Is there a way to electrically or electronically sense the position of a solenoid coil's armature? Some sort of supervisory device?
I've got a kitchen hood damper that is closed when a t-stat controlled solenoid is energized, OR, when a lever is pulled manually, which also happens to push up the solenoid's armature at the same time that the damper closes (via spring loaded action in the lever mechanism). I can't get any wires down to the solenoid and manual damper control location, yet I need to shut down the exhaust fan up in the roof whenever the damper is closed..whether by manually closing it or by electrically closing it (via t-stat controlled solenoid).
If there is no UL listed module of some sort that can electronically sense the position of the solenoid's armature (when core of the coil is fully in the coil, the impedence should be maximum, right?), then perhaps some sort of flow switch in the duct work could be used to shut down the fan whenever someone shuts the damper..though I'm thinking this would cause some delay, and caving in of the duct work. I don't know what sort of set-up would work, and still please the fire marshall. Any thoughts?

There are all sorts of limit switches that would work for you. They could be mounted next to the solenoid to compress with it, or be mounted to thevent itself. They supply a simple dry contact that would either close or open at need. Basically they are what is used on your dishwasher to tell if the door of the dishwasher is closed or not being built into the handle. Honeywell and others manufacture them. Check out Square D catalog section 19 for some ideas. You will want something that is grease resistant especially so that it does not stick on you.

Shane

there are all sorts of air flow switches that can be very sensitive. I do alot of HVAC work and have worked on lots and lots of different sorts of set ups that will shut down immediately if air flow is interupted.