Section Objectives
After you complete this section you will:
Understand the function of a multimeter.
Understand the difference between an ammeter, voltmeter, and ohmmeter.
What is a Multimeter?
A multimeter is a common device to measure voltages, resistance, and currents. The CompTIA A+ Hardware Service Technician exam expects a basic knowledge of working with a multimeter and how it functions.
Caution: Always use care when working around electronic components.
A multimeter combines a voltmeter, which measure voltage, a ohmmeter which measures resistance, and an ammeter, which measure current.
The Ammeter
An Ammeter measures current through a circuit. Since it measures the current, the ammeter should not interfere with the circuit, therefore it requires low resistance. In order to measure the current, the ammeter must be part of the circuit, therefore you must “break” the circuit so the ammeter can run in series with the circuit.
The Voltmeter
A Voltmeter is used to measure voltage, or potential difference in a circuit. A voltmeter runs in parallel with the circuit, the circuit does not need to be broken for a voltmeter. The voltmeter requires high resistance. The voltmeter is providing a parallel pathway, this is why a high resistance is required.
The Ohmmeter
An Ohmmeter measures resistance. In order to measure resistance, the circuit must not have a power supply connected. The ohmmeter functions by passing a small amount of current through the circuit and measuring the voltage.
After studying this section you should:
Understand the function of a multimeter.
Understand the different between an ammeter, voltmeter, and ohmmeter.
