MJLorton Solar Power and Electronic Measurement Equipment Forum
Youtube Video Episodes => YouTube Video Episodes => Topic started by: MJLorton on January 14, 2013, 02:26:53 AM
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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..
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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.
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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
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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!"
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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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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.
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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.
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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
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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?
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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.
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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?
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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.
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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 (http://www.uni-trend.com/manual2/UT71CDE%20Eng%20Manual.pdf)
-40ºC~40ºC
(3%+30)
40ºC~400ºC
(1%+30)
400ºC~1000ºC
2.5%
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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.
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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.
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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.
hehe, I really like that analogy! ;-)
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Thanks to everyone for posting value information and talking points on this review.
Another little piece to add that was asked about in the comments was the UT61E vs UT71D burden voltage:
I used a 1mA source and measured the burden voltage / voltage drop in both mA and uA ranges on both meters:
UT61E in uA -> 0.62V in mA -> 0.01V
UT71D in uA -> 0.49V in mA -> 0.006V
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I think you must do that with all the future reviews, to show burden voltage on current ranges. As well you can connect another meter and measure open circuit voltage on resistance, continuity and diode test functions. Not often shown and quite important.
Remember high burden voltage is what made Dave develop his popular uCurrent. Very useful comparison point, thugh you might have to do a measurement on each current range, though normally the 10A range will be under 200mV with a similar contribution from the test leads.
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<thread dig>
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.
I don't believe it is actually overshooting. While it autoranges the ADC just spews out live values and the displayed range/decimal point actually lags behind the digits. The digits also seem to be autoranging up while the decimal point is autoranging down. If the display shows 455.7V briefly then it is actually 45.57V, or 4.557v or .4557v. It's a quirk but hardly a deal breaker imo. If you keep it on a manual range, it won't overshoot.
With only a single PTC for input protection and glass M205 fuses, I'm going to agree with not using the UT71D on high power circuits.... Interesting that there is a spot on the PCB for a MOV or spark gap (marked SG1, between the PTC and fuse), and larger fuse holders. I wonder if the UT71E has those parts populated since it's selling point is that it does mains power measurement.
Other things that are surprising are that they have used (what appears to be) a genuine Analog Devices AD636 true rms converter when cyrustek make an equivalent clone, the ES636, it's even mentioned in the datasheet for the cyrustek es51966 that is used in the UT71. They also use a maxim MAX6190a 5ppm/ºC voltage reference and just generally seem to be going out of their way to use reputable brands even when they could probably get away with chinese equivalents.
Things that majorly suck about the UT71 are the annoying beep every time you touch anything and can only disable if you silence all beeps, the hopelessly slow continuity tester (it is actually also reversed biased, try testing a diode with it, wtf?), the 30 second maximum on the backlight, and the resistance mode that seems to only have 4000 counts of resolution.
One other thing to consider is that the UT71 is calibrated with a heap of resistor and capacitor trimmers. You are never going to get long term stability like a Fluke 87 which is trimmed digitally. I'm still happy to use mine as my secondary meter as long as it agrees with my 87V. It sure as hell beats paying for a premium brand datalogging meter with similar accuracy as well...
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I know it's an old thread but I think it's interesting to see the changes over the time UNI-T makes to the UT71s.
Today I got my UT-71E and had a look inside. I ordered a CEM DT-9939 (its an Extech EX542) with the UNI-T UT-71E in order to test both and decide which one to keep. It will be the UT-71E.
I was surprised about the fuses I found 8) (see the photos) and the slightly changed layout so you can add some MOVs directly on the board. So UNI-T seemes to do still board revisions.
Can someone give me an advice which type of MOV I should use for this?
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There is no real input protection aside from the PTC and the resistors. I would add a 275VAV MOV in the RV2 RV3 holes, not using the trio of holes joining the 3 MOV units. Another in the RV1 hole to the lead of RV3.
That might allow it to survive a 300 V spike without blowing up, though with them having used 250V resistors in the input side instead of higher voltage ones does not bode good. Nice meter, nice ranges but not something for use in high energy or any voltages above 220VAc household mains really.
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Thank you. You are right, the UT71 is not the best for high power and high voltage. I had a closer look to the CEM/Extech they did much more for this. My main usage is household voltage so it fits my needs but if I can get a little more security with simple modifications I will do.
Another idea could be to change the two resistors to higher voltage/power ones and add three MOV-07D821K (or better MOV-07D561K http://www.mouser.de/new/bourns/bournsMOV/ (http://www.mouser.de/new/bourns/bournsMOV/)) e.g. What do you think? There should be enough place in the housing for this.
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I can't believe I missed seeing U5 the first time around and not saying about it! :-X