Campbell Scientific CR6 CR6 Measurement and Control System - Page 329
Current Measurements - Details, 1.2.4 Resistance Measurements - Details
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Section 8. Operation • no high-thermal mass element incorporated in the wiring panel. • position of the internal-CR6-temperature thermistor in the wiring panel is not optimal. The absence of these design features causes significant error in the reference junction temperature measurement. If the CR6 must be used for thermocouple measurements, and those measurements must be better than 5 degrees in accuracy, an external reference junction, such as a multiplexer, should be used. In addition, you should carefully evaluate relevant parts of the Thermocouple Measurements section of the CR1000 Datalogger Operator's Manual, which is available at www.campbellsci.com. 8.1.2.3 Current Measurements - Details Reading List: • Current Measurements - Overview (p. 60) • Current Measurements - Details For a complete treatment of current-loop sensors (4 mA to 20 mA, for example), please consult the following publications available at www.campbellsci.com http://www.campbellsci.com: • Current Output Transducers Measured with Campbell Scientific Dataloggers (2MI-B) • CURS100 100 Ohm Current Shunt Terminal Input Module The CR6 is equipped to make resistive-bridge measurements with current excitation. See the section Resistance Measurements - Details (p. 329) for more information. 8.1.2.4 Resistance Measurements - Details See Reading List: • Resistance Measurements - Specifications (p. 93) • Resistance Measurements - Overview (p. 60) • Resistance Measurements - Details (p. 329) By supplying a precise and known voltage to a resistive-bridge circuit and measuring the returning voltage, resistance can be calculated. CRBasic instructions for measuring resistance include: BrHalf() - half-bridge BrHalf3W() - three-wire half-bridge BrHalf4W() - four-wire half-bridge BrFull() - four-wire full-bridge BrFull6W() - six-wire full-bridge Resistance() - current-excitation resistance Read More Available resistive-bridge completion modules are listed in the appendix Signal Conditioners (p. 597). The CR6 has six CRBasic bridge-measurement instructions. Table ResistiveBridge Circuits with Voltage Excitation (p. 330) shows ideal circuits and related equations. In the diagrams, resistors labeled Rs are normally the sensors and those 329