1. Distributed Control Systems

2. Distributed Control Systems
Collection of hardware and instrumentation necessary for implementing control systems
Provide the infrastructure (platform) for implementing advanced control algorithms

3. History of Control Hardware
Pneumatic Implementation:
Transmission: the signals transmitted pneumatically are slow responding and susceptible to interference.
Calculation: Mechanical computation devices must be relatively simple and tend to wear out quickly.

4. History (cont.) Electron analog implementation:
Transmission: analog signals are susceptible to noise, and signal quality degrades over long transmission line.
Calculation: the type of computations possible with electronic analog devices is still limited.

5. History (cont.) Digital Implementation:
Transmission: Digital signals are far less sensitive to noise.
Calculation: The computational devices are digital computers.

6. Advantages of Digital System
Digital computers are more flexible because they are programmable and no limitation to the complexity of the computations it can carry out.
Digital systems are more precise.
Digital system cost less to install and maintain
Digital data in electronic files can be printed out, displayed on color terminals, stored in highly compressed form.

7. Computer Control Networks
1. PC Control:
Good for small processes such as laboratory prototype or pilot plants, where the number of control loops is relatively small

8. Computer Control Networks
2. Programmable Logic Controllers:
specialized for non-continuous systems such as batch processes.
It can be used when interlocks are required; e.g., a flow control loop cannot be actuated unless a pump has been turned on.
During startup or shutdown of continuous processes.

9. Computer Control Networks
3. DCS
Most comprehensive

10. DCS Elements-1
Local Control Unit: This unit can handle 8 to 16 individual PID loops.
Data Acquisition Unit: Digital (discrete) and analog I/O can be handle.
Batch Sequencing Unit: This unit controls a timing counters, arbitrary function generators, and internal logic.
Local Display: This device provides analog display stations, and video display for readout.
Bulk Memory Unit: This unit is used to store and recall process data.

11. DCS Elements-2
General Purpose Computer : This unit is programmed by a customer or third party to perform optimization, advance control, expert system, etc
Central Operator Display: This unit typically contain several consoles for operator communication with the system, and multiple video color graphics display units
Data Highway : A serial digital data transmission link connecting all other components in the system. It allow for redundant data highway to reduce the risk of data loss
Local area Network (LAN)

12. Advantages of DCS
Access a large amount of current information from the data highway.
Monitoring trends of past process conditions.
Readily install new on-line measurements together with local computers.
Alternate quickly among standard control strategies and readjust controller parameters in software.
A sight full engineer can use the flexibility of the framework to implement his latest controller design ideas on the host computer.

13. Modes of Computer control
Manual
Automatic
PID with local set point
Supervisory
PID with remote set point (supervisory)
Advanced

14. Additional Advantage
Digital DCS systems are more flexible. Control algorithms can be changed and control configuration can be modified without having rewiring the system.

15. Categories of process information
Example
Type
Relay, Switch
Solenoid valve
Motor drive
1. Digital
Alphanumerical displays
2. Generalized digital
Turbine flow meter
Stepping motor
3. Pulse
Thermocouple or strain gauge (mill volt)
Process instrumentation (4-20 am)
Other sensors (0-5 Volt)
4. Analog

16. Interface between digital computer and analog instruments
(A/D) Transducers convert analog signals to digital signals. (Sensor Computer)
(D/A) Transducers convert digital signals to analog signals. (Computer Valve)

17. Data resolution due to digitization
Accuracy depends on resolution.
Resolution depends on number of bits:
Resolution = signal range × 1/(2m -1)
m = number of bits used by the digitizer (A/D) to represent the analog data

18. Data Resolution Signal = 0 - 1 Volt, 3 bit digitizer:
Analog range covered
Analog equivalent
Digital Equivalent
Binary representation
0 to 1/14
1/14 to 3/14
3/14 to 5/14
5/14 to 7/14
7/14 to 9/14
9/14 to 11/14
11/14 to 13/14
13/14 to 14/14
1/7
2/7
3/7
4/7
5/7
6/7 1 2 3 4 5 6 7
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
1 0 1
1 1 0
1 1 1

19. Data Resolution

20. Utilization of DCS DCS vendor job: Control Engineer Job:
installation
Control Engineer Job:
Configuration
Built-in PID control:
How to Tune the PID control?

21. Utilization of DCS Implementation of advanced control:
Developed software for control algorithms, DMC, Aspen, etc.
Control-oriented programming language supplied by the DCS vendors.
Self-developed programs using high-level programming languages (Fortran, C++)

22. Advanced control topology

23. DCS Vendors
Honeywell
Fisher-Rosemont
Baily
Foxboro
Yokogawa
Siemen

25. Introduction to Real-Time Systems

26. A typical real-time system

27. Sample Applications Agile Manufacturing Traffic control system
Here are a few examples that fall into the networked embedded systems category.
Consider the border monitoring system, each node performs: sensing, encryption, decryption, aggregation, and communication. Together, as a networked system they monitor the border.
Other applications are industrial wireless networks and traffic monitoring system.

28. Industrial Internet & Internet of Things

29. Real-time Systems -- Introduction
Real-time systems are defined as those systems in which the correctness of the system depends not only on the logical result of computation, but also on the time at which the results are produced.
Hard real-time systems (e.g., Avionics, Command & Control Systems).
Firm real-time systems (e.g., Banking, Online transaction processing).
Soft real-time systems (e.g., Video streaming).

30. Real-Time Systems -- Introduction
Hard deadline: penalty due to missing deadline is a higher order of magnitude than the reward in meeting the deadline
Firm deadline: penalty and reward are in the same order of magnitude
Soft deadline: penalty often lesser magnitude than reward

31. Example – Car driver Mission: Reaching the destination safely.
Controlled System: Car.
Operating environment: Road conditions.
Controlling System
- Human driver: Sensors - Eyes and Ears of the driver.
- Computer: Sensors - Cameras, Infrared receiver, Laser telemeter, Navigation system, Street maps.
Controls: Accelerator, Steering wheel, Break-pedal.
Actuators: Wheels, Engines, and Brakes.

32. Example – Car driver (contd)
Critical tasks: Steering and breaking.
Non-critical tasks: Turning on radio.
Performance is not an absolute one. It measures the goodness of the outcome relative to the best outcome possible under a given circumstance.
Cost of fulfilling the mission → Efficient solution.
Reliability of the driver → Fault-tolerance is a must.

33. Real-Time Tasks Periodic tasks
- Time-driven. Characteristics are known a priori
- Task Ti is characterized by (pi, ci)
E.g.: Task monitoring temperature of a patient in an ICU.
Aperiodic tasks
- Event-driven. Characteristics are not known a priori
- Task Ti is characterized by (ai, ri, ci, di)
E.g.: Task activated upon detecting change in patient’s condition.
Sporadic Tasks
Aeriodic tasks with known minimum inter-arrival time.
pi : task period    ai : arrival time    ri : ready time di : deadline     ci : worst case execution time.

34. Task constraints Deadline constraint Resource constraints
Shared access (read-read)
Exclusive access (write-x)
Precedence constraints
T1  T2: Task T2 can start executing only after T1 finishes its execution
Fault-tolerant Requirements
To achieve higher reliability for task execution
Redundancy in execution

35. Notion of Predictability
The most common denominator that is expected from a real-time system is predictability.
The behavior of the real-time system must be predictable which means that with certain assumptions about workload and failures, it should be possible to show at “design time” that all the timing constraints of the application will be met.
For static systems, 100% guarantees can be given at design time.
For dynamic systems, 100% guarantee cannot be given since the characteristics of tasks are not known a priori.
In dynamic systems, predictability means that once a task is admitted into the system, its guarantee should never be violated as long as the assumptions under which the task was admitted hold.

36. Computing systems
Uniprocessor, multiprocessor (multicore systems), distributed system, networked control systems

37. Common Misconceptions
Real-time computing is equivalent to fast computing.
Real-time programming is assembly coding, priority interrupt programming, and writing device drivers.
Real-time systems operate in a static environment.
The problems in real-time system design have all been solved in other areas of computer science.