Rate - Keithley 2010 User Manual

3-6 Measurement Options

Rate

The rate operation sets the integration time of the A/D converter, the period of time the input
signal is measured (also known as aperture). The integration time affects the usable digits, the
amount of reading noise, as well as the ultimate reading rate of the instrument. The integration
time is specified in parameters based on a number of power line cycles (NPLC), where 1 PLC
for 60Hz is 16.67msec and 1 PLC for 50Hz and 400Hz is 20msec.
In general, the fastest integration time (FAST (0.1 PLC) from the front panel, 0.01 PLC from
the bus) results in increased reading noise and fewer usable digits, while the slowest integration
time (SLOW (5PLC) from the front panel, 10PLC from the bus) provides the best common-
mode and normal-mode rejection. In-between settings are a compromise between speed and
noise.
The RATE parameters are explained as follows:
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•
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NOTE
FAST sets integration time to 0.1 PLC. Use FAST if speed is of primary importance (at
the expense of increased reading noise and fewer usable digits).
MEDium sets integration time to 1 PLC. Use MEDium when a compromise between
noise performance and speed is acceptable.
SLOW sets integration time to 5PLC. SLOW provides better noise performance at the
expense of speed.
The integration time can be set for any measurement function except frequency
(SLOW), period (SLOW), continuity (FAST), and diode test (MEDium). For frequency
and period, this value is gate time or aperture.
For the AC functions, MEDium and SLOW have no effect on the number of power line
cycles.