Electropneumatic solenoid valve, field device having solenoid valve and diagnostic method for electropneumatic solenoid valve

A field device for a process plant, comprising:

• a pneumatic control valve actuator having a control air chamber;
• and
• an electropneumatic solenoid valve including:
• an electromagnetic actuator having a coil that is configured to be energized and a solenoid armature configured to be movable relative to the coil;
• at least one air chamber into which three air channels open, the three air channels comprising a first air channel, a second air channel, and a control air channel;
• at least one valve member which, in a first closed position, is configured to close the first air channel and release the second air channel, and which, in a second closed position, is configured to close the second air channel and release the first air channel;
• a driver configured to:
• be movable in a first actuating direction and in a second actuating direction counter to the first actuating direction, and connect the valve member to the solenoid armature in a force-transmitting manner;
• a driver pretensioning spring, arranged between the driver and the solenoid armature, configured to provide a pretensioning force to the driver in a driving direction corresponding to the first actuating direction or second actuating direction;
• a restoring pretensioning spring, arranged between the driver and a core of the electromagnetic actuator that is immovable relative to the coil, configured to provide a restoring force to the driver against the driving direction;
• and
• diagnostic electronics configured to, during an activation of the coil for actuating the solenoid armature, detect a current flowing through the coil, based on a time difference between a first local current flow minimum corresponding to an impact of the valve member on a valve seat and a second local current flow minimum corresponding to an impact of the solenoid armature on a stopper, to provide a diagnostic result,
• wherein the first air channel is a vent channel for connection to a pneumatic source and the second air channel is a vent channel for connection to a pneumatic sink, the control air channel being connected to the control air chamber of the pneumatic control valve actuator.

A diagnostic method for an electropneumatic solenoid valve of a field device of a process plant, comprising:

• activating an electromagnetic actuator having a solenoid armature to actuate a valve member;
• detecting, as a first reference time, an impact of the valve member on a valve seat corresponding to a first current flow minimum;
• detecting, as a second reference time, an impact of the solenoid armature on a stopper of the electromagnetic actuator corresponding to a second current flow minimum;
• and
• determining a stop time difference between the first reference time and the second reference time.