EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: 3nigm4 on December 19, 2016, 02:13:15 pm
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Today the bought UT71D has arived and just the time to test it if power up, and a little teardown to see its iterior.
Here are some pictures but seems about the same as previous: glass fuses (enough for my usage)
The PCB is marked V20051010-12 71A
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Mine is from 12/2014 and has no glass fuses.. Very odd...
https://www.eevblog.com/forum/reviews/uni-t-multimeter-ut71d-unboxing-and-teardown/msg605921/#msg605921 (https://www.eevblog.com/forum/reviews/uni-t-multimeter-ut71d-unboxing-and-teardown/msg605921/#msg605921)
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As I understand it, Uni-T only supplies the better fuses to those destination countries which require them by regulation.
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Mine is from 12/2014 and has no glass fuses.. Very odd...
Yes, that is odd... from all the versions around, buying an Uni-T remembers me Forrest Gump's sentence: is "like a box of chocolates. You never know what you're gonna get"
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A very poor input protection.
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Other info to add:
- looking at the schema of the meter, the Voltage Reference IC is hooked to the second TI IC under the display and comunicate only to the MCU: that seams that the value compensation is made digitally by the MCU, and not by the ES51966 where its VRef is composed by resistors+cacitors+trimpot;
- the True RMS IC used is an AD636/ES636 that specifies that the accuracy is granted to 1kHz: higher frequencies compromise the accuracy; the IC is the same in many other meters where the accuracy for TRMS is granted to 1KHz... so there's no difference between UT71x and others 1kHz, even if Uni-T is reporting 100kHz bandwidth
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The specs for the UT71[cde] above 1kHz are bad.
1-10kHz: 3% + 30 counts
10-100kHz: 6% + 30 counts
I did an AC voltage frequency response test for a few DMMs. Including my UT-71C. I used an old Russian B1-9 AC calibrator as source. I did only test with 1Vrms (sine wave).
freq K2000 34401A UT-71C UT-61E
20 0.99963 0.99949 0.9877 0.9936
50 0.99990 0.99973 0.9961 1.0001
100 0.99997 0.99980 0.9975 1.0018
200 1.00003 0.99991 0.9978 1.0028
500 1.00003 1.00001 0.9982 1.0033
1k 1.00006 1.00004 1.0003 1.0030
2k 1.00006 1.00006 1.0043 1.0020
5k 1.00009 1.00010 1.0089 1.0001
10k 1.00010 1.00014 0.9962 1.0010
20k 1.00017 1.00019 0.9811 1.0083
50k 1.00015 1.00003 0.9826 1.0575
100k 0.99993 0.99964 0.9913 1.2083
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The specs for the UT71[cde] above 1kHz are bad.
1-10kHz: 3% + 30 counts
10-100kHz: 6% + 30 counts
I did an AC voltage frequency response test for a few DMMs. Including my UT-71C. I used an old Russian B1-9 AC calibrator as source. I did only test with 1Vrms (sine wave).
freq K2000 34401A UT-71C UT-61E
20 0.99963 0.99949 0.9877 0.9936
50 0.99990 0.99973 0.9961 1.0001
100 0.99997 0.99980 0.9975 1.0018
200 1.00003 0.99991 0.9978 1.0028
500 1.00003 1.00001 0.9982 1.0033
1k 1.00006 1.00004 1.0003 1.0030
2k 1.00006 1.00006 1.0043 1.0020
5k 1.00009 1.00010 1.0089 1.0001
10k 1.00010 1.00014 0.9962 1.0010
20k 1.00017 1.00019 0.9811 1.0083
50k 1.00015 1.00003 0.9826 1.0575
100k 0.99993 0.99964 0.9913 1.2083
I can believe the UT61E peaking to 1.2 at 100K. I had ran a 1 volt AC sweep of the last 61E I bought before I started to modify it (top graph). It peaked at 150KHz.