1. COMPUTER CONTROL OF PROCESSES

 

• Functions of a Process I/O Interface,

- Control the scanning and processing of all the inputs and outputs between the process and the computer.

- Provide conversions of signal levels, compensation for sensor range, and linearization of signals.

- Provide signal and sensor validity checks.

- Provide signal pre-processing and filtering.

- Provide measurements to the various other programming packages which have been converted to engineering units or interpreted in other ways.

- Provide alarm limit checks input-by-input.

• Some features found in computer control systems,

- timer initiated events - such as clock based sampling periods for a control loop

- Process initiated interrupts - Prioritized interrupt signals can be used to alert computers to standard notifications, or to initiate an emergency sequence when a critical failure has occurred.

- Control software - directs the operating points for the control system

- System and program initiated events - these are for system house keeping, and for communication to other computer systems in a network.

- Operator initiated events - requests for reports, changing of operating parameters, checking quality, etc.

 

• Interrupts

• Each computer has the ability to process interrupts.

• These interrupts can stop the microprocessor, and make it execute other subroutines.

• If no interrupts are received, the computer will always run the same program

• When interrupts are received, they are processed as urgent, or non-urgent.

• When an interrupt is processed, a small subroutine is run, and then execution returns to the original point in the interrupted program.

• If interrupts are not used, then the computer must continuously scan all of its inputs to see if any are critical. But this is not practical for real time processing.

 

• Linear Computer Controllers,

• Linear control theory can be converted into computer programs.

• Canonical form (Laplace/frequency domain) control rules can be converted into a form suitable for computers by using ‘z-transforms’

• State space control laws can be converted into computer code using matrix techniques, along with numerical integration.

• For example the PID control law has been used in many computer control programs to date.

• The figure below depicts a compute controlled process

 

• Advanced topics include,

- Feed forward controllers

- Adaptive controllers

- Optimal controllers

- Non-linear control systems

- Multi-input/Multi-output control systems

 

• An example of Computer-process interface

 

 

1.1 TEMPERTURE CONTROL

1.2 BATCH PROCESSING

1.3 COMPUTER PROCESS MONITORING

1.4 IMPLEMENTING A COMPUTER CONTROL SYSTEM

1.5 PRACTICE PROBLEMS

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