This is not a question, but may be need to notify observer

[Contemporaries]

When device was disconnected, at Phoebus GUI still display last value if not re-load GUI.
The observer cannot know whether the device is disconnected or the program error has occurred

Are there any parameters to set PV state to show status of the disconnected device?

[xiaoqiangwang]

It is possible to call Driver.setParamStatus on that PV.

This example is for a string typed PV,
https://github.com/paulscherrerinstitute/pcaspy/blob/master/example/alarm_severity.py