SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES

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 RH 207 Probe

01:

3

Reps

02:

4

IN Chan

03:1 Excite all reps w/EXchan 1

04:1 Temperature Loc 107 T #1

05:

4

Loc [:RH #1 ]

06:

1

Mult

07:

0

Offset

7.7ANEMOMETER 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

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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FIGURE 7.7-1. Wiring Diagram for Anemometer

7-5