Capacitive Sensor Inspection Circuit for Signal Line Breakage Detection
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Solution Overview
Problem
Capacitive humidity sensors face challenges in detecting signal line breakages and wiring issues due to the integration of constant current sources and AC voltage applications, which hinder effective inspection of failures such as line breaks or short-circuits.
Innovation Solution
The method involves a sensor device with a capacitive sensor unit, driving circuits, a capacitor, an amplifier circuit, and a switching circuit, where the capacitor is discharged and recharged with alternating driving voltages to determine if the output voltage from the amplifier circuit falls within predetermined normal ranges, allowing for the detection of signal line and wiring abnormalities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant current source is connected to the signal line for transferring electric charges to the charge amplifier from the sensor unit, then the breakage of the signal line can be detected in resistive sensors, but electric charges corresponding to the capacitance of the sensor element cannot be detected successfully in capacitive sensors
Solution Approach 1:
The patent divides the inspection process into separate stages: a first inspection stage that detects signal line breakage using a constant current source, and a second inspection stage that measures capacitance using AC voltage. This segmentation allows each inspection type to use its optimal method without interfering with the other, resolving the contradiction between breakage detection reliability and capacitance measurement precision.
Solution Approach 2:
The patent implements periodic inspection by alternating between different inspection stages. The constant current source is activated during the first inspection stage for breakage detection, then deactivated during the second inspection stage when AC voltage is applied for capacitance measurement. This periodic activation ensures that each inspection method operates under optimal conditions without continuous interference.
2Measurement precision
If AC voltage is applied to the sensor unit for capacitive sensing, then capacitance changes can be detected, but wiring lines of the driving circuit may be broken or short-circuited without detection
Solution Approach 1:
The patent segments the inspection into two distinct stages: the first inspection stage uses a constant current source to detect wiring line failures (breaks and short circuits), and the second inspection stage uses AC voltage to measure capacitance. This segmentation ensures that wiring line reliability is verified before capacitance measurement begins, preventing undetected failures during normal operation.
Solution Approach 2:
The patent performs wiring line failure detection as a preliminary action before capacitance measurement. By executing the first inspection stage using the constant current source first, the system ensures that any wiring line issues are identified and flagged before the second inspection stage performs capacitance measurement with AC voltage, preventing erroneous readings from undetected failures.
3Reliability
If the constant current source is used continuously for signal line inspection, then breakage detection is maintained, but the charge amplifier integrates the current and cannot detect electric charges corresponding to sensor capacitance
Solution Approach 1:
The patent implements periodic action by activating the constant current source only during the first inspection stage for breakage detection, then deactivating it during the second inspection stage for capacitance measurement. This periodic activation pattern maintains breakage detection capability when needed while eliminating interference with capacitance measurement, thereby improving overall inspection efficiency without sacrificing reliability.
Solution Approach 2:
The patent applies dynamics by making the constant current source dynamically controllable - it is turned on during the first inspection stage and turned off during the second inspection stage. This dynamic control allows the system to adapt the constant current source's operation to the specific inspection requirements of each stage, resolving the contradiction between maintaining breakage detection and enabling accurate capacitance 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 approach enables accurate inspection of signal line and wiring failures without interfering with normal capacitance measurements, effectively addressing the limitations of existing capacitive sensor inspection methods.
Implementation Method 1
a sensor element having a capacitance that changes according to humidity
Implementation Method 2
an amplifier circuit configured to output a voltage, which is obtained by amplifying a difference between a voltage of the signal terminal and a reference voltage
Implementation Method 3
a switching circuit configured to discharge electric charges accumulated in the capacitor
Data Source
AI summary
In a reset period of a first stage, a switching circuit is turned on, and high-level driving voltages are output from driving circuits. In a charge transfer period subsequent to the reset period, the switching circuit is turned off, and low-level driving voltages are output from the driving circuits. It is determined whether or not an output voltage of an amplifier circuit in the charge transfer period is included in a normal range. In the inspection of a second stage subsequent to the first stage, in the same manner as in the normal measurement, voltages having opposite phases are output from the driving circuits in the reset period and the charge transfer period, and it is determined whether or not the output voltage of the amplifier circuit in the charge transfer period is included in a normal range.