SUMMARY

The important points of this chapter are summarized in the following paragraphs. You should be familiar with these points before continuing with your studies of test equipment.

A MULTIMETER is a single meter that combines the functions of a dc ammeter, a dc voltmeter, an ac ammeter, an ac voltmeter, and an ohmmeter. Observe the following safety precautions when using a multimeter:

• De-energize and discharge the circuit completely before connecting a multimeter.
• Never apply power to the circuit while you are measuring resistance with an ohmmeter.
• Connect the ammeter in series for current measurements and in parallel for voltage measurements.
• Be certain the multimeter is switched to ac before attempting to measure ac circuits.
• Observe proper dc polarity when measuring dc circuits.
• Always start with the highest voltage or current range.
• Select a final range that allows a reading near the middle of the scale.
• Adjust the "0 ohms" reading after changing resistance ranges and before making a resistance measurement.

An ELECTRONIC DIGITAL MULTIMETER is used in sensitive electronic circuits where only extremely small amounts of energy can be extracted without disturbing the circuits under test, or causing them to be inoperative.

The DIFFERENTIAL VOLTMETER is a precision piece of test equipment used to compare an unknown voltage with an internal reference voltage and to indicate the difference in their values.

A SEMICONDUCTOR TEST SET is used to measure the beta of a transistor, the resistance appearing at the electrodes, and the reverse current of a transistor or semiconductor diode. It also measures a shorted or open condition of a diode, the forward transconductance of a field-effect transistor, and the condition of its own batteries.

Resistance, capacitance, and inductance are measured for precise accuracy by RCL BRIDGES. They are composed of capacitors, inductors, and resistors and operate on the principle of the Wheatstone bridge.