Basic Instruments and Measurements

Chapter 2

Basic Analog Meter

• • • • • D’Arsonval movement – stationary magnet, moving coil galvanometer.

Iron Vane Meter – two pieces of iron are placed inside a hollow core solenoid.

Current causes magnetic field to move a needle.

Extreme caution and care when handling an analog meter.

Proper polarity must be maintained

Meter Scales

• Linear meter scale – marks are evenly spaced.

• Note what range the dial of meter is set to when reading the value of the scale.

Ammeter

• • • Measures electrical current in a circuit.

– Amperes – – Milliamperes Microamperes Shunt is used to direct excess current away from meter.

Always connected in circuit.

Series with the

Voltmeter

• Measures electrical voltage present in a circuit: – Volts – Millivolts • Connected in Parallel with the circuit

Ohmmeters

• • • Measures the resistance of a device or part of a circuit: – – – – Megaohms Ohms Milliohms Microhms Zero the meter Battery inside the case used to measure resistance.

Other Meters

• • • Volt – Ohm – Milliammeter (VOM) Digital Multimeter (DMM) Computer Display meters

Electrical Diagrams

• • • Schematics Wiring Diagrams Symbols (see page 453 – 454)