for the following signals , Failed and Loss of echo signals .they going to go in separate cables to PLC or we can regroup them in one signal cable called general Fault ?
You can use a common fault signal. one general fault signal.
or as per your requirement and hardware availability.
While exchanging with supplier for ultrasinic level offer ,
I mention that ultrasonic level transmitter must be with Analog input for level measuring and Digital input for general fault,
As communication protocol how this could be possible ?
You could just do an analog level transmitter and set up a fail status within the configuration. Depending on your control system you could pull HART data into it and use it for diagnostics.