Signal transmission system for transmitting a main process variable and further data between a field device and a superordinate unit, and a corresponding method

A method for transmitting a main process variable and further data between a field device and a superordinate unit, the method comprising:

• transmitting at least the further data between the field device and the superordinate unit via an optocoupler arrangement of a signal transmission system, the system comprising:
• a first conversion arrangement;
• a second conversion arrangement;
• and
• the optocoupler arrangement connected between the first conversion arrangement and the second conversion arrangement,
• wherein the first conversion arrangement is configured to convert at least the further data exchanged between the field device and the superordinate unit into a data signal such that they are transmittable via the optocoupler arrangement, wherein the optocoupler arrangement is configured to transmit the data signal between the first conversion arrangement and the second conversion arrangement,
• wherein the second conversion arrangement is configured to convert the data signal to the further data exchanged between the field device and the superordinate unit and to transmit the further data to the field device, and
• wherein:
• the first conversion arrangement comprises a first HART modem which is configured to receive from the field device a field device input signal comprising the main process variables and the further data in the HART standard, and to filter out a HART data part from the field device input signal and to pass the HART data part as a data signal via the optocoupler arrangement to the second conversion arrangement,
• wherein the second conversion arrangement comprises a second HART modem configured to convert the data signal again to the further data in the HART standard, and
• wherein the second HART modem is configured to output the HART data part filtered out by the first HART modem after its conversion to the further data in the HART standard as a superordinate unit output signal which is output by the signal transmission system to the superordinate unit;
• and/or
• wherein:
• the second conversion arrangement comprises a second HART modem which is configured to receive from the superordinate unit a superordinate unit input signal comprising the main process variables and further data in the HART standard, and to filter out the HART data part and to pass the HART data part as a data signal via the optocoupler arrangement to the first conversion arrangement, wherein the first conversion arrangement comprises the first HART modem, which is configured to convert the data signal to the further data in the HART standard, and
• wherein the first HART modem is configured to output the HART data part filtered out by the second HART modem after its conversion to the further data in the HART standard as a field device output signal.