Campbell Scientific CR7 Measurement and Control System - Manual (Page 88)

SECTION 8. PROCESSING AND PROGRAM CONTROL EXAMPLES
8-6
09: P91 If Flag
01: 11 1 is set
02: 30 Then Do
10: P34 Z=X+F
01: 3 X Loc 0-540 WD
02: 360 F
03: 3 Z Loc [:0-540 WD ]
11: P95 End
12: P95 End
13: P95 End
14: P End Table 3
8.6 COVARIANCE CORRELATION
PROGRAMMING EXAMPLE
The example is a two level meteorological tower
with five sensors at each level. The three
components of the wind are measured using
prop anemometers. Two thermocouples (TC)
are used to measure ambient and wet-bulb
temperatures and calculate water vapor
pressure on-line. All sensors are scanned once
per second (1 Hz) and a five minute averaging
period with a 30 minute Output Interval is
specified. The example optimizes the input
measurement sequence for speed and shows
the instructions necessary to provide calibrated
inputs, properly ordered to produce the desired
outputs from the Covariance Correlation
(CV/CR) Instruction. Table 8.7-1 groups the
sensors according to measurement type and
gives the CR7 multiplier and offset.
The props can all be measured as single-ended
voltages, but the vertical wind prop calibration
differs from the U and V prop calibration. The
fastest input sequence is to measure both
levels (6 props) with a single instruction using
the U and V calibration and correct the W
measurements with the Fixed Multiply,
Instruction 37.
The type E thermocouples are measured on the
most sensitive input range, 5mV,
accommodating a ±80
o C range between the
measurement and CR7 reference junction. The
resolution is (.33µV/(60µV/
o C) or about 0.006
o C. Measuring absolute temperature with TCs
requires a reference junction temperature
measurement. This is measured with
Instruction 17.
The specified outputs determine the input order
required by the CV/CR Instruction. Table 8.6-2
lists the desired outputs from the two levels
along with the Input Storage locations for the
processed results.
TABLE 8.6-1. Example Sensor Description and CR7 Multiplier and Offset
DESCRIPTION SYMBOL SENSOR CALIB MEAS TYPE MULT OFFSET
Horiz. Wind U prop 18m/s/V S.E.V. .018m/s/mV 0.0
Horiz. Wind V prop 18m/s/V S.E.V. .018 0.0
Vert. Wind W prop 22m/s/V S.E.V. .022 0.0
Air Temp. Ta TC - TC DIFF. 1.0
o
C 0.0
Wet-bulb Temp. Tw TC - TC DIFF. 1.0
o
C 0.0
Vap. Pressure e derived - - - -