Author Topic: UNI-T UT71D review  (Read 64416 times)

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Offline Wytnucls

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Re: UNI-T UT71D review
« Reply #100 on: May 21, 2020, 01:59:40 pm »
Here is a quick update on the DCV accuracy drift of the UT71D after 6 years since the last check:
Not much drift observed, if any against the Hao Qi Xin voltage reference, Metrahit 30M and Keithley 2000:
2.5V  -5 digits  within +/-17 digits 
5.0V  -3 digits  within +/-7 digits
7.5V  -2 digits  within +/-9 digits
10V   -2 digits  within +/-10 digits

Still well within the published 0.05% of reading + 5 LSD

 
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Offline Wytnucls

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Re: UNI-T UT71D review
« Reply #101 on: May 23, 2020, 12:21:24 pm »
One feature, that I somehow consider as poorly designed, is the SEND function, used for pre-recorded readings.  For example, while doing some experiment with solar cells, batteries and LEDs, I used my DMM to take readings every minute and let it go for 12 hours or so.

What I disliked about the overall thing is that when time came to send the data back to the computer, the program didn't take into consideration my interval setting of 60 seconds between each reading.  It actually took the current computer's clock time and used that as the timestamp.  Since the unit is sending roughly 15-16 entries per second to the computer, I ended up with time intervals averaging 65ms instead of the 60 seconds I initially set it at the beginning.

There is a function in the PC software that allows you to set a start time for your data and the interval between readings. Just tick 'RecallData', set the time and the interval in seconds before you initiate the transfer.
 

Offline zgwforum

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Re: UNI-T UT71D review
« Reply #102 on: October 15, 2020, 01:05:43 am »
I have had my UT71D for 6 years.    I had it calibrated upon purchase by a local shop that specializes in electronic equipment calibration (I think it cost me $35).   Every reading was within specification(at least the ones that could be reasonably measured).

I have had 0 issues until recently.   Just touching the indicator dial or body of the meter changes the current reading.   Very annoying.    For example, I can not zero out the resistance reading because touching the REL[Delta] button changes the resistance reading. 

This meter has been VERY GENTLY used over the past 6 years.  Zero drops that I can remember. 

But this issue is relegating it to the trash.
 
That being said, I expect to buy another one....ugh.
 
 

Offline Wytnucls

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Re: UNI-T UT71D review
« Reply #103 on: October 15, 2020, 08:19:03 am »
Please post a short video of the unusual behavior, for more accurate troubleshooting.
I would recommend you install a fresh 9V battery, inspect the battery wiring to the PCB for chafing and change your location to see if the problem persists.

Probably not relevant, but in case your body is acting like an antenna, the RF field strength susceptibility is listed as usual accuracy + 5% of range in a field of up to 1V/m.
 

Offline AngoLito

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Re: UNI-T UT71D review
« Reply #104 on: October 22, 2020, 10:43:37 pm »
Hi,
I want to make a question about UT71E unit; I have bougth new unit and I'm confusing about "Peak" function:
When I measuring AC voltage, "Peak" function offers a peak AC voltage (it's Ok and reading are according to oscilloscope)  :-+ but when I triying to measure DC voltage, or DC current, I don't understand what multimeter shows... :--
Measuring a DC power supply adjusted to 10.0V; multimeter shows 10.0V (ok) but pressing "Peak" function, display shows about 14V... (even measuring a batery, voltage are incremented when  "peak" is On)
The result is voltage multiplicated by 1.4

DC power supply adjusted to 20V DC

[attach=1]


Activating "peak", reads goes to 28V DC


[attach=2]
It seems a fail function or damaged unit, but when measuring AC voltages, is correct
Or, maybe, I'm confused about "peak" function works  :-//

Please, someone have some idea?...

Thanks in advance...
 

Offline Wytnucls

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Re: UNI-T UT71D review
« Reply #105 on: October 23, 2020, 09:10:02 am »
Peak mode should only be used while measuring AC (voltage or current).

The maximum value attained by an alternating quantity during one cycle is called its Peak value.
It is also known as the maximum value of amplitude or crest value.

Crest factor= Vpeak/Vrms (for a sinusoidal signal, sqrt 2)

Nevertheless, trying to replicate your measurements, I get different results:

20Vdc 20.27 peak
10Vdc 10.27 peak
5Vdc    5.34 peak
3Vdc    3.05 peak
1 Vdc   1.05 peak

So, possibly some larger artifacts in your ADC.

If your meter gives reliable readings in AC mode, I wouldn't worry about the discrepancy.

Edit: I just realized that your meter is a 71E, with no separate Vdc position on the rotary selector. The PCB layout is different from my 71D and the W function may introduce some extra artifacts in the 'Peak Hold' measurement, like a constant sqrt 2 factor, equating Vdc with Vrms for a sinusoidal waveform.
« Last Edit: October 23, 2020, 09:46:26 am by Wytnucls »
 
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Offline AngoLito

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Re: UNI-T UT71D review
« Reply #106 on: October 24, 2020, 07:29:17 am »
Thank you very much for your fast answer  :-+

I imagined that "Peak" mode was only for AC; but it confused me because it can be activated on mV Dc function (it does not have mV AC)
If it's a function only under AC range, should not be able to activate on DC range... ::)

Anyway I have repeated the test measuring a dead battery; impossible to have any peak  value...
[attach=1]
Definitely, UT17E multiply any measured value by sqrt 2
[attach=2]


This is my PCB; it seems an updated version (due 1000V fuses classe)
[attach=3]

Certainly, measured AC and DC values are right; I will consider using Peak only under AC ranges  :-DMM



 


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