A remote position indicator for a movable member located in an inflammable atmosphere which comprises a variable resistor mechanically connected for adjustment by the movable member, an intrinsically safe power supply arranged to pass current through the variable resistor, an amplifier comprised entirely by one or more transistors and one or more resistors connected to receive the voltage signal delivered by the variable resistor, and a meter connected to receive the amplified signal delivered by the amplifier whereby to indicate the position of the movable member.
A position indicator for producing a variable maximum, variable resistance for supplying a variable amplitude signal to a computer indicating the degree of displacement of a controlled element along an axis includes a variable resistance resistor; a variable displacement element coupled to the variable resistor for varying the resistance of the variable resistor according to displacement of the element along an axis; a first fixed resistance resistor connected to first and second terminals of a transistor, the transistor being connected in series with the variable resistor to form a first series circuit; a second fixed resistance resistor, a potentiometer having a fixed resistance and a variable position contact, and a third fixed resistance resistor connected in series as a second series circuit that is connected in parallel to the first series circuit; and an amplifier having a first inverting input terminal and a second non-inverting input terminal connected to the variable resistor and the variable position contact, respectively, and an output terminal connected to a control terminal of the transistor.
