Author Topic: Multimeter Review / buyers guide: UNI-T UT71D  (Read 30100 times)

MJLorton

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Multimeter Review / buyers guide: UNI-T UT71D
« on: January 14, 2013, 02:26:53 AM »
Links to the video reviews:

Part1: http://www.youtube.com/watch?v=EBGEXVp18U0
Part2: http://www.youtube.com/watch?v=V8oXR_lrJyA

Photos of the inside..
« Last Edit: January 14, 2013, 03:57:28 AM by MJLorton »
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Monkeh

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #1 on: January 14, 2013, 11:51:16 AM »
The amp inputs do not use optical detection. The four solder joints go to the two halves of a split jack, one side is connected to the meter input, the other is connected to the sense circuit. When you short the two with a banana plug, it knows you've inserted it. The heat from attempting to desolder them could allow them to short together permanently, so don't try that again.

They should actually have pulled out from the case with some gentle prying, but it depends how it was constructed.
« Last Edit: January 14, 2013, 12:00:35 PM by Monkeh »

valentinc

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #2 on: January 14, 2013, 07:59:29 PM »
I have a UT71C and the board comes out without desoldering anything ...

On the other side of the PCB there is the main chip, a Cyrustek ES51966P

Under the first shield is a TI MSP430 custom labeled microcontroller and a EEPROM memory for the data logging

There are 2 display drivers HT1621B one on the each side of the PCB

And under the second shield it seems there are the resistive dividers and some compensations capacitors for the voltage measure


I have this multimeter for more than a year now, and I can say, that for electronics work on a bench is the cheapest one you can buy with this functionality
Valentin

jwrelectro

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #3 on: January 15, 2013, 02:12:20 PM »
Hi Martin I also posted this is the comments area of your video.

"Hi Martin, I give an example of the AC+DC function in my video jwrelectro: "Part 2 of 4 Review Amprobe AM-140-A" at around 8:50. The reason you saw no change is because you are measuring an AC mains voltage which in theory should have no DC component/offset. Nice video!"

MJLorton

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #4 on: January 16, 2013, 01:57:19 AM »
Hi Martin I also posted this is the comments area of your video.

"Hi Martin, I give an example of the AC+DC function in my video jwrelectro: "Part 2 of 4 Review Amprobe AM-140-A" at around 8:50. The reason you saw no change is because you are measuring an AC mains voltage which in theory should have no DC component/offset. Nice video!"
Thanks very much for that input...silly me!
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Administrator

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #5 on: January 16, 2013, 02:07:10 AM »
Folks...please take note.

I do not tolerate personal attacks and disrespectful debate between members on my forum. Keep it civil and respectful.

Sadly I have now banned two members and warned another. Offending posts have been removed.

Please flag any posts which may be of concern.

MJLorton

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #6 on: January 16, 2013, 02:12:27 AM »
I have a UT71C and the board comes out without desoldering anything ...

On the other side of the PCB there is the main chip, a Cyrustek ES51966P

Under the first shield is a TI MSP430 custom labeled microcontroller and a EEPROM memory for the data logging

There are 2 display drivers HT1621B one on the each side of the PCB

And under the second shield it seems there are the resistive dividers and some compensations capacitors for the voltage measure


I have this multimeter for more than a year now, and I can say, that for electronics work on a bench is the cheapest one you can buy with this functionality

Thanks for your post. As soon as I have time I will try the same procedure and keep my soldering iron turned off! :-)

Cheers, Martin.
Play, discover, learn and enjoy! (and don't be scared to make mistakes along the way!)

retiredcaps

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #7 on: January 16, 2013, 02:27:45 AM »
Keep it civil and respectful.
I will only add that people should learn the and practice the phrase

"Agree to disagree"

Wiki

http://en.wikipedia.org/wiki/Agree_to_disagree

retiredcaps

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #8 on: January 16, 2013, 02:29:30 AM »
I know the multimeter junkie did a review of the Uni-t 70D and he ran into suspicious battery low indicator as well.

http://www.youtube.com/watch?v=eYoadGf6sI8&list=UU6SZfovWpIZ9yVKJW28fvUg&index=11

I'm not sure if the 71D and 70D use the same CPU or not?
« Last Edit: January 16, 2013, 02:47:51 AM by retiredcaps »

retiredcaps

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #9 on: January 16, 2013, 02:42:49 AM »
Everyone who watches Martin knows he has certain pet peeves regarding multimeter functionality.

One of mine is overshoot.  When I see a multimeter overshoot dramatically, I automatically distrust it.  So at 31:28 (part 2) when the UT71D shows 455.7V AC on mains, I'm already never going to use that multimeter on anything high voltage.

Now everyone knows that it can't be right when connected to mains (only 240V AC), but what if I'm an electrician who works on "unknown" equipment/scenarios?  What if the multimeter first shows 800V AC and then settles to 400V AC?  Which one is right?  Can it possibly be 800V for a brief moment?

PS. The Fluke 17B overshoots.  I'm sure Martin will discover that when he reviews it.  Not by chance, I'm not an owner of the Fluke 15B or 17B.

See 2:22 into this video (Fluke 17B shows 6.83V first then 4.99V for a 5.0V reference).

http://www.youtube.com/watch?v=3y5wjaNusr0

PPS. I also noticed that Fluke multimeters that use Vchek like the Fluke 12 and 113 (just two examples) overshoot slightly.  For example, if the correct reading is 5.0V, the two above mentioned will show 5.02V and then 5.0V next.
« Last Edit: January 16, 2013, 02:49:05 AM by retiredcaps »

Mr Eastwood

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #10 on: January 16, 2013, 08:13:05 AM »
The other day I was looking over the UT71 C/D/E specs. for temperature measurement and it states..
Range: -40ºC~40ºC
Resolution: 0.1ºC
Accuracy: + - (3%+30)

Now I'm not great at math, but to me that means a reading of 29.4ºC as Martin measured in his superb video review would give a potential uncertainty of +- ~3.8ºC,  which seems quite misleading for something that displays at a 0.1ºC resolution?
Hey! Frisbee! Far out!

valentinc

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #11 on: January 16, 2013, 08:39:08 AM »
On the UNI-T website I see that they say -40 ... 1000 ºC and the specified accuracy is +/- 1% + 30 counts

http://www.uni-trend.com/UT71C.html

At a temperature of 29.4 ºC the uncertainty is +/- 0.294 ºC, this ignoring the +/- 30 counts

Anyway, a multimeter isn't a precise way to measure temperature ...

I think that for general purpose temperature measurements it's ok to have only 1 degree resolution and ignore what is after the decimal point.
Valentin

Mr Eastwood

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #12 on: January 16, 2013, 08:51:52 AM »
On the UNI-T website I see that they say -40 ... 1000 ºC and the specified accuracy is +/- 1% + 30 counts
http://www.uni-trend.com/UT71C.html
At a temperature of 29.4 ºC the uncertainty is +/- 0.294 ºC, this ignoring the +/- 30 counts
Anyway, a multimeter isn't a precise way to measure temperature ...
I think that for general purpose temperature measurements it's ok to have only 1 degree resolution and ignore what is after the decimal point.


The online html specs are not as complete as the manual specifications (manual - page 68)
http://www.uni-trend.com/manual2/UT71CDE%20Eng%20Manual.pdf

-40ºC~40ºC
(3%+30)

40ºC~400ºC
(1%+30)

400ºC~1000ºC
2.5%
Hey! Frisbee! Far out!

valentinc

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #13 on: January 16, 2013, 09:39:45 AM »
Yes, you are right. I didn't check the manual  :-[

From what I can see on wikipedia, a K type thermocouple has a sensivity of ~ 41 µV/°C so you must use a very precise low noise amplifier to get an accurate result. And of course that a cheap multimeter like this UNI-T can't afford to do that.
Valentin

SeanB

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Re: Multimeter Review / buyers guide: UNI-T UT71D
« Reply #14 on: January 16, 2013, 10:36:30 AM »
Difference between resolution and accuracy. you can buy a digital measure that has 5 digits of reading, but is only accurate to 4. Resolution is how many points you can distinguish over the scale range, it the number of separate points on the range. Accuracy is how close the reading on the scale refers to the real world signal you are measuring.

Think of having a meter rule with divisions of 0.01mm on it, but you are measuring between 2 points which have been marked with a child's crayon. You can read to 0.01mm, but your reading is in reality only going to be correct to 5mm ( the crayon thickness) either way of the correct value.