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4 - Programming Examples
138
Power Measurements
The MEASure and FETCh queries can return real, apparent, and reactive power measurements as well
as dc power and power factor using the following commands:
MEASure:POWer:AC:APParent? measures the ac component of apparent power in VA
MEASure:POWer:AC:REACtive? measures the reactive power
MEASure:POWer:AC:REAL? measures the in-phase component of power in watts
MEASure:POWer:AC:PFACtor? returns the output power factor
MEASure:POWer:AC:TOTal? measures the total real power being sourced
MEASure:POWer:DC? measures the dc component of power
Harmonic Measurements
The MEASure and FETCh queries can return the amplitude and phase of up to the 50th harmonic of
voltage and current. They can also return the total harmonic distortion in the output voltage or current. For
example, to return readings for an individual harmonic component, use the following commands:
MEASure:CURRent:HARMonic:AMPLitude? <harmonic_number>
MEASure:CURRent:HARMonic:PHASe? <harmonic_number>
MEASure:VOLTage:HARMonic:AMPLitude? <harmonic_number>
MEASure:VOLTage:HARMonic:PHASe? <harmonic_number>
Harmonic numbers are related to the programmed frequency of output voltage. Queries sent with an
argument of 0 return the dc component. An argument of 1 indicates the fundamental frequency, 2
indicates the second harmonic, 3 indicates the third, and so on. The maximum harmonic component that
can be read is limited by the fundamental measurement bandwidth, which is 12.5kHz. An error is
generated if a query is sent for a harmonic that has a frequency greater than 12.5kHz. To return all the
harmonic components with a single query, use the following commands:
MEASure:ARRay:CURRent:HARMonic:AMPLitude?
MEASure:ARRay:CURRent:HARMonic:PHASe?
MEASure:ARRay:VOLTage:HARMonic:AMPLitude?
MEASure:ARRay:VOLTage:HARMonic:PHASe?
These queries always return 51 data values, from the dc component up to the 50th harmonic. Any
harmonics that represent frequencies greater than 12.5kHz are returned as the value 0. To return the
percentage of total harmonic distortion in the output voltage or current, use the following commands:
MEASure:CURRent:HARMonic:THD?
MEASure:VOLTage:HARMonic:THD?
Simultaneous Output Phase Measurements (Agilent 6834B only)
You can return simultaneous measurements from all output phases of the three-phase ac source using
the FETCh query. Unlike MEASure queries, FETCh queries do not trigger the acquisition of new data
when they are executed.
You must first initiate the measurement trigger system and generate a measurement trigger as explained
in the following section "Triggering Measurements". When the measurement data has been acquired by
the voltage and current data buffers for each output phase, use INSTrument:NSELect to select each
phase, and FETCh to return the specified measurement data. The following commands return rms
voltage: