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MES-Terminal interlocks

Three Boolean variables are required.

Variable	Type	Description	Direction
HeartbeatToMES	BOOL	Blinker signal from PLC in three-second cycle (maximum 3 sec. signal pause and maximum 3 sec. signal)	From PLC to MES
HeartbeatToPLC	BOOL	Blinker signal from MES to PLC	From MES to PLC
EnableMachine	BOOL	MES set this variable. The machine may only start automatic mode if this variable is set to TRUE. Attention: If the status of HeartbeatAnSPS does not change for e.g. ten seconds, EnableMachine has to be ignored.	From MES to PLC

Signal status diagram 'MES terminal interlocks'

The pulse can be generated either by the PLC internally or in TC2/3 by the block MES_Lifebit.

Section 1: Machine gets release from MES-Terminal.
Section 2: MES-Terminal withdraws machine's enable (the next cycle should not be able to start). Recommendation: If EnableMachine = FALSE and the next cycle should be started, there should be a PLC error message, e.g. “Machine has no release from MES-Terminal”.
Section 3: Use case “Production without MES system”: If HeartbeatToPLC is not written, the machine is released as failover.

HeartbeatToMES	HeartbeatToPLC	EnableMachine	Is machine enabled?
Toggle	Toggle	TRUE	TRUE (see section 1)
Toggle	Toggle	FALSE	FALSE (see section 2)
Toggle	FALSE	TRUE	FALSE (not possible)
Toggle	FALSE	FALSE	TRUE (see section 3)