Campbell Scientific CR3000 Micrologger - Manual (Page 323)

Section 8. Operation
323
calibrated in terms of frequency (Hz
(p. 458)
) so are usually measured using the
PulseCount() frequency option.
• Accuracy of PulseCount() is limited by a small scan-interval error of ±(3
ppm of scan interval + 10 µs), plus the measurement resolution error of ±1 /
(scan interval). The sum is essentially ±1 / (scan interval).
• Use the LLAC4
(p. 562)
module to convert non-TTL level signals, including
low-level ac signals, to TTL levels for input into digital I/O channels C1 –
C8.
• When digital I/O channels C1 – C8 measure switch-closure inputs, pull-up
resistors may be required. Figure Connecting Switch Closures to Digital I/O
(p. 323)
show how pull-up resistors can be incorporated into a wiring scheme.
• As shown in figure Connecting Switch Closures to Digital I/O
(p. 323),
digital
I/O inputs, with regard to the 6.2-V Zener diode, have an input resistance of
100 kΩ with input voltages < 6.2 Vdc. For input voltages ≥ 6.2 Vdc, the
inputs have an input resistance of only 220 Ω.
Figure 103: Connecting switch closures to digital I/O
Using a pull-up resistor on digital I/O channels C1 - C8