In order for your blocks and chains to function, the Scan, Alarm, and Control program (SAC) processes them at the time interval you define. SAC processes your blocks and chains by:
- Scanning individual blocks in the chain, reading new I/O values and returning values to the process hardware.
- Alarming on incoming values if they exceed pre-defined limits you specify.
- Controlling the automation process by assuring that each block verifies or manipulates incoming values according to its configuration and sends values on to the next block in the chain.
The following figure shows SAC reading process values, sending these values through database chains, and returning the output values.
