Model 6485 Picoammeter Instruction Manual Range, Units, Digits, Rate, and Filters 4-5
Rate
The RATE key selects the integration time of the A/D converter. This is the period of time
the input signal is measured. 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, Model 6485 has a parabola-like shape for its speed vs. noise characteristics and
is shown in Figure 4-1. Model 6485 is optimized for the 1 PLC to 10 PLC reading rate. At
these speeds (lowest noise region in the graph), Model 6485 will make corrections for its
own internal drift and still be fast enough to settle a step response <100ms.
Figure 4-1
Speed vs. noise characteristics
Table 4-3
Ranges and values
Range <n> value
Display (5 -digit
resolution)
DDC
20mA
2mA
200µA
20µA
2µA
200nA
20nA
2nA
2E-2 or 0.02
2E-3 or 0.002
2E-4 or 0.0002
2E-5 or 0.00002
2E-6 or 0.000002
2E-7 or 0.0000002
2E-8 or 0.00000002
2E-9 or 0.000000002
00.0000 mA
0.00000 mA
000.000 µA
00.0000 µA
0.00000 µA
000.000 nA
00.0000 nA
0.00000 nA
R8
R7
R6
R5
R4
R3
R2
R1
Lowest
noise
region
Voltage
Noise
166.7µs 16.67ms 166.67ms
Integration Time
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