Section 8. Operation
375
instructions. Also,
PulseCount()
has the option of entering a number greater than
1
in the
POption
parameter. Doing so enters an averaging interval in
milliseconds for a direct running-average computation. However, use caution
when averaging. Averaging of any measurement reduces the certainty that the
result truly represents a real aspect of the phenomenon being measured.
Frequency Resolution Comparison
0.5 s Scan
5.0 s Scan
PulseCount()
,
POption
=
1
FR = 2 Hz
FR = 0.2 Hz
TimerIO()
,
Function
=
2
FR = 0.0011 Hz
FR = 0.00011 Hz
8.1.3.3.2 Frequency Measurement Q & A
Q
: When more than one pulse is in a scan interval, what does
TimerIO()
return
when configured for a frequency measurement? Does it average the measured
periods and compute the frequency from that (f = 1/T)? For example,
Scan
(50,mSec,10,0)
TimerIO
(WindSpd(),11111111,00022000,60,Sec)
A
: In the background, a 32-bit-timer counter is saved each time the signal
transitions as programmed (rising or falling). This counter is running at a fixed
high frequency. A count is also incremented for each transition. When the
TimerIO()
instruction executes, it uses the difference of time between the edge
prior to the last execution and the edge prior to this execution as the time
difference. The number of transitions that occur between these two times divided
by the time difference gives the calculated frequency. For multiple edges
occurring between execution intervals, this calculation does assume that the
frequency is not varying over the execution interval. The calculation returns the
average regardless of how the signal is changing.
8.1.3.4 Switch Closure and Open-Collector Measurements
Switch closure and open-collector signals can be measured on
P
or
C
terminals.
Mechanical-switch closures have a tendency to bounce before solidly closing.
Unless filtered, bounces can cause multiple counts per event. The CR800
automatically filters bounce. Because of the filtering, the maximum switch
closure frequency is less than the maximum high-frequency measurement
frequency. Sensors that commonly output a switch closure or open-collector
signal include:
•
Tipping-bucket rain gages
•
Switch closure anemometers
•
Flow meters
Data output options include counts, frequency (Hz), and running average.
Summary of Contents for CR800 Series
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Page 446: ...Section 8 Operation 446 8 11 2 Data Display FIGURE 100 CR1000KD Displaying Data ...
Page 448: ...Section 8 Operation 448 FIGURE 102 CR1000KD Real Time Custom ...
Page 449: ...Section 8 Operation 449 8 11 2 3 Final Storage Data FIGURE 103 CR1000KD Final Storage Data ...
Page 450: ...Section 8 Operation 450 8 11 3 Run Stop Program FIGURE 104 CR1000KD Run Stop Program ...
Page 452: ...Section 8 Operation 452 FIGURE 106 CR1000KD File Edit ...
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Page 523: ...Section 11 Glossary 523 FIGURE 116 Relationships of Accuracy Precision and Resolution ...
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