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# Example of Power, Voltage, and Current Monitoring

June 9, 2016

The following text describes monitoring voltage, current, and power delivered to a test load; the load in this example is a domestic kitchen refrigerator.

Transducers used:

ACT-010A current transducer is wired in series with the load.
AVT-150A voltage transducer is wired in parallel with the load.
PC5-010A is wired in series with the load for monitoring the current and in parallel with the load for monitoring the voltage.

The former transducers are examples. One other transducer that may be used includes the multifunction board level transducer, PTB. This board provides analog outputs proportional to each phase of true RMS.

This example uses digital meters, such as a 15660, which are scaled using precision load resistors.

Load resistors are selected as follows:

• Remember Ohm’s Law (R=V/I) where R is the resistance in ohms (Ω), V is the voltage that we want to apply to the digital meter, and I is the current from the transducer.
• The ACT-010A provides an output of 1 mADC at 10 amperes AC through terminals 3 and 4. 1 mADC represents 10 amperes AC. Adjust the decimal point of the digital meter so that it displays 10.00 with 1 mADC through 1000Ω load resistor.
• The AVT-150A provides an output of 1 mADC at 150 volts AC applied to terminals 3 and 4. 1 mADC represents 150 volts. Adjust the decimal point of the digital meter so that it displays 150.0 with 1 mADC through 15000Ω load resistor.
• The PC5-010A provides an output of 1 mADC at 1000 watts. 1 mADC represents 1000 watts. Adjust the decimal point on the digital meter so that it displays 1000 with 1 mADC through the 1000Ω resistor.

Now all three meters are scaled correctly and may be labeled amperes, volts, and watts. Note that the power does not equal volts times amperes (V*A). This is because the refrigerator has a power factor of 0.866 which is normal for older refrigerators. For the single-phase situation, power factor may be determined by dividing the power reading by the product of volts and amperes.

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Posted in: Application