Campbell Scientific CR10X CR10X Measurement and Control System - Page 88
Thermocouple Temperatures, Using The Optional Cr10tcr To, Measure The Reference, Temperature, Using
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SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES 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 7-4