Campbell Scientific CR7 Measurement and Control System - Manual (Page 96)

SECTION 9. INPUT/OUTPUT INSTRUCTIONS
9-6
The temperature value used in
compensating the RH value (Parameter 7)
must be obtained (see Instruction 11) prior
to executing Instruction 12.
The RH results are placed sequentially into the
input locations beginning with the first RH value.
In some situations the RH sensors might be
deployed such that only small temperature
variations exist within a given set of probes. In
these cases a single temperature may be used
to compensate the subset of RH measurements
instead of making a temperature measurement
for each RH probe. If the complete set of
temperature values are not needed, this
approach uses less input channels. Parameter
6 is used to specify how many consecutive RH
values get compensated per temperature
measurement.
In the 207 probe, the RH and temperature
elements use a common excitation line. Since
a single excitation channel can drive several
hundred probes, there is no
"measurements/excitation" parameter in
Instruction 12. NEVER EXCITE THE 207
PROBE WITH DC EXCITATION as the RH chip
will be damaged.
The maximum RH polynomial error is given
below:
Curve Fit Error --
Range (%RH) Error (%RH)
10 - 100 ±4
15 - 94 ±1
PAR. DATA
NO. TYPE DESCRIPTION
01: 2 Repetitions
02: 2 Analog card number for first
measurement
03: 2 Single-ended channel for first
measurement
04: 2 Excitation card number for
first measurement
05: 2 Excitation channel number
for first measurement
06: 2 Number of R.H.
measurements per
compensating temperature
measurement
07: 4 Input location for first
compensating temperature
measurement
08: 4 Input location for first
measurement
09: FP Multiplier
10: FP Offset
Input locations altered: 1 per repetition
*** 13 THERMOCOUPLE ***
TEMPERATURE, SINGLE ENDED
FUNCTION
This Instruction uses the selected thermocouple
calibration to calculate the thermocouple output
voltage at the reference temperature, then it
makes a SINGLE ENDED VOLTAGE
MEASUREMENT (Section 13.2) on the
thermocouple and adds the measured voltage
to the calculated reference voltage, then
converts the voltage to temperature in oC
(Section 13.4).
Table 9-3 gives the thermocouple type codes.
The reference temperature location will be
incremented by one each repetition if C is keyed
before entering Parameter 6. When this option
is exercised, two minus signs (--) will appear as
the right most characters of the display.
A multiplier of 1 and an offset of 0 yields
temperature in degrees C.
TABLE 9-3. Thermocouple Type Codes
Code Thermocouple Type
1 T (copper - constantan)
2 E (chromel - constantan)
3 K (chromel - alumel)
4 J (iron - constantan)
5 B (platinum - rhodium)
6 R (platinum - rhodium)
7 S (platinum - rhodium)
1X Output temperature difference between
Reference and Thermocouple
2X Skip every other single ended channel
8X TC input from A5B40 Isolation Amplifier
(use 5 V range)