Campbell Scientific CR10X Measurement and Control System - Manual (Page 119)

SECTION 8. PROCESSING AND PROGRAM CONTROL EXAMPLES
8-11
8.10 COVARIANCE CORRELATION
PROGRAMMING EXAMPLE
The example is a 2 level meteorological tower
with 5 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 5 minute subinterval
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
(COV/CORR) Instruction. Table 8.10-1 groups
the sensors according to measurement type and
gives the CR10X multiplier and offset.
The props can all be measured as single-ended
voltages. 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.
An AM25T Solid State Thermocouple Multiplexer is
used to measure the four Type E thermocouples.
The AM25T has a built in 1000 ohm PRT that is
used as a reference temperature for the
thermocouples. The thermocouples are measured
on the most sensitive input range, 2.5 mV,
accommodating a
± 40 o C range between the
measurement and AM25T TC reference junction.
The resolution is (.33 µV/(60 µV/
o C) or about
0.006 o C. Measuring absolute temperature with TCs
requires a reference junction temperature
measurement. The reference PRT is measured with
Instruction 6. Temperature is computed with
Instructions 59 and 16.
The specified outputs determine the input order
required by the COV/CORR Instruction. Table 8.10-2
lists the desired outputs from the two levels along with
the Input Storage locations for the processed results.
TABLE 8.10-1. Example Sensor Description and CR10X 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 - - - -
TABLE 8.10-2. Example Outputs and Input Storage Locations
LEVEL 1 OUTPUTS
MEANS LOC VARIANCES LOC COVARIANCES LOC CORRELATIONS LOC
M(W1) 20 V(W1) 25 CV(W1,U1) 30 CR(W1,U1) 34
M(U1) 21 V(U1) 26 CV(W1,V1) 31 CR(W1,V1) 35
M(V1) 22 V(V1) 27 CV(W1,Tal) 32
M(Tal) 23 V(Tal) 28 CV(W1,e1) 33
M(e1) 24 V(e1) 29
LEVEL 2 OUTPUTS
MEANS LOC VARIANCES LOC COVARIANCES LOC
M(W2) 36 V(W2) 41 CV(W2,U2) 46
M(U2) 37 V(U2) 42 CV(W2,V2) 47
M(V2) 38 V(V2) 43 CV(W2,Ta2) 48
M(Ta2) 39 V(Ta2) 44 CV(W2,e2) 49
M(e2) 40 V(e2) 45 CV(U2,V2) 50
CV(U2,Ta2) 51
CV(U2,e2) 52
CV(V2,Ta2) 53
CV(V2,e2) 54