I purchased this DMM when it was on sale for $19.99 CND or about $17.00 US as of March 2007. The regular price was $59.95. I have seen this DMM on sale a couple of times before but never as low as twenty dollars. Canadian Tire sells Mastercraft.
I purchased this DMM when it was on sale for $19.99 CND or about $17.00 US as of March 2007. The regular price was $59.95. I have seen this DMM on sale a couple of times before but never as low as twenty dollars. Canadian Tire sells Mastercraft.
It appears to be fairly well built and I have spent a little time doing some tests and comparisons to get a feel for the accuracy. As a brief summary it can do the regular stuff like measure AC and DC voltage, resistance and DC current. In addition it can measure capacitance, frequency, hFE, temperature and AC current up to 10 amps. It also has other features like auto ranging, diode checking, audible continuity checking and a few others.
For AC, DC voltage and current comparisons I generally used my Fluke model 75 DMM as it should have better accuracy than my other DMM's. For frequency response I used an HEWLETT-PACKARD 3555A Transmission Measuring Set as it is the most accurate instrument I have for measuring audio frequency response. Capacitance measurements were compared with an L/C Meter II capacitance meter that I believe to be quite accurate. Frequency measurements were compared with one of my other frequency counters, an Instek Model GFC-8010G.
All tests were done at room temperature and none were extensive.
RESISTANCE MEASUREMENTS
I tested a number of precision resistors, 1% or better ranging from a few Ohm to 330 K. They all appeared to measure within 1% on this meter.
AC VOLTAGE
Measuring my line voltage the DMM read 121.9 VAC. The Fluke meter read 122.5 VAC. I did not expect the readings to be off quite that much but I assume they are both within specifications. I also measured the line voltage with my Wavetek Meterman DMM. The Wavetek read 122.1 VAC only 0.2 volts different from the Mastercraft DMM. I do not know which meter reads closest to the actual value.
I did a frequency response using an audio oscillator and a HP Transmission Measuring Set. I set the voltage to 0.775 volts across 600 Ohms, 0 dBm. The DMM was virtually right on at 1000 Hz but fell of rapidly above that.
INPUT IMPEDANCE
According to the instruction manual the "AC/DC input impedance" is 10 K ohms. This seemed low so I decided to check it. I set a DC power supply to 10.0 volts using the Mastercraft DMM and then measured the voltage again through a 1 Meg Ohm resistor. The DMM read a little over 9.1 volts indicating that the input impedance was probably 10 Meg Ohms or better. I did not check it on AC.
DC VOLTAGE
I only did one DC voltage comparison test. A power supply voltage was set to 13.60 volts using the Fluke DMM. The voltage was then read with the Mastercraft DMM. The reading was 13.61 volts. It’s hard to get any better than that.
FREQUENCY
The DMM can measure frequencies up to 400 KHz which limits it usefulness for many Ham applications. I compared frequencies with one of my other counters at 110.9 Hz, 1000 Hz and at 400 KHz. They both read the same +/- 1 count. Since the DMM is limited in it's number of digits the resolution at 400 KHz is 100 Hz. The resolution between 5 KHz and 50 KHz is 10 Hz. 110.9 Hz is a popular CTCSS (PL) frequency. The DMM updated rapidly for the 110.9 Hz measurement. I had to run a 10 second gate on the other counter to get the 1/10 Hz resolution. My first guess was that the DMM measured the waveform period and then did the math. The instruction manual seems to indicate that auto ranging takes place when the most significant digit reaches 4. On this meter it takes place when the digit reaches 5 at least when measuring frequency.
I did not check to see how sensitive the DMM was for frequency in terms of voltage levels.
I can't see a lot of uses for a counter that only reads to 400 KHz and at reduced resolution as it gets higher in it's ranges. One application might be in a Field Day situation where you might want to measure the frequency of a portable generator. The instruction manual indicates that it can handle up to 250 volts or more precisely not to exceed 250 volts. On occasion I do have a requirement to read PL tones and other audio frequencies. This DMM would be my first choice over my other counters because of it's portability.
AC AMPERES
The DMM can measure AC to 10 Amps. The instructions warned not to make AC measurements on the 10 Ampere scale for more than 15 seconds. They also recommended a 30 minute cool down between measurements. This short measuring time could be a problem because it might not give enough time for everything to settle down in some measurement applications without doing some sort of creative set-up. The Fluke DMM can also read up to 10 amperes AC apparently without a time limitation. There is, however, a time limit on the Fluke meter if you attempt to make a current measurement above 10 Amps, maximum 20 Amps.
To measure the current for devices that use 120 VAC I obtained a 4" plastic electrical box with a plastic cover. I installed a standard AC switch and duplex receptacle and line cord. Two pin jacks were installed in the cover and wired in parallel with the switch. The idea was to power the device under test with the switch on and have the current passing mainly through the switch and then turning the switch off diverting the current through the meter via the pin jacks. It is very easy to have 120 VAC exposed on one of the meter probes if they are both not plugged into the pin jacks. This is the reason I used the plastic components. A plastic power bar could also be used if you can find space to the mount the pin jacks. Shorting a meter probe to a grounded metal electrical box could result in some interesting effects. You need to be careful doing this measurement. This set-up made measurements easier and reduced the amount of time the meter was connected to the circuit.
I measured the AC amperes of both my repeaters in the transmit and standby (RX only) comparing the Fluke and Mastercraft DMM's. All the readings were virtually identical.
DC AMPERES
I only made one DC amp comparison. With the two meters in series a reading of 100.0 MA on the Fluke meter read between 99.6 and 99.7 MA on the Mastercraft DMM, well within 1% of each other.
TEMPERATURE
Temperature can be measured using an optional probe. I do not have the probe. I am not sure if the probe is readily available locally and the instruction manual did not give a part number.
TRANSISTOR HFE MEASUREMENTS
I am assuming that this feature is mainly targeted at people that might want to identify defective transistors in existing equipment. I can’t comment much on this measurement other than it seems to work. I have tried testing a few transistors and I assume the readings are reasonably accurately under the DMM’s test conditions. I normally test suspect transistors using an analogue VOM (my Triplett 630A) on a resistance scale and look for shorts or a rough indication of transistor leakage or other anomalies. These tests can very often be done in circuit and you don’t have to be concerned about short lead lengths that might be a problem when testing for HFE. In my experience, most problem transistors can be identified this way. Also, unless you are working on vintage equipment this feature may not be all that useful.
CAPACITANCE MEASUREMENTS
The DMM can do a basic capacitor check to determine capacitor value. It cannot do other capacitor tests like ESR and leakage. I did some quick comparison tests using an L/C Meter II mentioned above. Generally capacitors 0.01 µf or above appear to read with acceptable accuracy on the Mastercraft DMM. For example, a capacitor with a reading of 0.01913 µf on the L/C Meter II read 0.01955 µf on Mastercraft DMM. The Mastercraft DMM read this capacitor in nf so there is a conversion here. The accuracy falls off with capacitors that are below 0.01 µf. The readings tend to be high. A capacitor that tested at 5000 pf exactly on the L/C Meter II read 5140 pf on the Mastercraft which is still not to bad. Don’t expect to read a typical air variable capacitor with useable accuracy even if you account for test lead capacity. The Mastercraft DMM can measure capacitors up to 100 µf.
CONCLUSION
In my opinion for twenty dollars this DMM was a very good buy. I can’t even say if the basic accuracy is worse than my very much more expensive Fluke meter that has fewer features although the Fluke meter may have better advertised specs. The Mastercraft DMM also has other features that I haven’t covered here.
DISCLAIMER:
The information above is the result of my observations and opinions. Your's may differ! Use this information at your own risk.