CR200/CR200X Series Dataloggers - Campbell Scientific
CR200/CR200X Series Dataloggers - Campbell Scientific
CR200/CR200X Series Dataloggers - Campbell Scientific
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Section 4. Sensor Support<br />
FIGURE. Pulse Input Types (p. 7) illustrates pulse input types measured by the<br />
<strong>CR200</strong>(X). Dedicated pulse input channel P_SW can be configured to read<br />
high- frequency pulses or switch closure, while P_LL can be configured to read<br />
a low-level AC signal. With a 100 kOhm pull-up resistor added to the wiring<br />
panel P_LL, C1, or C2 can measure pulse input signals (See Pulse Input (P_SW<br />
p. 44).<br />
4.4.1.1 Pulse Input (P_SW)<br />
Figure 30: Pulse Input Types<br />
Internal hardware routes high-frequency pulse to an inverting CMOS input<br />
buffer with input hysteresis. The CMOS input buffer is guaranteed to be an<br />
output zero level with its input ≥ 2.7 V, and guaranteed to be an output one with<br />
its input ≤ 0.9 V. An RC input filter with approximately a 1 µs time constant<br />
precedes the inverting CMOS input buffer, resulting in an amplitude reduction<br />
of high frequency signals between the P_SW terminal block and the inverting<br />
CMOS input buffer as illustrated in FIGURE. Amplitude reduction of pulsecount<br />
waveform. For a 0 to 5 Volt square wave applied to P_SW, the maximum<br />
frequency that can be counted in pulse input mode is approximately 1 kHz.<br />
Figure 31: Amplitude Reduction of Pulse-Count Waveform (before and<br />
after 1 ms time constant filter)<br />
44