Agilent Technologies N3280A Making Measurements, Generating Output Triggers, Average Measurements

Programming the DC Source - 5

Generating Output Triggers

After you have specified the appropriate trigger source, you can generate triggers as follows:

GPIB Triggers Send one of the following commands over the GPIB: TRIG:IMM (not affected by the trigger source setting)

*TRG

an IEEE-488 Group Execute Trigger bus command EXTernal Triggers Provide a negative-going TTL signal to the trigger input.

When the trigger system enters the Output Change state upon receipt of a trigger (see figure 5-1), the triggered functions are set to their programmed trigger levels. When the triggered actions are completed, the trigger system returns to the Idle state.

Making Measurements

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 average.

NOTE: There is one measurement buffer for each output channel in the dc source. However, only the following measurement parameters can be configured independently for each channel: SENSe:FUNCtion, SENSe:CURRent:RANGe.

There are two ways to make measurements:

♦Use the MEASure queries to immediately start acquiring new voltage or current data, and return measurements 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 a triggered measurement when you need to synchronize the data acquisition with a transition in the output voltage or current. Then use the FETCh queries to return the measurement data. FETCh queries do not trigger the acquisition of new measurement data, they only return the data that was acquired by the trigger. Note that if you acquired voltage data, you can only fetch voltage data.

Average Measurements

To measure the average output voltage or current, use:

MEAS:VOLT? (@<channel list>)

MEAS:CURR? (@<channel list>)

Average voltage and current is measured by acquiring a number of readings at the selected time interval, applying the selected 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 and noise. Refer to the discussion of the Window functions later in this chapter and in chapter 6. The power-on and *RST sample interval and sweep size settings yield a data acquisition time of 152 microseconds per measurement (5 data points at 30.4∝s intervals).

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. The two methods of increasing data acquisition time is to either increase the number of power line cycles, or increase the number of measurement samples and the time interval between samples.

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