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Overview of application
For some applications, such as the simulation of
European railway power systems, a low frequency
(16.6 Hz) ac waveform is required. Generating low
frequency waveforms with ac sources can present
testing challenges due to output power derating
and programming inaccuracies, depending on the
regulation technique used. If the ac source has
measurement capability, control of the measure-
ment sample period is necessary to capture suffi-
cient cycles of the output waveform to ensure
measurement accuracy.
The 6812A and 6813A can meet the above chal-
lenges at frequencies below 45 Hz. These two
models provide precise control of the waveform
generation and measurement system for optimal
operation at low frequencies. For this example,
the equipment under test will require an ac input
at 230 Vrms and 16.6 Hz. Real power, apparent
power, and power factor will be accurately meas-
ured using the high resolution current measure-
ment range.
Agilent 6812A and 6813A features used
• Programmable Vrms and frequency
• Realtime regulation mode
• Sinewave generation
• Programmable voltage and current sample rate
• Power measurement (power factor, VA, and Watts)
• x10 current measurement range
Advantages/benefits of the Agilent 6812A and
6813A solutions
• Programmable regulation mode allows for accu-
rate output voltage and current limit control.
• Programmable measurement sample rate pro-
vides high accuracy measurements for low
frequency signals.
• Use of the FETCh command provides fast
measurements from the same data buffers.
• x10 current measurement range increases
the accuracy for low current and low power
measurements.
Implementation details
How the 6812A and 6813A generate low frequency ac
waveforms and perform low frequency ac measurements
A 230 Vrms sinewave is programmed at a frequency
of 16.6 Hz. To perform measurements at this out-
put frequency, the programmable sample period is
increased from 25 microseconds to 75 microsec-
onds. A triggered acquisition of voltage and current
provide the data from which the power measure-
ments are calculated. This method of acquisition is
necessary since the MEASure command will reset
the sample period back to the default value of 25
microseconds. A FETCh command is sent to return
the real power (Watts), power factor, and apparent
power measurements from the same voltage and
current data buffer.
Agilent 6800 series setup
• Connect the ac source output to the ac input
of the equipment under test.
• Set the regulation mode to Realtime.
• Set the rms voltage to Fixed mode.
• Set the frequency to Fixed mode.
• Set the shape to sine.
• Set the rms voltage to 230 V.
• Set the frequency to 16.6 Hz.
• Enable the output.
• Set the measurement sample period to
75 microseconds.
• Trigger the acquisition of voltage and
current data.
• Fetch the real power.
• Fetch the power factor.
• Fetch the apparent power.
Application 6:
Operating the Agilent 6812A and 6813A at Low Frequencies