Chapter 6 Electromechan e r m m a ni cal a S Sy s st e e em s s 141 Copyright Goodheart-Willcox Co., Inc. Copyright Goodheart-Willcox Co., Inc. Activity 61- Electrical Meters Objectives Electrical meters are used to measure voltage, current, resistance, and other electrical quantities. There are two general types of electrical meters: analog and digital. Analog meters have a hand or pointer that moves according to the amount of the quantity being measured. This type of meter is seldom used today. The other type, digital meters, display numbers indicating the amount of the quantity that is measured. Digital meters are by far the most common type of meter used today. Measurements are made in many types of circuits. You should learn the proper procedure for measuring resistance, voltage, and current for working with robotic systems. These three measurements are the most common for electrical circuits. Meters used for testing electrical circuits are often referred to as multimeters, such as a DMM (digital multimeter), which is used to measure voltage, current, or resistance. A representative type of digital multi- meter will be discussed in this activity. Measuring Resistance and General Meter Use Many important electrical tests can be made by measuring resistance. Resistance is opposition to the flow of current in an electrical circuit. The current that flows fl fl in a circuit depends on the amount of resistance in that circuit. You should learn to measure resistance in an electrical circuit by using a meter. A multimeter is used to measure resistance, voltage, or current. The type of measurement can be changed by adjusting the function-select switch (or push button) to the desired measurement. Often, the current range is labeled mA (milliamperes) for measuring current, V for voltage, and the ohm symbol (Ω) V for measuring resistance. Also, a function-select switch or push button is pressed so that the meter may be used to measure alternating current (ac) values or direct current (dc) values. The ohms measurement function of a DMM is typically divided into ranges, such as 200 Ω, 2 kΩ, 20 kΩ and 20 MΩ. This type of meter is called a multirange meter and there are many different types used. The meter may be adjusted to any of the positions for measuring resistance. The test leads used with the meter are ordinarily black and red. These colors are used to help identify which lead is the positive or negative side. The positive (red) lead is inserted into the meter for voltage, resistance, and current measure- ments. The black lead (negative) is used as the common (COM) lead of the meter. Resistance values are sometimes indicated as K ohms (multiply by 1000) on the digital scale of the meter for some of the resistance ranges of the meter. Another type of digital meter is an autoranging meter. The range values do not need to be changed for larger or smaller voltages, currents, or resistances. To