Gas Sensor Control Circuit Short-Circuit Inspection
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Solution Overview
Problem
Existing gas detection apparatuses cannot effectively inspect for short circuits during startup, as improper current flow can damage the sensor element, and existing methods fail to prevent adverse effects on the gas sensor element due to excessive or reverse current flow during short-circuit detection.
Innovation Solution
A gas-sensor control circuit with an uninspected terminal impedance increasing circuit that isolates the gas sensor element from the circuit, allowing for safe short-circuit inspection by increasing the impedance and preventing excessive or improper current flow, using inspection currents and potential measurement to determine short circuits without damaging the sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If short-circuit inspection is performed during normal operation, then short-circuit detection capability is improved, but the gas sensor element is damaged by excessive or reverse current flow during startup
Solution Approach 1:
The patent applies preliminary action by performing short-circuit inspection before normal operation begins. The control circuit checks for short circuits in the wiring connected to detection cell electrodes during the startup phase, before any measurement currents are applied to the sensor. This prevents damage that would occur if inspection were delayed until normal operation, while ensuring the sensor is protected during the inspection process itself.
Solution Approach 2:
The patent uses an intermediary approach by introducing a controlled test current that is distinct from the normal measurement current. The control circuit applies a small test current specifically for inspection purposes, separate from the currents used during normal sensor operation. This intermediary current allows safe detection of short circuits without subjecting the sensor to the harmful excessive currents that would occur during normal operation if a short circuit were present.
2Object-affected harmful factors
If impedance is increased to isolate the sensor during inspection, then current flow control is improved, but circuit functionality is reduced
Solution Approach 1:
The patent applies dynamics by making the circuit impedance variable rather than fixed. The control circuit dynamically adjusts its output impedance based on the operational phase: during startup inspection, it maintains high impedance to limit current flow and protect the sensor; during normal operation, it switches to low impedance to ensure proper sensor functionality and measurement accuracy. This dynamic impedance control resolves the contradiction between protecting the sensor and maintaining circuit functionality.
Solution Approach 2:
The patent uses periodic action by alternating between different circuit states during the startup sequence. The control circuit periodically switches between high-impedance inspection mode and low-impedance normal operation mode. During brief inspection intervals at startup, high impedance is applied to detect short circuits; once inspection is complete and no short circuits are detected, the circuit transitions to normal low-impedance operation. This periodic switching allows both protection and functionality to be achieved at different times in the startup sequence.
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A gas detection apparatus (2, 2A) includes a gas sensor element (4, 110) and a gas-sensor control circuit (5, 5A, 150). The gas sensor element (4, 110) includes at least one sensor cell (14, 24, 120) including a solid electrolyte member and a pair of electrodes, and a plurality of external connection terminals (4T1, 4T2, 4T3, 110T1, 110T2) electrically connected to the electrodes of the sensor cell (14, 24, 120). The gas-sensor control circuit (5, 5A, 150) includes a plurality of control terminals (Vs+, COM, Ip+) electrically connected to respective ones of the external connection terminals (4T1, 4T2, 4T3, 110T1, 110T2) of the gas sensor element (4, 110), an inspection current supply circuit (43M, 43N, 43C, 155, 156) for supplying an inspection current to an inspected terminal (Vs+), which is a control terminal to be inspected for presence or absence of a short circuit to a predetermined potential, an inspection potential measurement circuit (41, 157) for measuring the potential of the inspected terminal (Vs+), and an uninspected terminal impedance increasing circuit (SW1 to SW3, SW6, SW101) for increasing the impedance of the gas-sensor control circuit (5, 5A, 150) as viewed from an uninspected terminal (COM, Ip+), which is a control terminal other than the inspected terminal (Vs+).