Introduction
Supervisory Control and Data Acquisition (SCADA) and Programmable Logic Controller (PLC) are two important terms in the industrial automation arena. Now, the question arises here, Is SCADA possible without PLC? If yes, How does this affect the system's performance?
In this blog, we are going to discuss this question in detail and also about the best practices to be followed while implementing SCADA without PLC.
Understanding SCADA and PLC
Before answering the main question, let’s explore what SCADA and PLC do in industrial automation.
An SCADA system monitors, controls and reports on the status of various devices and processes in real-time. It allows operators to view and respond to plant system events through a graphical representation of the equipment and processes they control.
Whereas, a PLC is a hardware controller that performs pre-determined tasks on the basis of input/output signals to ensure a process is properly controlled. It works as the central nervous system of an automated process, guaranteeing that everything proceeds accurately and efficiently.
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Can SCADA work without PLC
SCADA systems can survive without PLCs in certain cases, especially in small or non-critical applications. Here’s how:
Know the situation
In some cases, especially where budgets are tight, SCADA systems may be used to directly control small equipment setups or non-critical applications with Remote Terminal Units (RTUs) or other controllers. For instance, a small water utility may choose to use SCADA to directly read and control pumps and valves without PLCs.
Use RTUs and PACs
Remote Terminal Units (RTUs) and Programmable Automation Controllers (PACs) are devices that offer local control and can act as a bridge between the actual equipment and the SCADA system. PACs and RTUs can easily perform some of the real-time control functions that PLCs are used for.
Keep control logic simple
If your SCADA system is going to handle the control, keep the control logic simple. Complex algorithms can overload the processing capacity of the SCADA system. Narrow the scope of the control to just what is necessary and let the SCADA system perform the monitoring and supervisory functions.
Can HMI Work Without PLC
PLC can be removed from the equation entirely, but such an architecture is generally only practical for small or basic applications. Many HMIs (Human Machine Interface) can communicate directly with field devices using protocols like Modbus or Ethernet/IP. Some even include an embedded controller suitable for basic control applications.
This approach does have its drawbacks, however. The HMI is still only really intended for the human interface and Displaying the information. Complex control logic and other non-real-time or heavy-processing tasks can still be performed by a PLC. This makes the overall system less reliable, less maintainable, and less efficient, especially in more challenging industrial settings.
A small packaging line, for instance, might employ an HMI with an embedded controller to monitor basic parameters like conveyor belt speed or manual package cycles. The architecture can be simple, inexpensive, and easy to implement. It will not, however, be capable of managing more sophisticated automated control tasks.
In general, then, while an HMI may be used without a PLC, the combination of both is greatly superior for most industrial automation applications.
Case Study: Small Water Treatment Plant
Consider a small water treatment plant located in a rural area. The plant's primary goal is to ensure clean water supply with minimal operating costs. Budget constraints mean the plant cannot afford the traditional SCADA-PLC setup. Instead, the plant employs a SCADA system directly interfaced with RTUs to monitor and control its operations.
Implementation
- Monitoring Water Quality: The SCADA system acquires on a continuous basis data from sensors measuring pH, turbidity and other required water quality parameters.
- Controlling Pumps and Valves: The SCADA system, based on the acquired data, controls pumps and valves via RTUs ensuring the right water flow to the respective consumers or its treatment in the case of a waste-water treatment plant.
- Data Logging and Alerts: The SCADA acquires and logs data for historical reporting. It also issues alerts to the plant operators in case of any anomaly or required maintenance.
Results
- Cost: by not using PLCs, the plant does not have to spend money on initial equipment setup or ongoing maintenance.
- Complexity: the simplified control logic in the field is easily managed by the SCADA solution, providing the desired functions needed to operate the plant.
- Limitations: the plant recognizes that under normal operating conditions this configuration is advantageous. However, the SCADA solution may not be able to keep up with rapid response requirements or perform complex control algorithms that would be more efficiently programmed in a PLC.
Good Practices for SCADA Implementation without PLC
In case you still go ahead with SCADA implementation without PLC, here are some good practices to follow to ensure efficient and reliable SCADA implementation without PLC:
- Good Quality RTU and PAC: Invest in good quality RTU and PAC with reliable communication and processing power for local control logic.
- Simple Control Logic: Ensure control logic is simple and does not burden the SCADA system in any manner. This will ensure better performance and ease of debugging.
- Redundancy and Fail-safes: Use redundant networks for communications, power supplies and fail-safes where possible to ensure constant operation and reduce the likelihood of equipment failures causing system outages.
- Routine Maintenance: Perform periodic maintenance to ensure the SCADA system and equipment are kept in good working order. This will allow problems to be detected and addressed before they disrupt SCADA functionality.
- Thorough Testing: Thoroughly test the SCADA configuration before going live, and under a variety of conditions to simulate the control loads the system will be subject to.
Future of SCADA Without PLC
Technology is always evolving and improving. SCADA devices and RTU’s/PAC’s are no exception. SCADA devices are getting more powerful and may begin to take on more tasks traditionally performed by PLC’s and vice versa.
Instead of choosing between SCADA and PLC we may in the future have more versatile tools that will allow for greater automation and integration. Until that day arrives, the choice of going SCADA without PLC should be an application specific decision.
Conclusion
In conclusion, the statement ‘can SCADA work without PLC?’ is answered as a yes but it is recommended for limited scenarios such as small or non-critical applications. The popular combination of SCADA and PLC is still the best option for an industrial process with optimal control and monitoring. It provides the highest reliability and safety for a machine or device.
Know the advantages and disadvantages of SCADA and PLC systems to make the right choices according to your goals and restrictions. Whether it’s the implementation of both or SCADA without PLC, always design a solution that fits your needs.
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If you want to learn about data types used in PLC than ,Check out our detailed guide on PLC data types and their sizes.
Well explained thank you so much
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