3-6 Range, Digits, Rate, and Filter
Rate
The RATE key selects the integration time of the A/D converter. This is the period of time the
input signal is measured (also known as aperture). The integration time affects 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 (1/60) and 1 PLC for 50Hz (and 400Hz) is 20msec (1/50).
In general, the Model 2182 has a parabola-like shape for its speed vs. noise characteristics
and is shown in Figure 3-1. The Model 2182 is optimized for the 1 PLC to 5 PLC reading rate.
At these speeds (Lowest noise region in the graph), the Model 2182 will make corrections for
its own internal drift and still be fast enough to settle a step response <100ms.
Figure 3-1
Speed vs. noise characteristics
You can have a separate rate setting for voltage and temperature functions. The rate setting
for a voltage function applies to the other voltage function. For example, if you set DCV1 for
0.1 PLC (fast), DCV2 will also be set for 0.1 PLC (fast). Similarly, the rate setting for a
temperature function applies to the other temperature function. Setting TEMP1 for 5 PLC
(slow), also sets TEMP2 for 5 PLC (slow).
Front panel RATE selections are explained as follows:
• 0.1 PLC — Selects the fastest front panel integration time. Select 0.1 PLC (fast) if speed
is of primary importance (at the expense of increased reading noise).
•1 PLC — Selects a medium integration time. Select 1 PLC (medium) when a
compromise between noise performance and speed is acceptable.
•5 PLC — Selects the slowest front panel integration time. Selecting 5 PLC (slow)
provides better noise performance at the expense of speed.
Lowest
noise
region
Voltage
Noise
166.7µs 16.67ms 83.33ms
Aperture Time
1s
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