Campbell Scientific CR3000 Micrologger - Manual (Page 327)

Section 8. Operation
327
Figure 104: Amplitude reduction of pulse-count waveform (before and after
1-µs time constant filter)
8.1.5.4.3 Switch Bounce and NAN
NAN will be the result of a TimerIO() measurement if one of two conditions
occurs:
1. timeout expires
2. a signal on the channel is too fast (> 3 KHz)
When the input channel experiences this type of signal, the CR3000 operating
system disables the interrupt that is capturing the precise time until the next scan
is serviced. This is done so that the CR3000 does not get bogged down in
interrupts. An small RC filter retrofitted to the sensor switch should fix the
problem.
8.1.6 Period Averaging
The CR3000 can measure the period of a signal on any single-ended analog-input
channel (SE1 – 28). The specified number of cycles is timed with a resolution of
68 ns, making the resolution of the period measurement 68 ns divided by the
number of cycles chosen.
Low-level signals are amplified prior to a voltage comparator. The internal
voltage comparator is referenced to the user-entered threshold. The threshold
parameter allows a user to reference the internal voltage comparator to voltages
other than 0 V. For example, a threshold of 2500 mV allows a 0- to 5-Vdc digital
signal to be sensed by the internal comparator without the need of any additional