Gas Sensor Impedance Detection Circuit Using Hold Capacitor Noise Filtering
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Solution Overview
Problem
Conventional detection devices for sensor elements in gas sensors face accuracy issues due to noise interference, particularly heater noise, which complicates the detection of element impedance and requires complex configurations to avoid incorrect detection.
Innovation Solution
A detection device that uses an alternating current signal to update a hold value in a hold capacitor, limiting noise influence by comparing impedance response signals with a constant current circuit and discharging at a slower rate than charging, allowing for accurate impedance detection while minimizing noise impact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a low pass filter is placed before the hold circuit to eliminate noise, then noise elimination is improved, but the response speed of impedance detection deteriorates because the filter delays the voltage changed value
Solution Approach 1:
The invention extracts and eliminates only the noise component from the detection signal while preserving the essential impedance information. By using a hold circuit that compares the current detection signal with the held value and only updates when significant changes occur, the system removes noise without requiring aggressive filtering that would slow down the response.
Solution Approach 2:
The hold circuit dynamically adjusts its behavior based on the relationship between the current detection signal and the held value. When the signal changes significantly (indicating real impedance change), the hold circuit updates; when changes are minor (indicating noise), it maintains the held value. This dynamic approach allows fast response to real changes while filtering out noise.
2Object-affected harmful factors
If the timing of impedance detection is shifted to avoid heater noise, then noise elimination is improved, but device complexity increases due to required timing control circuits
Solution Approach 1:
The hold circuit automatically handles noise rejection without requiring external timing control. By continuously holding and comparing the detection signal, the circuit self-adjusts to ignore transient noise events (such as heater switching) while capturing genuine impedance changes. This eliminates the need for complex timing synchronization circuits.
Solution Approach 2:
The hold circuit provides continuous feedback by comparing the current detection signal with the held value. This feedback mechanism automatically compensates for noise interference without requiring predetermined timing adjustments, simplifying the overall system architecture while maintaining noise rejection capability.
3Measurement precision
If the hold circuit updates the hold value continuously, then measurement precision is improved, but noise influence increases causing incorrect detection
Solution Approach 1:
The hold circuit performs partial updates rather than continuous updates. It only updates the hold value when the detection signal significantly exceeds the held value, applying just enough action to capture real impedance changes while avoiding excessive updates that would incorporate noise into the measurement.
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 configuration enhances detection accuracy by effectively eliminating noise and simplifying the detection process, allowing for precise measurement of element impedance in gas sensors without the need for complex timing controls.
Implementation Method 1
detecting an element impedance of a sensor element on the basis of one of a current and a voltage of an impedance response signal which is alternately changed in response to an alternating current signal supplied to the sensor element
Implementation Method 2
a hold capacitor which holds the hold value and updates the hold value when receiving the impedance response signal every an alternating current period of the impedance response signal
Data Source
AI summary
In a sensor control circuit, an impedance signal output unit has a HPF, a P/H circuit, a LPF, etc., and detects an element impedance of a sensor element on the basis of an impedance response signal which is alternately changed in response to an alternating current signal supplied to the sensor element. The P/H circuit has an input comparator which inputs an impedance detection voltage Vz after the HPF, a rectifying element connected to the P/H circuit, and a hold capacitor which is charged by the output of the input comparator. The input comparator has a constant current circuit and a transistor. The constant current circuit limits an updating value of a hold voltage value Vph of the hold capacitor every alternating current period. The sensor control device detects the element impedance of the sensor element with high accuracy while preventing influence of noise.