Heya! Welcome to Crypto To You. Today on this occasion I am going to share Advanced Process Control (APC) with PLC and DCS: Function Blocks and Implementation.
In the world of process automation, basic PID control is just the beginning. Advanced Process Control (APC) represents the next level of sophistication—techniques that go beyond simple feedback control to optimize complex industrial processes.
"APC is typically implemented using function blocks or custom programming capabilities at the DCS level". In some cases, "APC resides at the supervisory control computer level". But increasingly, modern PLCs and DCS systems are capable of implementing sophisticated APC strategies directly.
This comprehensive guide covers everything you need to know about Advanced Process Control with PLC and DCS. You'll learn about function block implementation, cascade control, feedforward control, model-based control, and how to design effective APC schemes for industrial applications.
📌 WHAT IS ADVANCED PROCESS CONTROL (APC)?
Beyond Basic PID
Advanced Process Control encompasses a range of techniques that go beyond traditional PID control. These techniques are designed to handle complex process dynamics, multiple interacting variables, and challenging control objectives.
"Advanced Process Control (APC) engineers" need to understand "the key aspects of the underlying regulatory control system (DCS) as it relates to" advanced controllers. The foundation of APC is a well-tuned regulatory control layer.
APC vs. Regulatory Control
| Aspect | Regulatory Control | Advanced Process Control |
|---|---|---|
| Objective | Maintain setpoints | Optimize process performance |
| Complexity | Single-loop PID | Multi-variable, constraints |
| Time scale | Fast (seconds-minutes) | Slower (minutes-hours) |
| Implementation | Basic PID blocks | Function blocks, custom code |
Common APC Techniques
| Technique | Description | Application |
|---|---|---|
| Cascade Control | Two controllers in series | Temperature control with flow cascade |
| Feedforward Control | Compensate for disturbances | Reactor feed composition changes |
| Ratio Control | Maintain ratio between variables | Blending operations |
| Override Control | Switch between controllers | Constraint handling |
| Model Predictive Control (MPC) | Model-based optimization | Complex multi-variable processes |
📌 IMPLEMENTING APC IN PLC AND DCS
Function Block Approach
"Advanced process control is typically implemented using function blocks or custom programming capabilities at the DCS level". Modern PLCs and DCS systems provide extensive function block libraries for implementing APC strategies.
"The DCS and PLC have many powerful features that still remain under-utilized". Learning to leverage these capabilities is what separates advanced engineers from the rest.
Standard Function Blocks
Common function blocks for APC include:
| Function Block | Purpose |
|---|---|
| PID | Basic proportional-integral-derivative control |
| PID with Feedforward | PID with disturbance compensation |
| Cascade | Master-slave controller configuration |
| Ratio | Maintain set ratio between variables |
| Selector | Select between multiple inputs |
| Split Range | Split control output across multiple actuators |
Siemens PCS 7 APC Library
Siemens offers an "advanced APC (Advanced Process Control) library" for its PCS 7 DCS system. The library includes "pre-engineered function blocks, faceplates and human machine interface symbols".
This library enables engineers to implement sophisticated APC strategies without starting from scratch.
Hybrid Solutions
Modern automation systems increasingly blur the line between PLC and DCS. "ECS/ControlCenter system offers a hybrid solution, combining the benefits of traditional DCS systems with the flexibility of modern PLC/SCADA systems".
This hybrid approach allows engineers to implement APC strategies on cost-effective PLC platforms.
📌 COMMON APC STRATEGIES
Cascade Control
Cascade control uses two controllers in series—a master controller that sets the setpoint for a slave controller.
Example: Temperature control with flow cascade
Master controller: Temperature controller
Slave controller: Flow controller
Benefit: Faster response to flow disturbances
Feedforward Control
Feedforward control compensates for known disturbances before they affect the process.
Example: Reactor temperature control
Measured disturbance: Feed temperature
Feedforward action: Adjust heating based on feed temperature
Benefit: Proactive rather than reactive control
Ratio Control
Ratio control maintains a fixed ratio between two or more process variables.
Example: Blending operation
Controlled variable: Ratio of component A to component B
Manipulated variable: Flow of component B
Benefit: Consistent product quality
Override Control
Override control switches between multiple controllers based on process conditions.
Example: Constraint handling in a reactor
Primary controller: Temperature control
Override controller: Pressure limit
Benefit: Safe operation within constraints
📌 DESIGNING APC SCHEMES
Step 1: Understand the Process
Before designing any control scheme, you must understand the process:
Process dynamics: How does the process respond to changes?
Interactions: How do variables affect each other?
Constraints: What are the operating limits?
Objectives: What are you trying to achieve?
"The ability to look at a process flow diagram or P&ID and based on operations goals and objectives" is essential for effective APC design.
Step 2: Define Control Objectives
What are you controlling? (temperature, pressure, composition)
What are the constraints? (safety, equipment limits, product quality)
What are the economic objectives? (maximize throughput, minimize energy)
Step 3: Select the APC Strategy
Based on the process characteristics and objectives, select the appropriate strategy:
Simple disturbance: Feedforward control
Slow process with fast disturbance: Cascade control
Multiple interacting variables: Model Predictive Control (MPC)
Constraint handling: Override control
Step 4: Implement in PLC/DCS
Use standard function blocks where available
Develop custom blocks for specialized applications
Test thoroughly before commissioning
Step 5: Tune and Commission
Tune controllers for optimal performance
Test with process disturbances
Document settings for future reference
📌 WHY THIS COURSE: MASTER APC IMPLEMENTATION
Advanced Process Control is a high-value skill in process automation. The DCS450: Function Blocks for APC Implementation in DCS/PLC course provides comprehensive training on:
Design of continuous and batch control schemes inside any DCS/PLC
Interpreting process flow diagrams and P&IDs
Function block implementation for APC strategies
Practical tips for effective APC implementation
Additional Learning Resources
APC275: PLC/DCS-based Advanced Process Control Implementation Tips — Advanced APC implementation tips
APC200: Industrial Advanced Process Control Design and Optimization — APC principles and practice
Introduction to Regulatory Control — Foundation for APC engineers
📌 WHO SHOULD TAKE THIS COURSE
Process automation engineers designing control systems
Control systems engineers implementing APC strategies
DCS engineers configuring advanced control
PLC programmers expanding into process control
Chemical and process engineers working with automated systems
Students preparing for careers in process automation
📌 LEARNING PATH: APC IMPLEMENTATION
Phase 1: Fundamentals (0-2 Months)
Understand regulatory control and PID tuning
Learn function block programming in PLC/DCS
Study basic APC strategies (cascade, feedforward)
Phase 2: Advanced Strategies (2-4 Months)
Master ratio and override control
Study model-based control techniques
Learn from real-world examples
Recommended: APC275: PLC/DCS-based Advanced Process Control Implementation Tips
Phase 3: Professional Application (4-6 Months)
Design APC schemes for complex processes
Implement and tune in real PLC/DCS systems
Optimize for performance and efficiency
Recommended: APC200: Industrial Advanced Process Control Design and Optimization
📌 FINAL THOUGHTS
Advanced Process Control is the difference between a process that merely runs and a process that is optimized. "The DCS and PLC have many powerful features that still remain under-utilized". Learning to leverage these capabilities is what separates advanced automation engineers from the rest.
"Maximize the effectiveness of control scheme design and implementation in DCS or PLC". Whether you're implementing cascade control in a DCS or developing custom APC strategies in a PLC, the skills you develop will be in high demand across process industries.
Start building your APC expertise today with quality training and practice.
📌 AFFILIATE DISCLAIMER
Disclosure: Some of the links in this article are affiliate links. This means I may earn a commission if you click through and make a purchase, at no additional cost to you. I only recommend products and courses that I believe will provide value to my readers. All opinions expressed are my own.