Variable Amplitude Sensor Excitation for Process Measurement
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Solution Overview
Problem
Current process measurement systems face limitations in resolution and noise rejection due to fixed excitation voltage in analog-to-digital converters, which results in sub-optimal signal strength, especially at zero or near-zero differential pressure conditions.
Innovation Solution
Implementing a variable amplitude excitation scheme for capacitance sensors, where the excitation voltage is increased at zero differential pressure and reduced at full-scale pressure to maintain a constant signal charge, thereby maximizing signal-to-noise ratio across the entire operating range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fixed excitation voltage is used in analog-to-digital converter, then device complexity is reduced, but measurement precision deteriorates at zero or near-zero differential pressure conditions
Solution Approach 1:
The excitation voltage is made dynamic rather than fixed. The control circuit adjusts the excitation voltage amplitude based on the sensor signal level, increasing excitation at zero or near-zero differential pressure conditions to maximize signal strength and resolution, while reducing excitation at full-scale conditions to maintain consistent signal charge.
Solution Approach 2:
The excitation voltage parameter is changed dynamically based on operating conditions. The system monitors the sensor signal and adjusts the excitation voltage amplitude accordingly, changing from a fixed parameter to a variable parameter that adapts to different differential pressure conditions to optimize measurement precision.
2Measurement precision
If fixed excitation voltage is used, then ease of operation is improved, but noise rejection capability deteriorates
Solution Approach 1:
A feedback mechanism is implemented where the control circuit monitors the sensor signal from the analog-to-digital converter and uses this information to adjust the excitation voltage. This closed-loop feedback allows the system to automatically optimize signal strength and noise rejection without requiring manual intervention, maintaining ease of operation while improving measurement precision.
Solution Approach 2:
The system performs self-optimization by automatically adjusting its own excitation voltage based on the sensor signal conditions. The control circuit autonomously determines when to increase or decrease excitation voltage to maximize signal-to-noise ratio, allowing the system to service itself without external control while improving noise rejection capability.
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 approach enhances the resolution and noise rejection capabilities of the measurement system by optimizing signal strength and maintaining a consistent signal charge, even at low sensor capacitance values, leading to improved performance and precision.
Implementation Method 1
This transmitter employs a capacitive sensor having a deflectable sensing diaphragm and three or more capacitor electrodes which form separate capacitive sensing elements with the diaphragm
Implementation Method 2
The basic function of the CD modulator is to convert the capacitance ratio into a PDM (pulse density modulation) signal. For a CD modulator using sigma-delta architecture, the actual process involves converting a charge ratio into a PDM signal
Data Source
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AI summary
A process measurement system (30) includes a sensor (32) for producing a sensor signal as a function of a process parameter and a measurement circuit (34) that converts the sensor signal to measurement data. A control circuit (34) controls the amplitude of the sensor excitation to maximize signal strength over the entire operating ratio range of the sensor (32). This enhances resolution and noise rejection of the measurement circuit (34).