Anemometer With Photochopper Output; Wiring Diagram For Anemometer - Campbell Measurement and Control Module CR10 Operator's Manual

temperatures of the three probes which are
stored in Input Locations 1-3; the RH values are
stored in Input Locations 4-6. The temperature
measurements are made on single-ended input
channels 1-3, just as in example 7.5. The
program listed below is a continuation of the
program given in example 7.5.
CONNECTIONS
The black leads from the probes are connected
to excitation channel 1, the purple leads are
connected to analog ground (AG), and the clear
leads are connected to Ground (G). The red
leads are from the thermistor circuit and are
connected to single-ended channels 1-3 (1H,
1L, 2H). The white leads are from the RH
circuit and are connected to single-ended
channels 4-6 (2L, 3H, and 3L). The correct
order must be maintained when connecting the
red and white leads; i.e., the red lead from the
first probe is connected to single-ended
channel 1H and the white lead from that probe
is connected to single-ended channel 2L, etc.
PROGRAM (continuation of previous example)
02: P12
01: 3
02: 4
03: 1
04: 1
05: 4
06: 1
07: 0
7.7 ANEMOMETER WITH
PHOTOCHOPPER OUTPUT
An anemometer with a photochopper
transducer produces a pulse output which is
measured by the CR10's Pulse Count
Instruction. The Pulse Count Instruction with a
Configuration Code of 20, measures "high
frequency pulses", "discards data from
SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES
RH 207 Probe
Reps
IN Chan
Excite all reps w/EXchan 1
Temperature Loc 107 T #1
Loc [:RH #1 ]
Mult
Offset
FIGURE 7.7-1. Wiring Diagram for Anemometer
excessive intervals", and "outputs the reading
as a frequency" (Hz = pulses per second). The
frequency output is the only output option that
is independent of the scan rate.
The anemometer used in this example is the R. M.
Young Model 12102D Cup Anemometer, with a 10
window chopper wheel. The photochopper
circuitry is powered from the CR10 12 V supply;
AC power or back-up batteries should be used to
compensate for the increased current drain.
Wind speed is desired in meters per second
(m/s). There is a pulse each time a window in
the chopper wheel, which revolves with the
cups, allows light to pass from the source to the
photoreceptor. Because there are 10 windows
in the chopper wheel, there are 10 pulses per
revolution. Thus, 1 revolution per minute (rpm)
is equal to 10 pulses per 60 seconds (1 minute)
or 6 rpm = 1 pulse per second (Hz). The
manufacturer's calibration for relating wind
speed to rpm is:
Wind(m/s) =
(0.01632 m/s)/rpm x Xrpm + 0.2 m/s
The result of the Pulse Count Instruction
(Configuration Code = 20) is X pulses per sec.
(Hz). The multiplier and offset to convert XHz to
meters per second are: Wind (m/s) = (0.01632
m/s)/rpm x (6 rpm/Hz) x XHz + 0.2 m/s
Wind (m/s) =
(0.09792 m/s)/Hz x XHz + 0.2 m/s
PROGRAM
01: P3 Pulse
01: 1 Rep
02: 1 Pulse Input Chan
03: 20 High frequency; Output Hz.
04: 10 Loc [:WS MPH ]
05: .09792 Mult
06: 0.2 Offset
7-5