1-21CAPACITANCE MEASUREMENTSCapacitance measurements are usually taken with a capacitance meter. Capacitance tolerances varyeven more widely than resistance tolerances. Capacitance tolerances depend on the type of capacitor, thevalue of capacitance, and the voltage rating. The actual measurement of capacitance is very simple;however, you must make the important decision of whether to reject or to continue to use the capacitorafter it has been tested.The POWER FACTOR of a capacitor is important because it is an indication of the various losses ofa capacitor. Power losses can be traced to the dielectric, such as current leakage and dielectric absorption.Current leakage is of considerable importance, especially in electrolytic capacitors.Q-17.What is the term used to refer to the losses which can be traced to the dielectric of a capacitor?INDUCTANCE MEASUREMENTSInductance measurements are seldom required in the course of troubleshooting. However, inductancemeasurements are useful in some cases; therefore, bridges (discussed in the next section) are available formaking this test. You will find that many capacitance test sets can be used to measure inductance. Mostcapacitance test sets are furnished with inductance conversion charts if the test equipment scale is notcalibrated to read the value of inductance directly.CAPACITANCE, INDUCTANCE, AND RESISTANCE BRIDGESYou can measure capacitance, inductance, and resistance for precise accuracy by using ac bridges.These bridges are composed of capacitors, inductors, and resistors in a wide variety of combinations.These bridges are operated on the principle of a dc bridge called a WHEATSTONE BRIDGE.Wheatstone BridgeThe Wheatstone bridge is widely used for precision measurements of resistance. The circuit diagramfor a Wheatstone bridge is shown in figure 1-5. Resistors R1, R2, and R3 are precision, variable resistors.The value of R_{x} is an unknown value of resistance that must be determined. After the bridge has beenproperly balanced (galvanometer G reads zero), the unknown resistance may be determined by means of asimple formula. The galvanometer (an instrument that measures small amounts of current) is insertedacross terminals b and d to indicate the condition of balance. When the bridge is properly balanced, nodifference in potential exists across terminals b and d; when switch S2 is closed, the galvanometerreading is zero.