I recently picked up a Uni-T UT210E clamp meter. It's an interesting device for electronics use, since its clamp can measure DC current, it has a 2A range which gives you 1 mA resolution, and it only costs 35 USD.
I've looked at many different clamp meters, and typically they come with one or more of these limitations:
- They don't measure DC current, only AC current. Sometimes they claim DC current capability, but upon closer inspection you notice it's using the leads, no the clamp.
- They only work with high currents. The lowest range on many devices is 20A or 40A, which gives you 10mA resolution.
- They are expensive, often well into the 3 or even 4 digit USD range.
So what do you get for $35 with the UT210E? The meter comes in a soft case and some leads, whose shroud is detachable. The leads are Uni-T branded and claim Cat IV 600V with the shroud on, and they're pretty crappy overall. Very inflexible cables that tangle easily. Fortunately, for the primary intended use of the meter, the leads aren't required.
The clamp claims Cat II 600V and Cat III 300V, and opens to about 16mm, which is plenty. The movement has no play and feels solid. Between 15N and 20N of pressure is required to open the clamp.
Overall it's a small device that fits well into the hand. The display is mounted in such a way that it can be awkward to read, either because it's at an angle when pointing the clamp away from you, or because you're covering it with your hand when holding it with your right hand and your thumb on the clamp opening mechanism. Larger clamp meters have the display at the very bottom for this reason I guess.
The device does feel very solid in the hand, no flex or creaking. The small form factor helps give it stability. Materials are the same as on other Uni-T multimeters I've seen, it's fine. The red parts on the case (but not the clamp) are rubberized, not enough to provide shock protection though. While it certainly doesn't seem fragile, dropping the meter is probably a bad idea since the ferrite the clamp is made of might shatter.
So lets peek inside! It takes two AAA batteries, and the battery screw goes into a metal insert. This is good since in current measurement modes it consumes about 6mA (12mA with the backlight), so the batteries would last less than 200 hours. In the other modes it's only 2mA, but those won't see much use.
The back half of the case is held by two self-tapping screws into plastic. Not an issue, since there's not much reason to open the device, there are no fuses (all current measurement modes use the clamp.)
Inside the device there are a *lot* of passive components, in particular there's a whole bank of capacitors in the lower right. Input protection seems fair enough for the input jacks. I have no idea what's required for the clamp though, if anything at all. Even when measuring high currents, there's nothing dangerous going inside the meter I guess though? Experts, please speak up.
There are two larger chips. The one on the left is a
TI OPA4330 quad opamp (Markings: TI O4330A 44K G4 AN50), the one on the right is the
Hycom DMM Chip (Markings: Hycom H203 DTM0660L R3MR81A)
Let's test it! Here's my test setup. Basically I had my PSU output a current in constant current mode, it went through the clamp and by BM257, the latter I used to check against. Accuracy of the UT210E in DC current mode is 2% + 8 counts in the 2A range, and 2% + 3 counts in the 20A range.
As with any clamp meter in DC current mode, zeroing is important but can be finicky. I rested the meter on the table and tried not to move it when changing ranges or pressing the zero button. This way, zeroing was good for up to a minute, at which point it started to drift more than 2 or 3 mA. When holding it in your hand, you can expect to zero it for every single measurement if you care about single milliamps. With higher currents, the magnetic fields of the meters environment don't matter so much so you get more repeatable measurements. One way to increase the measured current btw is to loop the cable through the clamp several times, you'll just have to divide the reading by the number of loops.
Rotating the meter introduces errors of several dozen mA.
Cable position within the clamp does not matter btw. As long as the cable goes through the clamp, you get the same measurement.
On to the measurements!
BM257 - UT210E
08.42mA - 0.009A
17.89mA - 0.019A
48.86mA - 0.049A
097.6mA - 0.097A
497.8mA - 0.494A
1.990A - 1.985A
4.996A - 04.97AAs you can see, the two meters match up well, better than I expected! I tested voltage and resistance too against some precision references and precision resistors. It read 0.4% high on average in voltage mode (worst: 0.47% or 5 counts) and was generally bang on in resistance mode (worst: 0.2% or 2 counts.)
Screen update rate is unusually fast for Uni-T at around 4 updates per second. Unfortunately, other things are slow: the latched continuity tester is usable, but certainly not fast. Resistance autoranging is slow. Reading current with the clamp is also a tad slow, it usually a second or two for the value to come up to the right area, and then 2-3 seconds more for the last digit to stabilize, so current isn't instant.
In voltage mode, you get no overshoot, but usually have to wait 0.5-1 second to get a reading because of the autoranging (which you can't disable). It shows you ---- while it's doing that, and then gives you a stable value, I like that.
Non-Contact voltage measurement shows you whether you have a live wire, and it works well. The shape of the meter makes it clear where the sensor is (top of the clamp under the little bump); this can be frustrating with classic multimeters. It reacts quickly in about half a second, and you get a display on the screen, a flashing LED and the buzzer that beeps at you.
I didn't test any AC stuff.
Overall, for the price ($35), I recommend this meter for electronics hobbyists. It's cheap at $35, and you get usable DC mA readings (if you use it right, i.e. no moving after zeroing), without having to cut any wires. I wouldn't suggest it as a first or second multimeter, but after that, go for it!
Clamped it around everything I could find. Solar panels making 3.85 amps @ 250VDC. Car running with headlights, a/c, heater fan and rear demister showed 52 amps going through some fat wire into the fusebox. In particular, I have a 33V 30A DC supply that is great for charging car batteries but if you go over current it will trip out and switch off. Now I can wind the voltage up gradually and set it so the current doesn't go over and shut off.
