Test/review of Clamp meter UNI-T UT258A

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HKJ
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Test/review of Clamp meter UNI-T UT258A

Clamp meter UNI-T UT258A
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This is a clamp only meter, i.e. not really a DMM (Digital Multi Meter).
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The meter arrived in a cardboard box.
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It included the meter, a pouch, a CD, a USB/Serial cable and a manual in Chinese (A English version can be downloaded from UNI-T).
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Display
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The above picture shows all the segments on the display. It looks to be a standard DMM display, but this meter only uses part of it.
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Typical display during usage, it will show the number and what measurement is selected.
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Saving a value when pressing HOLD.
Functions
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Buttons:


  • Off/DC/AC: Slide the switch to desired mode.
  • HOLD: Use short press will freeze the display and save the current value. A longer press will switch to readout mode.

Rotary knob:

  • Zero: Turn the know to zero the current display, it is best done in DC mode.

Input
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The clamp is the only input to this meter.
Measurements

  • Current

    • The meter crashed a few times and had to be power cycled.
    • Both DC and AC will react on DC current, but the AC ranges show about 25% too high in one current direction.
    • Zero setting is common for AC and DC, but it is easier to adjust on DC due to the sign.
    • Clamp is rated for maximum 60A

  • Miscellaneous

    • Current consumption of meter is 12.3mA
    • Meter works down to 3.4V where it turns off, battery symbol show at 7.4V.
    • Meter has a small deviation below 3.6V.
    • Saved values are cleared when power is turned off.
    • Viewing angle is good, except from top.
    • Display updates around 3 times/sec
    • Will automatic turn power off in about 5 minutes.
    • Weight is 219g, with batteries.
    • Size is 216 × 65 × 35mm


TestDC
A test of DC shows that the DC offset is fairly stable and the current need to be above 10mA before it starts to work. When measuring high current (i.e. 10-60A) the clamp will be magnetized and need readjustment of zero or demagnetization before it shows correctly at low current again.
TestAC
AC also looks fine, but the sensitivity is not symmetrical around zero.
DMMschema
The meter has 3 current ranges, there can be some problems around the range change points.
Software
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The meter has a USB mini connector, this is a bit old fashioned.
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The cable is worse, it has a USB mini connector in one, but a old style RS232 serial connector in the other end. This means the USB connector is not USB, but RS232 signals.
setup
I downloaded the program, instead of using the CD. The installer is in English and looks fairly standard. There was no problems installing it.
start
But it would not start.
Tear down
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To open the meter I had to remove 3 screws.
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The zero adjust turns a trimpot, this is not good for long life.
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To get the PCB out I had to remove 4 more screws.
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Somebody has done a fairly bad job of removing the type numbers from the chips. There must be some OpAmps a voltage regulator, a mux (IC7: 74HC4051), probably a ADC (The processor only has 10 bit), the large IC is a processor (IC1: M430F… 8kB flash 256B ram) and there is a RS232 driver next to it (IC8: SP3232 RS232 driver with 13V output, not a good idea on a USB cable).
The USB connector is on a small add-on board.
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In this side is the the two switches and the display, that is on a add-on board with a COB chip on the back.
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Conclusion
Being a clamp only meter means that safety is fairly good, but probably not up to CAT III rating (The clamp has metal visible and there is a USB connector at the other end. The manual states 2KV/rms).
I had hoped for a really good meter for low current, it is fairly good and it do not drift nearly as much as many other clamp meters, but it has a couple of problems.
The meter do not read symmetrical in AC mode. The USB output with 13V RS232 signals is ridiculous, the firmware crashes frequently and do not save logged value when power is turned off. The PC software do not work out of the box.
Notes
How do I review a DMM

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

MRsDNF
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Thumbs Up . Thanks.

 

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

                      "My man mousehole needs one too"

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.

 

djozz
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Thanks, it looks rather old-fashioned, like old-school chinese stuff, Uni-T products usually look more modern.

I would love a clamp meter that measures low currents reliably.

whatsthepoint
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THX for the review.

So,I'm in the market for the best clamp meter DMM  for measuring low current that's below $100.00(US).

They all seem to have weaknesses.

never underestimate the power of stupid people in large groups

Pete7874
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whatsthepoint wrote:

So,I’m in the market for the best clamp meter DMM  for measuring low voltage that’s below $100.00(US).


The primary purpose of clamp meter is to measure current, not voltage.
whatsthepoint
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Pete7874 wrote:
whatsthepoint wrote:

So,I'm in the market for the best clamp meter DMM  for measuring low voltage that's below $100.00(US).

The primary purpose of clamp meter is to measure current, not voltage.

Sorry,that was another senior moment on my part.The err has been fixed but it will see use as a DMM also.

Now,how about my question?

never underestimate the power of stupid people in large groups

Pete7874
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How low of a current are we talking about? Most clamp meters struggle with accurate low current measurements. One way to get around it is to coil up a wire multiple times around the clamp, thus multiplying the current so that’s at a higher value, then just divide the measurement by the number of coils.

I like the Uni-T 210E, which HKJ tested in the past. I think I paid around $30 for it. I’d say it measures current OK once you get above 100-200 mA, and it can also be used as a basic DMM.

https://lygte-info.dk/review/DMMUNI-TUT210E%20UK.html

djozz
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I like the Uni-T 210E also, but had one fail after two years, it began to give erronous measurements whixh were jumping around, it was not a low battery thing. So I bought another one and that one is still doing fine after a year.

whatsthepoint
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My old 210E was going wonky  also so I'm looking for a replacement.

Is replacing a 210E with another 210E still the best choice in the below $100 price range?

I want to also use it as a DMM.

never underestimate the power of stupid people in large groups