Test/review of DMM UNI-T UT139C

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HKJ
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Test/review of DMM UNI-T UT139C

DMM UNI-T UT139C

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Uni-T has a large selection of DMM in their program, this model exist in A, B and C version, main difference is 2000, 4000 and 6000 count display, there is also a small variation of included functions. In this review I will look at the C version.

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The meter arrived in a red box with English and Chinese writing.

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The probes are branded UNI-T and rated for 10A and 1000V

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The removable tip must be on for best safety.

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The plug is fully shrouded.

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The thermocoupler has a single connector to the multimeter end, that is considerable better than the two loose bananaplugs.

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The tilting baile is just about stable enough to change range and use switches with one hand.

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The 600mA fuse is assible from the battery compartment.

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Display

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The above picture shows nearly all the segments on the display.

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Typical display during usage, it will show the number and what measurement is selected.
The circle with arrow shows that auto power off is enabled, hold down SELECT when turning on to disable this.

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The electric field detection (NCV) shows from 1 to 4 bar depending on field strength.



Functions

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Buttons:


  • Range: Switch to manual ranging and will also change range, hold down to get back to automatic
  • Max/Min: Starts recording min/max values, press the button to change between min/max (Both are saved) and max-min, hold down to exit.
  • Rel: Uses the current value as reference and will show all further readings relative to this, will change to manual range.
  • Hz %: Select Hz and duty cycle display, works on all AC volt and current ranges, will select duty cycle in HZ range.
  • Hold/light (Yellow): Will freeze the display, hold down to turn on background light
  • Select/VFC(Blue): Selects the ranges printed with blue on the rotary switch, hold down to enable a low pass filter on AC volt.

Rotary switch:

  • Off: Meter is turned off
  • V: Show DC and AC voltage, use Select for AC and “Hz %” for frequency an duty cycle.
  • mV: Show DC and AC voltage, use Select for AC and “Hz %” for frequency an duty cycle.
  • ohm: Resistance, continuity, diode and capacitance.
  • Hz %: Frequency
  • uA: Current DC and AC, use Select for AC and “Hz %” for frequency an duty cycle.
  • mA: Current DC and AC, use Select for AC and “Hz %” for frequency an duty cycle.
  • A: Current DC and AC, use Select for AC and “Hz %” for frequency an duty cycle.
  • NCV: Non contact voltage, i.e. electric field.
  • Clamp: External current clamp with 10mV/A


Input

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  • 10A: High current, it can only withstand 10+ ampere for a short time (Fuse is 10A).
  • mAuA: The lower current ranges, the selector switch will change between two different shunts (Fuse is 600mA).
  • CON: The common terminal for all ranges.
  • xxx: All other ranges, including external current clamp.




Measurements

  • Volt and frequency

    • Frequency counter and duty cycle can only be selected in AC ranges.
    • Frequency input do requires a zero crossing.
    • Frequency input requires about 0.02Vrms before it works.
    • Max/min needs about 350ms to capture a voltage.
    • At 0.1Vrms input frequency range is from 0.9Hz to 4MHz
    • At 1Vrms input frequency range is from 1Hz to 49MHz
    • AC volt can measure up to about 2kHz, true RMS will not work at this frequency
    • VFC only works in 600.0 and 600 volt mode and reduces bandwidth to about 800Hz
    • Input impedance is 10-11Mohm on DC and AC
    • Input impendance is high on mV DC range.

  • Current

    • Frequency counter and duty cycle can only be selected in AC ranges.
    • 10A range has audible alarm when current is 10A or above.

  • Ohm, Continuity, diode and capacity

    • Ohm is 0.97V open and 0.30mA shorted
    • Continuity is fast (About 20ms).
    • Continuity beeps when resistance is below 50ohm
    • Continuity is 1.01V open and 0.30mA shorted
    • Diode range uses 3.2V, max. display is 3.000V at 0.09mA, max. current is 1.21mA shorted
    • 70000uF takes about 10 seconds to measure.

  • Miscellaneous

    • Current consumption of meter is 1.3mA to 1.7mA (6mA with backlight)
    • Meter works down to 2.2V where meter turns off, battery symbol show at 2.4V.
    • Backlight only works down to about 2.7V
    • Reading is stable with varing battery voltage.
    • The meter usual need a couple of display update to reach the final value.
    • Viewing angle is good
    • Display updates around 3 times/sec
    • Backlight will automatic turn off in about 15 seconds.
    • Will automatic turn power off in about 15 minutes.
    • Standard probes fits fine, but cannot be seated fully.
    • Generally precision is within a few counts, but there are ranges where it is 20 counts out.
    • Weight is 354g without accessories, but with batteries and sleve.
    • Size is 175 × 81 × 47mm with sleve.

  • Probes

    • Probe resistanse 40mOhm for one
    • Probe wire is soft and 88cm long.



1uF

A look at the capacity measurement waveform.

DMMschema

It is just outside tolerances on the high ohms measurements (2% out)



Tear down


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3 screws (One was for the battery cover) and the back could be removed.

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The front required 4 screws for the terminals and 3 small screws for the circuit board.

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There is something under the display

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Two screws more to remove the display, but not the backlight, it is soldered to the circuit board.

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But I can bend it up (at least a few times).

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Here is the DMM chip (U1: DTM0660L) and the memory (U3: T24C02A) for calibration and functions setup. At the front is the NCV antenna and the indicator led (FG2). One of the voltage dividers are here (R1A, R1B, R1C, R1D: 4×2.5Mohm)

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Here is the range switch and some resistors.
A input chain (R2A, R2B, R2C: 3×300kohm), the uA shunt (R4: 99ohm) and the mA shunt (R5: 1ohm)

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On this side is the fuses, I wonder why the 600mA (F1) is longer than the 10A (F2). There is four MOV’s and two PTC for input protection. The transistors (Q2, Q3, Q8, Q9) do also look like protection. The 5 diodes (D1..D5) is protection for the uA and mA current range.

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Conclusion

This meter has all the usual functions and a few extra like NCV, VFC, external clamp (Any meter can use an external clamp, but this meter places the decimal point correct). As usual the burden voltage in the high mA is very bad.
The meter has a lot of protection and the fuses are rated for 600V, but I am lacking a current interrupt rating for the fuses.

This meter looks like it is fine for mains voltage and anything below.



Notes

UNI-T makes two versions of some meters, one living up to its CAT rating and one that do not.
UNI-T sell rebranded versions of their meters, i.e. you can get this meter with another name on it.

How do I review a DMM
More DMM reviews

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MRsDNF
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Nice review HKJ. Thanks. Thumbs Up

My current and or voltage measurements are only relevent to anything that I measure.

Budget light hobby proudly sponsored by my Mastercard and unknowingly paid for by a hard working wife. 

djozz said "it came with chinese lettering that is chinese to me".

old4570 said "I'm not an expert , so don't suffer from any such technical restrictions".

Old-Lumens. Highly admired and cherished member of Budget Light Forum. 11.5.2011 - 20.12.16. RIP.

 

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This meter looks really good for its pricetag. 

Any shortcoming worth mentioning versus the Aneng AN8008?

 

Thanks and cheers 

HKJ
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Barkuti wrote:

Any shortcoming worth mentioning versus the Aneng AN8008?

Burden voltage. But there are many advantages to this DMM, including more current ranges.

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Barkuti
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Well, I believe proper current measurement setups should be done with an external shunt, measuring the voltage drop across it; I guess it is just a minor shortcoming from such a point of view. 

The minimum backlit voltage is quite high to be of actual use with alkalines, I guess it would be wise to use a 14500 LiFePO4 plus a dummy cell with it.

 

Cheers Party

HKJ
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Barkuti wrote:

The minimum backlit voltage is quite high to be of actual use with alkalines, I guess it would be wise to use a 14500 LiFePO4 plus a dummy cell with it.

The backlight voltage is rather demanding, you will not get many hundred hours from a set of alkaline, before you have to replace it.
I do seldom use backlight, especially a 15 second one.

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Great review HKJ! Thanks.

Phlogiston
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Thank you for the review, HKJ.

I was interested to see that your meter had a good display and view angle.

I’ve had two UT139C meters, from different suppliers and six months apart. I had to send both of them back because the displays were incredibly poor.

Here’s a photo of what one of mine looked like, next to the old meter it was meant to be replacing:

I tried everything I could think of, too. Fresh cells in NiMH, alkaline and Li-Ion flavours. Turned the backlight on and off. Checked the manual for a contrast adjustment, couldn’t see one. I even took one of the meters apart to see if the display wasn’t quite seated properly or something. Nothing worked.

I’m vaguely wondering whether I should try for third time lucky, but I have to be honest and say that I probably won’t.

joechina
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Barkuti wrote:

This meter looks really good for its pricetag. 


Any shortcoming worth mentioning versus the Aneng AN8008?


 


Thanks and cheers 

Well, I think if you want only one meter in your household this is the one to buy.
You never know when sb. prope mains with it. That has some protection in it, unfortunately not savety certified.
The An8008 is only for low power stuff.

There is no perfect meter Smile

stolikat
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Great review! I think I will be picking one of these up.

Venom
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Can Energizer Ultimate Lithium be used in this DMM without any damage to the meter?

HKJ
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Venom wrote:
Can Energizer Ultimate Lithium be used in this DMM without any damage to the meter?

I would expect they can, but I do not know it.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

Barkuti
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Venom wrote:
Can Energizer Ultimate Lithium be used in this DMM without any damage to the meter?

The answer is yes, but why such insanely expensive cells for a low powered device which correctly operates with low drain alkalines? Sure, some can complain of leaks with some of them but, in my experience, this is hardly a real problem. I've even recharged inexpensive off-brand alkaline primaries with success and leak-free results.

 

Cheers 

Venom
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HKJ wrote:
Venom wrote:
Can Energizer Ultimate Lithium be used in this DMM without any damage to the meter?

I would expect they can, but I do not know it.

Thanks for the reply!

Venom
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Barkuti wrote:

Venom wrote:
Can Energizer Ultimate Lithium be used in this DMM without any damage to the meter?

The answer is yes, but why such insanely expensive cells for a low powered device which correctly operates with low drain alkalines? Sure, some can complain of leaks with some of them but, in my experience, this is hardly a real problem. I’ve even recharged inexpensive off-brand alkaline primaries with success and leak-free results.


 


Cheers 

The main reason beside the leaks is the backlit display may last a little bit longer.

everydaysurvivalgear
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Mine is dead it lasted maybe 2 and half years. The Multi mode with the diode, Ohms, continuity testing mode stopped working. It would just beep and reset when going into that mode i have a found a few more people with this issue also. Kind of disappointed although not super expensive mine cost me $ 70AUD when i bought it.

I checked and cleaned contacts no help, I tested fuses and changed batteries multiple times and no help. Checked the board no issues i can see.

Its weird i think it isn’t regulating the voltage to the chip in this one mode thus it keeps on resetting. It kind of smelt weird when i took it apart but nothing looks burnt and no reason why it would have burned. It stopped working after being left for a while.