Patent ID: 8807522
Filing Date: 2014-08-19
Classification: F15B,F16K,G05B

Abstract:
1. A positioner for receiving a DC electric current through a pair of electric wires from a higher-level system, generating a local operating power supply from the DC electric current signal, along with controlling a degree of opening of a regulator valve in accordance with a value of the DC electric current signal, and receiving an AC electric current signal that is superimposed on the DC electric signal current, comprising a variable impedance circuit wherein the impedance relative to the DC electric current signal is low and the impedance relative to the AC electric current signal is higher than the impedance relative to the DC electric current signal; wherein the variable impedance circuit comprises: an input line for a DC electric current signal and an AC electric current signal that is superimposed on the DC electric current signal; an output line for a DC electric current signal and an AC electric current signal that is superimposed on the DC electric current signal; a series circuit of a first resistor, a second resistor, and a third resistor, connected between the input line and the output line; a transistor having the collector thereof connected to the input line and the base thereof connected to connecting point between the second resistor and the third resistor; a fourth resistor connected between the emitter of the transistor and the output line; a first capacitor having one end thereof connected to connecting point between the second resistor and the third resistor; a fifth resistor connected between the other end of the first capacitor and the output line; a second capacitor having one end thereof connected to the connecting point between the first resistor and the second resistor; and a sixth resistor connected between the other end of the second capacitor and the output line.