Sheathed Sensor Error Compensation Circuit
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Solution Overview
Problem
Existing sensors, such as thermocouples and RTD elements, are prone to measurement errors due to changes in isolation resistance and parasitic lead-to-ground voltage, which are not effectively addressed by current methods that require separate connections to the protective sheath and do not compensate for resistance between the sheath and effective ground.
Innovation Solution
A circuit with a voltage measurement and correction measurement system that calculates and compensates for measurement errors by switching between reference voltages and measuring currents, allowing for error calculation and correction without direct insulation resistance measurement, and also accounts for resistance between the sheath and actual electric ground.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate connection to the protective sheath is used to measure insulation resistance, then the insulation resistance can be tested, but the resistance between the sheath and effective ground cannot be compensated for
Solution Approach 1:
The patent introduces a virtual ground node as an intermediary that allows the measurement system to account for the potential difference between the protective sheath and effective ground. By routing measurement currents through this virtual ground and calculating the associated voltage drops, the system compensates for ground potential differences without requiring a direct physical connection to the sheath for ground reference.
Solution Approach 2:
The measurement circuit is designed to perform multiple functions using the same connection structure. The two-wire connection serves both as the sensor signal path and as the path for injecting measurement currents to determine both insulation resistance and ground potential differences. This multi-functional approach eliminates the need for separate connections while maintaining measurement accuracy.
2Object-affected harmful factors
If the sensor is embedded in a sheath with insulation resistance, then electrical isolation is provided, but leakage current occurs when isolation resistance is too low
Solution Approach 1:
The system continuously monitors the insulation resistance by injecting measurement currents and measuring the resulting voltages. This feedback information is used to calculate and compensate for leakage currents in real-time, allowing the system to maintain measurement accuracy even when the insulation resistance varies or becomes relatively low.
Solution Approach 2:
The patent converts the harmful effect of finite insulation resistance into a measurable parameter. By intentionally injecting measurement currents through the insulation path and measuring the resulting voltages, the system transforms the leakage current from an unaccounted error source into a quantifiable value that can be compensated for in the final measurement.
3Reliability
If the sheath is at a different electric potential than ground, then a voltage difference exists, but leakage current influences the sensor measurement
Solution Approach 1:
The virtual ground node serves as an intermediary reference that captures the potential difference between the sheath and effective ground. By using this virtual ground as the reference for voltage measurements, the system automatically compensates for ground potential differences without requiring the measurement leads to be at the same potential as the effective ground.
Solution Approach 2:
The system dynamically calculates and adjusts for the ground potential difference parameter based on measured currents and known resistances. By changing the reference parameter from fixed ground to a dynamically determined virtual ground potential, the system maintains measurement precision despite varying sheath potentials.
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
This solution enables accurate compensation for measurement errors caused by insulation resistance and parasitic lead-to-ground voltage, improving the reliability of sensor readings by calculating error values and correcting sensor readouts without the need for direct insulation resistance measurement.
Implementation Method 1
a voltage measurement circuit for measuring a voltage difference between the first terminal and the second terminal
Implementation Method 2
a correction measurement circuit for measuring a current running from the first terminal through the switching unit
Implementation Method 3
a switching unit for controllably switching an electrical connection between a first state and a second state in which the first terminal is electrically connected to respectively a first reference voltage and a second reference voltage
Data Source
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AI summary
The present invention relates to a circuit (1) for determining and/or compensating for a measurement error of a sheathed sensor due to a property of a sheath of that sheathed sensor. The circuit comprises a first and second terminal (2,3) for connecting to a pair of sensor signal leads (12,13) of a sensor element (11) in a sheathed sensor (10) and a voltage measurement circuit (4) for generating a measurement signal indicative of a measured voltage difference (Vd) between the terminals (2,3). The circuit comprises a switching unit (5) for controllably switching an electrical connection between a first and a second state (S1, S2) in which the first terminal (2) is respectively connected to a first and a second reference voltage (V1, V2). The circuit comprises a correction measurement circuit (6) for generating a correction signal indicative of that a measured current (I) running from the first terminal (2) through the switching unit (5). The circuit comprises a controller (7) for receiving the measurement and correction signal in both the first and second state. The controller is adapted for calculating an error value indicative of the measurement error and/or a sensor readout value that is corrected for the measurement error by taking the measurement and correction signal into account as obtained in both the first and second state.