Electricity is something that cannot be seen. We can only see the effects of it.
When a circuit is not operating correctly, it is very difficult to look at it and discover what is wrong.
Meters are used to measure the effects of electricity. Meters are precision instruments that can be damaged easily so certain precautions must be taken:
Precautions When Using Meters
Observe the following precautions:
Voltmeters
Voltmeters are giant resistors that draw minimal current from the source. Voltmeters are meant to measure the potential difference between two points.
The meter must be connected in parallel with the load.
It is a good idea to test the voltmeter on a known circuit first.
Ammeters
Ammeters are designed with low resistance so they do not add unwanted resistance to the circuit.
Connect an ammeter in series with the circuit. If connected in parallel, it would cause a short circuit and blow the fuse in the meter.
Wattmeters
The wattmeter has four test leads. Two are for current and two are for voltage.
Power is the product of both the voltage and the current so the wattmeter measures the effects of both and multiplies them to give the power.
Connect the voltage coil in parallel with the load.
Connect the current coil in series with the load.
Do not exceed the power rating of the meter.
Ohmmeters
Ohmmeters are used to measure resistance. They have their own source of EMF (battery) and must not be used on a live circuit.
The scale on most ohmmeters reads backwards to other meters. Zero is on the right and infinity is on the left.
Many ohmmeters will have a zero adjustment. Always zero the meter before using. Do this by shorting the two leads together.
Electrical Meter Safety
The video below explains how not all electrical meters are created equal. Make sure you understand the ratings of your meter and what situations it can be used in.
Video!
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