Hood Position Detection for Add-on Alarm Systems

Introduction

For add-on alarm systems the open or closed position of the hood can be monitored with Reed Sensors. A Reed Switch (normally open) and the actuating magnet are combined in one unit for this application.

Here the Reed Switch is mounted parallel to the actuation magnet and a small ferromagnetic shield is placed in between these two components. The ferromagnetic shield shunts the magnetic field produced by the magnet, thereby minimizing its effect on the open Reed Switch. With the hood closed, the ferromagnetic shield is positioned between the switch and the magnet, blocking the magnetic field. When the hood is opened, the spring driven ferromagnetic shunt is removed, activating and closing the Reed Switch. This in turn activates the alarm system. This approach is simple and very reliable.