Signal transmission system

A transducer for a signal transmission system, comprising:

• a sensor for capturing a measured value, an electronic unit,
• a power source, and
• a comparator
• wherein the transducer is able to provide an impressed current in a range between 4 and 20 mA to an output connector and which is proportional to the captured measured value,
• wherein an input of the comparator is connected to the output connector, so that a serial data stream is derivable from a pulsing voltage that is present on the output connector.

A control and evaluation unit for a signal transmission system, comprising:

• a load that is connected to a signal input and
• a microprocessor that captures and evaluates a voltage that drops across the load or a current that flows through the load,
• wherein the load is connected in series to at least one electrical component, at which a direct current appears when a current flows through the electrical component,
• wherein the at least one electrical component is bridgeable by a switch, and
• wherein the microprocessor compares the voltage that drops across the load or the current that flows through the load when the electrical component is bridged to the voltage that drops across the load or the current that flows through the load when the electrical component is connected in series to the load and detects an error when a threshold is exceeded or fallen below.