“WAIT” body

In order to create the desired timer, the body of the POU must be programmed as follows:

At first it is checked whether Q has already been set at TRUE (as though the counting had already been executed), in this case we change nothing with the occupation of ZAB, but we call the Function Block ZAB without input (in order to check whether the time period is already over).

Otherwise we set the variable IN in ZAB at FALSE, and therefore at the same time ET at 0 and Q at FALSE. In this way all variables are set at the desired initial condition. Now we assign the necessary time from the variable TIME into the variable PT, and call ZAB with IN:=TRUE. In the function block ZAB the variable ET is now calculated until it reaches the value TIME, then Q is set at FALSE.

The negated value of Q is saved in OK after each execution of WAIT. As soon as Q is FALSE, then OK produces TRUE.

The timer is finished at this point. Now it is time to combine our two function blocks WAIT and SEQUENCE in the main program PLC_PRG.