Chapter 21 Electrical Test and Measurement Equipment 407 Continuity Test Mode Some multimeters include a continuity test mode where an audible signal indicates the presence of a low resistance. Th is feature allows checking for continuity without hav- ing to look at the multimeter display. In the continuity test mode, the DMM provides voltage to the circuit under test. C A U T I O N Never connect a DMM in the continuity test mode to an energized circuit or the DMM may be irrepa- rably damaged. Advanced DMM Functions Some multimeters are even capable of communicating with a computer, allowing you to plot periodic measurements and determine how the value measured changes over time. To overcome the problem of slow variations in the value measured, many digital multimeters include a bar graph in the display. Th e bar graph simulates the move- ment of a meter needle so you can get a sense of the rate of change occurring while the display is continuously counting. See Figure 21-14. Many multimeters are capable of measuring tem- perature with the aid of a thermocouple. An example of a DMM and a thermocouple is shown in Figure 21-15. Some multimeters even have a thermocouple provided in the accessory package that comes with the meter. Th e thermocouple is a contact-type temperature device. It measures the temperature of whatever it is contacting. It is capable of measuring the air temperature. T E C H T I P Thermocouples A thermocouple is a device that uses the junction of dissimilar metals to generate a voltage propor- tional to the temperature. Most advanced multimeters are labeled True RMS. RMS refers to the term “root-mean-square,” which is a type of averaging (integration) of a sinusoidal alternat- ing current waveform. In simpler terms, it is the amount of AC voltage that would produce the same amount of power that a DC voltage would. Goodheart-Willcox Publisher Figure 21-14. This digital multimeter display includes a bar graph along the lower portion of the display area. The bar graph provides a visual representation of the fl uctuations in the reading. Thermocouple attachment Connected to temperature input jack Set to measure temperature Goodheart-Willcox Publisher Figure 21-15. With a thermocouple attached, this DMM can measure temperature. Bar graph Copyright Goodheart-Willcox Co., Inc.