your question ... look herehttp://www.voltagestandard.com/- is not advertising by any mean. Given price I think these are decent. I usually get the best meter calibrated and then use that as reference for the other ones I have around.I have a Fluke 8842A that is supposed to be 100 times more accurate than the UT58C, so I used that and and for such I cheapie I used the bench supply.DC and Amps DC, and Ohms were compared with the 8842.AC and ~A .. the UT58 is not trms so really I did that just ballpark compared with another non RMS I have around.Hz, the UT58 measures up to an "astonishing" 20Khz , it was compared with an HP 8385A freq counter. I managed to get it right; there is a separate pot one on 2Khz and one on 20Khz that's why first time one range was off.Capacitance I had to compare with my fluke 87 V because that the only meter I have capacitance measurements relatively decent (the 8842 does not have cap) but I manged to get only the 100uF range OK, in rest the UT is all over the placeOr maybe I turned the wrong pot. I i think I have to budget for a decent LC meter ... but then I want ESR bla bla

author: cosmin1
author_rank: Regular Contributor
timestamp: January 16, 2018, 06:21:37 am
content: .. bad post

author: hernani33
author_rank: Newbie
timestamp: May 09, 2020, 06:10:26 pm
content: hello,can youe send me schematic for ut58e?do you have schematic for ut58D or you know where i can find it.coelho.hernani@sapo.ptthankshernani coelho