193 Copyright Goodheart-Willcox Co., Inc. Name __________________________________________ Date _______________________ Class ______________________ Schematic Diagram The true value of the displayed 120.0 V can be between 118.5 V and 121.5 V due to meter error. Accuracy is ± 1.5 V Max value Displayed value Min value Tolerance 118.0 118.5 119.0 119.5 120.0 120.5 121.0 121.5 122.0 Goodheart-Willcox Publisher Figure 10.2-1. (Continued) 2. Get your instructor’s approval before powering up the lab board. 3. Plug in board into outlet. 4. Before turning the switch on, measure the source voltage between TP1 and any neutral terminal. Line voltage should be displayed. Leave one probe on TP1 and test the other neutral terminals. 5. Record the line voltage. 6. Find the accuracy for ac voltage in the specification section of your manual. 7. Apply the formula: ± (displayed value × % error) + (resolution × # of digits). 8. Perform the calculation for the measured value and record. Formula Example Consider for example: the displayed value 240.0 V. This means the accuracy given in the specification is ± (1% + 3 digits). The percent error is 1%, so use 0.01 in the above formula. The resolution is given in a separate column as 100 mV or is included with the range value as 600.9. In either case 0.1 is the least significant digit to be multiplied by the number of digits in the equation. So, the equation is set up as follows for the example. ± (240.0 × 0.01) + (0.1 × 3) 2.4 + 0.3 = 2.7 V Thus, the tolerance is ± 2.7 V. The actual voltage is between 237.3 and 242.7 V. Pro Tip Continued