The invention relates to a circuit arrangement for establishing compatibility between a field device or an interface device for a field device and a diagnostic system pertaining to a control system, to the output of which the interface device or field device can be connected. The diagnostic system is adapted to send, via the output of the control system, a test signal to the interface device or field device and to emit an error signal when an electrical response at the output of the control system lies outside an expectancy range. The circuit arrangement comprises voltage influencing means for influencing a voltage at the output of the control system. The circuit arrangement is characterized in that the voltage influencing means comprises a controllable power source with which power source a current can be produced for influencing a voltage at the output of the control system, that electronic analyzing and controlling means are present to identify a test signal at the output of the control system, that the analyzing and controlling means are adapted, on identification of a test signal, to instruct the controllable power source to adjust a target voltage at the output of the control system, which target voltage is to be within the expectancy range. Additionally, the invention relates to a corresponding method for establishing compatibility.