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Programming the DC Source - 5
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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 30.4µs 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.