Compensation Circuit for Piezo-Resistive Bridge Temperature Error
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Solution Overview
Problem
Existing compensation methods for piezo-resistive bridges are inefficient in reducing span error over a wide temperature range, often wasting power supply voltage and requiring costly micro-controllers or ASICs due to non-linear compensation and limited temperature range.
Innovation Solution
A compensation circuit using a combination of impedance circuits, including amplifiers, diodes, and resistors, that provide non-inverting and inverting input terminals, and negative and positive feedback loops to adjust bridge excitation dynamically with temperature changes, minimizing voltage waste and extending temperature range without the need for micro-controllers or ASICs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resistance is placed in series with the bridge to compensate for temperature-induced resistance variation, then the bridge sensitivity loss is compensated, but about two-thirds of the available power supply voltage is wasted
Solution Approach 1:
The patent changes the resistance value dynamically by using a temperature-dependent resistor (thermistor) whose resistance varies with temperature. This allows the compensation network to adjust the bridge excitation voltage automatically according to temperature changes, achieving temperature compensation without wasting fixed voltage drops across series resistors.
Solution Approach 2:
The patent implements a feedback mechanism where the temperature-dependent resistor senses temperature changes and automatically adjusts the bridge excitation voltage in response. This closed-loop approach ensures that the bridge output remains stable across temperature variations while efficiently utilizing the available power supply voltage.
2Device complexity
If a series resistance compensation method is used to achieve self-compensation, then the compensation is simple, but it is not usable over a wide temperature range because it is non-linear
Solution Approach 1:
The patent employs a temperature-dependent resistor whose resistance parameter changes with temperature in a non-linear fashion that matches the bridge's temperature characteristics. This allows the simple RC compensation network to effectively cover a wide temperature range by dynamically adjusting the compensation amount according to temperature.
Solution Approach 2:
The temperature-dependent resistor automatically adjusts the compensation level based on the ambient temperature without requiring external control or complex circuitry. The component self-regulates the bridge excitation voltage to maintain accurate measurements across the full operating temperature range.
3Adaptability or versatility
If a micro-controller based ASIC is used to provide non-linear signal path for compensation, then compensation over wider temperature range is achieved, but the cost is prohibitive due to DO-178 software certification requirements
Solution Approach 1:
The patent replaces the electronic control system (micro-controller based ASIC requiring software certification) with a passive analog compensation network using temperature-dependent resistors and RC circuits. This analog approach achieves the same temperature compensation function without requiring complex software validation, significantly reducing manufacturing cost and certification complexity.
Solution Approach 2:
The patent uses inexpensive passive components (resistors, capacitors, and a temperature-dependent resistor) instead of expensive micro-controller based ASICs. These simple components achieve the required temperature compensation without the high cost and certification burden of programmable devices.
4Adaptability or versatility
If an ASIC with DO-254 certification is used for compensation, then temperature range coverage is improved, but obsolescence issues arise in the 40 year long life cycles encountered in the aerospace industry
Solution Approach 1:
The patent uses passive analog components with long operational lifetimes instead of programmable ASICs that face obsolescence. The temperature-dependent resistor and passive RC networks have no moving parts, no software to update, and can operate reliably for decades, matching the 40-year lifecycle requirements of aerospace applications.
Solution Approach 2:
The patent replaces programmable electronic systems with timeless analog circuitry that does not suffer from software obsolescence or hardware end-of-life issues. The passive compensation network remains functional throughout the entire product lifecycle without requiring updates or replacements.
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 achieves a more temperature-independent output signal with reduced span error across a broader temperature range, minimizing power waste and avoiding the cost and obsolescence issues associated with micro-controllers or ASICs, while maintaining effective bridge excitation.
Implementation Method 1
the third impedance may include a diode such that exceeding a forward threshold voltage of the diode allows current to flow from the amplifier output node through the positive feedback loop to the bridge output node
Data Source
AI summary
A device for adjusting a signal to a thermally sensitive bridge circuit that may have an impedance coupled to the bridge circuit and an impedance circuit also coupled to the bridge circuit. The impedance circuit may incorporate an amplifier having a non-inverting input coupled to the bridge circuit, a signal adjusting circuit coupled to the output terminal of the amplifier and to the bridge circuit, and an amplifier circuit coupled to the output of the amplifier. The signal adjusting circuit may include a unidirectional current flow mechanism such as a diode.