Once you select the correct scale and type of value to be measured, it is important to realize what the meter actually does when you take measurement. There is no magic involved but realizing what is actually taking place can make the difference between accurately and safely diagnosing reading and obtaining misleading information.

Continuity / Resistance

These two terms are often confused because they are similar in nature. In both cases the actual mechanics Of the measurement is done by the meter sending a voltage out over one lead and measuring the amount that is picked up on the other lead. The meter selects the scale by dropping the voltage through resistors (shunts) that are selected with the scales. Lower voltage will be required to push through smaller resistance and still show a value in the ranged of the display. (This is why you should never measure resistance or continuity with the power on. It is very easy to exceed the circuit capability, especially in 120/240 applications).

Continuity is a measurement of connection. Any voltage returning within a certain range sounds tone. Unfortunately, the operating range can be from zero up to a hundred ohms or more and can give you misleading information. This measurement is seldom usable for anything but detecting the presence of connection.

Resistance is a measurement of the opposition to electron flow in a circuit. The value is expressed in ohms and gives you the best representation of how good a connection is between two points. When measuring to determine a good connection always use the resistance scale to insure you can also diagnose the condition of the connection rather than just the presence of connection.



Voltage

When measuring voltage the meter is performing a comparison between the potential on the two leads. In other words, it measures the distance of the voltage on the red vs. the black lead. Understanding this is very important, as a zero reading does not necessarily mean there is no voltage present. There can be 600 volts present in the circuit, but if it is felt on both leads at the same time the display will show zero. Another condition that should be watched for is when one of the points measured is not part of the circuit. An open (loose wire, burned contacts, bad coil) circuit will not have any value to the meter. There is a large difference between zero volts and no connection. Once again, just because the meter reads zero, don't assume there is no voltage present. It is always advisable to double check for the presence of voltage before attempting to service any unit. By checking the ground (this is one of the few times when using ground as a measuring point is advisable).



Current

The only time currant is present is in complete circuit. Therefore, you cannot measure currant outside the circuit like you can with voltage or resistance. Unless you have an inductive coil (clamp or meter) it is necessary for the currant in the circuit to run through the meter to measure it. The only way this can happen is to open the circuit and put the meter in series with the currant flow. Unfortunately, most meters can only handle half an Amp (500ma) in this manner. Although some can handle up to 10 amps and/or have accessories that allow higher readings. Exceeding the capability of the current monitoring circuit can damage meters without this capacity.