Campbell CR200 Manuel de l'opérateur télécharger pdf (Page 58)

Section 4. Sensor Support

FIGURE. Pulse Input Types (p. 7) illustrates pulse input types measured by the

CR200(X). Dedicated pulse input channel P_SW can be configured to read

high- frequency pulses or switch closure, while P_LL can be configured to read

a low-level AC signal. With a 100 kOhm pull-up resistor added to the wiring

panel P_LL, C1, or C2 can measure pulse input signals (See Pulse Input (P_SW

p. 44).

Figure 30: Pulse Input Types

4.4.1.1 Pulse Input (P_SW)

Internal hardware routes high-frequency pulse to an inverting CMOS input

buffer with input hysteresis. The CMOS input buffer is guaranteed to be an

output zero level with its input ≥ 2.7 V, and guaranteed to be an output one with

its input ≤ 0.9 V. An RC input filter with approximately a 1 µs time constant

precedes the inverting CMOS input buffer, resulting in an amplitude reduction

of high frequency signals between the P_SW terminal block and the inverting

CMOS input buffer as illustrated in FIGURE. Amplitude reduction of pulse-

count waveform. For a 0 to 5 Volt square wave applied to P_SW, the maximum

frequency that can be counted in pulse input mode is approximately 1 kHz.

Figure 31: Amplitude Reduction of Pulse-Count Waveform (before and

after 1 ms time constant filter)

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Campbell CR200 Manuel de l'opérateur Page 58