The marine limit switch AXH is a common mechanical travel switch on ships, mainly used to detect the opening and closing status of cabin doors (such as bridge doors and watertight doors), and convert the mechanical position signal into an electrical signal, which is fed back to the control system.
Specification and Option The AXH series typically comes in different specifications, with the main differences lying in voltage and current capacity, to accommodate varying control circuit requirements:
Model
Application scenarios
Main parameters
AXH-250V 10A
High load, main circuit control
250V 10A
AXH 24V 2A
Low power, signal detection
24V 2A
Selection recommendations: If the switch directly controls a door motor or high-power equipment, AXH-250V 10A should be selected; if it is only used for signal detection (such as PLC input), AXH24 2A is sufficient to meet the requirements.
Core Functions
The core function of the AXH limit switch on the cabin door is position detection and status feedback:
Position detection: When the door leaf moves to the limit position of being fully opened or fully closed, the bump block on the door frame or door leaf will touch the roller or push rod of the AXH switch.
State feedback: The action of the contacts inside the switch, outputting an electrical signal of "on" or "off ". This signal is typically used for： Interlock control: For example, on the bridge, certain navigational equipment may not be able to be activated when the door is not fully closed. Status indication: Display the real-time status of the door on the control panel (e.g., a red light indicates that the door is not properly closed). Alarm system: It triggers an alarm when the door is in an abnormal state.
Installation and Maintenance
Installation location: It is usually installed on the door frame, coordinating with the striker on the door leaf. During installation, it must be ensured that the striker can accurately and reliably touch the roller of the switch, and the switch itself is firmly fixed without any shaking.
Environmental adaptability: Marine AXH switches are typically designed to be waterproof and resistant to salt spray, with their casings often made of copper or alloy to withstand corrosion from humid marine air.
Common Faults：The push rod is broken, the contact is poorly connected, and the internal spring is malfunctioning. If there is a false alarm of door status or control failure, it is important to check whether the limit switch is stuck or damaged.
In the marine cabin door control system, the AXH limit switch primarily serves as a "position sensor" and a "safety interlock trigger". By detecting the physical position of the door, it sends electrical signals indicating "fully opened" or "fully closed" to the control system, thereby triggering subsequent interlocking actions.
The following is the specific implementation logic of it in linkage control:
1. Core linkage logic: position detection and signal feedback AXH limit switches are typically installed at the extreme positions of a door frame or door leaf (such as the fully open and fully closed positions). When the door moves to a specific position, the striker on the door presses or releases the roller/plunger of the switch, causing the internal contact state to change (normally open to normally closed, or normally closed to normally open).
Closing in place signal: After the door is fully closed, the AXH switch is triggered, outputting a "door closed" signal. Fully open signal: After the door is fully opened, the AXH switch on the other side is triggered, outputting a "door is open" signal.
2. Linked control scenario
Scenario One: Automatic stop of door operator (electric door) Control logic: When the door moves to its extreme position (fully open or fully closed), the AXH switch is triggered, and its signal is input to the contactor or PLC in the door motor control box.
Action result: The control system immediately cuts off the power supply to the door motor, stopping the door movement and preventing the motor from stalling or the door body from colliding with the door frame, thus playing a role in mechanical limit protection.
Scenario Two: Sealing and Alarming of Watertight Doors Control logic: For watertight doors, only when the "closed in place" signal is valid, will the control system activate the clamping device (such as a hydraulic or pneumatic locking mechanism) to press the door firmly against the door frame, ensuring watertightness.
Action result: If the door is not properly closed (AXH not triggered), the system will emit audible and visual alarms to prompt the crew to check, and may prevent the ship from entering a specific navigation state.
Scene Three: Interlocking with the ship navigation system Control logic: In important areas such as the bridge or engine room, the control system will detect the door's open/closed status. If the door is in the "open" state (AXH has not given a close signal), the system may restrict certain operations (such as prohibiting the start of the main engine or limiting the speed).
Action result: Ensure that the cabin door is in a safe state under specific operating conditions to prevent accidents.
3. Wiring and implementation method AXH limit switches typically employ normally open (NO) or normally closed (NC) contacts to connect into control circuits:
Normally open contact (NO): It is disconnected when the door is not in place and closed when it is in place. It is commonly used to activate the clamping device or disarm the alarm. Normally closed contact (NC): It is closed when the door is not in place and disconnected when it is in place. It is commonly used to cut off the motor power supply (as a stop signal).
Summary: The AXH limit switch provides precise position feedback for the cabin door control system through a simple "on/off" signal, making it an indispensable key component for achieving automated operation and safety interlocking.
