Agilent Technologies 6632B, 6634B, 66332A Making Measurements, Voltage and Current Measurements

Programming the DC Source - 3

Making Measurements

The dc source has the ability to make several types of voltage or current measurements. The measurement capabilities of the Agilent 66312A and Agilent 66332A models are particulary useful for loads that draw current in pulses.

NOTE: You cannot measure output voltage and current simultaneously.

All measurements are performed by digitizing the instantaneous output voltage or current for a defined number of samples and sample interval, storing the results in a buffer, and then calculating the measured result. Many parameters of the measurement are programmable. These include the number of samples, the time interval between samples, the bandwidth, and the method of triggering. Note that there is a tradeoff between these parameters and the speed, accuracy, and stability of the measurement in the presence of noise.

There are two ways to make measurements:

♦Use the MEASure commands to immediately start acquiring new voltage or current data, and return measurement calculations from this data as soon as the buffer is full. This is the easiest way to make measurements, since it requires no explicit trigger programming.

♦Use an acquisition trigger to acquire the data. Then use the FETCh commands to return calculations from the data that was retrieved by the acquisition trigger. This method gives you the flexibility to synchronize the data acquisition with a transition in the output voltage or current. FETCh commands do not trigger the acquisition of new measurement data, but they can be used to return many different calculations from the data that was retrieved by the acquisition trigger. Note that if you take a voltage measurement, you can fetch only voltage data.

Making triggered measurements with the acquisition trigger system is discussed under "Triggering Measurements".

NOTE: For each MEASure form of the query, there is a corresponding query that begins with the header FETCh. FETCh queries perform the same calculation as their MEASure counterparts, but do not cause new data to be acquired. Data acquired by an explicit trigger or a previously programmed MEASure command are used.

Voltage and Current Measurements

The SCPI language provides a number of MEASure and FETCh queries which return various measurement parameters of voltage and current waveforms.

DC Measurements

To measure the dc output voltage or current, use:

MEASure:VOLTage? or

MEASure:CURRent?

Dc voltage and current is measured by acquiring a number of readings at the selected time interval, applying a Hanning window function to the readings, and averaging the readings. Windowing is a signal conditioning process that reduces the error in dc measurements made in the presence of periodic signals such as line ripple. At power-on and after a *RST command, the following parameters are set:

SENSe:SWEep:TINTerval 15.6E-6

SENSe:SWEep:POINts 2048

23