Kredsløb til overførsel af en målestrøm fra en i sig selv sikker sensor til et i sig selv ikke sikkert område

摘要

The sensor Ä1Ü is located in an intrinsically safe region Ä10Ü and is connected with a current measuring resistor in a non-intrinsically safe region Ä20Ü. The sensor output is in the 4-20 mA range, and is supplied from the secondary of a transformer Ä2Ü via a rectifier unit Ä8Ü and a conditioning stage Ä9Ü. The transformer has a primary with two windings Ä21,22Ü which are coupled to an output stage arrangement Ä31Ü, in which the current measuring resistor connected to the centre tap of the transformer primary. The voltage developed across the resistor is fed to an offset unit, and subsequently to a voltage to current converter (7),