True Electrical Quantity Measurements

True measurements of electrical quantities such as current, resistance, voltage, reactance, frequency and phase are rarely made outside standardizing laboratories, because of the difficulties of the required procedures. For example, the ohm was defined in 1893 as the resistance of a column of mercury 1 mm square and 106.3 cm long at a temperature of 0 degrees C. That is not a practical standard for field use, because even if an electronic technician had a column of mercury generally like that there would be no practical way outside a standards laboratory to measure the physical dimensions or the temperature with extraordinary accuracy. Because of problems like that, ordinary field measurements are made instead by devices calibrated against reasonably accurate standards that themselves were calibrated by comparison with more accurate standards that themselves were calibrated in laboratories by comparison with basic standards. ©2005 Tigertek, Inc. All rights reserved.

• June Fact-of-the-Day Index