Positioner

摘要

A voltage/current converting circuit is provided in a stage prior to a communication circuit. An over-current preventing circuit is incorporated into the voltage/current converting circuit. The voltage/current converting circuit converts a DC voltage signal into a DC electric current signal, and converts an AC voltage signal into an AC electric current signal. Moreover, the voltage/current converting circuit keeps the excessively large electric current that would flow into the internal circuitry thereof to no more than a predetermined electric current value (for example, no more than 30 mA) when the positioner is connected in error to the voltage source side without a load resistance connected.

主权项

1. A positioner receiving a DC electric signal through a pair of electric wires from a higher-level system to produce its own operating power supply from the DC electric signal that is supplied, and controlling the degree of opening of a regulator valve in accordance with a value of the supplied DC electric signal, comprising:
a current inputting-type communication circuit receiving an AC electric signal sent from the higher-level system superimposed on the DC electric signal; and a voltage/current converting circuit, provided in a stage prior to the communication circuit, converting the voltage into an electric current and sending the electric current to the communication circuit if the DC electric signal from the higher-level system is a voltage; wherein the voltage/current converting circuit is provided with an over-current preventing circuit preventing the flow of an electric current higher than a specific electric current value.