Fieldbus unit for a two-conductor fieldbus

摘要

A fieldbus unit for connection of a field device to a fieldbus comprising two conductors is designed to transfer a signal via the fieldbus by modulation of an electrical current drawn by the field device. The fieldbus unit comprises: an electrical current control transistor, through which the electrical current drawn by the field device flows, wherein the electrical current drawn by the field device is controlled via a base current of the electrical current control transistor; a bipolar transistor, via whose emitter-collector, electrical current path the base current for driving the electrical current control transistor flows; as well as an electrical current controller, which produces an electrical current control signal for controlling the electrical current drawn by the field device. The base of the bipolar transistor is placed at an essentially constant potential, which is so selected, that the bipolar transistor supplies the electrical current control transistor a base current sufficient for start-up of the field device, when the electrical current controller is not supplied with electrical current and delivers no electrical current control signal. The electrical current controller feeds the electrical current control signal via the emitter-collector, electrical current path of the bipolar transistor.

主权项

1. A fieldbus unit for the connection of a field device to a fieldbus comprising two conductors, wherein the fieldbus unit is designed for transferring a signal over the fieldbus by modulation of an electrical current drawn by the field device, the fieldbus unit, comprises:
an electrical current control transistor, through which the electrical current drawn by the field device flows, wherein the electrical current drawn by the field device is controlled via a base current of said electrical current control transistor; an electrical current controller, which produces an electrical current control signal for controlling the electrical current drawn by the field device; and a bipolar transistor, which is operated in common base configuration and via whose emitter-collector, electrical current path the base current for operating said electrical current control transistor flows, wherein: the base of said bipolar transistor is kept at an essentially constant potential, which so is selected, that said bipolar transistor supplies said electrical current control transistor a base current sufficient for start-up of the field device, when said electrical current controller is not supplied with electrical current and delivers no electrical current control signal; and said electrical current controller feeds the electrical current control signal via the emitter-collector, electrical current path of the bipolar transistor.