You're not overthinking it, this is a tricky requirement. Mechanical with no modification to the door or frame, operating on the outside of a swinging door... that's a specific problem.Here's a breakdown of why your ideas might (or might not) work, and some other potential solutions

Why a Standard Limit Switch May Not Be Ideal (But Could Still Work):
Durability

Industrial limit switches are usually pretty robust, but constant door swinging can be hard on them. You'd need a good quality switch designed for repeated actuation.

Adjustment

This is key. The adjustable roller arm is a good starting point, but you'll likely need to fine-tune its position.

Aesthetics

A clunky industrial limit switch stuck to the wall near a high-tech MRI room door might look a bit out of place. Concealing it would improve the aesthetic appeal.

Tampering/Bumping

Could someone accidentally bump or mess with the roller arm, rendering the interlock ineffective?

Reliability

Dust and debris are always a concern, especially in a veterinary setting.

Other Potential Solutions & Considerations


Heavy-Duty Roller Plunger Switch

Like a limit switch, but with a robust spring-loaded plunger. Mount the switch on the wall. As the door closes, the door edge pushes in the plunger.

Pros

More direct actuation than a roller arm, potentially more reliable if the alignment is good.

Cons

Needs precise alignment. Still somewhat exposed.2.

Proximity (Inductive) Sensor with a Mechanical Actuator

This is a two-part system. You mount an inductive proximity sensor on the wall. Instead of a magnet, you mount a small, non-magnetic metal target on the edge of the door where it swings closed. As the door closes, the target comes within range of the sensor. The sensor then provides a signal to the MRI.

Pros

Completely contactless. No mechanical wear on the sensor itself.

Cons

Requires a small metal target on the door edge. Inductive sensors have a limited sensing range (typically only a few millimeters), so the door has to be very close to the sensor when closed. More expensive than a simple limit switch.3.

A "Striker Plate" and Lever Arm Arrangement Mount a small, robust housing on the wall. Inside the housing is a lever arm connected to a reliable switch. On the edge of the door, you attach a small striker plate or similar that will positively engage with the lever arm as the door closes, rotating the arm and actuating the switch. Pros

More protected than a standard limit switch. Can be designed to be quite reliable.

Cons

Requires some fabrication to create the housing and striker plate. Needs precise alignment.4.

Optical Sensors (Light Beam)

A transmitter on the wall sends a beam of light to a receiver. When the door is closed, the beam is broken, and the interlock is activated.

Pros

Non-contact, reliable, relatively easy to install.

Cons

Can be affected by dust or other obscurations. Safety ratings might be needed (e.g., light curtains for industrial applications).5.

Consider the Safety Requirements

This is not just about preventing the MRI from operating. Think about how* critical the interlock is to safety. If a failure of the interlock could lead to a dangerous situation for staff or animals, you might need to use a safety-rated limit switch or sensor and design the system to be fail-safe.

Recommendation

Given your constraints, I'd lean towards a

well-protected, industrial-grade, heavy-duty roller plunger switch, OR the "Striker Plate" and Lever Arm Arrangement.Action Plan


Talk to the MRI Vendor (Again)

Push them harder. They've likely encountered this before, and even if they don't provide a specific product, they may have more detailed specifications or suggestions.2.

Draw a Detailed Sketch

Draw out the door swing and available mounting points on the wall and door edge. This will help you visualize the best solution.3.

Prototype

If possible, buy a couple of different types of switches or sensors and experiment with them on a mock-up door setup.4.

Document Everything: Thoroughly document the chosen solution, including the switch model, wiring diagram, and any adjustments made. Provide this documentation to the facility management for future maintenance.Good luck! This is a challenging problem, but with careful planning and the right choice of components, you can create a reliable and safe interlock system. Flag for review