Probe Interface Circuit for High-Temperature Low-Leakage Measurement
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Solution Overview
Problem
Existing interface units for coupling measuring probes to measuring systems face issues with high temperature resistance, current leakage, and signal distortion, particularly when measuring probes with active voltage sources are exposed to temperatures above 100°C, leading to inaccurate measurements and potential damage.
Innovation Solution
An interface unit with a decoupling circuit using transistors with insulated gates and operational amplifiers to maintain a stable output voltage, reducing current leakage and signal distortion across a wide range of input voltages, and compensating for manufacturing tolerances, while maintaining low residual current through the sensor element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the input stage circuit is switched off or in unpowered state during high temperature process, then energy consumption is reduced, but residual current rises due to low impedance of operational amplifier causing signal drift and sensor damage
Solution Approach 1:
The patent introduces an intermediary circuit between the operational amplifier and the sensor element that acts as a buffer. This intermediary maintains high impedance even when the operational amplifier is in unpowered state, preventing residual current from flowing through the sensor element while allowing the operational amplifier to be switched off for energy savings.
Solution Approach 2:
The input stage circuit is segmented into multiple functional blocks: the operational amplifier, the intermediary buffering circuit, and the sensor interface. This segmentation allows the operational amplifier to be switched off independently while the intermediary circuit maintains the high impedance barrier, separating the energy consumption function from the signal protection function.
2Adaptability or versatility
If the measuring probe is exposed to high temperature above 100°C, then measurement range is extended, but glass resistance decreases drastically causing current leakage and measurement errors
Solution Approach 1:
The patent introduces an intermediary buffering circuit that mediates between the temperature-sensitive sensor element and the operational amplifier. This intermediary maintains a stable high impedance barrier that is not affected by temperature-induced changes in sensor resistance, thereby protecting the measurement precision across extended temperature ranges.
Solution Approach 2:
The patent compensates for temperature-induced parameter changes by introducing an intermediary circuit with fixed electrical characteristics. While the sensor element's resistance changes with temperature, the intermediary circuit maintains constant high impedance, effectively decoupling the measurement system from temperature variations and preserving measurement accuracy.
3Reliability
If electrostatic discharge protection diode is used in operational amplifier, then protection against ESD is improved, but at high temperatures the diode causes short circuits and worsens reliability
Solution Approach 1:
The patent extracts the electrostatic discharge protection function from the operational amplifier by placing it in the intermediary buffering circuit instead. This relocation allows the use of protection diodes in a circuit stage that does not directly contact the temperature-sensitive sensor element, preventing thermal short circuits while maintaining ESD protection capability.
Solution Approach 2:
The intermediary buffering circuit serves as a protective mediator that isolates the operational amplifier's ESD protection diodes from the temperature-sensitive sensor path. The diodes are positioned in the intermediary stage where they can provide ESD protection without being exposed to the high temperature conditions that would cause them to fail and short circuit the sensor element.
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 interface unit effectively transmits accurate measurements with minimal offset voltage and reduced residual current, even at high temperatures, extending the lifespan of measuring probes like solid-state pH sensors and maintaining measurement accuracy across a wide voltage range.
Implementation Method 1
a first transistor (T1) with an insulated gate terminal coupled to the input
Implementation Method 2
In order to amplify the voltage of the measuring signal to a suitable level, it is known to couple the output of the sensing element of the measuring probe to an input stage circuit provided with an operational amplifier
Data Source
AI summary
The present disclosure relates an interface unit having an input for receiving an input voltage from an electrochemical measuring probe; a first transistor; a first operational amplifier; a second transistor; and a second operational amplifier. The first operational amplifier is arranged to provide a variable tension to a first source terminal of the first transistor, in accordance with a comparison between a reference voltage and a second resistor voltage, in order to control an operating point of the first transistor.