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• TOF / TOF_S, TOF_LTIME

TOF / TOF_S, TOF_LTIME

Type	Function block TOF is available as standard (non-safety-related) and safety-related type (TOF_S). For the safety-related type, the safety-related data types (SAFE*) are expected at the formal parameters. There is no safety-related type for LTIME.
Description	Provides a timer for delayed switching off. When the IN input switches from TRUE to FALSE, the Q output is reset to FALSE after the delay time has elapsed. If the IN input is TRUE, the output Q will be TRUE. If IN changes from TRUE to FALSE, switching off is delayed for the duration of the time interval applied to the input PT. After PT has elapsed, Q is set to FALSE. The elapsed time interval is indicated at the output ET.
Notes	The input IN and the output Q can be negated. Note: The negation of formal parameters is not supported in safety-related code (SNOLD). Function blocks have to be instantiated. The instance name of the function block has to be declared in the 'Variables' table of the POU where the FB is going to be used. The instance name must be unique within the POU.
Parameters	Inputs IN Data type: (SAFE)BOOL Description: If a falling edge is detected, the off-delay timing is started. PT Data type: TOF / TOF_S: (SAFE)TIME TOF_LTIME: LTIME Description: Preset time interval for the delay. The time value must be positive. Outputs Q Data type: (SAFE)BOOL Description: TRUE if IN = TRUE and ET < PT. FALSE if IN = FALSE and ET >= PT. ET Data type: TO / TOF_S: (SAFE)TIME TOF_LTIME: LTIME Description: Elapsed time interval.
Timing Diagram	Timing diagram 0 The IN input is FALSE. As a result, Q is also set to FALSE. 1 IN switches from FALSE to TRUE. Q is set to TRUE immediately. 2 IN switches from TRUE to FALSE. The measurement of the elapsed time is started. 3 When the delay time PT has elapsed (ET = PT), Q is reset to FALSE. 4 IN switches from FALSE to TRUE. Q is set to TRUE immediately. 5 IN switches from TRUE to FALSE. The measurement of the elapsed time is started once more. 6 IN switches back to TRUE before the PT has elapsed. As a result, Q remains TRUE. 7 IN switches from TRUE to FALSE again. The measurement of the elapsed time is started once more. 8 When the delay time PT has elapsed (ET = PT), Q is reset to FALSE.