Specifications

Section 4. Sensor Support

4-30

Sensor

Pulse Channel

Ground

FIGURE 4.5-1. Schematic of a Pulse Sensor on a CR1000

The PulseCount() instruction cannot be used in a Slow Sequence

scan.

Execution of PulseCount() within a scan involves determining the accumulated

counts in each dedicated 24-bit counter since execution of the last

PulseCount(). PulseCount() parameter (POption) determines if the output will

be in counts (POption = 0) or frequency (POption = 1). Counts are the

preferred output option for measuring number of tips from a tipping bucket rain

gage, or the number of times a door opens. Many pulse sensors, such as

anemometers and flow meters, are calibrated in terms of frequency (Hz or

counts / second), and are best measured with the frequency option.

Resolution of the pulse counters is one count. Resolution of frequency is (1 /

measurement interval). For example, the frequency resolution of PulseCount()

returning a result every 1 second is 1 Hz. Accuracy is limited by a small scan

interval error of ±(3 ppm of scan interval + 10 μs) plus the measurement

resolution error of ± 1 Hz. The sum is essentially ± 1 Hz. Extending a 1

second measurement interval to 10 seconds, either by increasing the scan

interval or by averaging, improves the resulting frequency resolution from 1 Hz

to 0.1 Hz. Averaging can be accomplished by the Average(), AvgRun(), and

AvgSpa() instructions. Alternatively, entering a number greater than 1 in

(POption) parameter is to enter an averaging interval in milliseconds for a

direct running average computation.

4.5.1 Pulse Input Channels P1 and P2

Read more! Review pulse counter specifications in Section 3.3. Review

pulse counter programming in CRBASIC Help for the PulseCount()

instruction.

FIGURE 4.5-2 illustrates pulse input types measured by the CR1000.

Dedicated pulse input channels P1 and P2 can be configured to read high-

frequency pulses, low-level AC signals, or switch closure.

Input channel expansion devices for all input types are available

from Campbell Scientific.

NOTE