Voltage And Current Measurements; Pulse Measurements - Agilent Technologies 66311A User Manual

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Programming the DC Source - 7

sample interval and the number of data points so that and integral number of waveform cycles will end

up in the measurement buffer.

Voltage and Current Measurements

The HP 66311A has a number of waveform measurement capabilities. The SCPI language MEASure and

FETCh queries are used to return the various measurement parameters of voltage and current waveforms.

Average Measurements

To measure the average output voltage or current, use:

MEASure:VOLTage?

MEASure:CURRent?

Average voltage and current is measured by acquiring a number of readings at the selected time interval,

applying the Hanning window function to the readings, and averaging the readings. Windowing is a

signal conditioning process that reduces the error in average measurements made in the presence of

periodic signals such as pulse current waveforms, which are generated when TDMA cellular phones are

transmitting. The power-on and *RST sample interval and sweep size settings yield a data acquisition

time of 32 milliseconds per measurement.

Ripple rejection is a function of the number of cycles of the ripple frequency contained in the acquisition

window. More cycles in the acquisition window results in better ripple rejection. If you increase the data

acquisition time for each measurement to 45 microseconds for example, this results in 5.53 cycles in the

acquisition window at 60 Hz, for a ripple rejection of about 70 dB.

RMS Measurements

To read the rms content of a voltage or current waveform, use:

MEASure:VOLTage:ACDC? or

MEASure:CURRent:ACDC?

This returns the total rms measurement.

Making rms or average measurements on ac waveforms for which a non-integral number of cycles of data

has been acquired may result in measurement errors due to the last partial cycle of acquired data. The

instrument reduces this error by using a Hanning window function when making the measurement. If the

measurement readings vary from sample to sample, try increasing the data acquisition time to reduce

measurement error.

Use fetch queries to return pulse measurement data in the shortest time. The fetch functions do not

trigger the acquisition of new measurement data, but are used to return different calculations from the

data that was retrieved by the acquisition trigger. If you take a voltage measurement you can fetch only

voltage data; if you take a current measurement you can fetch only current data, otherwise an error will

occur.

The dc source has several measurement queries that return key parameters of pulse waveforms as shown

in Figure 7-3.

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