Campbell Scientific CR9000X Measurement and Control System - Manual (Page 260)

Section 7. Measurement Instructions
7-36
7.6 Pulse/Timing/State Measurements
PulseCount (Dest, Reps, PSlot, PChan, PConfig, POption, Mult, Offset)
The PulseCount instruction sets up pulse measurements using the twelve 16
bit counter channels on the CR9070 or the twelve 32 bit counters channels on
the CR9071E Counter module. There are three pulse types or configurations
that may be measured using these Counter modules:
High Frequency: All twelve pulse channels can be configured for high frequency inputs. This
configuration is used for the higher frequency pulse inputs (up to 1 MHz). The
pulse count is incremented when the signal rises from below 1.5 VDC to above
3.5 VDC. Because of the input filter's 200 nanosecond time constant, higher
frequencies will require larger input transitions. The minimum pulse width that
can be detected is 500 ns. The maximum input voltage is
± 20 V.
Low Level AC: The first 8 frequency input channels can be configured for low level ac inputs.
This option is used to count the frequency of low level ac signals from such
sensors as a magnetic pick up. The minimum input voltage that can be
counted is 25 mV RMS and the signal must be zero crossing. At this
minimum voltage, frequencies up to 10 kHz can be measured. For input voltage
greater than 50 mV, frequencies up to 20 kHz can be measured. Again, the
maximum input voltage is 20 V.
Switch Closure: Channels 9 through 12 can be configured as Switch Closure inputs. The switch
closure (dry contact) should be connected between the pulse channel and
ground. When the contact is open, the pulse channel is pulled to 5 volts
through a 100 kOhm pull up resistor. When the contact is closed, the pulse
channel is pulled to ground. The count is incremented when the channel is
pulled high. The minimum switch close time is 5 msec. The minimum switch
open time is 5 msec. The maximum bounce time without being counted is 1
msec open.
Using the Poption parameter, you can configure the output as Counts,
Frequency over the scan interval, or as a Running Average Frequency for a set
duration.
This instruction must not be placed inside a conditional
statement, SubScan, or in a Slow Sequence Scan.
The PulseCount instruction must be executed once before the
pulse or control port is ready for input. This may be of particular
concern for programs with long scan intervals. For example, the
PulseCount instruction will not yield a valid output until the turn
of the second hour if the PulseCount instruction is used within a
program with a scan interval of 1 hour.
See Section 3.4 Pulse Count Measurements for additional measurement
information.
NOTE