3.4 Monitoring operant (M) – diagnosis without stop

In addition to S and I there is the operant M for monitoring. It is used for passive observation of signals. If a signal is outside the target state, the zone generates a message, but the process continues.

Typical application: Monitoring of an optional sensor, a temperature or a secondary condition. This gives the operator hints without stopping the process.

In the HMI M-messages appear yellow – as diagnostics, not as errors.