UNI-T UT71D review

[Wytnucls]

1.   Introduction


 
Here is a review of one the UNI-T flagship multimeter series, the 40,000 count UT71D, which is the only one with a massive 9,999 registers for internal logging.
It arrives as a reasonably priced comprehensive package, providing everything one needs to utilize all its features, at no extra cost.
Most high-end manufacturers will charge extra for logging software and RS232 PC communication hardware.
On some meters, the internal logged data is not even accessible to the user, unless the meter has a PC connection.
Four other models are available in the series:
Two meters with a 20,000 count, the base unit 71A with reduced accuracy, no internal logging and no temperature measurement and the 71B with 100 memory registers.
Two more meters complete the line-up with a 40,000 count, the 71C, otherwise identical to the 71B and the 71E, also with 100 memory registers, but capable of dual measurements, voltage and current to display power data (W, VAr, VA, PF)
I have owned the 71B and the 71D for a couple of years now, both bought in China from electronics shops, with a one-year warranty.
Most people will be familiar with these DMMs already, as Martin Lorton has released a couple of videos about the 71D. They will be linked at the end of this review. Dave has a 71A in his multimeter trunk, but hasn't reviewed it yet.
Martin did a pretty good job with his review, so I will expand on some of the most important features from an owner’s perspective and mostly avoid a repeat of what he has covered already.

2.   What’s in the box?


 
The soft nylon case is pretty useful, sturdy and large enough to accommodate a few extra items, like screw-on probe hooks and SMD tweezers.
The meter itself is quite light for its size (395g), as it lacks a beefy rubber holster, but has enough heft to not feel cheap at all. At first sight, the LCD appears surprisingly and pleasantly very large.
The first set of probes I got with the 71B were great, very flexible, made from silicone, whereas the later batch came with stiff PVC leads and, while adequate, are best replaced by something more pliable.
The short lead croc clips are very useful and I reach for them all the time.
The logging software is on a CD, installs easily on a windows machine and provides enough features to satisfy most users.
The USB optical module fits snuggly on the top of the meter, looks well-made and has a useful cable length of about 1.5 meter.
The K-type thermocouple works fine but looks rather flimsy and fragile.
The slip-on probe croc clips are ok, but I rarely use them.
The Chinglish manual explains most of the features, but has a few mistakes and some omissions. Still, it's pretty good by Chinese standards.

3.   Ergonomics
The meter has a pleasant sleek narrow body with very little padding, which doesn't take much room on the bench, and a big ergonomic range switch which emits a mildly annoying beep at each selection.
The meter feels surprisingly sturdy, with no creaking detected when trying to twist the body.
It is probably not the ideal meter for someone who throws stuff in a heavy toolbox, but is quite at ease on an electronic bench.
The front plate has 8 switches, with 6 of them providing multiple functions. Getting on top of the menu system and features requires some practice, but is well worth the effort for someone who wants to use all the features they paid for.
The meter has separate DC and AC voltage positions, DC mV, C/F temperature, uA, mA , 4-20mA  percentage loop, Hz and duty cycle.
The 9V battery compartment is a bit tight but manageable and the lid is held in place with a machined screw fitting into a metal insert.
Unfortunately, there is no direct access to the fuses and 4 self-tapping screws need to come out, to split the case open.
Some people complained about the short bale which has a shallow angle, but it never bothered me and I fixed the slight rattle with a small rubber damper.
One of the best features of the meter is the large LCD display which has good contrast and a 2-step bright backlight. The curved glass increases reflections, so possibly not the best for use in a lab with multiple light sources.


 

[Wytnucls]

4.   Features
The ADC has a true RMS 40,000 count and a faster 4000 count option on start-up, if required.
The meter window displays 3 parameters at once, a feature which is very useful for Max/Min measurements, for instance. All the display options can be seen by pressing ‘Hold’ while turning the meter on.
The yellow button provides an AC+DC measurement for voltage and current. The AC bandwidth is reduced on current from 100KHz to 10kHz. AC+DC is also available on current ranges.
Here is a bandwidth comparison with a Gossen 26s, which has a bandwidth of 20kHz:



The Max/Min feature takes a reading every 2 seconds, with both extremes displayed on the top row 4,000 count places. Further presses of the button toggles the readings to the main window for a higher resolution.
Peak Hold can capture 10uS transients on fluctuating voltages and currents. It is much faster than the standard 250uS. It is also useful to display peak voltages of a sine waveform.
Internal storage has 9,999 registers and all can be recalled and viewed directly on the meter (I can't do that on my Gossen 30M). Stored data includes measurement type and units.
The bar graph can be removed through the menu options and can also be modified with the zero in the middle of the scale.

There is a Pass/Fail feature, providing an aural warning if the entered top (fast beeps) and bottom (slow beeps) limits are exceeded by the new measurement. Procedure: SET UP LOW- SET (HOLD to move to next digit +/- to alter digit - Exit) SET UP HIGH (same procedure) Press STORE to set limits to OFF

The caps are discharged automatically through the 1.1K PTC before measurement, if they carry excess voltage. Capacitance measurement covers a wide range from 1pF up to 40mF.
Here is a comparison with 2 LCR meters for capacitance measurements and a picture showing temperature readings:

 

Frequency can be measured accurately, up to 40MHz.
Thermocouple temperature is displayed with a 0.1C resolution.
The meter has auto ranging and the current range is usually displayed in the top left window, with the frequency, when relevant, displayed in the top right place.
The ‘REL’ button is useful to get rid of test leads resistance or capacitance for accurate small caps and low value resistor measurements (<400 Ohms). The top right display shows the reading at the time the REL button was pressed. The top left display shows the current reading and the main display shows the difference between the two, staying in the original range. Caution: The meter does not auto range anymore in that mode, showing OL above the current range.



Less useful for most casual users is the 4-20mA loop feature, which displays mA current in a percentage format.

5.   Safety
This is probably the most contentious aspect of the meter.
It does have one 1.1K PTC and two current limiting resistors (1K and 100K)
Less conspicuous are the crowbar transistor circuits protecting the meter up to 1000V.
It also has aural warnings on the current jacks, to prevent dangerous selections.
The current ranges are protected by 2 fast acting glass fuses of 10A and 500mA respectively.
The uA and mA ranges also have a diode bridge, including a Zener diode, to clamp high voltages.
There is a low battery voltage warning, during which measurements are not to be relied upon.
That configuration with glass fuses doesn’t comply with the latest IEC regulations and a new PCB version was released with extra space on the board for HRC fuses and wider creepage distances.
The meter was never tested by independent safety organizations, so its rating of CAT III 1000V/ CAT IV 600V is still under question.
It is best to avoid using this meter on high power circuits until proper testing has been published.



6.   Accuracy
General accuracy is respectable, at 0.025%+5 on the mV DC range and 0.05%+5 on Volt DC.
The DC current accuracy is 0.1%+15 on the mA/uA ranges.
The burden voltage is a little high at 5mV/mA on the 40mA range and 500uV/uA on the 400uA range (1.8mV/mA and 100uV/uA on the Fluke meters).
The resistance tolerance is 0.3%+8 up to 40kOhm and on caps, 1.2%+20 up to 400uF.
Frequency readings are usually spot on, at 0.01%+8 up to 40MHz.
AC current measurement, because of the true RMS converter limitation of 10% of range, is tricky. There is a zone between 400mA and 1A, where AC measurements are not to be trusted. Ideally, the meter should have had a 4A extra range, to cover the dead zone. DC current measurements are not affected.
The cold junction temperature is tapped on a transistor PN junction on the middle of the PCB and with the provided K-type probe, measurements are good up to 230C. Accuracy is quoted at 1%+30 above 40C.
Peak Hold accuracy is 1.2% of scale+25digits for voltage and current.
Over the last 2 years, my UT71 meters have experienced very little drift, and stayed within the original 12 month guaranteed accuracy deviations.
The 2ppm/C Maxim external voltage reference has a maximum drift of 50ppm/1000 hours and usually settles down after that period.
Here is a recent comparison of least significant digits on DC Volt and resistance between my most accurate Gossen 30M as a reference and the Gossen 26S, 71B and 71D (All the meters have their original calibration):

[Wytnucls]

7.   Calibration
Calibration is best done with the closed-case procedure, with the aid of an accurate voltage/resistance standard or calibrator for all ranges.
To enter closed-case calibration, push ‘Exit’ and the blue button together on start up. Press ‘Hold’ to capture correct inputs (multiples of 19).
Otherwise, pots can be tweaked internally:
VR1 AC current (1A 60Hz)
VR2 DC volt multi-turn pot
VR3 AC volt
VR4 Temperature cold junction with probes shorted for ambient temp
VR5 AC+DC volt <50 digits with probes shorted.





8.   PCB Architecture



The meter has a double-sided board with most components on one side.
The switches, the ADC, the LCD, one of the LCD controllers and the backlight LEDs are on the reverse side.
The piezo speaker is anchored on the back case with spring contacts to the main board.
A small PCB placed on top of the current jacks provides the detection for the aural warning.
The whole meter can easily be disassembled without de-soldering any parts.
Metal cans shield the microcontroller and the precision resistor network.
The soldering quality is generally fine, with flux residue in some places where a few components where hand-soldered.
   


9.   Operation
Here are some of the most important aspects of the meter that can affect your measurements.
Settling times for capacitance are for 400uF 1.5 seconds, for 4mF 3.75seconds and for 40mF 7.5 seconds. The bar graph movement gives an indication of the time left for big caps readings.
The auto discharge can take some time, depending on the initial voltage
The adjustable auto power off (APO) can be disabled or set to 10, 20 or 30 minutes.
The backlight has 2 levels of brightness and is adjustable to 10, 20 or 30 seconds.
The ‘Peak Hold’ can capture fast transients of at least 10uS duration.
The bar graph updates 10 times per second and has 40 segments.
The Low/High aural warning triggers stay in memory, even after meter shutdown, so the values need to be removed from the set up screen, after each use.
The voltage impedance is 10MOhm, except for mV, which is 2.5GOhm.
Continuity beep is triggered below 50Ohm and the testing voltage is set at -1.2V.
The diode open voltage is 2.8V. Most LEDs light up (YGRW) and the forward voltage is displayed, except for the white LED.
The storage interval default to 1 second, but can be increased up to 255 seconds.
A new series of data can be appended to the existing ones in memory or set to overwrite them and start anew from register 0001.
In ‘Recall’ mode, it is possible to page through the previous recordings with the ‘+’ and ‘–‘ keys. Each data point was stored with its unit and type of measurement.
Press ‘Hold’ while in ‘Recall’ mode to send all readings in memory to the PC software.
When measuring AC voltage the true RMS reading is valid from 10% of the range upwards and cannot exceed the max crest factor of 3.0. The frequency should be kept below 100 kHz for an accurate measurement.
In AC+DC mode, add 1%+35d to the AC accuracy specifications.
5A is the limit for continuous measurement.
Current draw is an average of 7mA and the 9V battery should last about 100 hours.

Here is a digest of procedures for proper memory storage operation:

There is no memory delete prompt as such.
All one can do is append a new batch of data to the existing data in memory or choose to overwrite the existing data from the beginning.

To store new data in memory:
Press STORE key
Press HOLD key if you want to overwrite old data, otherwise skip this step
Press STORE key to set recording interval (then + key repeatedly to set from 0 to 255 seconds) (Hold key continuously for fast scroll)
Press STORE key to start recording
Press EXIT key to stop recording

To review stored data:
Push STORE key for 1 second (RECALL)
Select registry number with the + or - keys
Press HOLD key to send all stored data in memory to computer via USB

At any time, to send a single measurement reading to the computer via USB, push MAXMIN key for 1 second

[Wytnucls]

10.   PC software



The meter comes standard with a USB RS232 cable with an optical connection module.
The software may seem pretty contrived at first, but its functionality is quite acceptable, after some experimentation.
Toggle the ‘USB connect’ soft button to stop and start your logging session.
Values can be entered in the Min/Max windows for aural exceedance warning.
Tick the ‘Repeat’ function to suppress non-changing measurements.
Enter your required sampling interval in seconds in the next window.
Afterwards, the log can be saved as an Excel worksheet or sent to a printer.
Use the ‘Recall data’ feature when you want to retrieve data from the meter’s internal memory. You can set a start time to match the original capture if you wish and also match the logging interval of the original data capture .
The graph is the most frustrating. You have to use your mouse to select the area of interest. Drag right with the left mouse button pushed in to select a small window and when you’re done, drag left to zoom out to the original graph.
Hold the right mouse button in and drag to reposition your viewing window.
Tick ‘Fill’ for a blue bar graph instead of a continuous line.
Choose a number of points per page if required and press ‘+’ to enlarge the graph window.
Multiple meter logging is possible, in two separate windows.
Fast logging (8 samples per second) in real time is possible, wen the meter is in 4,000 count mode.

11.   Components
U1 ES51966P Cyrustek dual-slope ADC
U2 M430F149 micro controller TI
U3 U9 HT1621B Holtek LCD controller x2
U4 Opamp STEZ832 062C (thermocouple cold junction circuit)
U5 ES636 (AD636J) TRMS to DC converter 1% error, crest 6 (Cav=10uF)
U6 Dual Opamp STEZ832 062C (frequency circuit)
U7 Voltage regulator 5.5V
U8 Voltage regulator 3.5V
U10 24LC515H Memory microchip CMOS I2C Serial EEPROM 512K
U11 HCF4011 Multiplex NAND gates AESA
U12 Maxim MAX6190A bandgap voltage reference 2ppm/C 1.25V 50ppm/1000hrs
U13 Dual Opamp ST7444 72C (TRMS circuit)
U14 Precision Opamp OP1177 AO47 (V Ref circuit)

1 PTC (WMZ11-75HV 1.1K)
2 Crystal Oscillators (4 MHz for the ADC and 32 kHz for the TI uC)
8 Precision metal film resistors 1W TCA5C6 (4x2.5M and 1M11, 101K, 10K1, 1K01) (0.05% resistance tolerance and 10ppm/C). More recent boards (from REV6) have SMD precision resistors instead, replacing the through hole resistor network.
 




12.   Value
Nowadays, the UT71D meter sells for about 135.00 USD, including shipping costs on eBay, from Hong Kong and China sellers.
I still haven’t found another meter that comes close to the specifications and features of this UNI-T, at this price point.

13.   Variants
They were a few rebranded meters available in Europe and the US, but I think that most have been discontinued by now.
It is still possible to find a Tenma, Voltcraft and a few others on numerous internet sites, but not necessarily with the same set of features as the originals.
 


14.   Modifications
There usually is space for HRC fuses and an MOV/spark gap on the board, but while probably made safer, doesn’t necessarily meet the latest safety regulations.
There have been several board revisions over the years, so this may not be always feasible, depending on the PCB configuration.
I didn't bother modifying the 71D and I would advise against it if you only work with low power circuits, like I am. I soldered a few extra bits in the 71B, but it was more for the fun of the exercise rather that a quest for total safety.
Here is a picture of the modifications on my 71B:


 
15.   Criticisms
Here are most of the perceived flaws mentioned by some owners. While some are justified, others might just be nit-picking.
The reflective LCD curved acrylic cover was mentioned a few times as a nuisance in rooms with multiple light sources.
The lack of a blank insert for the USB plug recess was also criticized. The one provided with the UT61 is a perfect fit though.
It has an irritatingly slow continuity, but at least the signal is latched.
I did find a way to achieve a faster continuity test which doesn't involve any modifications:
1. Turn the range switch to Ohm and select the diode mode by pressing the blue button twice. You are now in the 4V range.
2. Press the RANGE/SETUP button until the meter beeps and displays OFF in the 'low' setting.
3. Press the HOLD button once to access the count display.
4. Press the HOLD button repeatedly to select each number in turn.
5. Change each number with the + and - buttons until your display reads 27400 or slightly lower and press EXIT to store it.
6. You are now in a fast mode for your continuity testing, staying in the diode range.
7. When you are done with the continuity testing, press RANGE/SETUP until it beeps again, then press STORE to display OFF in the low mode.
8. Press EXIT to return the meter to its usual state.
It is a bit of a convoluted procedure, but at least the function is available if you don't have another meter at hand.

Of course, the glass fuses elicited a lot of scorn, but, at the time of production, high voltage HRC fuses were not a safety requirement. On the positive side, if you blow them regularly, they are dirt cheap to replace.
The bale angle is sometimes considered too shallow. 30 degree from horizontal, which is fine for me.
It has a too slow LCD update rate for some, with one refresh per 2-3 seconds. (My Gossen 26S behaves the same way)
The battery compartment is too tight for comfort. It is a tight fit, but no enough to provoke lasting frustration, in my view.
The meter is fragile and may not survive a drop test. Probably true, but for electronic work, if kept on the bench, it should be relatively safe from any damage.

16.   Conclusion
I never regretted buying these two meters and although I have acquired a few more ‘respectable’ ones since then, I still reach for the 71s on a regular basis.
I think they have tremendous value for money and are ideal for hobbyists who don’t want to spend a fortune on top-end meters and their optional logging accessories.
Of course, they are not perfect by any means, but UNI-T managed to produce a dependable full-featured meter, at an affordable price.
The inaccuracies on low ACA are a concern, especially on the 71E, so keep that in mind if you're considering buying one of those meters.
Hopefully, the next version will be even better and will comply fully with the latest safety regulations.

Martin Lorton's review:

[Wytnucls]

I have attached here the most relevant datasheets and any other useful information:

1.AD636 TRMS to DC converter: http://www.farnell.com/datasheets/1780748.pdf
2.Maxim voltage reference MAX6190: http://datasheets.maximintegrated.com/en/ds/MAX6190-MAX6198.pdf
3.Calibration procedure: https://www.eevblog.com/forum/testgear/uni-t-ut71d-review/?action=dlattach;attach=93453
4.EEPROM memory chip: https://www.eevblog.com/forum/testgear/uni-t-ut71d-review/?action=dlattach;attach=93454
5.Holtek LCD controller: https://www.eevblog.com/forum/testgear/uni-t-ut71d-review/?action=dlattach;attach=93455
6.TI microcontroller MSP430F: http://html.alldatasheet.com/html-pdf/82008/TI/MSP430F147/24/1/MSP430F147.html

[retiredcaps]

Thanks for a thorough review and follow up after 2 years of operation.  Most people just do the initial review when it is new and don't bother to update afterwards in terms of accuracy, reliability, usage, etc. 

[miguelvp]

Yeah, thank you, I was reading it as you were updating the images, since I have the 71B a lot of it pertains my DMM.

So again, Thank you very much and thanks for maintaining the DMM spreadsheet!

[Wytnucls]

Glad someone appreciates the effort and, hopefully, the review will help owners master their new shiny equipment and dispel some preconceived ideas about the UT71.

[Lightages]

Good review! I agree on all the points and the UT71X series does offer quite a bit for the money for electronics use. All your opinions are on the mark IMHO. Generally, Uni-T seems to offer good value for the money within the limitations you have mentioned.

I had a bit of a bad experience with my UT71E being out of spec but it is alright now.

[Wytnucls]

Thank you. Feel free to add some of your comments over here about your personal experience with the 71E and its extra features, when you find some spare time. 

[Vgkid]

Thanks for the good write up, I was considering of grabbing a c-specced one to replace my Fluke 87-1.

[Lightages]

Just remember that the UT71X series comes nowhere close to the safety and build quality of the Fluke. Keep the UT71X s away from electrical work and high energy circuits. They are in no way a replacement for the 87 series, more like a compliment for electronics work.

[Vgkid]

I will mainly use it for lower voltage stuff, along with fixing my 87.

[XOIIO]

If possible, could you list the rest of the chips on that model, and maybe dump the EEPROM of yours? I have a feeling this and the UT71C are identical and you could hack the meter to unlock the rest of the storage. I'm also interested in increasing the backlight duration but I don't have what I need to dump ROM's yet, so it would be a chance to look around in there ahead of time.

https://www.eevblog.com/forum/testgear/hacking-the-uni-t-ut71c-(wipneed-help)/

[miguelvp]

You already asked him that and he said he didn't have the equipment to dump the eeprom.

Edit: https://www.eevblog.com/forum/testgear/multimeter-software-that-workes-with-many-brands/msg440279/#msg440279

[XOIIO]

You already asked him that and he said he didn't have the equipment to dump the eeprom.

Edit: https://www.eevblog.com/forum/testgear/multimeter-software-that-workes-with-many-brands/msg440279/#msg440279

derp

[Wytnucls]

If possible, could you list the rest of the chips on that model
https://www.eevblog.com/forum/testgear/hacking-the-uni-t-ut71c-(wipneed-help)/

All the components are listed already.

[miguelvp]

derp 

Fixed it for you

[Wytnucls]

Here is a spreadsheet that may interest some people. It shows the performance one can expect from the 71 series multimeters, while measuring resistance.
The accuracy tolerances aren't as tight as on the Gossen or Fluke machines, but at least the results stay within specifications, even after 2 years without calibration.
As far as I understand, the meter passes a low current through the DUT resistor and then measures the voltage on the mV scale to derive the resistance. The test current will vary, depending on the range selected.
There are fluctuations at times, but generally the multiple test results are consistent and repeatable.
If you need very accurate Ohm measurements though, the more expensive meters will have a distinct advantage.

All meters are compared to the 30M used as a standard.
The light blue columns show the least significant digits deviations and the purple ones, the maximum deviation allowed within that range.
I hope it all makes sense.
(As an aside, the Gossen 26S shows incredible performance, as the original and probably last calibration was done in 2006!)

[XOIIO]

Hmm, I was wondering, do you know where/if there is a trim pot to cal the resistance? That would make adding an MOV easy.

[Wytnucls]

All the potentiometers are listed in post #2.
There is no pot for resistance calibration.
The only calibration available is closed-case, through software, for each range, with a calibrator or accurate resistance source.

[XOIIO]

All the potentiometers are listed in post #2.
There is no pot for resistance calibration.
The only calibration available is closed-case, through software, for each range, with a calibrator or accurate resistance source.

Ah alright, I was hoping you just forgot to list it, that's too bad. Guess I won't be adding any MOV's

[Wytnucls]

Some people complained that the temperature readings were way out on their meters.
Here is a picture of my 2 meters with the Gossen 30M as a reference, each using a different thermocouple wit the tips bunched together in a sealed environment and allowed to settle for about 10 minutes.
All the meters have their original temperature calibration. If you find that yours is way out, calibration is possible by tweaking the temperature potentiometers on the Uni-T PCBs.
According to the meter booklet, the K-type probe is good up to 230C. Above that temperature, a rod contact probe has to be used.
Accuracy is given as 3%+30 digits between -40C and 40C, which I think is very conservative for the middle of that range. Above 40C, it increases to 1%+30, until 400C. Maximum range is 1000C.
Accuracy on the Gossen 30M for the K-type is 0.7%+0.3K, which is about half a degree at 22C.

[Wytnucls]

Here is a screenshot of the waveforms of the 71D and 26S, while measuring 100uF 10V caps of the same batch.
The meters have different measurement methods:
The 71D (blue trace) charges the cap to a low voltage with a constant current, then measures the capacitance through an RC discharge and then displays the reading at the end of the RC curve. The cap is discharged before the next measurement.
The 28S charges and discharges through an RC circuit with a higher voltage than the 71D and doesn't discharge the cap in between measurements.
The LCR meter gives a capacitance of 96uF and 98uF for the 2 caps.
The 71D measured 107.3uF and 110.1uF.
The 28S measured 114.7uF and 115.8F.

[Shock]

I have two new Uni-T 71Ds (same batch) and temp testing show approx 2 degrees C difference when the same thermocouple was used on both meters at room temp.  The thermocouples on both meters themselves are a fairly close match.  I suspect one meter is reading low and is out of cal.

[deadshort]

Have just brought a UT71D very pleased with it. In the box is a note

       "Manual Amendment in order to meet new CE standards, the following amendments are made:
         Alligator clamp - removed
         Safety clamp - removed"

Their are no Alligator clip to go on the test leads/probes and no short test leads with alligator clip. Their is 2 covers that fit on the test probes so that only about 2mm of probe protrude. The fuses are still 250volt!

[Wytnucls]

If your meter came with the latest PCB revision, it would be quite easy to install the required 1000V fuses and clips yourself.
If you're only going to use it on low power circuits, don't bother with an upgrade, as the glass fuses are much cheaper to replace.
Too bad the short croc test leads aren't included anymore, they are quite useful.

[torr032]

Can the continuity on UT71 series meter be modded to be fast, unlatched. I prefer unlatched continuity over latched one, for the electronic use unlatched is far more useful as it can reveal contact quality.

[Lightages]

No it can't be modified. You can use the hack that Wytnucls has discovered for improving the pseed. If you want unlatched you would need to add a separate continuity tester circuit and hack it in somehow.

[torr032]

No it can't be modified. You can use the hack that Wytnucls has discovered for improving the pseed. If you want unlatched you would need to add a separate continuity tester circuit and hack it in somehow.

No, latched continuity doesn't suit me at all, fast or slow doesn't matter since it lie about contact quality.. I am looking for a good quality dmm with an unlatched continuity and with a dual display and ac+dc simultaneous voltage measurement.

[Lightages]

Perhaps it is better to start a new thread asking for such a recommendation instead of hijacking this thread.

[WackyGerman]

Even this multimeter may be ok for electronic hobbyists who use it only with low voltage , this multimeter is a dangerously piece of shit with whimpy fucking glass fuses and non effective overload protection , marked with a cat rating which is light-years far away from the reality . Normally this crap has no place on the market and has to be removed from the market and annihilated at the expense of the manufacturer . It s a rip off and playing with the life of the customer with a wrong marking of the cat rating is not excuseable . Please don t support this crap companies and buy a decent multimeter from a good reliable company

[Wytnucls]

Calm down, not everybody can afford a 700 Euros Gossen DMM to use on their electronic projects.
The requirement for HRC fuses only came in force with the latest regulations and only applies to Europe, at the moment.
Uni-T is upgrading their meters to comply and is sending the newly developed ones, like the UT-181, for independent testing in the USA.

[Lightages]

It is still a good meter for the bench and electronics! But I am looking forward to seeing the new series.

[Wytnucls]

Had a quick play with Franky's UT-181. It has all the bells and whistles with big improvements all round, but it won't be cheap, at just under $300,00.
Would be keen to order one, but I need another meter like I need a hole in the head!

[Lightages]

I think the new UT171X series might be more in line with normal price levels, especially the UT171B. If it is all that it appears t could be then it will become a real competitor to the major brands. As it is, the 181 looks really nice but we are waiting on Franky to show us more!

As far as the UT71D goes, it is still a great meter for electronics, except for the really bad continuity test.  I have yet to hear a problem with a UT71D, but I now know I am not the only one who has a received a UT71E way out of specification as I have heard of another. Maybe it was a bad calibration run on a batch.

[Wytnucls]

To illustrate the fast transient capture of the 71D, I fed it a 3V 10uS pulse at 50Hz from a function generator. The meter easily registers the pulses and displays the pulse voltage in 'Peak Hold' mode, all the way down to 100mVpp.
Most meters need a minimum repetitive pulse duration of 250uS for proper capture.
Peak Hold data can be logged to the computer in real time, at 15 samples per second.

[sbose]

@Wytnucls
does UT71D has overshoot issue like the UT61E?

edit : fixed the model name

[Wytnucls]

Namaste,
No overshoot noticed when tested between 5V and 35V DC, in 5V increments with auto ranging.
Fairly large overshoot and settling time on 220V AC, due to slow auto ranging. No overshoot or display delay when on proper manual range selection.
I did the same test on 220V AC with a Fluke 185, which had no overshoot on auto ranging.

[sbose]

Nomoshkar,
and thanks for the information  .

[teslafan]

Wytnucls,
"16.   Conclusion
I never regretted buying these two meters and although I have acquired a few more ‘respectable’ ones since then, I still reach for the 71s on a regular basis."  Is the 71s a typo? S/B 71d? I don't see that model in the multimeter spreadsheet, if legit, will it be in a future update?
Fantastastic info, xclnt job!
Thanks

[DanielS]

Wytnucls,
"16.   Conclusion
I never regretted buying these two meters and although I have acquired a few more ‘respectable’ ones since then, I still reach for the 71s on a regular basis."  Is the 71s a typo? S/B 71d? I don't see that model in the multimeter spreadsheet, if legit, will it be in a future update?

It is not a typo: it is simply plural for referring to whatever flavors of the 71 he has access to if he has more than one and possibly different variants.

[teslafan]

 

[Wytnucls]

Something peculiar was brought to my attention recently:
AC current measurement, because of the true RMS converter limitation of 10% of range, is tricky. There is a zone between 400mA and 1A, where measurements are not to be trusted. Ideally, the meter should have had a 4A extra range, to cover the dead zone. DC current measurements are not affected.
Check your equipment, as all true RMS meters which lack an intermediate A range could be affected.
The Fluke has a 5A range and the Gossen a 3A range.

[DBoulanger]

Good day,

I clearly understand that this topic, the "UNI-T UT71D review", has been created and posted a little while ago, nevertheless I would like to take a moment and thank Wytnucls for his great and pretty much indepth review of this DMM.

I do have one on my workbench, for over 2 years now, and it does a good job for me.  As previously stated, there are quite a few nice features for the price.  For an electronic hobbyist like me, this is an adequate tool.  I rarely use it for main voltage.  I used it a few times to troubleshoot some electrical wiring in the breaker panel, but these times were really the exception to the rule.

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.

Fortunate enough each entry have its own number, incrementing by 1, so I used that to recalculate the adequate timestamps.  This is not a catastrophic issue but when you're not prepared for that, it surely takes you by surprise and "Plan B" must show up quickly if you want to resume your work.

Despite that little misadventure, overall I'm really satisfied with this DMM.  Great deal for the features and the price was right for an hobbyist like me with a somehow limited hobby budget.

Thank you again Wytnucls for posting this extended review.

[Wytnucls]

Glad you appreciate the effort.
To register the correct time stamp, the meter would need an internal clock, which the UT71 series doesn't have. Very few meters have one and they generally tend to be on the expensive side. The new UT171C and UT181A have an internal time reference and should be able to spit out the data with proper time stamps.
It doesn't always make sense: My old Gossen 26S has a clock and a stopwatch, but no internal memory (except for the 26M), whereas the expensive Gossen 30M has 30,000 registers, but no real time reference either.
Fortunately, as you pointed out, this is easily corrected after transfer to PC memory.
On some meters, the captured data is not accessible on the screen. It has to be transferred to the PC for final viewing, forcing you to buy their pricy IR cable and software. Thankfully, this is not the case on the UT71D.

[Wytnucls]

A new member sent me this cryptic message (machine translation). I gather he is concerned about the last digit repeatability and stability of the UT71 when measuring DC volt in an average circuit.
I shot a video of a power supply measurement on the mV DC range, compared to a Keithley 2000, to show that the last significant digit is reliable. (Accuracy on DC mV range is 0.025%+5)

When measuring the voltage reference, and will be, as shown in surveys range UT71s. And it will match the specifications ± 5 LSD.
But we use the meter in different schemes. We have little interest or ideal conditions ideal solution calibrator more 10MOhm.
What in actual measurements? Performing the measurement in real circuits will be the behavior of a meter - it is necessary to carry out 3-4 times a single point measurement.
In the course of 3-4 measurements will be shown on the display various figures around exactly about 0,01V. And if again to make 3-4 metering numbers may be repeated in exactly four bars, but the average from this, there will be more precise 0,01V.
Thoughts:
a) Vref can not be so quickly drift back and forth.
b) C-integr - adsorption? But in other schemes meter measures according to the specification.
in) Bugs MCU?
d) Eureka! This behavior is a meter in different schemes with different total resistance. At the measuring point it can reach tens of radioactive elements.

Please, you are faced with the phenomenon of line UT71s? How can I explain? 3-4 times in one measuring point - different values around 0,01-0,02V.
On what basis can we assert that the accuracy and resolution in millivolts 0,005V, if the inaccuracy and uncertainty of the real measurement is much worse? (Not taking into account the thermal instability and rounding rules).
1) How do you personally consider this strange behavior and the real meter accuracy is more accurate 3 1/2?
2) Only Conrad points to the newest multimeters +10 LSD. What does this mean? It exists closer to the real.
3) We have the resolution bench UT71s - 10mV. In fact, it is not feasible for the same reason - a large uncertainty and inaccuracy of the far-right digit.

[measurementpoint]

Machine translation. Important precision of thought.
Talking about the behavior of the Meter is not in the tests. There Multimeter conforms to the specification.
Talk about practical applications. In most real in-circuit measurement - at one point - measuring cycles 3-4 times - the display will show around 0.01V.
Thus, taking the average, we can not follow exactly the best 0,01V.


Excuse me, I am now corrected.

Excuse me, did not clarify earlier. My observations and speech in the range of 39,999 - as the main series of stabilized voltage will lie here 5-6-8-9-12-24. The illustrated display in the cycle 3-4 times measuring one point - about around 0,01V. And never close to exactly 0,005V

[gamarilla]

My UT71D meter has very high current consumption when it auto-powered off. I couldn't measure it yet but it drains the battery overnight if I forget to power it off.

Is it a problem with my unit or is a design flaw? Do you guys have this issue?

[retiredcaps]

My UT71D meter has very high current consumption when it auto-powered off. I couldn't measure it yet but it drains the battery overnight if I forget to power it off.

In Martin's video at 26:15, he measures the current consumption.  At off, it s 0.0mA.  The others varies from 3.5mA to 9mA depending on the function you use. 14mA for backlight.



If you assume a 9V battery is 500mA and you left it on for 12 hours assuming auto power-off works, that implies it is drawing roughly 41mA in auto power-off.  I would say your meter has a problem.

[Wytnucls]

My UT71D meter has very high current consumption when it auto-powered off. I couldn't measure it yet but it drains the battery overnight if I forget to power it off.

Is it a problem with my unit or is a design flaw? Do you guys have this issue?

The drain on the 9V battery while in 'auto power off' mode (DCV position) should be 40uA (measured with Keithley 2000 on the 10 mA range).

[joeqsmith]

I had ran a similar test some time ago with a Fluke 87V, Extech EX540 and the Brymen BM869s.   The Extech was by far able to detect the shortest pulse of the three.   I picked up a UNI-T 181A and thought I would add it to the mix. 

These were similar but with a 2V peak rather than 3.   Again, I would grab a scope and really have no need but I do find it interesting that the 181A is not even close to what you saw with your 71D. 

To illustrate the fast transient capture of the 71D, I fed it a 3V 10uS pulse at 50Hz from a function generator. The meter easily registers the pulses and displays the pulse voltage in 'Peak Hold' mode, all the way down to 100mVpp.
Most meters need a minimum repetitive pulse duration of 250uS for proper capture.
Peak Hold data can be logged to the computer in real time, at 15 samples per second.

[Wytnucls]

It is a feature of the Taiwanese Cyrustek ES51966 IC (peak capture patent 476418), as fitted to the UT71D. Uni-T may have overlooked its existence, as it isn't mentioned in the manual.
The UT181A uses a different IC, which probably lacks the fast transient capture capability.
The Fluke 867B and its lesser siblings are the only other meters I know of, that can match the 10us transient capture of the 71D.
The FLIR DM93 should be able to do it too, as it uses the same IC as the 71D, but it isn't documented.

[joeqsmith]

Thanks.  I was wondering more if they felt this was an important feature why they did not implement it on their newer meter.    I had a look at the patent.  They don't really talk about what drove it other than cost and battery life unless I missed something.  I can't think of one time that it would have come in handy.     

I am curious, what do you use it for?   

[Wytnucls]

This thread is a meter review and as such, looks at all the features of the UT71D. What I use the meter for is irrelevant.
Like I said, I don't think Uni-Trend paid much attention to the glitch capture capability of the IC they chose to fit in their meter. The same goes for FLIR.
Fluke on the other hand, made it an important feature of the 867B, seen as a convenient and cheaper alternative to a bulky oscilloscope in the field. I'm pretty sure someone found it useful then.
Most meters have a peak capture feature. In this instance, the 71D happens to do it better than most other meters.

I also looked at the patent, but couldn't make much of it, as I don't read Mandarin. There are schematics of the circuits involved, but I haven't looked at them in great detail.

Here is the link if anybody wants to have a go at it:
http://twpat-simple.tipo.gov.tw/tipotwoc/tipotwekm

[joeqsmith]

No problem.  I just figured you would have some idea what to use this feature for.   Fluke's site does talk about using it to capture line transients (even with the 87V).  I don't see there being enough information to do much good.  Did you try capturing anything higher than the 3V?  Something more on par with some sort of simulated line transient?     

The patent engine has a translate feature.   Attached is the English translation. 

[Wytnucls]

There isn't much to gather from the patent. It is used like any peak detect feature on any multimeter. The only difference is that it is more sensitive that most (10us for a repetitive transient with lowest amplitude 100mV on the 4V range).
Line voltage transient detection may be one use. Picking up current transients on a 4~20mA loop may be another. Logging is available in Peak mode, at 15 readings per second.
Characterizing the whole Peak mode would be time consuming and would require some substantial testing gear. This is something most manufacturers haven't done properly either.
I'll leave that task to someone who may actually need the feature and is willing to devote some time testing the meter over the whole voltage and current gamut.

http://www.fluke.com/fluke/uses/comunidad/fluke-news-plus/articlecategories/dmms/under-used_functions
http://www.tek.com/sites/tek.com/files/media/document/resources/Peak_Detection_AN.pdf

[joeqsmith]

I had not thought about the 4-20mA.   Did you try to see if it could capture that same even in this range?  I was only looking at voltage when I ran those quick checks.   

Line voltage transient detection may be one use. Picking up current transients on a 4~20mA loop may be another. Logging is available in Peak mode, at 15 readings per second.

[Wytnucls]

I did try to capture a fast mA current transient with the meter, but my gear is not really up to the task, so the test is not conclusive.
Let me know if you're successful on your side with another meter and I'll try to replicate your set-up here, if possible.

[joeqsmith]

I was thinking to use a resistor in series with the meter and pulse the voltage to get the 4 to 20ish.   

I started out with 0.5Hz 50% just to get things setup
181A read 20.017/4.002
869s read 20.022/4.002

At 50Hz, 500uS pulse
181A reads 20.11
869s reads 20.9

50uS pulse
181A reads 20.13
869s reads 9.4 ***

20uS pulse
181A reads 17.74
869s reads 8.5

Now the funny one is the Extech which was really good in voltage mode.   In current mode even with a 5mS pulse, it could not detect it. 

 

Went back to repeat the voltage test with the Extech and realized I had forgot how to use the peak mode.  I then tried the peak detect in current mode and it worked.       It also turns out the 181A needs a fair amount of time to settle.  Several seconds (5 or more)     The Brymen on the other is correct.   

Here is the new data for the Extech and the UNI-T.
 
50uS   EX540 19.86mA,  UT181A 20.13mA
20uS   EX540 19.86mA,  UT181A 20.16mA
10uS   EX540 19.85mA,  UT181A 20.13mA
5uS     EX540 19.80mA,  UT181A 20.17mA
2uS     EX540 18.68mA,  UT181A 15.97mA
1uS     EX540 15.43mA,  UT181A 10.94mA


Thinking back, what was the fastest 4-20 I ever worked on.....   

[Wytnucls]

Someone was having difficulties with the internal logging features of the meter.
Here is a digest of procedures for proper operation:

There is no memory delete prompt as such.
All one can do is append a new batch of data to the existing data in memory or choose to overwrite the existing data from the beginning.

To store new data in memory:
Press STORE key
Press HOLD key if you want to overwrite old data, otherwise skip this step
Press STORE key to set recording interval (then + key repeatedly to set from 0 to 255 seconds) (Hold + key continuously for fast scroll)
Press STORE key to start recording
Press EXIT key to stop recording

To review stored data:
Push STORE key for 1 second (RECALL)
Select sample with + or - keys
Press HOLD key to send all stored data in memory to computer via USB

At any time, to send a single measurement reading to the computer via USB, push MAXMIN (SEND) key for 1 second then EXIT.

[Wytnucls]

Here a link to the early version 1.10 of the logging software, for anybody who needs the RecallData function which was deleted from the later version 3.0.
RecallData allows you to download stored data to the computer, specifying original logging start time and interval, instead of default settings.

https://www.dropbox.com/s/9c5nrzuwx40800h/UT71C_D_E_setup.exe?dl=0

[Wytnucls]

The graph on the old version is also more useful, as the one on the new version doesn't allow scaling.
For instance, here is an old 9V battery voltage recovery graph in real time, after a large load was removed (500 seconds):

[gerrylix]

Here a link to the early version 1.10 of the logging software, for anybody who needs the RecallData function which was deleted from the later version 3.0.
RecallData allows you to download stored data to the computer, specifying original logging start time and interval, instead of default settings.

https://www.dropbox.com/s/9c5nrzuwx40800h/UT71C_D_E_setup.exe?dl=0

Thanks again for uploading the 1.1 version the other day.
Sadly the "Recall function" for multiple storage entries isn't working with any version.
After hours of trying v1.1 and v3 i switched over to an open source project called sigrok!
The sigrok cli (https://sigrok.org/) with the right commands parsed all of my 174 datapoints in 1 second.

Install sigrok cli then use Zadig, that came with it, to exchange the already installed USB driver of the USB-serial/USBHID-serial with the zadig one.
Afterwards head over to the cmd prompt(i prefer http://cmder.net/ over windows one but not neccesary) and "cd" the folder where sigrok-cli.exe resides and use:

sigrok-cli --driver uni-t-ut71d:conn=VID.PID --continuous -o test.txt -O analog
(USE VID and PID of the right USBport, i.e.: 1a86.e008)
-o specifies the outputfile
-O specifies the format
-V shows the fileformat

After that, start the DMM and follow the instructions to recall from Wytnucls.
Hint:
Use USBdeview(http://www.nirsoft.net/utils/usb_devices_view.html) to find the correct USB port and VID/PID.
Never use "sigrok-cli -scan" with the UT71D or the hardware hangs and you may have to disable+enable the port .

Greets

[Wytnucls]

Sadly the "Recall function" for multiple storage entries isn't working with any version.
After hours of trying v1.1 and v3 i switched over to an open source project called sigrok!

Are you saying that you can't transfer data from the 71D memory to your computer?

[gerrylix]

Exactly, i can't transfer it to the offical uni-t software.
The DMM is running through the entries and sending them but the software only gets the first entry, doesn't matter which version i use.
Normal logging is possible, in "live" mode but stored values aren't transfered.
Maybe it's because of this:
"The communication parameters are 2400 baud, 7o1. However, the vendor software opens the serial port with 8n1 settings, so the vendor protocol descriptions are slightly off. "

[Wytnucls]

I don't have a problem here on Windows 10, with UT71D version 1.10. Just tried 180 entries, which all transferred. The only problem is that the graph seems to stop after 142 points.
The transfer is lightning fast.

Tried a transfer again, 210 data entries, with a higher starting voltage. Everything went through, including all points on the graph.

[gerrylix]

I don't have a problem here on Windows 10, with UT71D version 1.10. Just tried 180 entries, which all transferred. The only problem is that the graph seems to stop after 142 points.
The transfer is lightning fast.

Tried a transfer again, 210 data entries, with a higher starting voltage. Everything went through, including all points on the graph.

Damn, then its maybe an issue with win7 pro.
Tried it on two different machines.

Facinating that sigrok has no problems getting the datapoints under win 7.

[Wytnucls]

It was transferring perfectly too on my old Sony Win 7 machine. I am surprised to hear that yours has a problem.
Try reinstalling the software perhaps.

[gerrylix]

It was transferring perfectly too on my old Sony Win 7 machine. I am surprised to hear that yours has a problem.
Try reinstalling the software perhaps.

Tried to reinstall v1.1 and v3 two times.
Once on my small log-netbook and on my main machine, both seem to have the same issue.

I have to say i became a fan of the sigrok lib after one day.
Maybe i'll build some GUI around the library for my DMM's and dataloggers.

Thanks for the effort Wytnucls 

[Breizh13]

Hello all from France,

this week I received my UT71D from Batronix DE. Nice meter except the stand which is too small, and so, the meter is too inclined.

My problem is with the recalling datas feature. It don't work on windows Xp and Windows 10. I tried release V1.0 and V3.0 with the same poor result.

When I do that
"To review stored data:
Push STORE key for 1 second (RECALL)
Select sample with + or - keys
Press HOLD key to send all stored data in memory to computer via USB"

I just get the first record.

And when I check the "Recall data" option on the the V1.0, nothing append!!

I could see that I am not the only one with this problem. Can aanyone give us help to solve that?

PS: I sent an email today to the vendor. Maybe he can help.

Philippe
Salon de Provence
France

[Wytnucls]

Batronix is selling the newer version of the UT71D, with the 1000V HRC fuses. I suspect the download feature might not work properly on that meter anymore. Contact Batronix for an explanation or have a look at the Sigrok software.

[Shock]

What differences are present on the PCB just different fuse holders and fuses?

[Wytnucls]

I presume it would be erroneous software loaded at the factory, if all new meters behave the same way.
A few components were moved to make room for the fuses, but it is essentially the same meter.

[abraxa]

I have to say i became a fan of the sigrok lib after one day.
Maybe i'll build some GUI around the library for my DMM's and dataloggers.

There is sigrok-meter btw, which runs fine on linux but since we don't use Windows really, we would appreciate it if someone would be willing to figure out what's needed to make it run on Windows as well. Probably just the python bindings for libsigrok. If you'd be willing, you'd have a GUI right away instead of having to write it
Either way we're glad you find sigrok useful!

[WackyGerman]

Ok  for the new fuses but still  for the crappy input jacks . Why don t they fit them like in the EU version of the 61 series ? 

[Wytnucls]

What do you mean? They look the same to me.

[Shock]

Wytnucls do you know a decent source of suitable replacement 500mA HRC fuses that would fit the 71D?

[Wytnucls]

If by decent you mean cheap, I don't.
Otherwise, Jaycar has a SIBA fuse that should fit (in the 1000V model at least):
https://www.jaycar.com.au/fuse-for-cat-iv-dmm-1kv-500ma/p/SF2278

I don't think there are any 1000V HRC fuses that would fit the original glass fuse holders, unless they are moved further apart (not recommended).

[Wytnucls]

There is now a Bluetooth adapter for the 71 series:
UT-D07A with software for iPhone and Android.

[spikey1973]

@abraxa and Wytnucls (well the rest too ofcourse)

i just recieved my ut71c (from china, production 01-2017)
i just got sigrok installed on my 17.04 ubuntu.

am not really how to get the data from the meter to pulseview, and or which drivers to use.  Unfortunately i do not have the time at the moment to dive into the subject. so if anyone is willing to give me some hints i would truely appreciate it!

secondly, i took the time to open the meter up as i was curious about the fuses.. specially as i read some about newer models having the better fuses?
anyway, that didn't count for mine.. shouldn't have expected it either, as the price was really low.
I made some picture as mine is a 71c instead of the 71d, thought maybe it could be helpfull, although i don't see much difference from the D model myself.



(doesn't seem to work well :/, but when i click the broken image links, i can still see them here.)

anyway, there is the space to upgrade the fuses so i would like to do that at one time in the future.
have googled for the fuses.. but really didn't find any. also it is really difficult to if it is a surface mount pcb fuse or a massive fusebox fuse when just looking at picture.

So as Wytnucls lives in belgium, just as i do. can i ask where you got yours? for your b upgrade?

additionally something else the three empty spots onm the left on the pcb are for varistors? would there be any use in trying to find out what varistors where "intended there", whould that help (a little) as security upgrade? (keep i'm mind i'm reallly not sure what i'm asking here)

additionally, if anyone has the bluetooth adaptor Wytnucls talked about.. maybe some inside pictures? see if we can build one with a mini / micro arduino board with bluetooth board?
Anyway, thanks for this tutorial, made me even more happy with my meter then i already was.

kind greats. Matt

ps: about measuring higher voltages.. i guess a quick check of voltage and frequency on a 230V 50hz european mains should still be oke! not? 

[spikey1973]

Ps: to anyone Interested, I ordered the ut-d07 today so once it arrives I will let people know.. and post some pictures of a small review (maybe it would be better to lend it to someone local who would be more knowledged )

Anyway . I will keep informed.

[picitup]

@Breizh13 did you ever make any progress on sending the internal data to the PC?  I have exactly the same problem on a meter I bought this week.

I know the setup is all OK, because if I press and hold SEND, the program logs data to the pc in real time as expected, however when I press RECALL -> the data runs through on the meter quickly, but the software doesn't capture it.

I tried the supplied version of the software (3.0) and the version from this thread (1.1) on Windows 7 and 8 but no joy.

Cheers

Steve

[picitup]

I had another play with this, and looked at the IR led on the back of the meter through my phone camera.  Funnily enough, I couldn't see it through my main camera, but the reverse camera worked well. When I press SEND, the led blips every second or so and when I press RECALL ->, the led seems lit pretty much continuously, so it looks like the meter is working as expected, pointing to a bug in the software.

I also tried my UT61E serial adaptor until I realised that the LED positions are swapped from the UT61E to the UT71D.  Bummer.

[myf]

Hello,

I use ut-61 and the uni-t usb link works fine with sigrok, but you must send a reset from the laptop just before tracking data to sigrok.

I use this short python program : about 10 lines at the end of this page.

https://www.cnx-software.com/2015/03/07/sigrok-and-pulseview-in-ubuntu-14-04-with-uni-t-ut61e-digital-multimeter/

Have a nice day!

F. (from France)

[picitup]

Hi @myf Thanks for your reply.  I've not used Linux for decades so am looking for a windows solution.  I see there is a windows version of sigrok - is the main method of obtaining data by Python scripts?

Cheers

Steve

[myf]

Hello, (again)

I suppose you use windows, I read that uni-t cdrom runs out-of-the-box on windows. Maybe you dislike the interface and you prefer a ascii-raw data.

I do not understand if you have a rs-232 cable or a usb-cable. I use my ut61with usb-cable I must reset it before every use, but I get a rs-232 cable in the new box.

I saw 2 versions of this ut-d04 usb-cable with 2 hardware / firmware / signature, and in both cases I must reset it.

I do not know if this is interface is the same as yours. Are interfaces the same fom ut-61 and ut-71?

I do not know, but I feel that Python3 sources run the same way under linux and windows. Might you want I run some tests about reading DMM data from Python? I'm not sure I can do it, but  I can try.

[picitup]

Hi :-)

Yes I use Windows and the software does run, but doesn't seem to work properly.  It only supports com1-4 and my first com port is 6.  Also the data dump function from internal memory doesn't seem to work.

The physical interfaces of the UT61E and UT71D are identical apart from the former is RS232 and the latter is USB.  This is the opposite of what I said earlier.  I checked the transmit led using the rear camera of my phone, which I've just found out mirrors the image. 

Armed with that knowledge and remembering you have to have DTR high to power the serial adaptor, I've just got the UT61E RS232 cable working with the UT71E using Termite.  With Termite you can click on the DTR led and it will set that output high and it works well.

Here's some raw data for a taster:

000051101
000061101
000051101
000061101
000051101
000051101
000051101
000051101
000051101
000051101
000061101
000061101
000051101
000051101
000051101

I think i can paste this into a spreadsheet and parse it quite easily so job done.

I'll do some more over the weekend and post it up.

Thank you for your kind offer to try Python under Windows.

Cheers

Steve

[myf]

Thank you, !

So your ut-61 is right, your interface is rs-232, and is awake as claim the kermit-telnet interface.

You are looking for translating ut-protocol to ascii data.

For the ut61 there are a lot of program which do this translate.
Do you have a Python2 on your laptop ? With python2 (not Python3) this program may be right.

https://github.com/pklaus/ut61e_python/blob/master/ut61e/es51922.py

There are others programs which translate this protocol. One day, I compile one in C language.
Maybe you can download if you prefer C-language.

https://sourceforge.net/projects/ut61/files/ut61-1.0-beta2.tar.bz2/download

But I read on sigrok page that getting inside data memory will be impossible. Can you read this inner memory with the uni-t-cd ?

https://sigrok.org/wiki/UNI-T_UT71x_series#Protocol

I feel there are 2 steps for this program : first read data, second translate data.

I hope theses information help you.

Have a nice day !

F.

[picitup]

Hi again @myf and I appreciate all the links you sent me.  The most useful one for my UT71D was the last  one:

https://sigrok.org/wiki/UNI-T_UT71x_series#Protocol

Which offers some brief information on the protocol and the VC960 link at the bottom takes you through to a page which described the protocol in more detail.  This page isn't completely correct as testing showed that some of the range characters were different on my UT71D.

So to review from the start here's what I did:

1) Log data internally in the 71D on the DCV range and connected a small solar panel to the meter and pointed it towards the window for a bit less than a day.
2) Transferred the data to Termite with at UT61E serial cable ($10 from Aliexpress) with 2400,7,O,1 settings.  Don't forget to click the DTR led which makes it high and supplies power to the serial lead electronics.
3) Copied the serial data from Termit and pasted it into an Openoffice spreadsheet
4) Wrote a parser for the data using spreadsheet functions such As LEFT, MID and VLOOKUP.

Piccies of the sheet are below and the columns contain the following:

A - The raw data
B - The data with leading zeroes to make it fixed length
C - The raw multimeter data (no decimal point)
D - The function selected EG DCV looked up from the tables
E - The range EG 4V looked up from the tables
F - Time - F4 = F1 then F5 =F4+$H$1/24/3600 etc.....
G - Measured Value complete with decimal point with divisor looked up in the tables.

I tested pretty much all functions, but not all ranges so there may be some errors.  My AC volts test is max. 10v, DC is max 60v and frequency is max 25MHz.

All frequency measurements are normalised to Hz so they can be plotted on a graph if/when the range changes.

The data format is (mostly!)

213492501
213562501
213512501

Where digits 1-5 are the measured value, digit 6 is the range code and 7 is the function code.

I've attached some piccies of the main spreadsheet and lookup table and also the spreadsheet in .xls format if it's any use to anybody.

It's been quite a bit of work but it was fun and you will see from the graph on the piccy that it does, indeed, get dark of a night time and light in the morning in the UK.  I think the little square bump is our security light turning on and off followed by a couple of car headlights.

[myf]

Hi Picitup,

Thanks a lot for your detailed answer !

Might you explain a bit, my english is too poor. I don't understand if ut-71 is designed by (A) or (B)

(A)
Can you get "inner stored data" in ut-71, with a time-stamp ?
Do you send a character code to ask it from the PC to the ut-71 ?
Do you get all this previous data when you connect the rs-232 link ?
Can you get them twice or more ?

(B)
Do you only get the 20-hours long measures as soon as they are made? and the inner memory can't be read by the rs-232 link.
So you must link the pc and the dmm at the very beginning of the measures.

Have a nice day !

[picitup]

Hi @myf I hope you are well :-)

Your English is fine!

I like to share this information, because someone else can correct my mistakes!

To answer your questions:

a) The UT71D has no time stamp, so you must note the time and date when you start recording on a piece of paper.  I guess this helps save memory.  If you look at the Termite data in the picture above, that is exactly what you get out of the UT71D so I have fields in the spreadsheet for time and interval to produce the time column.

There is no communication from the PC to the UT71D.  The multimeter only has a TX LED and the interface cable only has an RX sensor, so data is sent by the 71D 'blind'.  If you send data from the 71D, it just spits it out with no handshaking, even if the cable is not connected.

Yes it works fine with the UT61E RS232 link.  That is what I have been using.  I can't use the USB interface as it doesn't work with the UNI-T software!

Yes you can send the data to the PC, and it is still stored in the 71D so you can send it as many times as you like.  When you record some more data, you can choose to overwrite existing data, or append data to the existing storage.

b) No.  If you connect to the PC and long press SEND, it logs data to the PC in real time.  However, if you choose to store to internal memory, you can store 9,999 records internally without a PC.  So you can start it recording on site, then come back the next day, pick up your meter, take it back to the office and dump the data there.  This is one of the features that made me buy the 71D.

The data I showed in the pictures (solar panel out the window) was logged without a PC.  The next day I pressed EXIT to finish the logging and connected it to a PC and dumped the data into Termite.

I hope that answers everything.

Kind Regards

Steve

[picitup]

Oh, I forgot to mention.  The internal log data is stored in some kind of flash memory.  My meter was turned off overnight and in the morning the log data was still present.  Then I removed the battery and switched the meter on for an hour and when I replaced the battery, the data was once again, still present.  Very handy :-)

It would be nice if you could set the logging frequency to more than 255 seconds - maybe 255 minutes?  And if you could also set the log count so if you cannot attend quickly, the meter could, say log 1,000 entries and then auto power off.

We live in hope....

[hkmk23]

I just wanted to say thank you on the forum for the terrific help WYTNUCLS gave me in pm's. He was a terrific help and this sort of guy s what makes being a member of a forum worthwhile. Thanks W. Just found out you live in Belgium, I live in SW France, so anytime you are passing near Tarn and Garonne give me a call.

[Wytnucls]

Glad I could help. Been in your neck of the woods before. Thanks for the invite.

[cosmin1]

Hello.
Did anybody observe some constrast issues on this UT71D?
Mine has not that good contrast when i watch from above.
Maybe with some dump mod...

[cosmin1]

Anybody?

[cosmin1]

Found the EEPROM. Can somebody help me with dump editing?

[andrew.heard]

Can anyone confirm graph zooming with the UNI-Trend Windows interface program works? The only reference I can find (by Wytnucls) is to left+click mouse drag, but versions 1.3? and 3.0 ignore any attempt to zoom. The graph Y-axis is scaled +/-40,000.

[andrew.heard]

Exactly, i can't transfer it to the offical uni-t software.
The DMM is running through the entries and sending them but the software only gets the first entry, doesn't matter which version i use.
Normal logging is possible, in "live" mode but stored values aren't transfered.
Maybe it's because of this:
"The communication parameters are 2400 baud, 7o1. However, the vendor software opens the serial port with 8n1 settings, so the vendor protocol descriptions are slightly off. "

Sadly I have exactly the same issue with the UT71D I have just bought. Logging in "live" mode (hold MAXMIN) works fine, UT71C_D_E.exe displays each value, but hold RECALL > press HOLD > shows all entries on the DMM screen but nothing in UT71C_D_E.exe. Unfortunately though sigrok-cli is not saving anything although I followed the instructions for USBDeview, zadig & sigrok-cli. Can anyone help? The whole point of buying this meter was for its offline logging ability.

The original poster was not 100% clear on the settings for zadig. I performed: main menu > Options > List All Devices > select USB to Serial > click Replace Driver. When I next run USBDeview there is a red dot on the LHS of USB to Serial. This is the only issue I can think that may be wrong. And of course, now UT71C_D_E.exe doesn't work because its driver has been replaced.

PS (2 hours later) - solved - in zadig I have used the libusb-win32 driver, and possibly more importantly sigrok-cli had an output file option of -o test,txt but the directory C:\Program Files (x86)\sigrok\sigrok-cli (possibly) didn't have write access. When I used this command line, all finally worked:

sigrok-cli --driver uni-t-ut71d:conn=1a86.e008 --continuous -o c:\temp\test.txt -O analog

Note the logging option -l 5 was useful in tracking down the issue.

[Wytnucls]

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

[Wytnucls]

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.

[zgwforum]

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.
 

[Wytnucls]

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.

[AngoLito]

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




Activating "peak", reads goes to 28V DC



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...

[Wytnucls]

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.

[AngoLito]

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...

Definitely, UT17E multiply any measured value by sqrt 2



This is my PCB; it seems an updated version (due 1000V fuses classe)


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