Clampmeter DC current measurement - using UT210e

[Brumby]

The following is not meant to be anything more than a sharing of my experiences in using my UT210e for doing DC current measurements with the clamping jaws.  I am not planning of working through the theory, but if discussion wants to travel that path, I am all for it.

Most clamp meters can only do current measurements in the AC domain and some of those can be really cheap and even the cheap ones can give useful measurements if you keep within their limitations - notably frequency.  DC current measurement is more challenging and requires something different to the simple loop antenna approach.

The UT210e is one of those meters that can do it, but there are a couple of tips I would like to offer that have come from my efforts to get consistent results using one of these.


First, my testing setup:
I have 2 LED strips salvaged from an old TV that are mounted under my desk.  (These have been invaluable in locating things dropped on the floor.)  Each has it's own wiring running back to a bench power supply.  Here, I have separated the wires in order to have easy access for the clamp.



Once switched on to the 2A range, the Select button is pressed once to switch the meter into DC mode.



Bring the clamp up NEXT TO the wiring you want to measure - in the position you will be using to perform the measurements (or as close as possible).  Do NOT put any wires through the clamp jaws!
You will likely get a non-trivial reading:  (I have had some instances where I get a reading of over 200mA.)



Keep the meter in that position and press the Zero button



You will now have a reading that will be close to zero.  If you are lucky, it will be zero.



It's important to keep the meter in the same orientation!!  Here's what can happen with just changing the angle - and I've had variations of 30mA or more doing this ... and we haven't even tried taking a measurement yet!

[Brumby]

But now we are ready to take measurements.

As an exercise, I took measurements of each individual circuit and then one of both, to see whether the sum of the individual circuits was the same as it was for both together.




181mA + 163mA = 344mA   Spot on!

This seemed to good to be true, so I did it again....




176mA + 163mA  = 339mA  <>  334mA  -  Which is more representative of the results I usually get.

[beanflying]

For a cheapy they stack up really well as one EVERY user should consider having in their kit.

The DC Amps functionality for someone like me who plays with High Power R/C for example is a lot easier to drop across a battery wire than break in a dedicated high current meter as an example. Other than that it just sits in my on site bag with some long life rechargeable in it and does it's thing with another meter with some fancier functions this one doesn't have. 

[Specmaster]

I added one to my kit a couple of years back, doesn't get used all that much but when you need it is very good, and it is perfect for doing work on your car to boot, especially to if the battery is being charged as cars no longer have ammeters fitted these days.

[Brumby]

Interestingly, the very first time I used mine for a real purpose was exactly that - checking alternator current on my car!

[Ed.Kloonk]

The following is not meant to be anything more than a sharing of my experiences in using my UT210e for doing DC current measurements with the clamping jaws.  I am not planning of working through the theory, but if discussion wants to travel that path, I am all for it.

I have the dick smith(?) one similar but not the same. Must be 15 years old. Most clunky meter I have and if not for the DC amps feature would have gotten the heave-ho long ago. So poorly made.

Good for when you'd prefer not to break into a DC circuit. Unfortunately, for things in the wild, I only trust it to nearest amp.

With automotive current such as alternators and trailers and other big-ticket items, I often just measure the voltage at two points* with the fluke and (used to !) do the sums in my head. And often because I only had the Fluke MM when asked about things.

* two points could mean the battery terminal and the alternator terminal, for example. Surprising amount of resistance available to get a feel for your alternator health.

[joeqsmith]

So far the only problem I have seen with the UT210E is function switch failures.  Maybe five of them now have failed.  I have yet to plug the leads into one to use any of the other functions.

The first one I bought I managed to screw up the magnetics to where the meter would no longer zero.   I made a degauss coil for it and after resetting the magnetics, aligned the two meters I have.   For the $30 or so USD I paid, they were well worth it.   


***
I reverse engineered the front end and added a buffered analog output to drive my scope
https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/msg927685/#msg927685

My degauss coil
https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/msg1040540/#msg1040540

Many people started to reverse engineer the prom to add features to the 210E.   We were have a lot of fun with the meter.   Seems the mods were brought in to try and maintain order and I stopped posting to help ease the tension. 
https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/msg1048561/#msg1048561

After a few months of letting the thread return to normal,  I decided to make one last series of posts where I redesigned the entire front end including the sensor to improve the bandwidth.  To avoid having the mods called back in,  I walked away from the thread.  It looks like most what was posted after this was just playing with the prom.   
https://www.eevblog.com/forum/testgear/a-look-at-the-uni-t-ut210e/msg1101265/#msg1101265

demonstrating my degauss coil


demonstrating my redesigned UT210E

[AVGresponding]

The following is not meant to be anything more than a sharing of my experiences in using my UT210e for doing DC current measurements with the clamping jaws.  I am not planning of working through the theory, but if discussion wants to travel that path, I am all for it.

I have the dick smith(?) one similar but not the same. Must be 15 years old. Most clunky meter I have and if not for the DC amps feature would have gotten the heave-ho long ago. So poorly made.

Good for when you'd prefer not to break into a DC circuit. Unfortunately, for things in the wild, I only trust it to nearest amp.

With automotive current such as alternators and trailers and other big-ticket items, I often just measure the voltage at two points* with the fluke and (used to !) do the sums in my head. And often because I only had the Fluke MM when asked about things.

* two points could mean the battery terminal and the alternator terminal, for example. Surprising amount of resistance available to get a feel for your alternator health.

Have you checked it against a known good multimeter? My Mastech MS2108A is surprisingly accurate, for the money, and I'd expect the Unit-T to be as good.

[Peter_O]

I bought a UT210e some years ago to check heater currents of my 3D printers. The UT210e seemed to be the lowest price reasonable choice for a DC clamp meter.

@joeqsmith, thx for sharing your mod and scope experience!

For comparison: I recently got a Micsig CP2100A scope current probe, which is 800kHz by spec. Attached a quick and dirty bode plot, run with +/- 1V RMS into 50Ohms and a 10µs sqare wave signal. The Micsig is about 220 Euros.

For anybody on a tighter budget your mod is brilliant.

[joeqsmith]

For comparison: I recently got a Micsig CP2100A scope current probe, which is 800kHz by spec. Attached a quick and dirty bode plot, run with +/- 1V RMS into 50Ohms and a 10µs sqare wave signal. The Micsig is about 220 Euros.

For anybody on a tighter budget your mod is brilliant.

The CP2100A looks like a decent probe.   

... it can also perform zeroing and demagnetization automatically or manually.

, it has a degauss coil built into the head?  Have you tried to magnetize it to see how well it works?     

For a simple low cost approach, I attempted to replicated a wideband current sensor from an article I had read.  I made a video where I compared it with several others I had on-hand. The description has a link to the original article.

[Peter_O]

<snip:>
...
it has a degauss coil built into the head?  Have you tried to magnetize it to see how well it works?     

No, I tried near to nothing so far. The Micsig is quite new on my desk. I plan to start a seperate topic about it to avoid spoiling this one.   

[Hydron]

Worth noting that "800kHz" in the micsig was actually a >2MHz (I think more like 3MHz) -3dB point in reality when I tested it. Am interested in what the actual difference is between the two models (the more expensive one actually specifies this sort of bandwidth).

Both the uni-t and the micsig are great value, I have them both at work and the only reason why I don't have a micsig current probe at home is that I have a couple of the Tektronix A630x probes. Uni-t would be my first buy when on a budget, but given their different form factors and abilities one doesn't replace the other.

The instructions about keeping the probe in the orientation it will be used in when zeroing is spot on - when you look at the fields due to current in the wire they're on the same order as the earth's field, hence any magnetic circuit with a gap (e.g. for the hall or magneto resistive sensor like the micsig or uni-t uses) will have a strong reaction to orientation when in a sensitive range. Problem is solved in the Tek probes by using a thin film hall sensor, a nulling coil, shielding and lapped core mating surfaces, but this comes with a major price increase (though some cheaper options of the same type have thankfully started to appear on AliExpress etc).

[DaneLaw]

210E seems to be a fan favorite amongst the hobby segment and the prices you could get them for like 5 years back (25 to 30US), it was a no-brainer., nowadays and the last 3 to 4 years.. quite a few others that also deliver 1mA res. and also delivers dual display (hz) and cost around the same 30 to 35US, like the ACM91 & ACM92... though haven't tried them.
I only got two stand-alone AC/DC clamp meters and both quite cheap models as my use case is solely household and hobby-use (Unit-T210E and HT208D), after I got my scope a few years back and was curious to look at current waveforms as a newcomer on a strict budget trying to learn and wanted to see the current waveform on high powered lasers., - I went down the cheapest Chinese rabbit hole for AC&DC clamp meters for scopes, and purchase four different AC/DC versions / though two of them is mainly intended for DMM and quite high current signals.
Hantek CC65 40US (20k) ETCR007 50US (100K), AllsunEM264 25US, and HP615 12US.(all incl. shipping)
Among these cheap variants, it was hit-and-miss., and they varied a lot- noise, sensitivity, and accuracy' as some of them are clearly intended for high current signals, but the Hantek CC65 had way the cleanest signal, and the ETCR007 was horrendously noisy even though it is also intended for low current signals. (sub 60A)and was the most expensive at just under 50 bucks..

 

 

 

CC65 20K / ETCR007 100k
https://i.imgur.com/Cj2B5AJ.mp4
12US HP615.
https://i.imgur.com/pgAQYxY.mp4
But the convenience of these stand-alone AC&DC current clamp meters.. are second to none and my 210E is quite spot on if take my precautions in the 2A range, while the 20A & the 100A range.. I recall the figures were not that accurate (on my unit).