Relay Contact Voltage Detection for Welded Contact Diagnosis
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Solution Overview
Problem
Existing relay contact abnormality detection circuits face challenges in accurately detecting welded contacts due to unwanted current flow through photocouplers when capacitors are coupled to electrical circuits, leading to inaccurate differentiation between open and closed states.
Innovation Solution
An abnormality detection circuit is designed with a comparative voltage detection circuit and separate voltage detection circuits for each relay contact, applying voltage from an AC power source irrespective of the contact state, and using photocouplers to detect voltage differences based on duty and phase differences to determine normal or abnormal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a capacitor is coupled to the electrical circuit to reduce noise, then noise reduction is improved, but voltage is applied to the photocoupler even when the contact is open, causing current flow that prevents precise detection of open and closed states
Solution Approach 1:
The patent divides the detection function into two separate circuits: a comparative voltage detection circuit that is always active and a voltage detection circuit that is activated only when the relay contact is closed. This segmentation allows the system to maintain noise reduction capabilities while achieving precise detection by comparing voltage states between the two circuits.
Solution Approach 2:
The patent introduces a comparative voltage detection circuit as an intermediary reference that provides a baseline voltage state. By comparing the voltage from this intermediary circuit with the voltage detection circuit, the system can distinguish between open and closed states even in the presence of capacitor-induced current flow.
2Device complexity
If a single photocoupler is used to detect welded contact based on current, then device complexity is reduced, but detection precision deteriorates due to unwanted current flow from capacitors
Solution Approach 1:
The patent segments the detection system into two distinct voltage detection circuits with different activation conditions. This segmentation enables precise welded contact detection by comparing voltage states, overcoming the limitations of single-photocoupler current-based detection while maintaining reasonable circuit complexity.
Solution Approach 2:
The patent changes the detection parameter from current-based detection to voltage-based detection. By monitoring voltage differences between the comparative voltage detection circuit and the voltage detection circuit, the system achieves more precise detection of relay contact states and welded contacts.
3Adaptability or versatility
If voltage is applied to the voltage detection circuit irrespective of contact state, then detection coverage is improved, but the ability to distinguish open and closed states deteriorates due to continuous current flow
Solution Approach 1:
The patent implements dynamic control of the voltage detection circuit, activating it only when the relay contact is closed. This dynamic approach allows the system to maintain broad detection coverage through the always-active comparative voltage detection circuit while achieving precise state differentiation by selectively enabling the voltage detection circuit based on contact state.
Solution Approach 2:
The voltage detection circuit is activated periodically or selectively based on the relay contact state, creating distinct detection phases. This periodic activation pattern enables the system to differentiate between open and closed states by comparing voltage readings taken under different activation conditions.
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 solution allows for precise detection of relay contact abnormalities, even when capacitors are present, by comparing voltages applied to the comparative and voltage detection circuits, effectively distinguishing between open and closed states and identifying welding issues.
Implementation Method 1
can detect a welded contact based on current detected from the photocoupler
Data Source
AI summary
An abnormality detection circuit includes a first voltage detection circuit to which a voltage is applied from an AC power source when a first relay contact is closed and a second voltage detection circuit to which a voltage is applied from the AC power source when a second relay contact is closed. One end of the first voltage detection circuit is connected to the AC power source via the second wiring line while passing through no other switch. One end of the second voltage detection circuit is connected to the AC power source via the first wiring line while passing through no other switch. Abnormalities of the first and second relay contacts are detected by comparing the voltage applied to a comparative voltage detection circuit with each of the voltages applied to the first and second voltage detection circuits, respectively.