The field of electricity, accurate quantitative measurements are essential. A technician commonly works with current, voltage , and resistance.
Ammeters, voltmeters, and ohmmeters are used to provide the essential measurements. A good understanding of the design and operation of electrical measuring meters is important.
INTRODUCTION TO METERS
Meters are the means by which the invisible action of electrons can be detected and measured. Meters are indispensable in examining the operation of a circuit.
Two types of meters are available. One type is the analog meter, which uses a graduated scale with a pointer . The other type is the digital meter, which provides a reading in numbers . Digital meters are easier to read and provide a more accurate reading than analog meters.
However, analog meters provide a better graphic display of rapid changes in current or voltage.
TYPES OF METERS
- An ammeter is used to measure current in a circuit. An ammeter can be considered a flow meter. It measures the number of electrons flowing past a given point in a circuit. The electrons must flow through the ammeter to obtain a reading , and this is accomplished by opening the circuit and inserting the ammeter.
- A voltmeter is used to measure the voltage (difference of potential) between two points in a circuit. A voltmeter can be considered a pressure gauge, used to measure the electrical pressure in a circuit .
- Resistance is measured with an ohmmeter. To measure resistance, a voltage is placed across the device to be measured, inducing a current flow through the device. When there is little resistance, a large current flows and the ohmmeter registers a low resistance. When there is great resistance, a small current flows and the ohmmeter registers a high resistance.
MULTIMETERS
When working on a piece of equipment, many different measurements must be taken. To eliminate the need for several meters, the voltmeter, ammeter, and ohmmeter can be combined into a single instrument called a multimeter. An analog multimeter is referred to as a volt-ohm-milliammeter (VOM). A digital multimeter is also referred to as a DMM.
MEASURING CURRENT
MEASURING VOLTAGE
MEASURING RESISTANCE
READING METER SCALES
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