An analog voltmeter is a precision instrument used to measure voltage values in electrical or electronic circuits. Analog multimeters are voltmeters that also measure current, resistance and other circuit values. In the following paragraphs you will be presented with the simple steps to take to measure resistance with an analog voltmeter or multimeter.
Step 1 - Turn Off Power to the Circuit or Device
This can’t be stressed enough. The power to the circuit or device must be turned off. This is due to the fact that an analog voltmeter that also measures resistance has an internal power source is uses to make those measurements. Addition of another power source could damage or destroy your analog voltmeter.
Step 2 - Remove Device or Load from Circuit
This step is important to complete if possible because unless proper polarity is observed with semiconducting devices in other parts of the circuit, the rest of the circuit will interfere with the measurement of the electrical resistance you are trying to take, unless the resistance is so low as to counteract that interference.
Step 3 - Set Meter for Proper Resistance Scale
Your analog voltmeter will have a rotating switch with which you select the various measurement functions. If you’re not sure what the resistance of the device should be, you should start at the highest and work down. Keep in mind that meter accuracy is greatest when the indicating needle is in the middle half of its arc.
Step 4 - Calibrate the Meter
Your analog meter will have either one or two calibration knobs. If there are 2, then they will be labeled infinity (symbolized by the number 8 laid on its side) and 0. Plug the leads into the color correct sockets. Hold the tips of the leads together between the thumb and forefinger of one hand and turn the proper calibration knob until the needle reads perfectly at 0. Release the leads. If there are 2 knobs, then you will need to adjust the one labeled infinity all the way until it reads perfectly at infinity.
Step 5 - Take Measurement
With the analog meter set on the correct scale to obtain a mid-swing reading and properly calibrated, the meter is now ready to take an accurate reading of resistance. Place one lead on the point of electrical input for the device you’re measuring and the other lead on the point of electrical output. Observe the swing of the needle until it stabilizes and take your reading. When taking resistance measurements with an analog meter, there are 2 very important things to keep in mind. These are:
- Analog meters are most accurate when the measurement is taken when the needle is indicating in the middle half of its swing. Accuracy tapers off at either end. Set the measurement range (example: 200Ohm, 2K Ohm, 20M Ohm, etc) to obtain readings from this section of the scale.
- Every time the measurement range is changed, the meter should be recalibrated in order to ensure the most accurate readings.