142 2 Industri I d d s ia l l Rob o bo tics i s Fu un ddamentals Copyright Goodheart-Willcox Co., Inc. Copyright Goodheart-Willcox Co., Inc. measure resistance with this meter, the negative (black) lead is inserted in the COM jack and the positive (red) lead is placed in the V/Ohm jack. The function select switch of the meter is rotated to the ohm (resistance) symbol. Resistance values are indicated on the digital scale of the meter. Measuring Voltage Voltage is applied to electrical equipment to initiate operation. A technician should to be able to measure voltage in order to check the operation of equipment. Many electrical problems develop due to either too much or too little voltage being applied to the equipment. Multimeters are used to measure voltage in an electrical circuit. Typical voltage ranges of a DMM might be 200mV (millivolts), 2V, 20V, 200V and 1000V. When the function-select switch or push button is adjusted to 1000V on the dc volts range, for example, the meter can measure up to 1000 volts dc. The same is true for the other ranges of dc voltage. The voltage value of each range is the maximum voltage that may be measured on that range. When making voltage measurements, adjust the function-select switch or push button to the highest range of dc voltage to be measured. The red test lead should be put into the V-Ω-A jack. The black test lead should be put into the COM jack. Voltage values are measured with the meter connected in parallel with the circuit or component being measured. Voltage values are indicated in volt units on the digital scale of b the meter. To measure voltage with an autoranging meter, the negative (black) lead is inserted in the COM jack and the positive (red) lead is placed in the V/Ohm jack. The function select switch is placed in one of the voltage settings: mV for mil- livolts, V for dc voltage, or V ~ for ac voltage. Voltage values are usually indicated V directly in volts on the digital scale of the meter for each range. Measuring Current Current fl ows through a complete electrical circuit when voltage is applied. Many fl important tests are made by measuring current flow in an electrical circuit. The fl current values in an electrical circuit depend on the amount of resistance in the circuit. Learning to use a multimeter to measure current in an electrical circuit is also important. To measure the current through a circuit, fi rst make sure no voltage is applied fi to the circuit while you are connecting the meter. Current is measured with the meter in series with the circuit. The fi rst step of the procedure for measuring cur- fi rent is to remove a connecting wire from the circuit at the point where the current will be measured. Set the multimeter to the highest current range. Connect the negative test lead to the most negative point of the circuit and the positive test lead nearest the positive power source terminal. After the meter has been connected in this manner, voltage may be applied to the circuit. If necessary, adjust the meter to a lower range to get an accurate current reading. The current value should never exceed the value of range setting of the meter. The current value is read directly on the scale of the meter. Now look at the controls of a typical multimeter being used for measuring cur- rent. The current ranges might be 2 mA (milliamperes), 20 mA, and 200 mA. For example, when the function-select switch or push button is adjusted to 2000 mA on the current range, the meter measures up to 2000 mA (2 amperes). The same is true for the other ranges of current in terms of the maximum current reading. The