Copyright Goodheart-Willcox Co., Inc. 188 Essential Electrical Skills for HVACR: Theory and Labs 10.7 Features There are many added features that a digital meter can have based on its make. These additional features include the following: • Data hold. Captures and records the value displayed. This value is displayed until the feature is turned off or the meter is turned off. • Max hold. Captures and records the maximum value displayed while taking a measurement within a specified amount of time. This value is displayed until the feature is turned off or the meter is turned off. • Min hold. Captures and records the minimum value displayed while taking a measurement within a specified amount of time. This value is displayed until the feature is turned off or the meter is turned off. • Inrush or Lock Rotor Amperage. Captures and records the initial current draw of an inductive load. The inrush current happens too quickly for the human eye to see. Therefore, the meter must capture the value within a fraction of second and record it. The range must be set correctly before using this feature. This value is displayed until the feature is turned off or the meter is turned off. • Back lit display. Allows user to see the display in low-light conditions. • Work light. Used to light up low-light areas and make measurements safely. • Automatic range select. The best resolution for the measurement taken is displayed. Modern quality meters reliably select the best range for best accuracy. • Manual range select. It can select a range based on resolution preference. An example is to round value to whole numbers. • Temperature. Measure temperature in Fahrenheit and Centigrade scales with the included thermocouple. Many meters allow for user calibration, which is preferred. • Dual display. The inductive clamp uses a dedicated display thus allowing the display for any of the other functions to be used simultaneously. • True RMS. A meter measures the power dissipated by a resistor instead of calculating the RMS value. This is more accurate since it is a measure of true power used. Summary • Analog meters and digital meters can only measure current. • Analog meters use a magnetic movement that uses a pointer to move across a calibrated scale. • Analog meters configure the internal circuitry to translate the measured current into the selected function values: volts, ohms, or current. • A digital meter is a device that displays electrical quantities as a numerical value rather than a position on a meter. • Digital meters are more accurate than analog meters. • Digital meters convert analog signals to digital information. The digital information is processed by a microprocessor and sent to the display. • Due to the miniaturization of electronics, digital meters perform many functions. • Included in most digital meters are capacitor, diode, continuity, frequency, noncontact voltage, and recording functions in addition to the basic volt- milliamps-ohms functions. • Test leads should be checked for damage before using and periodically tested for intermittent failure by using the ohmmeter function. • The wattmeter measures true power and power factor. • The megohmmeter uses high voltages to check wire insulation condition. Owner’s Manual Refer to the owner’s manual for the safe and correct way to use any feature. Pro Tip