The purpose of this article is to examine the Tenma 72-7222 Digital Clamp Multimeter supplied for review by element-14/Farnell/Newark. The Tenma is a strongly featured yet inexpensive piece of test equipment – and considerably good value when you consider there is a current clamp for measuring high AC currents. So let’s have a look and see what we have.
The Tenma arrives in a retail box, and generally nicely packaged. Naturally this has nothing to do with the performance of the meter at all, but at least they made an effort:
Opening up we find a nicely rounded group of items: the meter itself, some no-name AAA cells, test leads, a thermocouple for temperature measurement, a surprisingly articulate and well-written user manual, and the unit itself – all within a nice pouch. Wow – a pouch. Agilent? Fluke? All that money for a DMM and you don’t include a pouch?
Recent test equipment reviewers have made pulling apart the unit part of the review – so here goes… the back comes off easily:
No user-replaceable fuses… instead a PTC. A closer look at the PCB:
A very neat and organised PCB layout. There are plastic tabs that hold the PCB in along with a screw, however the case flexed too much for me to warrant removing the PCB completely. The spring for the clamp meter is locked in nicely and very strong, it won’t give up for a long time. Pulling the clamp base out reveals the rest of the PCB:
Installation of the battery is two stage procedure, first you need to remove a screw and then slide out the rear door:
… then insert the AAA cells into a frame, which is then inserted inside the unit:
The physical feel of the unit is relative to the purchase price, the plastic is simple and could be quite brittle if the unit was dropped from a height. The user manual claims the unit can be dropped from up to a height of one metre. Onto carpet? Yes. Concrete? Perhaps not. However like all test equipment one would hope the user would take care of it whenever possible. The clamp meter is very strong due to the large spring inside the handle, which can be opened up to around 28mm. The included leads are just on one meter long including the length of the probe:
The leads are rated to Category I 1000V (overkill – the meter can’t go that high) and 600 V Category II – “This category refers to local-level electrical distribution, such as that provided by a standard wall outlet or plug in loads (for example, 115 AC voltage for U.S. or 200 AC voltage for Europe). Examples of Measurement Category II are measurements performed on household appliances, portable tools, and similar modules” – definition from from National Instruments. Unlike discount DMMs from unknown suppliers you can trust the rating to be true – otherwise element-14 wouldn’t be selling it.
- Voltage Measuring Range DC:200mV, 2V, 20V, 200V, 600V
- Voltage Measuring Range AC:2V, 20V, 200V, 600V
- Current Measuring Range AC:2A, 20A, 200A, 400A
- Resistance Measuring Range:200ohm, 2kohm, 20kohm, 200kohm, 2Mohm, 20Mohm
- Temperature Measuring Range:-40°C to +1000°C
- DMM Response Type:True RMS
- DMM Functions:AC Current, AC/DC Voltage, Resistance, Temperature
- Display Count:1999
- AC Current Range Accuracy:± (1.5% + 5d)
- AC Voltage Range Accuracy:± (1.2% + 5d)
- Accuracy:± (1.0% + 3d)
- Current AC Max:400A
- Current Range AC:2A, 20A, 200A, 400A
- DC Voltage Range Accuracy1:± (0.8% + 1d)
- Resistance Range Accuracy:± (1.0% + 2d)
- Temperature Measuring Range:-40°C to +1000°C
The only measurement missed out on is DC current, however there is the Tenma 72-7224 which has DC current and frequency ranges. Finally, all the modes and buttons can be selected while holding the meter with one hand – for both left- and right-handed folk.
Normally I would compare the measurements against my Agilent U1272A, however it’s out to lunch. Instead, a Fluke 233. First, AC voltage from the mains:
Next, a few DC voltage measurements:
Now for some resistance measurements. Higher values near the maximum of 20M Ohm can take around four seconds to measure:
Forward voltage of a 1N4004 diode:
Now off to the kitchen for some more measurements – first with the thermocouple:
The boiling water test – 100 degrees Celsius (you can also select Fahrenheit if so inclined):
And now to test out the AC current clamp meter function with a 10A kettle at boiling point. First, using the 20A current range:
And then again on the 400A current range:
As always, it’s best to use the multimeter range that more closely corresponds with the current under test. The meter also has a continuity test with a beeper, however it was somewhat slow and would often take around one second to register – so nothing too impressive on that front. The meter can record the maximum value with the grey button, or hold a reading using the yellow button.
The Tenma 72-7222 works as advertised, and as expected. It is a solid little unit that if looked after should last a few years at a minimum. It certainly has a few limitations, such as the 1999 count display, lack of backlight, and the average continuity function. But don’t let that put you off. For the price – under Au$30 – it is a certified deal. If you need a clamp current meter for odd jobs or a casual-use multimeter and you are on a limited budget, the Tenma will certainly prove a worthwhile purchase. Full-size images are available on Flickr.
Thanks for reading! Have fun and keep checking into tronixstuff.com. Why not follow things on twitter, Google+, subscribe for email updates or RSS using the links on the right-hand column, or join our Google Group – dedicated to the projects and related items on this website. Sign up – it’s free, helpful to each other – and we can all learn something.