Defeat resistant interlock/monitoring system

A magnetically actuated interlock device for an electrical system, the interlock device comprising:

• first and second magnetically actuable reed switches mechanically biased to a normally closed switching state and mounted in parallel orientation on a circuit board separated by a predetermined distance;
• first and second biasing magnets positioned in parallel relationship alongside the first and second switches respectively to establish a magnetically biased open switching state thereof;
• an actuator comprising first and second actuator magnets for changing the magnetically biased state of the first and second switches back to the closed state when located in a predetermined position proximate to the magnetically biased first and second switches;
• and
• third and fourth magnetically actuable switches mechanically biased to a normally closed switching state and mounted on the circuit board in the absence of a magnetic biasing field;
• the switches being connected in a series circuit operable in the closed state to permit electrical operation of the electrical current flow only when the actuator is at said predetermined position;
• the third and fourth switches being spaced between the first and second switches so that the actuator, when located at said predetermined position, does not change the switching state of the third and fourth switches;
• and
• the third and fourth switches being oriented so that the third switch is parallel to the first and second switches and the fourth switch is normal to the first, second and third switches and overlies the third switch in approximately intersecting relationship so that an external magnetic field cannot change the switching state of the first and second switches without changing the switching state of either the third or fourth switch.

A method for magnetically activating an interlock for an electrical system, the method comprising:

• positioning first and second magnetically actuable switches normally biased mechanically to a first switching state at a predetermined spacing;
• positioning third and fourth magnetically actuable switches normally biased mechanically to said first switching state between the first and second switches;
• magnetically biasing the first and second switches into a second switching state without magnetically biasing the third and fourth switches;
• actuating the interlock system by simultaneously locating separate external magnetic fields within a predetermined proximity to the first and second magnetically biased switches so that said first and second switches change back to the first switching state;
• and
• mutually orienting the third and fourth switches between the first and second switches so that a single foreign magnetic field cannot change the switching state of the first and second switches without changing the switching state of one of the third and fourth switches.