Signal transmission system

A measuring system comprising:

• a signal transmission system for digital signal transmission, including:
• a transmitter circuit with a signal input and with a signal output;
• a receiver circuit with a signal input and with a signal output;
• and
• a signal cable for the electrical connection of the transmitter circuit and the receiver circuit, the signal cable having a pair of signal conductors and a terminating resistor electrically connecting the signal conductors at a receiver circuit side respective line end;
• wherein the signal output of the transmitter circuit and the signal input of the receiver circuit are electrically connected to one another by means of the signal cable such that a current loop involving the signal output of the transmitter circuit, the pair of signal conductors of the signal cable, and a current divider formed by the terminating resistor and the signal input of the receiver circuit is formed;
• wherein the transmitter circuit is configured to drive a loop current with a current magnitude and a predeterminable current direction in the current loop such that a signal voltage proportional to the magnitude of the loop current and a polarity dependent on the current direction of the loop current drops over the terminating resistor;
• wherein the receiver circuit is configured to convert an input voltage into a corresponding output voltage such that, when the input voltage exceeds a positive first switching voltage threshold, the output voltage assumes a positive first voltage level and that when the input voltage exceeds the positive first switching voltage threshold, the output voltage holds the first voltage level, respectively;
• wherein the receiver circuit has an hysteresis, namely a dependence of the output voltage both on the input voltage and on an instantaneous voltage level of the output voltage, such that the output voltage which has the first voltage level further holds the first voltage level even if the input voltage falls below the first switching voltage threshold but nevertheless remains above a second switching voltage threshold that is non-zero;
• wherein the transmitter circuit is configured to modulate a digital input signal present at its signal input onto the loop current;
• and
• wherein the transmitter circuit is configured to adjust the current of the loop current as a function of the digital input signal at the signal input such that the loop current is allowed to flow in a first current direction in the current loop when the digital input signal has a first signal state and that the loop current flowing in the first current direction has or can have at least two successively differing in each case non-zero positive currents, of which a positive first current magnitude is greater than a first switching current threshold, defined as a ratio of the first switching voltage threshold of the receiver circuit to the resistance value of the terminating resistor, and a second current magnitude less than the first switching current threshold but greater than a second switching current threshold, defined as a ratio of the second switching voltage threshold of the receiver circuit to the resistance value of the terminating resistor;
• a sensor which is configured to detect at least one measurement variable and to convert the at least one measurement variable into at least one, primary sensor signal representing the same measurement variable at a signal output;
• and
• a converter electronics-with a measurement signal input and with a data output for digital user data;
• wherein the converter electronics are configured to receive and evaluate the at least one sensor signal or a secondary signal derived therefrom via the measurement signal input, and
• wherein the converter electronics are configured to output digital useful data containing the same measured values at the data output.