TENMA - 72-7720 - MULTIMETER DIGITAL HANDHELD, 3-1/2 DIGIT
I just purchased a #72-7720 and was disappointed to find that the range information is difficult to read. The white on grey is easy to read, but the grey on grey is difficult to view. The DC volt, AC amp, and Fcx are easy to read. The DC amp, Ohms, and AC volt ranges are very difficult to see printed grey on grey.
April 26, 2012
The variety of measurement functions provided by this multimeter, and the accuracy specifications on some of those measurements, are things you would expect to find in a meter costing considerably more.
What you get: The meter comes with two sets of leads, a temperature probe, and a nine volt battery.
One set of leads has probes on the end, while the other has allegator clips. While it is nice to have both options, the leads with the allegator clips are only seven inches long, limiting their utility. The probe leads are a generous 41.5 inches long.
The battery needs to be installed before the meter will operate. This requires a small philips screwdriver, so be sure you have one if you order this meter. In the unit I received the screw on the battery compartment had been screwed in very tightly, but I was able to get it open after a bit of effort.
The accuracy specifications are generally quite good for a multimeter under $100. The only qualification here is that the maximum count is 1999, so errors in the last digit matter more than in meters with a larger count. For example, when measuring a 19 volt voltage, you can use the 20 volt range, which has an accuracy of 0.5% of reading + 1 digit, giving an accuracy of about 0.55% of reading. But if you want to measure a voltage of 20 volts, you need to use the 200 volt range, where 1 digit is equal to 0.1 volts, and the error becomes 1% of reading. Note that because the maximum count is 1999 and not 2000, the 20 volt range can only measure a maximum of 19.99 volts.
DC voltage: The 2, 20, and 200 volt ranges have an accuracy of 0.5% + 1 digit. There is a 200 millivolt range with an error of 0.5% + 3 digits. And there is a 1000 volt range with an error of 0.8% + 2 digits.
AC voltage: The 2, 20, and 200 volt range have an accuracy of 0.8% + 3 digits. The maximum range is 750 volts AC, with an accuracy of 1.2% + 3 digits.
Resistance: The meter has a rated accuracy of 0.8% + 3 digits on the 200 ohm range, and an accuracy of 0.8% + 1 digit on the 2K through 2M ranges. I measured a the values of a number of 0.1% resistors ranging from 120 ohms to 1 megaohm, and the measured values never differed from the nominal values by more than 0.2%, meaning that the accuracy of the meter was 0.3% or better.
In addition to the the above mentioned ranges, the meter also has a 200 megaohm range. It is impressive that a meter in this price range can measure resistances that high, but the rated accuracy is less impressive: 5% + 10 digits. Most of the 10 digit error is due to a fixed offset, which you can subtract out. My meter reports a resistance of zero as 0.9M and a resistance of 1.0M as 1.9M.
Capacitance: To measure capacitance, the meter generates an AC signal with a DC offset (so that the voltage across an electrolytic capacitor will always be positive) and measures the AC impedance. The ranges are 20nF, 200nF, 2uF, and 100uF. The accuracy is 4% + 3 digits for the first three ranges and 5% + 4 digits for the 100uF range (and if I understand the documentation correctly, the 5% + 4 accuracy only applies to capacitances of 30uF or less). When I measured a 0.01uF 1% capacitor the reading was about 2% below the nominal value, which means that the reading was below the actual capacitance but within the specified error range.
A larger number of capacitance ranges would be useful, especially at the low end.
Other functions, which I have not used enough to comment on, include current (AC & DC), continuity, diode test, and frequency.
Most functions are protected up to 250 VAC, which is larger than any voltages a hobbyist is likely to work with. The voltage functions (except the 200 mV range) are protected up to 750 VAC / 1000 VDC. The 20 and 200 mA ranges are protected by a 500 mA fuse. The 20 amp range is not fuse protected.
The controls are simple: a power switch, a hold switch (which preserves the current reading), and a rotary dial to set the range.
Occasionally I've pushed the power button down far enough to turn on the meter, but not far enough down so that it catches, meaning that the meter turns back off when I release the button.
The hold switch does its job, and an H on the display informs you that you are getting a held reading rather than a current measurment.
Groups of settings on the rotary switch are indicated by alternating white and grey labels. For example, the DC volt ranges are labeled with white text while the AC volt ranges are labeled with grey text. The downside of this is that the grey text is hard to read.
On the other hand, the display is easily readable, and includes a backlight so it can be read even in the dark. The backlight comes on only when a sensor detects low light levels, so it won't consume power (which would reduce battery life) under normal illumination condistions.
The meter can be positioned at either a 35 or 45 degree angle from the horizontal using a two position flap which folds out from the back of the meter. I haven't felt the need to use this feature since I have no trouble reading the meter when it is lying flat.
To avoid running down the battery if you forget to turn the meter off, the meter will go into sleep mode if you leave it idle for 10 minutes. To exit sleep mode, you turn the meter off and then back on again.
To measure current, the range must be selected and the red lead must be plugged into the mA or 20A plug, depending on the range. Less intutively, to measure capacitance, the red lead is left where it is but the black lead is moved to the mA socket. If you neglect to do this, the capacitance is registered as zero. More confusing is what happens if you switch from capacitance to resistance without moving the black lead back to its normal plug. On the higher resistance ranges, the result will be an incorrect but not infinite reading.
Conclusion: In this review I've noted a few issues with this meter, but they are minor. If you expect to use a multimeter day in and day out, it's probably worth spending the money to get something like the Fluke 87 V. For the hobbyist or occasional user, this meter offers good value for the money.
January 14, 2011