4 anemometer with photochopper output – Campbell Scientific CR510 Basic Datalogger User Manual
Page 81
SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES
7-3
02:
Do (P86)
1: 41
Set Port 1 High
03:
Excitation with Delay (P22)
1:
2
Ex Channel
2:
0
Delay w/Ex (units = 0.01 sec)
3: 15
Delay after Ex (units = 0.01
sec)
4:
0
mV Excitation
04:
Volts (SE) (P1)
1:
1
Reps
2:
5
2500 mV Slow Range
3:
2
SE Channel
4:
2
Loc [ RH ]
5:
.1
Mult
6:
0
Offset
05:
Do (P86)
1: 51
Set Port 1 Low
7.4 ANEMOMETER WITH
PHOTOCHOPPER OUTPUT
An anemometer with a photochopper
transducer produces a pulse output which is
measured by the CR510's Pulse Count
Instruction. The Pulse Count Instruction with a
Configuration Code of 20, measures "high
frequency pulses", "discards data from
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 CR510 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
∗
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:
Pulse (P3)
1:
1
Reps
2:
1
Pulse Input Channel
3: 20
High Frequency, Output Hz
4: 10
Loc [ WS_mph ]
5:
.09792 Mult
6:
.2
Offset
CR510
FIGURE 7.4-1. Wiring Diagram for Anemometer