Valve Actuator Torque Measurement via AC Phase Shift
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Solution Overview
Problem
Measuring torque produced by alternating current (AC) motors in valve actuators is challenging due to the lack of significant change in AC current with increasing torque, making it difficult to derive torque from current measurements, and existing mechanical and electrical sensors are complex and costly.
Innovation Solution
Measuring the time interval between the first zero crossing of the AC voltage waveform and the second zero crossing of the AC current waveform to determine the phase shift, which correlates with the torque produced by the AC motor, using a microcontroller and torque measurement component in a valve actuator system.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mechanical-based sensors (strain gauges, brackets) are used to measure torque, then torque measurement capability is achieved, but weight and cost of the actuator increase
Solution Approach 1:
The patent replaces mechanical-based torque sensors (strain gauges, brackets) with an electrical measurement system that uses a current sensor to detect the phase shift between voltage and current waveforms. This substitution eliminates the need for mechanical components, thereby reducing actuator weight while maintaining torque measurement capability.
Solution Approach 2:
The patent introduces an electrical intermediary (current sensor and phase shift measurement system) to indirectly measure torque. Instead of directly measuring mechanical torque with physical sensors, the system measures the electrical current phase shift, which correlates with torque output. This intermediary approach avoids the weight penalty of direct mechanical sensors.
2Measurement precision
If mechanical-based sensors (strain gauges, brackets) are used to measure torque, then torque measurement capability is achieved, but cost of the actuator increases
Solution Approach 1:
The patent replaces expensive mechanical torque sensors with a more cost-effective electrical measurement system. The current sensor and phase shift measurement circuitry are less costly than mechanical strain gauges and brackets, reducing the overall actuator cost while maintaining measurement precision.
Solution Approach 2:
The patent uses electrical signals as a copy or representation of mechanical torque. By measuring the phase shift in current waveform, which correlates with torque, the system creates an electrical copy of the mechanical state without requiring physical mechanical sensors. This approach reduces manufacturing complexity and cost.
3Measurement precision
If conventional electrical sensors are used to monitor torque, then torque measurement capability is achieved, but design complexity increases making the system difficult and costly to manufacture
Solution Approach 1:
The patent makes the current sensor serve multiple functions: it is used for both motor control and torque measurement. By utilizing the same current sensor for both purposes, the system eliminates the need for separate torque sensing circuitry, thereby reducing design complexity while maintaining torque measurement capability.
Solution Approach 2:
The patent merges the torque measurement function with the existing motor control system. The phase shift measurement is integrated into the control circuitry, combining multiple functions into a unified system. This merging reduces the number of separate components and simplifies the overall design.
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 method allows for accurate torque measurement, verifying the valve's closed position, facilitating preventative maintenance, and ensuring safe operation by confirming a fluid-tight seal, while reducing system complexity and manufacturing costs compared to traditional sensor-based systems.
Implementation Method 1
Some valve actuators, such as those that are implemented in marine environments like ocean liners and military ships, use one or more alternating current (AC) motors as the drive mechanism for operating the associated valve.
Implementation Method 2
The torque may be determined by measuring a time interval related to a phase shift between the waveform of the AC voltage applied to the AC motor and the waveform of the AC current drawn by the AC motor.
Data Source
AI summary
Disclosed is a valve actuator configured to determine, during operation of a valve by an alternating current (AC) motor of the valve actuator, an amount of torque produced by the AC motor. A process for measuring the amount of torque produced by the AC motor includes actuating a valve using the AC motor of the valve actuator, measuring, by a microcontroller of the valve actuator and during the actuating of the valve, a time interval between: (i) a first zero crossing of a waveform of AC voltage applied to the AC motor, and (ii) a second zero crossing of a waveform of AC current drawn by the AC motor, and determining, based on the time interval, an amount of torque produced by the AC motor during the actuating.