Which device is necessary for maintaining synchronization between doors in a double-door elevator system?

The necessity for maintaining synchronization between doors in a double-door elevator system primarily hinges on the function of a cable relating device. This device plays a crucial role in ensuring that both doors open and close in unison, providing smooth and safe operation.

When an elevator's doors operate in pairs, it is essential for both doors to move together to prevent any hazards such as one door opening while the other remains closed, which could cause injury or damage. The cable relating device typically connects the two doors mechanically or electronically, ensuring that any movement of one door is mirrored by the other. This synchronization is vital for the safety and efficiency of the elevator system.

In contrast, while other devices such as trip switches, relays, and mechanical links have their own functions within the elevator system, they do not specifically ensure the synchronized operation of double doors. Trip switches may activate doors or safety features, relays might control electrical circuits, and mechanical links could connect various components, but they do not directly maintain synchronization between the two doors in the way that a cable relating device does. Hence, the correct answer stands out clearly for its specific function in achieving door synchronization.