Copyright Goodheart-Willcox Co., Inc. 186 Essential Electrical Skills for HVACR: Theory and Labs There are also specifications for how the measured values on a meter are displayed. A meter display is rated by the number of digits and counts. Digits indicate the amount of num- bers it can appear on the display, while counts indicate the highest value it can display. Some examples are the following: • 3 1/2 : 2,000. A 3 1/2 display has 4 digits, but the most significant digit can only be a 0 or 1. Therefore, the display range is 0.001 to 1999. This is also called a 2000 count display. • 3 5/6 : 6000. A 3 5/6 display has 4 digits but the most significant digit is between 0 and 5. Therefore, the display range is 0.001 to 5999. This is also called a 6000 count display. • 4 3/4 : 40,000. A 4 3/4 display has 5 digits but the most significant digit can only be a 3. Therefore, the display range is 0.0001 to 39999. This is also called a 40,000 count display. Consider measuring voltage, and the display shows 120.0 V. The 600 V range must be used, and the least significant digit is 100 mV. This means the display shows one decimal in the tenth place. The displayed information and resolution detail values are plugged into a formula to derive the range of values that the mea- surement can be. Range = ± (0.01 × 120.0) + (0.100 × 3) = 1.5 V Thus, the error in the measurement is ±1.5 V. This means the actual voltage is between 118.5 and 121.5 V. This is providing the temperature is between 32 and 104°F, and relative humidity is below 75% for the specific meter used in this example. The error rate increases when the temperature and humidity are outside the given parameters. Accuracy Specification Accuracy is interpreted given the range, resolution, and accuracy from a typical specification. See Figure 10-24. Note that the accuracy is the same for each range. Pro Tip Accurate and precise XX XX Higher resolution 1 2 0 Precise Accurate XX XX X X X X Low resolution 1 2 0 Goodheart-Willcox Publisher Figure 10-23. Accuracy, precision, and resolution examples. Range Resolution Accuracy O/L Protection 600 mV 0.1 mV 6 V 1 mV 60 V 10 mV ± (1.0 % + 3 digits) 1000 V rms 600 V 100 mV 750 V 1.0 V Figure 10-24. Meter specifications for classifying accuracy. Goodheart-Willcox Publisher