This document discusses direct digital control and supervisory control. It describes the functional blocks of a direct digital control system, including hardware for interfacing with the process and executing control strategies. The document outlines the tasks performed by a DDC's microprocessor, and explains two algorithms - position and velocity - for programming multi-loop control. Supervisory control provides monitoring and override functions for direct digital control systems.

1. ICE401: PROCESS INSTRUMENTATION
AND CONTROL
Class 43
Direct Digital and Supervisory Control
Dr. S. Meenatchisundaram
Email: meenasundar@gmail.com
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

2. Direct Digital Control (DDC):
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015
• The DDC directly interfaces to the process for data acquisition
and control purpose.
• That is, it has necessary hardware for directly interfacing (opto-
isolator, signal conditioner, ADC, etc.) and reading data from
process.
• It should also have memory and arithmetic capability to execute
required P, P+I, P+I+D control strategy.
• At the same time, the interface to control vale should also be
part of DDC.
• Figure in the next slide shows the various functional blocks of a
DDC system.

3. Direct Digital Control (DDC):
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

4. DDC Software:
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015
• The microprocessor performs the following tasks.
1. It reads the various process variables from different transmitters through
multiplexer and ADC.
2. It determines the error for each control loop and executes control strategy
for each loop.
3. It outputs the correction value to control vale through DAC.
• The main part, DDC software is program for control loops.
• There are two algorithms for programming a three more control.
• Position Algorithm
• Velocity Algorithm

5. Position Algorithm:
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

6. Position Algorithm:
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

7. Position Algorithm:
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

8. Position Algorithm:
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

9. Velocity Algorithm:
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

10. Velocity Algorithm:
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

11. Supervisory Control:
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015

12. References:
• Computer-Based Industrial Control, 2/e, By Krishna Kant, PHI.
Process Instrumentation and Control (ICE 401)
Dr. S.Meenatchisundaram, MIT, Manipal, Aug – Nov 2015