Review and tear-down of UNI-T UT612 LCR meter

[Wytnucls]

1.Presentation:
The LCR meter comes in a professional-looking strong plastic box with a built in carry handle and internal protective foam cut-outs. It offers some really good protection and stores all accessories: Tweezers, USB cable, jack adaptor, battery, Simplified Chinese manual, sotfware CD, the shorting plate and the warranty card. This one was made in December 2012.

2.Ergonomics:
It feels a bit light for a bulky-looking, squarish meter (374gr), compared to the thick skinned CEM with its heavy 6 AA batteries, for example.
It has a skinny plastic bail holding the meter at a precarious 60 degree angle from vertical, but has a locking mechanism for the bail in both open and closed positions. The bail is very similar to the one fitted to the UT-61E.
The square bodywork could have been made a bit more curvy, to make it more comfortable to hold in the hand, like the 61E.
The LCD is well protected, with an extra window, which forms part of the enclosure. It comes with solid state switches with rubber push buttons, which unfortunately sound a bit hollow when pushed.
There is a perimeter ledge around the power and function buttons which makes them uncomfortable to the touch, but helps to prevent unwanted activation, if something happens to be lying flat on those buttons. A feature the CEM meter sorely lacks.
The most used buttons (Power and Function) really stand-out, being made of a bright yellow and blue rubber, with the colour black used for the lesser remaining buttons.
There is a slight rattle from the folded bail, when the meter is moved around on the bench. There are no rubber pads underneath, so the meter tends to slide around too easily, when lying flat on the bench.
A self-tapping screw for the battery compartment hides a flimsy soft 9 volt battery connector.
3 self tapping screws and 2 clips on top of the unit are holding both tight-fitting clamshell body together. It is an adequate construction, but could have been made more rigid. It also sounds a bit hollow when tapped, because of the thin rubberized plastic walls and large internal volume.
Unlike the Mastech, which is using the same chipset, it has a dedicated calibration button on the front face.  I cannot understand Mastech's thinking actually, because I use that calibration button all the time. They go and hide it away in the most awkward position.
There are 3 buttons with dual functions, reducing the need for a confusing multitude of pushbuttons, like those found on the IET machine.
The jacks are good and sturdy, made of one piece metal tubing, with connectors screwed on internally.
The mini USB connector is located at the top of the unit, with APO (auto power off) override, when USB is powering the meter.

[Wytnucls]

3.Functions:
The meter comes with a 9V battery, but can also be powered independently through the 5V USB connection. It will keep working, even if the 9V battery is removed.
The USB datalogging stream is sent to the computer through the same USB connector. The meter comes with a CD containing the dedicated software and some user notes in English.
There is an auto detection of components, which is the standard configuration at power-up, with a manual selection also possible, through a toggle switch, labelled 'FUNC".
The standard 1 kHz frequency can be modified at any time and the secondary parameter can also be changed, when in manual mode.
Automatic serial/parallel mode selection is done according to device under test, with manual override possible in manual mode.
Other functions are:
'Sorting' mode, (manual selection of % deviation) with a Pass or Fail message. (0.25%, 0.5%, 1%, 2%, 5%, 10%, 20% and +80%~-20%)
Sorting is only available in manual mode with an ideal DUT connected to the meter. Pressing 'SET UP' will allow you to change the range of the ideal reference device, using the lateral arrow keys. Pressing 'ENTER' will now allow you to change the value of the reference DUT, using all arrow keys. Another press of 'ENTER' will bring you into the tolerance selection.
'Calibration' mode, to null the test leads or tweezers with shielding and guard connection.
Press 'CAL' to access 'Open' mode, with an open circuit (loose test leads), then 'CAL' again to enter a countdown to 30s. 'PASS' or 'FAIL' should appear on screen. Press 'CAL' again, if the first test was successful, to enter the 'Short' mode, with a closed circuit (shorting bar or test leads connected together) then 'CAL' again for a 30s countdown with 'PASS' or 'FAIL' message. Press 'CAL' again to exit this mode.
Calibration should be done each time accurate measurements are required or if different test leads are connected.
'Relative' mode to display a deviation as a %, from a reference DUT. It is only available in manual mode. Pressing 'REL' to access the feature, brings up a triangular icon on screen. Connecting another similar device, will display a difference in value as a percentage of the initial measurement. Pressing 'REL' again will display the initial value with a flashing triangle (delta) as a warning. A long press of 'REL' will exit this mode.
'USB' mode, to send a data stream to logging computer. The data consists of primary value, mode and unit, secondary value, mode and unit and the testing frequency. A computer icon appears in the screen. APO goes off, as soon as the USB cable provides 5V to the meter. The Baud rate is 9600.

4.Usage:
The LCD is easy to read, but is best seen from a slight angle (10 to 20 degrees from vertical), just like the CEM DT-9935. All the UT612 meters seem to behave the same way, so it was either designed like that or UNI-T and CEM bought a whole batch of faulty LCDs a few years ago. 
It isn't really an issue, once you're aware of the unusual behaviour.
The backlight is fairly strong and evenly spread and will last for 60 seconds after activation.
The LCD has a bargraph, marked as a percentage of full range (20,000 count). For example, a 100 ohm resistor will register as 50%.
There is a reduced count of easy access buttons, compared to other meters, making it easy to make the right selections in a minimum of time.
Convenient use of USB for both logging and external power ( works great, unlike the Mastech external power unit)
It comes in a fairly small size (224mmx172mmx59mm), just a little bit bigger than the UT61E. No unnecessary bulk, like on the Mastech behemoth.
It is light, with a single 9V battery.
It comes with a great hard protective storage case, like the IET 5000 meter, which is quite unusual at that price point.
It has 10 reliable solid state buttons instead of a multitude of soft PCB contact buttons like on most other meters (14 on the CEM LCR meter).
One has no control over the APO (Auto Power Off). It is always active with the battery, but goes off when powered through USB. After 3 beeps, the meter will auto shutdown after about 6 minutes of inactivity, when powered by the battery.
The piezo beeper can be heard loud and clear, unlike the one in the CEM meter, which is rather quiet.
The SMD tweezers come with an extra shield lead for connection to one of the guard jacks.
Low battery warning and shutdown is triggered at 5.5V.
Available frequencies are: 100Hz, 120Hz, 1KHz, 10KHz and 100KHz.
The measured secondary parameters are Q, D, ESR, Rp and Theta.
The shielding test lead connection to Guard should be used while measuring resistances above 10M Ohms, to minimize noise and parasitic effects.
Large caps should be measured in series at 120Hz, small ones in parallel, at 1 KHZ, if less than 0.01 uF. Large filter inductors above 200H, should be measured at 120Hz, small audio/RF inductors at 1 or 10 KHz, if less than 2 mH.

5.Limitations:
20,000 count on primary display, 2,000 count on secondary.
No voltage can be applied to the jacks.
There is no input protection.
4 wire measurement is possible (removing PCB trace resistance only, not contact point resistance) with the special jack adapter, but doesn't work with Kelvin testing leads.
No DC bias can be applied to the jacks.
The meter impedance is 120 Ohms and the test current is 4.5mA~5mA RMS.

6.Construction:
The 2 halves of the meter can be easily separated, by disconnecting the joining wires, if required. The USB PCB is held in place by one screw and the battery wires and battery connector can be threaded through, once a little trap door with clips is removed. There is no shielding in the bottom piece, just like all the meters using this chipset.
4 self-tapping screws are holding the main PCB in place.
Don't undo the topmost screws which secure the backlit LCD to the PCB, unless you have to. 2 LEDs are installed for backlighting through a large diffuser. The whole LCD/diffuser/Zebra connectors/LEDs contraption is difficult to put back together correctly, even after careful dismantling.

It is a double-sided PCB, with a limited number of components, as the chipset does most of the work:
U1 Cyrustek ES51919Q
U2 Cyrustek ES51920A (Not the S model, like the CEM or Mastech)
U3 24C02H Serial I2C EEPROM 2KB
U4 TI 430G2202 2KB flash 256B RAM 20-TSSOP uController
U5 3.5V voltage regulator
U6 5.0V voltage regulator
U7 TI AEH7M Multiplexer/De-multiplexer
U8 TI AEH7M Multiplexer/De-multiplexer

1 VR trimpot (probably Ohm adjustment)
2 crystal oscillators (3.999/24.000)

There is also a small separate PCB for the USB connector in the bottom shell. 3 unsightly wires provide USB data link and power connection. The wires are soldered directly to the PCB, instead of connectors, then covered with sealant to provide some stress relief.

[Wytnucls]

7.Software:
There is a convenient dedicated USB push-button to activate the PC connection.
Just install the UNI-T software that came on the included CD (unlike the IET) and no special drivers are required. The software will look familiar to the owners of UNI-T 61E and 71B/C/D/E. Be aware that I found an incompatibility with my USB Logitech MX mouse, so I have to disconnect it while using the logging software, otherwise the meter is not seen by the PC.
The program is a bit cumbersome at first, with its 1 second interval constant logging, but becomes quite useful after some taming.
I found that the best way to log samples, is to measure the first one, then log the data with the software connection button on the top left of the window, then immediately turn it off, after it appears in the list. Then repeat the procedure for each component. Leave the 'Repeat' and 'Sample interval' unselected. The Graphing software is unwieldy, with its auto vertical axis scaling based on measured value and full range, with no option of zooming on the pertinent area. A picture of the graph can be saved as a bitmap though.
The samples are logged as value (with a maximum of 60,000 apparently), current mode and units with the secondary parameter data and a date/time stamp included. It is much better than the Mastech software, which doesn't log much of anything.
The list can then be saved to an Excel spreadsheet with all parameters.
The Pass/Fail logging is also possible as seen on the picture below.

8.Overall value:
Fantastic price for such a full functionality, with no additional costs for USB logging, unlike the IET 5000.
I paid 115$ in China with tax included (17%). It costs slightly more on eBay.
Great convenience with USB power and logging at the same time. It doesn't even need costly batteries, it can run from USB power alone.
Auto APO selection depending on whether the machine is powered by battery or USB.
Fast accurate measurements. (Twice as fast as the CEM meter)
There is a Hold feature to freeze the display.
In China, the meter comes with a 1 year warranty.
The testing voltage is only 0.6V, allowing in circuit testing.
Overall, a well built LCR meter for the price-conscious hobbyist. Possibly not the most accurate LCR meter out there, but very useful nonetheless.

[BravoV]

Great review & tear down, thank you ! 

0.6 V in circuit testing

If this is not troubling you too much, please do a measurement with a scope at the measuring signal, say like at cap with low esr and high esr, really curious to see if it maintains the strict low voltage signal across different DUTs.

Interesting piece of gear, looking at it's price, have to agree this is quite a bang for the buck.

[Wytnucls]

Here you go:
As expected, voltage
without DUT                       0.613V RMS
with 47.0 Ohm resistor        0.159V RMS       
with 0.24 Ohm ESR cap       0.014V RMS
The meter impedance is 120 Ohms and the test current is 4.5mA~5mA RMS.
I have also uploaded here the Cyrustek LCR bridge ES51919/ES51920 chipset information and the datasheet for the multiplexers.

[Wytnucls]

Here are the resolutions and accuracies on all ranges, copied from the UNI-T booklet:
(The capacitance page has a sticker to correct the stated 2%+5 accuracy of the 1 KHz 2000uF range)

[grenert]

Thanks for your review, it seems very reasonably priced for what you get.  I don't see how you could do four-wire measurement with the adapter when the jacks are only two-wire with guarding.

[Wytnucls]

You get 4 wires to the jacks, eliminating the resistance of the traces, with little resistance remaining afterwards, through direct contact of the DUT with the adapter and the jacks. Not fully 4 wires like with Kelvin clips, but pretty close.

[robrenz]

Very nice review Wytnucls    For the price it seems very good. If you could make or source the split banana jacks that are in the DE-5000 you could replace the jacks and carry the 4 wire measurement out to split banana attachments.  I have not compared the specs but this at first glance looks better than the Mastech.

[Wytnucls]

That sounds like open-heart surgery, but I'm sure somebody will give it a go, now that you mentioned it! 

[BravoV]

Here you go:
As expected, voltage
without DUT                       0.613V RMS
with 47.0 Ohm resistor        0.159V RMS       
with 0.24 Ohm ESR cap       0.014V RMS
I have also uploaded here the Cyrustek LCR bridge ES51919/ES51920 chipset information and the datasheet for the multiplexers.

Thanks a lot.

vPP only at 0.47 

[chickenHeadKnob]

That sounds like open-heart surgery, but I'm sure somebody will give it a go, now that you mentioned it! 

good review and photos. I don't think it would be anywhere near as hard as surgery. The only hang-up might be the dimensions of the replacement jack sockets, as most people would still want to retain the same case. The one advantage of the mastech and any meter with the slot style sockets is that it is practical to make your own kelvin adapters from double sided copper-clad pcb material. You don't even need to plate the copper, it is fairly easy to burnish and clean the contact patches each time you want to switch adapters.

[iloveelectronics]

Do you have any issue with the viewing angle of your UT612? I bought one a while ago but the LCD is terrible. I can barely see anything if I look directly at it. It has to be viewed from like a 30 or 45 degree angle to see things clearer.

[BravoV]

Do you have any issue with the viewing angle of your UT612? I bought one a while ago but the LCD is terrible. I can barely see anything if I look directly at it. It has to be viewed from like a 30 or 45 degree angle to see things clearer.

From above photos, it doesn't look to have this problem, photoshoots of your lcd from various angles please.

[iloveelectronics]

From above photos, it doesn't look to have this problem, photoshoots of your lcd from various angles please.

I tried, but somehow it always looks better on photos. In real life the display is really pathetic.

[uprightsquire]

Perhaps video?

[Wytnucls]

Do you have any issue with the viewing angle of your UT612? I bought one a while ago but the LCD is terrible. I can barely see anything if I look directly at it. It has to be viewed from like a 30 or 45 degree angle to see things clearer.

Hi Franki,
Yes, I mention it in the review somewhere. Mine is possibly not as bad as yours. The CEM DT-9935 LCR meter has the same quirk. I actually took my CEM back to the shop for a replacement, but the new one was just the same. So, I now call it a feature. 
Looking at it straight on, the digits are slightly fuzzy and dimmer. The screen becomes sharp, from about 10-20 degrees from the vertical. It's not really an issue, once you get used to it. Especially, if one uses the meter lying flat on the bench.
The backlight makes the effect a little worse.
I'll try to shoot a video to capture the strange behaviour.

[Hydrawerk]

Thank you for the review. Unfortunately, this UT612 is IMHO not better than my DT-9935... It has the same disadvantages. No 4-wire measurement and no input protection. It must have a slightly different chipset, if it works faster... In Czech republic you can buy the dt-9935 quite cheap for 75 € (Euro). http://www.gme.cz/digitalni-multimetry-s-funkci-rlc/multifunkcni-rlc-metr-cem-dt-9935-p722-436/ The UT612 is always much more expensive, at least in Czech Republic.
If I wanted a better quality LCR meter, I would buy the Mastech MS5308. It has AFAIK better true 4-wire probes.

https://www.eevblog.com/forum/testgear/mastech-ms5308-lcr-meter-with-esr-measurement-on-discount-at-the-moment/

[Wytnucls]

None of the LCR meters based on the Cyrustek chipset have input protection, not even the IET 5000. Some, like the CEM can handle a maximum of 30 volts on the input jacks.
The UNI-T has a small advantage over the CEM for measurement, providing 4 wires to the input jacks.
If you need genuine 4 wire measurement with Kelvin clips, indeed rather buy the Mastech or the IET 5000.
The main advantage of the UNI-T meter is the convenience of the mini-USB connection for power and communication. The CEM doesn't have external power or datalogging.
I haven't seen the IET logging software yet, but the UNI-T has a more advanced logging program than the Mastech.

[Hydrawerk]

Well, the DT-9935 also has four jacks, but it is not much useful. The absence of external power supply is a big disadvantage...
Anyway, I don't know how many people actually need the datalogger via USB feature.

[Wytnucls]

I didn't say 4 jacks, but 4 wires or 4 traces on the PCB going to the 2 input jacks, not the guard jacks. The CEM only uses 2 traces.
After proper calibration, there would be extremely little difference between measurements with Kelvin clips and the UNI-T adapter.
I think you have a wrong conception of what Kelvin clips are for. There are really useful to measure small resistance at a distance, which do require long leads to the DUT. In other circumstances, with very short electric paths to the DUT and proper meter calibration, measurements would be essentially the same. I don't know how many people actually need the Kelvin clips feature.

[alm]

The long leads you can compensate for, their resistance is constant. Kelvin connections are critical once contact resistance between the probe/clip and DUT becomes significant. This contact resistance often varies between measurements, and may be dependent on force. Kelvin connections can compensate for this variation.

[Spawn]

Thanks for the review Wytnucls, this one is looking really nice with its case and all. The one I reviewed was low end for sure, this reminds me the difference in the insulation testers I got, UT501 and UT511.

If you want quality with Uni-T you have to pay more for it, but the price is still good on the market compared to other equipment makers.   

[BravoV]

I didn't say 4 jacks, but 4 wires or 4 traces on the PCB going to the 2 input jacks, not the guard jacks.

Wytnucls, assuming I don't mind voiding warranty by doing some minor surgery and do some mod at the connectors, is it possible to have 4 wires Kelvin clip ? I can't see clearly at the board detail at the input section from your board photo.

[Wytnucls]

Here is a better PCB picture, with a close-up of the jacks. At first glance, it seems possible to modify for a proper 4-wire measurement system. You would need to investigate further, before you start hacking at your meter.
I think you would be better off buying an LCR meter with the 4-wire function out of the box, if you desperately need that feature. I personally think Kelvin clips are a bit overrated on a low resolution machine like this and I bet you won't see any dramatic increase in accuracy, after your modification.
Nevertheless, it might be easier to use the 'Guard' jacks for the 2 additional 4-wire connections, as a guard connection is only useful if you measure a resistance above 10 MOhms anyway. If you want to keep a 'Guard' connection, it would be relatively easy to install a fifth jack with a PCB plane connection for that purpose.