6 temperature with calibrated thermocouples – Campbell Scientific CR7 Measurement and Control System User Manual
Page 72
SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES
7-4
PROGRAM
01:
P17
Panel Temperature
01:
1
IN Card
02:
1
Loc [:PANL TEMP]
02:
P13
Thermocouple Temp (SE)
01:
5
Reps
02:
2
5000 uV slow Range
03:
1
IN Card
04:
2
IN Chan
05:
22
Type E (Skip every other chan)
06:
1
Ref Temp Loc PANL TEMP
07:
2
Loc [:S.E. T#1 ]
08:
1
Mult
09:
0
Offset
03:
P14
Thermocouple Temp (DIFF)
01:
5
Reps
02:
1
1500 uV slow Range
03:
1
IN Card
04:
1
IN Chan
05:
12
Type E (Temp difference)
06:
2--
Ref Temp Loc S.E. T#1
07:
7
Loc [:DIFF T #1]
08:
1
Mult
09:
0
Offset
When the temperature of the R junction is
outside of the CR7 reference junction
compensation range (Table 13.4-3), the TCs
must be connected in the normal fashion, one
TC per input channel; both temperatures
measured and one subtracted from the other to
find the difference. This must be done because
any error in the reference junction
compensation becomes an error in the
temperature difference.
7.6 TEMPERATURE WITH CALIBRATED
THERMOCOUPLES
Thermocouple calibration (Section 13.4) results
in a slope correction. The correction must be
applied only to the thermocouple output. When
Instructions 13 and 14 are used to measure
temperature, the temperature is the sum of the
reference temperature and the temperature
difference calculated from the thermocouple
output. The correction must be applied to the
temperature difference before the reference
temperature is added.
Example A demonstrates the use of a scaling
array (Instruction 53) to correct the calibration of
four individually calibrated thermocouples.
Another means of applying a correction factor to
a number of thermocouples is to group together
those with a similar correction factor. In
example B, the slope correction factor for a
group of 5 thermocouples is entered as the
multiplier (Parameter 8) in the instruction to
read those thermocouples. The example only
shows one group of thermocouples. If there
were several groups with similar correction
factors, Instruction 14 would be used to read
and correct each group.
After the slope correction is made, a loop is
used to add the reference temperature to the
corrected temperature differences.
CONNECTIONS
The thermocouples are connected in the normal
manner: chromel to Hi and constantan to Low.
In both examples, the first thermocouple is
connected to Channel 1. Care must be taken
that the correction factors called for in the
programming match the channels that the
calibrated thermocouples are connected to.
PROGRAM A
01:
P17
Panel Temperature
01:
1
IN Card
02:
1
Loc [:REF TEMP ]
02:
P14
Thermocouple Temp (DIFF)
01:
4
Reps
02:
3
15 mV slow Range
03:
1
IN Card
04:
1
IN Chan
05:
12
Type E (Temp difference)
06:
1
Ref Temp Loc REF TEMP
07:
2
Loc [:TC temp#1]
08:
1
Mult
09:
0
Offset
03:
P53
Scaling Array (A*loc +B)
01:
2
Start Loc [:TC temp#1]
02:
.99255 A1
03:
0
B1
04:
.99703 A2
05:
0
B2
06:
1.0045
A3
07:
0
B3
08:
1.0075
A4
09:
0
B4