Technical data

Appendix
27.6 Sample Programs
Programming with STEP 7
642 Manual, 05/2010, A5E02789666-01
27.6.2.3 Creating the FB for the Motor
What is Required of the FB?
The FB for the motor contains the following logical functions:
• There is a start and a stop input.
• A series of interlocks allow the operation of the devices (pumps and agitator motor). The status
of the interlocks is saved in the temporary local data (L stack) of OB1 ("Motor_enable,"
"Valve_enable") and is logically combined with the start and stop inputs when the FB for the
motor is processed.
• Feedback from the devices must appear within a certain time. Otherwise, it is assumed that an
error or fault has occurred. The function then stops the motor.
• The point in time and the duration of the response or error/fault cycle must be specified.
• If the start button is pressed and the motor enabled, the device switches itself on and runs until
the stop button is pressed.
• When the device is switched on, a timer starts to run. If the response signal from the device is
not received before the timer has expired, the device stops.
Specifying the Inputs and Outputs
The following figure shows the inputs and outputs of the general FB for the motor.