Campbell CR10X, Operator'S Manual

Page: 88 / 362

SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES
7-4
7.3 THERMOCOUPLE TEMPERATURES
USING THE OPTIONAL CR10TCR TO
MEASURE THE REFERENCE
TEMPERATURE
The CR10TCR Thermocouple Reference is a
temperature reference for thermocouples
measured with the CR10X Measurement and
Control Module. When installed, the CR10TCR
lies between the two analog input terminal strips
of the CR10X Wiring Panel (see Figure 7.3-1).
The CR10TCR circuitry, measurement, and
specifications are equivalent to Campbell
Scientific's 107 Temperature Probe.
The CR10TCR is connected to single-ended
channel 1 (1H), excitation channel 3 (E3) and
analog ground (AG). It is measured with
Instruction 11 which excites the probe with a
2 VAC excitation, makes a single ended
measurement and calculates temperature (
°
C).
Five differential thermocouples are measured
with Instruction 14.
The temperature (
°
C) of the CR10TCR is stored
in Input Location 1 and the thermocouple
temperatures (
°
C) in Locations 2-6.
PROGRAM
01: Temp (107) (P11)
1:
1 Reps
2: 1 SE Channel
3: 3 Excite all reps w/Exchan 3
4: 1 Loc [ Ref_Temp ]
5: 1 Mult
6: 0 Offset
02: Thermocouple Temp (DIFF) (P14)
1:
5 Reps
2: 21
±
2.5 mV 60 Hz Rejection
Range
3: 2 DIFF Channel
4: 1 Type T (Copper-Constantan)
5: 1 Ref Temp Loc [ Ref_Temp ]
6: 2 Loc [ TC#1 ]
7: 1 Mult
8: 0 Offset
7.4 THERMOCOUPLE TEMPERATURES
USING AN EXTERNAL REFERENCE
JUNCTION
When a number of thermocouple measurements
are made at some distance from the CR10X, it is
often better to use a reference junction box located
at the site rather than use the CR10TCR
Thermocouple Reference. Use of the external
reference junction reduces the required length of
expensive thermocouple wire as regular copper
wire can be used between the junction box (J-box)
and CR10X. In addition, if the temperature
gradient between the J-box and the thermocouple
measurement junction is smaller than the gradient
between the CR10X and the measurement
junction, thermocouple accuracy is improved.
FIGURE 7.4-1. Thermocouples with External Reference Junction