Pressure sensitive sensor and control unit and method of using same

Claim 1

A variable resistance operated load energizing circuit that includes: a. a direct current source having positive and negative terminals; b. a controlled rectifier that has a cathode, anode and gate; c. a transistor that has a base, collector and emitter; d. a unijunction transistor that has first and second base terminals and an emitter; e. a capacitor; f. variable resistance sensing means in which the resistance varies in proportion to a change in a physical variable to which said sensing means is subjected, said sensing means including first and second terminals; g. an electrically operated load having first and second terminals; h. first electrical conducting means connecting said positive terminal of said direct current source, and said first terminal of said sensing means; i. second electrical conducting means connecting said positive terminal of said direct current source to said second terminal of said load, and said second base terminal of said unijunction transistor; j. third electrical conducting means connecting said first terminal of said load to said collector of said transistor, said emitter of said transistor to said anode of said controlled rectifier and said cathode of said controlled rectifier to said negative terminal; k. fourth electrical conducting means connecting said base of said transistor and said emitter of said unijunction transistor to said capacitor; e. fifth electrical conducting means connecting said first base terminal of said unijunction transistor to said negative terminal; m. sixth electrical conducting means including a first resistance element connecting said first electrical conducting means to a portion of said fourth electrical conducting means between said capacitor and said base of said transistor; and n. seventh electrical conducting means connecting said second terminal of said sensing means to said gate of said controlled rectifier and to said negative terminal, with said capacitor continuously having an electrical charge built up thereon from said current source through said fourth and sixth electrical conducting means until a voltage is impressed on said base of a first magnitude sufficient to render said transistor conductive whereupon if a voltage of triggering magnitude is impressed on said gate from said sensing means said load is energized by a current flow through said rectifier, transistor and second and third electrical conducting means, with said charge on said capacitor continuing to increase until a voltage is impressed on said emitter of a second magnitude that is greater than the magnitude of the voltage that flows through said unijunction from said second terminal thereof, said unijunction when said voltage of said second magnitude is reached becoming momentarily conductive to allow said capacitor to discharge through said fifth conducting means to the negative terminal, and the discharge of said capacitor lowering the voltage impressed on said base below said first magnitude, with said transistor momentarily becoming non-conductive until said capacitor again becomes charged to the extent that said voltage of said first magnitude is impressed on said base, and said load ceasing to be electrically energized when said resistance of said sensing means increases to the extent that a voltage of triggering magnitude is not impressed on said gate and said voltage on said base is less than said first magnitude.