Thermocouple Input Unit Voltage Drop Correction
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Solution Overview
Problem
Existing temperature measurement methods using thermocouples with compensating wires require complex preparations and costly circuit structures to correct measurement errors caused by wire resistance, involving pre-measurement of resistance values and use of alternating current for disconnection detection.
Innovation Solution
A temperature input unit with disconnection detection means, a thermocouple detection circuit, a temperature measurement resistor detection circuit, and a connection switch to calculate and correct thermoelectromotive force errors by predicting voltage drops from wire resistance, allowing for simplified temperature measurement without pre-measuring resistance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a direct current is fed to the thermocouple and compensating wire for disconnection detection, then disconnection can be detected, but a voltage drop error occurs in the measured thermoelectromotive force
Solution Approach 1:
The patent applies periodic action by using alternating current instead of direct current for disconnection detection. The alternating current periodically flows through the compensating wire, allowing detection of disconnection through changes in current characteristics while minimizing continuous voltage drop that would affect thermoelectromotive force measurement accuracy.
Solution Approach 2:
The patent applies preliminary action by measuring the resistance value of the compensating wire before temperature measurement. This pre-measurement allows the system to calculate and compensate for voltage drop errors in advance, improving the accuracy of subsequent thermoelectromotive force measurements without affecting the actual temperature measurement process.
2Measurement precision
If the resistance value of the compensating wire is pre-measured and used to correct the thermoelectromotive force, then measurement accuracy is improved, but complicated user preparations are required
Solution Approach 1:
The patent applies self-service by enabling the system to automatically measure the resistance value of the compensating wire and perform error correction without requiring user intervention. The control unit automatically executes the correction process using the measured resistance value, eliminating the need for users to manually measure resistance or perform complex preparation steps.
Solution Approach 2:
The patent applies preliminary action by automatically performing resistance measurement and error correction calculations before the actual temperature measurement. This pre-processing of correction data simplifies the user operation while maintaining high measurement accuracy.
3Measurement precision
If alternating current is used for disconnection detection as described in Patent Literature 1, then thermoelectromotive force measurement error is avoided, but the circuit structure becomes complex and costly
Solution Approach 1:
The patent applies universality by making the compensating wire serve multiple functions: it acts as both a temperature compensation element and a disconnection detection conductor. By measuring the resistance of this multi-functional wire and using it for error correction, the patent avoids adding separate alternating current detection circuits, thereby simplifying the overall circuit structure while maintaining measurement precision.
Solution Approach 2:
The patent applies parameter changes by utilizing the resistance parameter of the compensating wire for error correction purposes. By measuring and compensating based on resistance values, the system achieves accurate temperature measurement without requiring complex alternating current circuitry, thus reducing device complexity while maintaining precision.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables accurate temperature measurement correction without complex user preparations and costly circuit modifications, eliminating the need for pre-measuring compensating wire resistance and using alternating currents, thus simplifying the measurement process.
Implementation Method 1
A temperature sensor including a thermocouple measures temperature based on a thermoelectromotive force generated in the thermocouple that changes in accordance with temperature changes
Implementation Method 2
The compensating wire is a conductive wire connecting the thermocouple and the measuring device
Implementation Method 3
feeding a weak direct current to the thermocouple and the compensating wire causes a voltage drop resulting from the resistance in the compensating wire
Data Source
AI summary
A temperature input unit includes a disconnection detection circuit that measures a temperature of a measurement target with at least one of a thermocouple or a temperature measurement resistor and feeds a disconnection detection current for disconnection detection to the thermocouple and a compensating wire connected to the thermocouple. A controller controls, before measuring the temperature of the measurement target with the thermocouple, a terminal switch and an input circuit switch to connect the compensating wire to a temperature measurement resistor input circuit and an A/D converter, and calculates a predicted value of a voltage drop resulting from resistance of the compensating wire occurring in response to the disconnection detection current. The controller controls the terminal switch and the input circuit switch to connect the compensating wire to a thermocouple input circuit and the A/D converter, and subtracts the predicted value from a measured value of the thermoelectromotive force detected by the thermocouple input circuit to calculate a corrected measured value of the thermoelectromotive force.