Campbell Scientific CR10TCR Thermocouple Reference - Manual (Page 6)

CR10TCR THERMOCOUPLE REFERENCE
2
3. INSTALLATION AND WIRING
The wiring diagram for the CR10TCR is shown
in Figure 1. The probe requires a single-ended
analog input channel and an excitation channel.
After the CR10TCR and thermocouple are
connected to the datalogger, install the wiring
panel cover (Figure 2 and 3).
FIGURE 2. Wiring Diagram
FIGURE 3. Wiring Panel, CR10TCR, and
Wiring Panel Cover
FIGURE 4. CR10TCR Installed on the CR10
Wiring Panel
4. PROGRAMMING
Instruction 11 is used to measure the CR10TCR.
Instruction 11 provides AC excitation, makes a
single ended voltage measurement, and
calculates temperature with a fifth order
polynomial. A multiplier of 1.0 and an offset of
0.0 yields temperature in Celsius. For Fahrenheit,
use a multiplier of 1.8 and an offset of 32.
CAUTION: The reference temperature for
thermocouples must be in degrees Celsius.
EXAMPLE 1. Sample CR10 Instructions
01: P11 Temp 107 Probe
01: 1 Rep
02: 1 IN Chan
03: 3 Excite all reps w/EXchan 3
04: 15* Loc [:Ref_Temp]
05: 1 Mult
06: 0 Offset
* Proper entries will vary with program and
input location.
5. INSTRUCTION 11 DETAILS
Understanding the details in this section are not
necessary for general operation of the CR10TCR
with Campbell Scientific's dataloggers.
Instruction 11 outputs a precise 2 VAC excitation and
measures the voltage drop due to the sensor
resistance (Figure 5). The thermistor resistance
changes with temperature. Instruction 11 calculates
the ratio of voltage measured to excitation voltage
(Vs/Vx) which is related to resistance, as shown below:
Vs/Vx = 1000/(Rs+249000+1000)
where Rs is the resistance of the thermistor.
See the measurement section of the datalogger
manual for more information on bridge
measurements.
Instruction 11 then calculates temperature using a
fifth order polynomial equation correlating Vs/Vx with
temperature. The polynomial coefficients are given
in Table 3. The polynomial input is (Vs/Vx)*800.
Resistance and datalogger output at several
temperatures are shown in Table 4.
Black
Red
Clear
FIGURE 5. CR10TCR Reference Temperature
Schematics
Analog
Ground; Clear
Switched
Excitation;
Black (E3)
Single-Ended Input; Red (1H)