Keithley 2303, Руководство пользователя

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4-2 Long Integration Measurements
Overview
Long integration is an average measurement of one or more pulses. The integration time
period can be as long as 60 seconds. Since long integration is an average measurement, the inte-
gration time period should be a complete period, or integral number of periods for a pulse train.
NOTE For Models 2303 and 2303B, long integration current measurements are automatical-
ly performed on the 5A range. For Model 2303-PJ, pulse current measurements can
be performed on either the 5A range or 500mA range.
Long integration measurement is accomplished by taking an integral number of integration
cycles during the total measurement time. An integration cycle is the line cycle period (16.67ms
for 60Hz) plus a small processing time.
The system calculates the number of integration cycles required based on the total time and
rounds down to the nearest integer. Therefore, the actual measurement time can be slightly less
than the requested measurement time by up to one line cycle time.
Long integration is a technique to extend the capabilities of the power supply A/D circuit
beyond its maximum integration time period. The A/D can measure pulses up to 833ms. To
extend this time period for longer pulses, the long integration technique uses a filtered and sam-
pled measurement of the waveform. This gives the power supply the ability to measure signals
with periods up to 60 seconds.
The filtering of the waveform adds some restrictions to the types of pulses being measured.
If a pulse train has a high duty cycle, where the off time is less than 200ms, the first period of
the measured waveform will not have settled to steady state, therefore it will be an inaccurate
measurement. In all cases where the off or low time is less than 200ms, the filtered pulse will
have reached steady state in the second cycle of the waveform and, therefore, can be accurately
measured. In other words, to measure a periodic waveform with low times less than 200ms (high
duty cycle), start measurements after the first period occurs. This is not a problem for one-shot
pulses or for pulses with off times greater than 200ms.
The long integration measurement can be triggered to start on the rising or falling edge of a
detected pulse. A third option, neither edge, lets you start the long integration measurement as
soon as the long integration function is selected (assuming the output is on). This option does
not need a valid trigger level to generate a reading. It will perform a measurement and produce
a reading of the current even if a pulse is not present. Therefore, with NEITHER selected, the
NO PULSE message will not appear on the display.