Campbell Scientific CR10XTCR Thermocouple Reference - Manual (Page 8)

CR10XTCR Thermocouple Reference
4
EXAMPLE 1. Sample CR10X Instructions
01: Temp 107 Probe (P11)
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 CR10XTCR 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. CR10XTCR Reference Temperature Schematics