Part Number: 72-7765 [Datasheet]
Function: Handheld Digital Multimeter
Special Features: Auto Ranging, Diode Tester, Continuity Buzzer, Transistor hFE Measurement, Low Battery Display, Inactivity Timer with Auto Shutoff, AC and DC Voltage and Current Measurements, Resistance Measurements
Rating: 4.5 / 5
Review Summary: This meter is lightweight, durable, inexpensive, and from a reputable manufacturer. The wide range of measurements are as accurate as one could hope for in a low cost device, and the control is simple and intuitive. Although the unfused 10A input terminal could pose a problem, there are plenty of other features to make this DMM a great addition to any hobbyist's toolbox.
I recently received a new digital multimeter - the Tenma 72-7765. I have been using DMMs for most my life for various purposes, so I am no stranger to their operation and shortcomings. This particular model has not dissapointed; in fact, I have been very happy with its overall operation.
The product comes with the meter, batteries, operating manual, and a set of test probes. The first thing to notice is the quality of the device. It has obviously been well crafted. The post terminal inputs are the standard size, so test probes from other test equipment can be used, and the supplied probes will work with other equipment.
To access the battery compartment or change the internal fuse, the meter must be opened up. Of course, the meter should be set to the "OFF" position and the test leads should be removed before attempting to open the case. The meter has a protective sleeve to absorb shock when dropped which must be removed to open the case. A pair of small phillips-head screws on the bottom of the back of the meter are easily removed with the right sized screwdriver, and the case can then be opened.A pair of AAA batteries are required for operation. Because of this lower supply voltage, it is likely that the meter uses less current than similar meters requiring a 9V battery. Also, because a typical AAA battery has about twice the capacity as a 9V battery, they should last about twice as long.
Also worth noting here is that none of the circuit components are exposed, so you are unlikely to damage anything when servicing the meter. Aside from changing the batteries, the only other reason to open the case is to change the fuse. The center input terminal can measure voltage, resistance, and current up to 400mA. This current limit is enforced by a 500mA, fast blowing tube fuse. The manual notes that replacing this fuse should only result from improper use. For larger currents, the current input terminal should be used. This terminal allows current measurements up to 10A; however, this terminal is unfused and the meter has a printed warning reading, "MAX 10 sec EACH 15 min", meaning consecutive measurements of the full 10A are not the best idea.
This terminal does not have a fuse, and a large wire with slits in it serves as the calibrated current shunt, as shown in the above image. This current shunt will effectively serve as a fuse if repeatedly large currents are applied, as the wire will break, likely at one of the calibration slits. I would like to have seen a fuse here, but this is really the only complaint I have with the meter, although it is a pretty common problem with lower cost test equipment.
Taking measurements is very straightforward. Connect the test probes to the appropriate input terminals and set the dial to the desired measurement setting. Although the meter is auto ranging, the appropriate resolution for current measurements must still be selected for satisfactory readings to be obtained. Aside from the standard voltage, current, and resistance measurements, this meter can also measure diodes and transistors and has an audible continuity tester. All of these features work very well. While capacitance, frequency, and temperature measurements would be a nice, these additions would significantly raise the price of this meter and are not that important for the average hobbyist. Also, the resolution and accuracy of each measurement could be better, but they should be well within the acceptable range for most hobby applications, especially considering the low cost of the meter. I compared the readings to a very cheap DMM, a Craftsmen model I've had for a while, and a high-end digital multimeter from Agilent and found the results to be well within the provided specifications.
If you are looking for a low cost, highly functional digital multimeter, then this is a good one to go with. The Tenma brand is well established, and the quality of this meter is appreciated. Although it will not yield as accurate of results as more expensive models, nor does it have advanced features, it will prove to be a valuable tool for for most hobby applications.