Campbell Scientific CR6 CR6 Measurement and Control System - Page 328
Thermocouple Measurements
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Section 8. Operation For a VoltSe() instruction, B is determined as part of self-calibration only if the parameter MeasOff = 0. An exception is B for VoltSe() on the ±5000 input range with fN1 (p. 496) = 15000, which is always determined in self-calibration for use internally. For a VoltDiff() instruction, B is determined as part of self-calibration only if the parameter RevDiff = 0. VoltSe() and VoltDiff() instructions, on a given input range with the same integration durations, use the same G values but different B values. The three input-voltage ranges (±5000 mV, ±1000 mV, and ±200 mV), in combination with the three most common fN1 (p. 496) settings (15000, 50, and 60) result in a maximum of 9 different gains (G), and 9 offsets for VoltSe() measurements (B), and 9 offsets for VoltDiff() measurements (B) to be determined during CR6 selfcalibration (maximum of 27 values). These values can be viewed in the Status table, with entries identified as listed in table Status Table Calibration Entries. Automatic self-calibration can be overridden with the Calibrate() instruction, which forces a calibration for each execution, and does not employ low-pass filtering on the newly determined G and B values. The Calibrate() instruction has two parameters: CalRange and Dest. CalRange determines whether to calibrate only the necessary input ranges for a given CRBasic program (CalRange = 0) or to calibrate all input ranges (CalRange ≠ 0). The Dest parameter should be of sufficient dimension for all returned G and B values, which is a minimum of two for the automatic self-calibration of VoltSE() including B (offset) for the ±5000 mV input range with first 15000 fN1, and a maximum of 27 for all inputvoltage ranges used and key fN1 (p. 496) values selected by the operating system. An example use of the Calibrate() instruction programmed to calibrate all input ranges is given in the following CRBasic code snip: 'Calibrate(Dest,Range) Calibrate(cal(1),true) where Dest is an array of 27 variables, and Range ≠ 0 to calibrate all input ranges. Results of this command are listed in the table Calibrate() Instruction Results. Table 70. Status Table Calibration Entries A table of calibration values is not yet available for the CR6 Table 71. Calibrate() Instruction Results A table of calibration values is not yet available for the CR6 8.1.2.2 Thermocouple Measurements Thermocouple measurements are special case voltage measurements. Thermocouples are easy to use with the CR6. They are also inexpensive. However, despite the use of a thermocouple in the Quickstart Tutorial (p. 35), the CR6 is not designed for accurate thermocouple measurement when thermocouples are attached directly to the wiring panel. CR6 design features that cause thermocouple measurement inaccuracy include: • lack of an insulating wiring-terminal cover. 328