Section 8. Operation
C Terminals
•
Maximum input frequency <1 kHz
•
CRBasic instruction:
TimerIO()
•
Rising or falling edges of a square-wave signal are detected:
o
Rising edge — transition from <1.5 Vdc to >3.5 Vdc.
o
Falling edge — transition from >3.5 Vdc to <1.5 Vdc.
•
Edge-timing resolution is approximately 540 ns.
8.1.3.6 Edge Counting
Edge counts can be measured on
C
terminals.
o
C Terminals
•
Maximum input frequency 400 kHz
•
CRBasic instruction:
TimerIO()
•
Rising or falling edges of a square-wave signal are detected:
o
Rising edge — transition from <1.5 Vdc to >3.5 Vdc.
o
Falling edge — transition from >3.5 Vdc to <1.5 Vdc.
8.1.3.7 Pulse Measurement Tips
Basic connection of pulse-output sensors is illustrated in table
Switch Closures
and Open Collectors
(p. 356,
p. 357)
The
PulseCount()
instruction, whether measuring pulse inputs on
P
or
C
terminals, uses dedicated 24-bit counters to accumulate all counts over the
programmed scan interval. The resolution of pulse counters is one count or 1 Hz.
Counters are read at the beginning of each scan and then cleared. Counters will
overflow if accumulated counts exceed 16,777,216, resulting in erroneous
measurements.
•
Counts are the preferred
PulseCount()
output option when measuring the
number of tips from a tipping-bucket rain gage or the number of times a door
opens. Many pulse-output sensors, such as anemometers and flow meters,
are calibrated in terms of frequency (
Hz
(p. 517)
) so are usually measured using
the
PulseCount()
frequency-output option.
•
Accuracy of
PulseCount()
is limited by a small scan-interval error of ±(3
ppm of scan in 10 µs), plus the measurement resolution error of ±1 /
(scan interval). The sum is essentially ±1 / (scan interval).
•
Use the
LLAC4
(p. 646)
module to convert non-TTL-level signals, including
low-level ac signals, to TTL levels for input into
C
terminals.
•
As shown in the table
Switch Closures and Open Collectors on C Terminals
(p. 357),
C
terminals, 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,
C
terminals have an input resistance of only 220 Ω.
356
Summary of Contents for CR1000
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Page 457: ...Section 8 Operation 8 8 1 3 Final Memory Tables Figure 119 Final Memory Tables 457 ...
Page 458: ...Section 8 Operation 8 8 2 Run Stop Program Figure 120 Run Stop Program 458 ...
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Page 461: ...Section 8 Operation 8 8 4 PCCard Memory Card Display Figure 123 PCCard CF Card Display 461 ...
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