PLC connection unit working process module
When a process is controlled by a controller that uses sensor data to make decisions and
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update the results to drive actuators, as shown in view the separation of controller and process.
The process is a reality that will change over time. Actuators drive the system to new states (or modes).
This means that the controller is limited by available sensors, if entry is not available, the controller will not be able to detect a condition.
The separation of controller and process
The cycle control is a continuous cycle of PLC reading inputs, solving the ladder logic, then changing the outputs.
Like any computer this does not occur immediately. V. The cycle of a PLC cycle scan shows the basic operation of a PLC.
When the device is turned on initially the PLC has a quick health check to ensure that equipment is operating correctly.
If there is a problem the PLC will stop and indicate that there is an error. For example, if the PLC backup battery is low and the electricity is off, the memory is corrupted and it will result in an error. If the PLC passes the integrity check then analyzed (read) all the entries.
After the input values are stored in the logic of scale will be reviewed (solved) using the stored values - not the current values. This is done to avoid logic problems when inputs change during the ladder logic scan.
When the ladder logic full analysis results are examined (the output values will be changed). Once the system returns to a test of consistency, and the cycle continues indefinitely.
Unlike conventional computers, the entire program will be executed every scan. Typical times for each phase is of the order of milliseconds.
This picture is scan cycle of PLC
