Thermal resistance connection method
heat resistance is the resistance changes of temperature change is converted to electrical component at a time, usually need to get the resistance signal through wire transfer to the computer control device or other instrument on at a time. Industrial heat resistance is installed in production field, and there is a certain distance between control room, so heat resistance of the wire on the measured results will have great influence.
thermal resistance connection methods:
two wire: in the thermal resistance of a wire at each end connection to elicit resistance signal way call two wire: this kind of wire method is very simple, there must be lead resistance r, but because of the connection wire r size and material of the wire and the length of the factors, so this method is only applicable to lead at a lower measuring accuracy
three-wire system: the heat resistance of roots on one end of a wire, the other end connected to the two lead way called three wire system, the way which is equipped with a bridge, can be better to eliminate the influence of the lead resistance, is the most commonly used in industrial process control.
four wire: in the root systems of thermal resistance on both ends of the two wire connection way called four wire, two of the root lead to provide constant current (I) for thermal resistance, the voltage signal into R U, again through the other two root lead to guide U to secondary instrument. Is this way of lead can completely eliminate the resistance of the lead, it is mainly used for high precision temperature detection.
thermal resistance using three wire connection. Using three wire system is to eliminate the measuring error caused by the connection wire resistance. This is because the measuring thermal resistance of circuit is usually unbalanced bridge. Thermal resistance as a bridge bridge arm resistance, its connection wire ( From the thermal resistance is controlled by the) This part also become a part of the bridge arm resistance, resistance is unknown and change with environment temperature, cause measurement error. Using three wire system, will lead a received the power supply end of the bridge, the rest of the two respectively from thermal resistance of bridge arm and adjacent bridge arm, this eliminates the wire line resistance measurement error.
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key words: thermal resistance, thermocouple, thermal resistance, platinum resistance, PT100, PT1000, pressure sensor and digital temperature sensor