Gas Sensor ADC Timing Shift for Heater Noise Suppression
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Solution Overview
Problem
Existing gas concentration detection devices face challenges in accurately suppressing noise interference during moving average processing of sensor signals, which affects detection accuracy.
Innovation Solution
The implementation of a timing adjuster circuit, comprising a synchronization circuit and a delay circuit, that shifts the heater energization timing relative to the ADC conversion timing, preventing noise generated by heater control from affecting AD conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If moving average processing is performed on sensor signals sampled at predetermined intervals, then the detection of gas concentration can be achieved, but noise interference from heater PWM control affects the measurement precision
Solution Approach 1:
The synchronization circuit performs preliminary action by adjusting the timing of ADC conversion to occur at specific phases relative to the heater PWM control cycle. By proactively setting the conversion timing to avoid noise generation periods, the system prevents noise interference before it affects the measurement, rather than attempting to filter it afterward.
Solution Approach 2:
The synchronization circuit acts as an intermediary between the heater control system and the ADC conversion process. It mediates the timing relationship between these two components, ensuring that ADC conversion occurs only when the heater is not generating noise, thus protecting the measurement system from harmful interference.
2Measurement precision
If the sampling rate is increased to improve detection accuracy, then more data points are obtained, but noise interference becomes more prominent and affects measurement precision
Solution Approach 1:
The synchronization circuit serves as an intermediary that controls the timing of ADC conversions relative to the heater PWM cycle. By coordinating the sampling instances with the noise-free periods of the heater operation, it enables high-rate sampling without proportionally increasing noise contamination, thus maintaining measurement precision even at higher sampling rates.
3Measurement precision
If the heater control timing is synchronized with the sampling cycle to cancel out noise, then noise cancellation is achieved, but the noise suppression is insufficient and measurement precision remains compromised
Solution Approach 1:
The synchronization circuit extracts and eliminates the harmful timing relationship between heater control and ADC conversion. By separating the conversion timing from the noise generation periods of the PWM cycle, it removes the source of interference rather than merely attempting to cancel it through averaging, thereby achieving reliable noise suppression.
Solution Approach 2:
The synchronization circuit acts as an intermediary that decouples the timing of heater control from ADC conversion. It introduces a controlled timing offset that prevents simultaneous occurrence of noise generation and signal sampling, thereby achieving sufficient noise avoidance that was not attainable through simple synchronization.
Data Source
AI summary
A gas concentration detection device includes: a gas concentration sensor having a gas sensor element that outputs an electric signal according to a gas concentration and a heater that heats the gas sensor element; a heater controller controlling energization and de-energization of the heater; a sensor controller having an ADC AD-converting the electric signal from an analog signal to a digital signal in synchronization with a sampling clock (fs) and detecting the gas concentration based on an output signal of the AD converter; and a timing adjuster shifting a switching timing of energization control from a conversion timing at which the AD converter performs the AD conversion.