CR1000 Manual - Campbell Scientific

Section 8. Operation
Table 73. Time Constants (τ)
Measurement
τ
Pulse channel, high-frequency mode 1.2
Pulse channel, switch-closure mode 3300
Pulse channel, low-level ac mode
See table Filter Attenuation of
Frequency Signals (p. 321) footnote
Digital I/O, high-frequency mode 0.025
Digital I/O, switch-closure mode 0.025
Table 74. Filter Attenuation of Frequency Signals.
As shown for low-level ac inputs, increasing voltage is required at increasing frequencies to
overcome filter attenuation on pulse-input channels*.
ac mV (RMS)
20
200
2000
5000
Maximum Frequency
20
200
10,000
20,000
*8.5-ms time constant filter (19 Hz 3 dB frequency) for low-amplitude signals. 1-ms time
constant (159 Hz 3 dB frequency) for larger (> 0.7 V) amplitude signals.
Figure 101: Amplitude reduction of pulse-count waveform (before and after
1-µs time constant filter)
321