Capacitance Detection Circuit Moisture Protection
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Solution Overview
Problem
Existing capacitance detection circuits face challenges in maintaining high insulation resistance and reducing noise, particularly due to moisture absorption, which complicates the structure and increases production costs.
Innovation Solution
A capacitance detection circuit with a moisture absorption reduction area on the printed circuit board, featuring a resist-applied area surrounded by a non-resist-applied band-like separation area, prevents insulation resistance deterioration and noise increase, allowing for accurate detection of small capacitance values without requiring an airproof circuit board.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional capacitance detection circuit is used without special moisture protection, then the circuit structure remains simple and production cost is low, but insulation resistance deteriorates due to moisture absorption and noise increases
Solution Approach 1:
The circuit board is divided into a moisture absorption reduction area and a non-moisture absorption reduction area. The moisture absorption reduction area includes a first circuit component (capacitance detection circuit) and is covered with a moisture-proof coating, while the second circuit component is located in the non-moisture absorption reduction area without special moisture protection. This segmentation allows selective moisture protection only where needed, maintaining insulation resistance for sensitive components while keeping the overall structure relatively simple.
Solution Approach 2:
The moisture-proof coating is applied locally only to the moisture absorption reduction area rather than the entire circuit board. This local quality approach provides targeted protection to the capacitance detection circuit which is sensitive to moisture, while avoiding the complexity and cost of protecting the entire board uniformly.
2Reliability
If an airproof circuit board structure is implemented to prevent moisture absorption, then insulation resistance is maintained, but the device complexity and production cost increase
Solution Approach 1:
Instead of implementing a complete airproof structure for the entire circuit board, the invention segments the board into areas requiring moisture protection and areas that do not. Only the moisture absorption reduction area containing the capacitance detection circuit is covered with a moisture-proof coating, significantly reducing production cost while maintaining insulation resistance where critical.
Solution Approach 2:
The moisture-proof coating is applied selectively to specific areas rather than uniformly across the entire board. This local quality approach reduces material costs and manufacturing complexity while providing sufficient protection to the sensitive capacitance detection circuit.
3Reliability
If the entire circuit board is covered with moisture-proof coating, then insulation resistance is maintained, but manufacturing complexity and cost increase
Solution Approach 1:
The circuit board is segmented into a moisture absorption reduction area and a non-moisture absorption reduction area. The moisture-proof coating is applied only to the moisture absorption reduction area, creating a simplified coating structure that avoids the complexity of covering the entire board while maintaining insulation resistance where needed.
Solution Approach 2:
The moisture-proof coating provides local quality protection to the moisture absorption reduction area rather than uniform coverage. This reduces the overall coating complexity and manufacturing steps while ensuring insulation resistance is maintained in the critical area containing the capacitance detection circuit.
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3
AI summary
The present invention provides a capacitance detection circuit that has a simple configuration and that is capable of preventing a decrease in insulation resistance caused by deterioration of hygroscopicity. The capacitance detection circuit has at least a carrier signal generating circuit (21) that supplies a carrier signal to one of movable and fixed electrodes; an operational amplifier (Q21) that has input terminals, with the other one of the movable and fixed electrodes of a physical sensor (1) being input to one of the input terminals while the other one of the terminals being connected to the ground; and a printed circuit board (30) on which the physical quantity sensor, the carrier signal generating circuit, and the operational amplifier are mounted. An insulation-secured area (Ais) on the printed circuit board is configured as a moisture absorption reduction area (A1), including at least an electrode connection part of the physical quantity sensor, an input-side connection part of the operational amplifier, and a connection part connected to the input side of the operational amplifier out of connection parts of input-side circuit components connected between the electrode connection part and the input-side connection part.