System and method for communication between a level switch field device and a controller in a field device communication system

Method of performing a proof-test in a field device communication system comprising:

• a level switch sensor, comprising, a first 10BASE-T1L physical layer, PHY, chip;
• a first self-oscillating element configured to generate a first frequency signal indicative of a sensed level state and to output the first frequency signal to the 10BASE-T1L PHY chip via a Media-Independent Interface (MII);
• and a second self-oscillating element configured to generate a second frequency signal forming a trigger signal, and to provide the trigger signal to the 10BASE-T1L PHY chip to trigger a transmission of the first frequency signal;
• a controller, comprising a second 10BASE-T1L physical layer, PHY, chip, and processing circuitry configured to receive and process MII-signals from the level switch sensor via the second 10BASE-T1L PHY chip to determine a level state and sensor status, and
• an intrinsically safe 2-wire connection connecting the first PHY-chip of the level switch sensor to the second PHY-chip of the controller, the 2-wire connection being configured to provide both power and communication, wherein the method comprises, by the controller:
• transmitting a proof-test activation signal to the level switch sensor via the second 10BASE-T1L PHY chip;
• and
• by the level switch sensor, simulating a fault condition in the level switch sensor in response to receiving the proof-test activation signal.