Multitesters (digital multitesters
and analog multitesters, sometimes called VOM: Volt-Ohm-Milliampere Meter) are a combination of voltmeter, ammeter, resistance meter and other types of electronic meter. They are invaluable for troubleshooting home and automobile electrical and electronic problems.
The article below will talk about the advantages, drawbacks and useful features of both digital multimeters and analog multimeters.
Autoranging Digital Multimeters
Digital multimeters are deservedly popular. However users need to be aware of their limitations.
- Accurate. The best DMMs can have accuracies as high as plus or minus 0.1% but 1% to 2% is more common.
- Easy to use. Autoranging DMMs automatically switch the internal circuit to the correct measuring range.
- Wide range of features. Advanced DMMs can measure waveform frequency and duty cycle (edging into oscilloscope territory).
- LCD display can be too dim to read easily. Some models have a backlit display but this will reduce battery life.
- Not suitable for measuring fluctuations and transients.
- No zero adjustment for resistance measurement, except on advanced models.
- Automatic power-off.
- Back-lit display, with “always on” option.
- Analog bar graph for quick reading of fluctuations. This is a killer feature, available on professional models costing hundreds of dollars. It allows a DMM to have the advantages of both analog and digital meters.
- Selectable auto or manual ranging.
- Display of minimum, maximum and average readings.
- Measurement hold feature.
- Connection to PC for automatic periodic data-logging.
- Automatic AC/DC voltage detection and measurement switching.
- Non-contact AC voltage detector. For identifying live wires.
Old-style analog moving-needle multimeters have significant advantages and a few drawbacks.
- Can measure fluctuations and transients. Analog meters can measure low frequency fluctuations, to a certain extent.
- No batteries required. Batteries are needed for the resistance meter but the voltmeter and ammeter will work without batteries.
- Good for quick readings. The analog needle reacts quickly, making it suitable for fast probing of multiple points. High, medium and low readings are easily seen with a glance at the needle.
- Good for tuning electronic circuits to a specified value (example: setting a trim or variable resistor) as the needle’s speed and relative position provides useful feedback.
- Limited accuracy. Accuracies range from plus or minus 1% to 4% of full scale (depending on the model and the type of measurement). A reading in the middle of the scale (half full scale) will have half the accuracy (2% to 8%).
- No autoranging. For more precise readings, the meter needs to be manually set so that the needle is almost at maximum (full scale deflection).
- Possible to read the wrong scale by mistake.
- Scale can be difficult to read.
- Delicate. The needle’s mechanism is delicate and accuracy can be affected if the multimeter is dropped.
- Many measurement ranges. The more ranges available, the better the chances that the meter can be used close to full scale deflection for high accuracy.
- 50 micro amps measurement range. More common is the less sensitive 200 micro amps range.