Coupling Circuit With Intrinsically Safe Characteristics
Original Publication Date: 1979-Jan-01
Included in the Prior Art Database: 2005-Feb-19
A circuit is described that facilitates the coupling of the amplifier electronics of an explosion-proof magnetic card subsystem to the read head in a security system, such as the IBM Controlled Access System (CAS). It is necessary that an explosion-proof magnetic card reader of this nature be designed for approval by the Underwriters Laboratories, Inc. (U/L). This is accomplished by designing an intrinsically safe feed-through circuit and adapter to inhibit any hazardous voltage and current from reaching the magnetic card read head. Also, the reader has to function at -70 degrees F as this is the U/L criteria for explosion testing for Class 1, Group D devices. This circuit will operate at least in the range of -70 degrees F to +135 degrees F.