Abstract: An actuator is disclosed which operates on the principle of the variable magnetic properties of materials with respect to temperature. As temperature is raised past Curie temperature, magnetic permeability of certain materials drops significantly to a value close to free space permeability. However, depending on the material selection, magnetic permeability may be significantly higher below Curie temperature. This principle is used to cause magnetic attractive force to move an actuator at one temperature, while permitting a return spring force to move the actuator at another temperature by changing the pathway traversed by most magnetic lines of flux from a magnetic source. The actuator may be employed to provide a temperature activated electrical switch or fluid valve. The temperature activated valves are suited to use in high temperature environments, such as SAGD wells.

Abstract: A fire condition detection and control system for use with air moving and filtering units. The system includes one or more remote fire condition detection units, which sense heat or smoke and, upon such sensing, transmit a signal indicative of an alarm condition to one or more air moving and filtering units located within a containment area. The transmission is by wireless radio frequency transmission and/or a wired transmission line or cable. The air moving and filtering units detect the alarm condition and disconnect power to the blower motor of the air moving and filtering unit. The receiver and control circuitry may be integral with the air moving and filtering unit, or may be part of a separate control unit that plugs into conventional air moving and filtering units.

Abstract: A circuit which monitors air flow by comparing the speed of a fan to a predetermined frequency. A Hall effect device detects magnetic pulses representative of the fan speed and provides a corresponding electrical signal. This signal is compared with a predetermined threshold frequency by a retriggerable monostable multivibrator. A digital delay circuit isolates pace conditions and a relay circuit provides an indication of the fan speed status.

Abstract: A safety circuit which connects a condition responsive circuit to a cyclic signal detecting circuit. In order to provide the cyclic signal detecting circuit with a continuous cyclic input, the condition responsive circuit and a cyclic redundancy checker is provided. The cyclic redundancy checker identifies a specific series of logic bits from the condition responsive circuit and responds favorably only to that series of logic bits. If any other series of logic bits occurs, the cyclic redundancy checker of the system ceases to function, thereby causing the cyclic signal detecting circuit to cease to function and it in turn opens a series contact to deenergize a critical load in a control system.