Section 8. Operation
306
Table 68. Time Constants (τ)
Measurement τ
Pulse channel, low-level ac mode
See table Filter Attenuation of
Frequency Signals
(p. 306) footnote
Digital I/O, high-frequency mode 0.025
Digital I/O, switch-closure mode 0.025
Table 69. 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) Maximum Frequency
20
200
2000
5000
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 96: Amplitude reduction of pulse-count waveform (before and after
1-µs time constant filter)
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