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SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES
7-4
FIGURE 7.4-1. Thermocouples with External Reference Junction
In the following example, an external temperature
measurement is used as the reference for 5
thermocouple measurements. A Campbell
Scientific 107 Temperature Probe is used to
measure the reference temperature. The
connection scheme is shown in Figure 7.4-1.
If a more accurate reference temperature is
needed, Campbell Scientific's TCR6 utilizes a
100 ohm PRT to measure the reference
temperature and provides better insulation for a
more isothermal reference.
The temperature (°C) of the 107 Probe is stored
in Input Location 1 and the thermocouple
temperatures (°C) in Locations 2-6.
PROGRAM
01: P11 Temp 107 Probe
01: 1 Rep
02: 11 IN Chan
03: 1 Excite all reps w/EXchan 1
04: 1 Loc [:REF TEMP ]
05: 1 Mult
06: 0 Offset
02: P14 Thermocouple Temp (DIFF)
01: 5 Reps
02: 22 7.5 mV 60 Hz rejection Range
03: 1 IN Chan
04: 1 Type T (Copper-
Constantan)
05: 1 Ref Temp Loc REF TEMP
06: 2 Loc [:TC #1 ]
07: 1 Mult
08: 0 Offset
7.5 107 TEMPERATURE PROBE
Instruction 11 excites Campbell Scientific's 107
Thermistor Probe (or the thermistor portion of the 207
temperature and relative humidity probe) with a 2 VAC
excitation, makes a single ended measurement and
calculates temperature (°C) with a fifth order
polynomial. In this example, the temperatures are
obtained from three 107 probes. The measurements
are made on single-ended channels 1-3 and the
temperatures are stored in Input Locations 1-3.
CONNECTIONS
The black leads from the probes go to
excitation channel 1, the purple leads go to
analog ground (AG), the clear leads go to
ground (G), and the red leads go to single-
ended channels 1, 2, and 3 (channel 1H,
channel 1L, and channel 2H, respectively).
PROGRAM
01: P11 Temp 107 Probe
01: 3 Reps
02: 1 IN Chan
03: 1 Excite all reps w/EXchan 1
04: 1 Loc [:107 T #1 ]
05: 1 Mult
06: 0 Offset
7.6 207 TEMPERATURE AND RH
PROBE
Instruction 12 excites and measures the RH
portion of the Campbell Scientific 207
Temperature and Relative Humidity probe.
This instruction relies on a previously measured
temperature (°C) to compute RH from the probe
resistance. Instruction 11 is used to obtain the