Campbell Scientific CR9000X Measurement and Control System - Manual (Page 49)

Overview
Pulse Counting
The CR9070 has 12 Pulse input channels with 16 bit counters. These channels
count on the rising edge of the input signal and can be configured to output
Counts or Signal Frequency. The maximum input voltage allowed on these
channels is
± 20 volts. The resolution of the frequency measurement is 1/scan
interval (e.g., a PulseCount instruction in a 1 second scan has a frequency
resolution of 1 Hz, a 0.5 second scan gives a resolution of 2 Hz, and a 1 ms
scan gives a resolution of 1000 Hz). The resolution can be increased through
using the running average parameter of the PulseCount instruction. The
resultant measurement will bounce around by the resolution.
These twelve channels are further segmented based on the input signal's
characteristics.
Channels 1-8: The first 8 Pulse input channels can be configured as Low
Level AC inputs to count the frequency of low level AC
signals from such sensors as a magnetic pickups. The
minimum input voltage that can be counted is 20 mV RMS
with a max frequency of 10 KHz. With input amplitudes
greater than 50 mV RMS, up to 20 KHz signals can be read.
The maximum allowable input voltage for this or the high
frequency mode is 20 VDC.
Channels 1 through 8 can also be configured to measure
"High Frequency" pulses, which are signals that have
transitions from below 1.5 volts to above 3.5 volts. High
Level Frequency input up to 5 MHz can be measured. If
possible, it is preferable to place Low Level measurement
inputs and high frequency measurement inputs on opposite
ends of the module to eliminate the possible of crosstalk.
Channels 9-12: The last 4 Pulse channels (9-12) can be configured as Switch
Closure inputs. The dry contact switch should be connected
between the Pulse port and ground. When the switch is open,
the port is pulled to 5 volts through a 100 kohm pull up
resistor. Maximum frequency : 100 Hz.
Channels 9 through 12 can also be configured to measure
"High Frequency" pulses, which are signals that have
transitions from below 1.5 volts to above 3.5 volts. High
Level Frequency input up to 5 MHz can be measured.
CR9070 SUPPORTED MEASUREMENT/CONTROL INSTRUCTIONS:
PulseCount Count Pulses or Frequency
ReadI/O Read State of I/O Channels
TimerIO Interval and Timing Measurements
WriteI/O Set State of I/O Channels
See Section 3.4 Pulse Count Measurements for measurement details.
See Section 7 Measurement Instructions for Measurement Instruction details.
See Section 9.2 Data Logger Status/ Control for Control Instruction details.
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