WATTMETERS Test Instruments & Measuring DevicesWATTMETERSWattmeters are used to determine DC power or real AC power delivered to theload.EO 1.2 STATE the electrical parameters measured by each ofthe following in-place measuring devices:d. WattmeterEO 1.3 EXPLAIN how the following electrical test equipmentand measuring devices are connected to a circuit:d. WattmeterWattmeterThe wattmeter is an instrumentFigure 11 Wattmeter Schematicwhich measures DC power or trueAC power. The wattmeter usesfixed coils to indicate current,while the movable coil indicatesvoltage (Figure 11). Coils LI1 andLI2 are the fixed coils in serieswith one another and serve as anammeter. The two I terminals areconnected in series with the load.The movable coil Lv, and itsmultiplier resistor Rs, are used as avoltmeter, with the V terminalsconnected in parallel with the load.The meter deflection isproportional to the VI, which ispower.Wattmeters are rated in terms oftheir maximum current, voltage, and power. All of these ratings must be observed to preventdamage to the meter.Equation (14-15) is the mathematical representation of calculating power in a DC circuit.(14-15)PVI or PI2RES-14 Page 20 Rev. 0
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