Author Topic: Uni-T UT120C review and tear down  (Read 26075 times)

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Offline Wytnucls

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Uni-T UT120C review and tear down
« on: January 13, 2013, 03:25:15 am »
I just bought this cute mini DMM in Hong Kong for 105 HK$ or about 13.50 US$. I had wanted to buy it before but couldn't find it anywhere. The meter is sold sealed in a plastic blister with a small operating manual written in simplified Chinese and a warranty card.
The UT120 range consists of three models, the 120C being top of the line, with current measurement (uA/mA only) and a 400mV scale. The UT120A model doesn't have the capacitance function, otherwise it is identical to the 120B model.
The meter has reasonable specs for something this cheap:
4000 count, auto-ranging, auto shutdown (after 30 minutes), V/mV/mA/uA (DC/AC), Ohms, Diode, Caps, Continuity, Hz and duty cycle (%). It also has a relative mode and the usual data hold function.
It is well made, with a sturdy case and very legible LCD screen (no backlight). It runs off a 3V CR2032 battery and has a low battery warning icon that comes on at 2.4V.
It is fitted with small, permanently attached probes, which are quite adequate and rated, like the meter, CAT II 600V. The leads are PVC, marked 24AWG and they feel a bit stiff compared to the usual silicone ones.
The function selector rotary switch has some unwanted friction, but it can still be turned with just one finger.
It is sold in a see-through case, with some removable plastic film protection on the black part of the face plate, which I only noticed after wondering for a few minutes why the screen was so washed out!  ::)
Here are the specs:
DCV          400mV/4V/40V/600V                             ±(0.8%+3)
ACV          4V/40V/400V/600V                                ±(1.2%+3)
DCA          400uA/4mA/40mA/400mA                      ±(1.0%+3)
ACA          400uA/4mA/40mA/400mA                      ±(1.5%+5)
Ohms        400/4K/40K/400K/4M/40M                    ±(1%+2)
Caps         4n/40n/400n/4uF/40uF/100uF               ±(4%+3)
Freq          10Hz~100KHz                                       ±(0.5%+3) (>30VRMS between 10kHz and 100 kHz)
Duty Cycle    0.1%~99.9%                                     ±(0.1%)
Impedance   <10MOhms
The continuity buzzer is not latched, but quite responsive, although a bit scratchy.
Diode test open voltage is 1.44V, so won't light up any LEDs or display the voltage drop.
Some people might appreciate that the meter doesn't beep when the range switch is moved to another mode.
It is definitely pocket size at 76 grams and here are the dimensions:110mm X 58.2mm X 10.8mm
« Last Edit: January 13, 2015, 03:24:26 pm by Wytnucls »
 
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Offline Wytnucls

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Re: Uni-T UT120C review and tear down
« Reply #1 on: January 13, 2013, 03:28:31 am »
Here are some pictures of the inside, which show a well laid out PCB with mostly SMD parts and with few glaring issues, in my opinion.
There is only one screw, which fits into a receiving metal insert, holding the back in place, after it has snapped in its position.
There are no screws on the PCB, it fits in a slot at the top of the case and is held in place by plastic clips, which are part of the case.
It has a 400mA fuse for the mA range and a PTC on the other functions, for input protection.
It is a self recovery 250V 400mA fuse overcurrent protector (WH250 400): http://en.b2b168.com/s168-29888660.html
PPTC (Polymeric PTC, Polyswitch) http://en.wikipedia.org/wiki/Resettable_fuse

As you can see, the piezo speaker is sitting just behind the LCD screen, which may explain why the sound is rather faint.
I will test its accuracy against my other meters, when I get home.
This particular meter came from China, left the factory on 20th Nov 2012 and carries a China warranty only, valid for 1 year.

The PCB is quite barren, understandably, with most functions accomplished by U2, the DMM ADC, which is hiding under a blob of black epoxy.
There are no voltage regulators, the ADC works directly off the 3V battery.
The cruciform battery holder looks a bit crude, but it does the job.

4 trim pots can be found:
VR1: DC Volt adjustment
VR2: AC Volt adjustment
VR3: Capacitance adjustment
VR4: DC mA adjustment

The burden voltage on the mA range is 3.45mV/mA and 102uV/uA on the uA range, which is pretty good compared to the UT71D (5.33mV/mA and 500uV/uA). For reference the Fluke 87V has a burden voltage of 1.80mV/mA on the mA range and 102uV/uA on the uA range.
The resistances involved include the current shunt, the polyswitch and the leads (3.45 Ohms on mA and 102 Ohms on uA)

The see-through plastic protective case is a bit bulky, but it shields the meter quite well.
One feature I hadn't noticed, is that the meter can be used with the translucent case closed. There is a clear aperture over the LCD screen and 2 openings in the case for the probe leads to pass through.
So, once the proper selection has been made with the range switch, the case can be closed and the meter can be used in a rough and dirty environment, without having to worry about contamination. It is kind of rainproof, but certainly not waterproof.
« Last Edit: April 10, 2013, 06:06:41 am by Wytnucls »
 
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Offline SeanB

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Re: Uni-T UT120C review and tear down
« Reply #2 on: January 13, 2013, 04:01:40 am »
Interesting little unit there, quite compact and a nice little emergency unit.

Where do you call home?
 

Offline Wytnucls

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Re: Uni-T UT120C review and tear down
« Reply #3 on: January 13, 2013, 04:05:02 am »
Home?
mmm....right now: Mauritius, Jo'burg and Belgium.  ;)
 

Offline Lightages

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Re: Uni-T UT120C review and tear down
« Reply #4 on: January 13, 2013, 04:40:11 am »
That looks like a nice step up from the UT10A. I am interested to hear about the accuracy. The fuse is a self resetting fuse?
 

Offline SeanB

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Re: Uni-T UT120C review and tear down
« Reply #5 on: January 13, 2013, 04:54:07 am »
Seeing as they use PTC units and not a fuse in sight they must be self resetting.
 

Offline Wytnucls

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Re: Uni-T UT120C review and tear down
« Reply #6 on: January 13, 2013, 05:03:02 am »
It is a self recovery 250V 400mA fuse overcurrent protector (WH250 400):
http://en.b2b168.com/s168-29888660.html
PPTC (Polymeric PTC, Polyswitch)
http://en.wikipedia.org/wiki/Resettable_fuse
« Last Edit: January 13, 2013, 05:29:38 am by Wytnucls »
 

Offline Lightages

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Re: Uni-T UT120C review and tear down
« Reply #7 on: January 13, 2013, 05:40:10 am »
Oh well, anther lie from Uni-T about their CAT rating then. 250V does not even come close to the CATII 600V rating. Still a nice little meter.
 

Offline Wytnucls

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Re: Uni-T UT120C review and tear down
« Reply #8 on: January 13, 2013, 05:42:57 am »
I'm installing a 600V Fluke fuse in it. It might just bulge a little bit!  ;)
At least, with this meter, you can't have the leads in the wrong jacks, while measuring voltages.
« Last Edit: January 13, 2013, 04:07:18 pm by Wytnucls »
 

Offline Spawn

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Re: Uni-T UT120C review and tear down
« Reply #9 on: January 13, 2013, 06:33:48 am »
Nice meter, but I am not sure if it is compacter than a UT10A with its hard case, I have two Uni-T  UT10A’s flying around so I can grab whenever I want, like in my car or in the living room, and also have a Amprobe DM78C in my work jacket and its really handy, I wouldn’t recommend to measure mains with it but low voltage/current installations and continuity testing goes perfect, I don’t need to walk to my toolbox every time.

Offline Wytnucls

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Re: Uni-T UT120C review and tear down
« Reply #10 on: January 13, 2013, 07:35:34 am »
The case is a bit bulky, but it protects the meter quite well.
One feature I hadn't noticed, is that the meter can be used with the translucent case closed. There is a clear aperture over the LCD screen and 2 openings in the case for the probe leads to pass through.
So, once the proper selection has been made with the range switch, the case can be closed and the meter can be used in a rough and dirty environment, without having to worry about contamination. It is kind of rainproof, but certainly not waterproof.
« Last Edit: January 13, 2013, 08:40:02 am by Wytnucls »
 

Offline Wytnucls

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Re: Uni-T UT120C review and tear down
« Reply #11 on: January 16, 2013, 12:36:08 am »
Here are a few screen shots of DC Volt measurements: 2V, 12V, 30V
 
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Offline Wytnucls

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Re: Uni-T UT120C review and tear down
« Reply #12 on: January 16, 2013, 12:42:13 am »
AC Volt and mA measurements: 12.4VAC and 225 mA AC
« Last Edit: January 16, 2013, 01:02:03 am by Wytnucls »
 
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Offline Wytnucls

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Re: Uni-T UT120C review and tear down
« Reply #13 on: January 16, 2013, 01:11:19 am »
Some uA and mA DC measurements: 166uA, 55 mA, 220 mA
 
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Offline Wytnucls

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Re: Uni-T UT120C review and tear down
« Reply #14 on: January 16, 2013, 01:22:11 am »
Resistance and Capacitance measurements: 56kOhms and 22uF
I won't bore you with the rest. Let's just say that everything seems to be well within published tolerances.
Volt, mA and capacitance range accuracy can be adjusted with trim pots.

The constant current delivered for resistance measurement is 170uA.

The capacitance measurement uses a 40uA constant current. The peculiar voltage build up on a 22uF cap is shown here on the oscilloscope. Bear in mind that the maximum capacitance range is 100uF.
« Last Edit: May 12, 2013, 07:17:34 pm by Wytnucls »
 
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Offline Wytnucls

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Re: Uni-T UT120C review and tear down
« Reply #15 on: January 17, 2013, 11:44:33 pm »
Here is a short video showing 220V RMS (310V peak) mains voltage measurement and testing of the 600V overvoltage protection on other ranges:
In case you wonder, I live on a small island and the mains voltage has a lot of fluctuations.

« Last Edit: May 12, 2013, 07:18:25 pm by Wytnucls »
 
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Offline darko31

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Re: Uni-T UT120C review and tear down
« Reply #16 on: September 07, 2013, 05:48:27 am »
I've bought this little meter, although UT120B version, they didn't have the C version at the store. I'm pretty happy with it, I only use it lightly, and only problem/limitation I've found is that it can't light up most of the LEDs because voltage across test leads is only 1.5V when in diode tester mode. Otherwise, great little meter.
 

Offline jancelot

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Re: Uni-T UT120C review and tear down
« Reply #17 on: May 10, 2015, 01:42:38 am »
The 120C is available at Dealextreme for 18 USD free shipping.
 

Online Fungus

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Re: Uni-T UT120C review and tear down
« Reply #18 on: May 21, 2015, 01:43:39 am »
Mine just arrived.

I haven't put it through its paces yet but I like the size and I like the little case it comes in. First impressions are that it's exactly what I wanted.


Edit: I just did some basic function tests. Numbers are all reasonably good - within a couple of digits on a 4000 count meter is good enough!)

Auto-ranging is a bit slow on the Ohms range (a couple of seconds to take a reading). Continuity buzzer is fast but scratchy (not latching).

Still happy so far.
« Last Edit: May 21, 2015, 03:18:30 am by Fungus »
 


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