Wheatstone Bridge Sensor Self-Testing for Web Tension
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Solution Overview
Problem
Existing web tension measurement systems fail to detect failures in strain gauges, leading to nonsensical values that can result in web tearing or overstretching, posing safety risks in web tension regulation, especially in paper machines.
Innovation Solution
A method using a Wheatstone bridge with force sensors that includes a loading test to detect failures by comparing tensile stress signals with and without loading, outputting an error signal to prevent damage, and ensuring only functional measurements are passed to downstream components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If strain gauges are used to measure web tension, then measurement capability is provided, but sensor failure leads to nonsensical values causing web tearing or overstretching
Solution Approach 1:
The patent applies preliminary action by performing a functional test of the strain gauge before it is used for actual measurement. The test involves applying a known test force to the sensor and checking whether the expected output signal is generated. This preliminary verification ensures the sensor is functioning correctly before any web tension measurement occurs, preventing failures from causing web tearing or overstretching.
Solution Approach 2:
The patent implements feedback by continuously monitoring the sensor output and comparing it against expected values. When the sensor is used for measurement, the system checks whether the output signal corresponds to a physically plausible tensile force. If the sensor produces nonsensical values, the system detects this anomaly and triggers an alarm, preventing incorrect measurements from causing web damage.
2Reliability
If strain gauges are used to measure web tension, then measurement capability is provided, but failure detection is not possible without additional testing components
Solution Approach 1:
The patent applies universality by designing the test force application mechanism to serve dual purposes: it can apply test forces during calibration and functional testing, and it can also serve as part of the normal measurement system. The same mechanical components used for measurement (bending bars, force sensors) are also used for testing, eliminating the need for separate dedicated test equipment and reducing overall system complexity.
Solution Approach 2:
The patent implements self-service by enabling the sensor to test itself through the functional test procedure. The strain gauge is subjected to a controlled test force and its own output signal is evaluated to determine its functionality. This self-testing capability eliminates the need for external complex testing equipment and allows the sensor to verify its own operational status independently.
3Reliability
If functional test is performed continuously, then sensor failure is detected in real-time, but measurement cycles are interrupted for testing
Solution Approach 1:
The patent applies periodic action by implementing functional tests at regular intervals rather than continuously. The system performs measurement cycles followed by periodic functional tests, allowing both continuous productivity and reliable failure detection. The test frequency can be adjusted based on operational requirements, ensuring sensors are tested sufficiently often to detect failures while minimizing interruptions to normal measurement operations.
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 method effectively detects sensor failures in real-time, preventing damage by isolating faulty measurements and ensuring safe operation of web tension regulation systems.
Implementation Method 1
Force sensors (7) which are preferably formed by strain gauges are fitted to the double bending bars (5). These strain gauges are connected in the form of a Wheatstone bridge in order to achieve the lowest possible temperature dependence and drift of the sensor.
Implementation Method 2
The diagonal voltage of the Wheatstone bridge is amplified by an amplifier which mainly has the task of keeping resistive loads, which could corrupt the measurement result, away from the Wheatstone bridge. In addition, the amplifier may also amplify the voltage in order to bring the measurement signal to a voltage range which can be easily processed.
Data Source
AI summary
In a method for measuring the tensile stress of a running web, force sensors (7) are connected in the form of a Wheatstone bridge (11). An amplifier (18) amplifies a diagonal voltage (17) of the Wheatstone bridge (11). In order to be able to detect whether at least one of the force sensors (7) is defective, the Wheatstone bridge (11) can be loaded using at least one resistor (26) by means of at least one switch (24, 25). Comparing the measured values, with loading, with the measured values, without loading, determines whether the force sensors (7) of the Wheatstone bridge (11) are functional. Otherwise, an active error signal (28) is output.