Category Archive: PLC Programming

Understanding Safety PLCs

A major component behind the efficient functioning of today’s process control systems is the programmable logic controller, or PLC. Uniquely suited to withstand tough industrial environments, PLCs serve to reliably automate many manufacturing systems, such as assembly lines or industrial equipment.

However, in certain applications, such as those involving machinery that poses a risk of operator injury, an additional layer of protection is required. That is where the safety PLC comes into play. This blog will discuss the general purpose of the safety PLC and its capabilities as well as its advantages over the standard PLC.

What is a Safety PLC?

 

Understanding Safety PLCs

A safety PLC is still capable of supporting all the key manufacturing applications that a standard PLC does. Its biggest difference, however, is that it also integrates safety functions that allow it to control key safety systems as well. The key objectives of safety PLCs are:

  • Do not fail
  • If failure is unavoidable, fail only in only the safest and most predictable way possible

The safety PLC meets these objectives by incorporating multiple redundant microprocessors. These built-in redundancy layers are a key capability because it means safety PLCs can eliminate the need for safety relays that are often used to create redundancy in the standard PLC. Safety PLC platforms include several standard diagnostic systems which enable them to continuously monitor inputs and outputs, searching for any potentially unsafe conditions. If these monitoring mechanisms detect an internal failure, a safe shutdown is initiated.

At its highest safety integrity level, a safety PLC is capable of detecting over 99% of potential system failures. This makes them suitable for use in applications that could cause harm to the employees, operators, environment, business, and equipment, including applications and installations that need to meet IEC 61511 and IEC 61508.

Safety PLCs vs Standard PLCs

Although similar to the standard PLC, a set of rigorous international standards must be met to be considered a safety PLC. The key to implementing PLC safety systems is to incorporate the best of PLC capabilities and integrate a safety controller into a single system.

The main benefit of standard PLCs is that they are simple to wire, easy to use, and do not require experienced technicians for troubleshooting purposes. This will generally make them more affordable; however, they typically have no way of detecting wiring errors on input/output (I/O), such as channel mismatches, ground faults, and short circuits. Different output types can lead to additional instability, and problems may tend to increase with an increase in the number of relay types. Delays in communication between components can lead to difficulties in diagnosis, which can be catastrophic in certain industrial applications.

Cost should never be the primary motivator when it comes to ensuring the safety of personnel, the business, the environment, and the community. Even though there are some additional costs associated with purchasing and maintaining safety PLCs because of their rigorous adherence to safety standards, the peace of mind, security, and benefits of these controllers definitely outweigh any cost concerns:

  • Safety PLCs offer networking of input-output devices and diagnostics via human-machine interfaces. This can help to alleviate some installation costs.
  • Robust diagnostics or information tracking capabilities are easily integrated and provide flexibility in many safety-essential applications.
  • Financial and human resources can be minimized in field wiring, as safety PLCs serve to eliminate the need for safety relays.
  • A safety PLC system is easy to modify as it only requires basic programming updates, without installing additional relays or necessitating any wiring changes.

Safety PLCs from Turner Integrated Systems

At Turner Integrated Systems, we are capable of designing safety PLCs for a wide range of applications that require extra protection. Located in Rochester, New York, we have in-depth experience in many PLC categories, and we custom-design systems to meet specific safety and operational requirements for each project. Contact us today for more information about our safety PLCs.

PLCs and SCADA Systems in the Wastewater Treatment Industry

From cooking and drinking to bathing and washing to product manufacturing to waste management, water plays a role in many of our day-to-day applications. Once it has served its role in these applications, it is not simply discarded. It is categorized as wastewater—also referred to as sewage—and sent to a wastewater treatment facility, where it is cleaned up for reuse. This water use cycle ensures we maintain a sustainable supply of safe water for the future.

The wastewater treatment process is highly complex, requiring accurate and precise measurement and control over various equipment (e.g., pumps, purifiers, and filters) and equipment parameters (e.g., pressure, flow, and filtration). By integrating measurement and control technologies into operations, wastewater facilities can ensure they achieve and maintain the proper process conditions for effective and efficient water and wastewater treatment. In recent years, programmable logic controllers (PLCs) and supervisory control and data acquisition (SCADA) systems have grown in popularity within the industry as facilities work to manage the increase in wastewater stemming from rising water use across the residential, commercial, and industrial sectors.

Importance of PLCs in Wastewater Treatment

Programmable logical controllers (PLCs) are ruggedized digital computers often utilized for industrial process automation. They can be used to automate a single process or machine function or an entire system setup by stopping, starting, slowing, or speeding equipment operation in response to inputs from connected devices (e.g., control panels and sensors).

In the wastewater industry, these devices help ensure treatment operations proceed smoothly with little to no human operator involvement. Some of the equipment they are typically used to control include filtration and aeration units.PLCS & SCADA Systems

Compared to older automation technology (e.g., relays and timing mechanisms), PLCs have a number of advantages, such as:

  • Greater ease of use. PLCs require less time and resources to integrate as they can simply be reprogrammed to suit different process requirements and restrictions. In contrast, older automation technologies needed to be rewired to accommodate new specifications.
  • Better process reliability. PLCs automate equipment operation based on data provided by various sensors and input devices. This function ensures the process conditions remain appropriate at any given time.
  • Lower labor requirements. Automating wastewater treatment operations reduces the workload of human operators, freeing them up to focus on other important facility tasks.

Importance of SCADA Systems in Wastewater Treatment

PLCs are an essential component of supervisory control and data acquisition (SCADA) systems. SCADA systems consist of a collection of hardware and software components that collect, transmit, and distribute data across various devices within a network. The information can then be analyzed to determine whether any system adjustments are needed.

In the wastewater treatment industry, these systems are used to ensure the quality of the processed water. They provide graphical and numerical data about different process instruments and equipment and enable human operators to adjust operations accordingly in response to the provided information. These functions help ensure conditions during water treatment operations remain at effective and safe levels.

Some of the benefits of integrating SCADA systems in water and wastewater treatment facilities include:

  • Improved use of existing infrastructure and resources
  • Reduced risk of operator overload in situations where multiple system alarms may occur within a short period of time
  • Enhanced monitoring of remote and vulnerable sites
  • Decreased costs for utility companies and customers
  • Better oversight over systems and processes
  • Automated data collection and reporting operations

PLC and SCADA Solutions for the Wastewater Treatment Industry at Turner

PLCs and SCADA systems are key to improving water quality, increasing process efficiency, reducing labor costs, and more in wastewater treatment facilities. If you’re looking to integrate them into your facility, turn to the experts at Turner Integrated Systems.

We design, manufacture, and install control systems for a wide range of industries, including the wastewater treatment industry. Whether you need assistance with PLC programming and implementation, SCADA integration, hazardous areas design, or something else, we’ve got you covered. We will deliver an appropriate control solution and discuss how to properly use and maintain it to ensure it operates smoothly.

To learn more about our control system capabilities and how we can benefit your wastewater treatment facility, contact us today.

PLC Programming Practices

As with any type of programming, there is no one way to develop logic for an application or a process. This of course leads to the ability to make decisions that are based on the specific tasks or operations that need to occur. However, the flexibility of PLC programming environments provide ample opportunity to create a colossal mess.

At Turner Integrated Systems we adhere to specific guidelines for PLC programming practices. Not only has this proven to serve our customers well, but it has also been an asset to ensuring our team is consistent with each other allowing for simple diagnostics and clear understanding of modifications when changes need to be made.

In addition to simplifying future changes and troubleshooting, some of these best practices have drastically improved HMI and SCADA development times.

PLC Programming

Top 5 Guidelines

Here are just a few of the main guidelines we follow:

Tag Naming

On most modern PLC platforms, PLC tags are name-based and not just register-based addresses. This evolution has certainly made great improvements in interpreting logic and development efficiency, but it can get messy quickly without a proper naming convention for the tags. Aside from that, it can even lead to misdiagnosing logic issues if a tag is considered to be missing, but in reality it wasn’t named as expected. 

On a basic level, tag names should begin with the device or process that the tag is associated with, followed by the function of the tag. This makes it simple when determining the full list of tags in play with a search for a device. 

Also, many tag naming systems have a limit to the number of characters allowed. Even if a character limit didn’t exist, long tag names gets difficult to manage. This being the case, it’s a good idea to have well documented short-codes for functions. We use codes that have been around in the process control world for decades. 

Device identification should also be as simple as possible. We use the device ID as found on the process and instrumentation diagram. For example, a run status input for Pump 1 should be titled P1.YI, P1/YI or P1_YI depending on the tag organization structure of the PLC in use. Along with each tag a description should be included in the tag properties that clearly explains the function of the tag.

UDTs

UDTs or “User Defined Tags” is another tool that should be considered when developing PLC software. UDTs help group the key tags of a device or a logic function to allow for the building of tag templates.UDTs

This concept aids significantly in the assurance that tag names are consistent. When using UDTs an instance of the UDT can be created which automatically creates all of the related tags required for the device or process.

Logic Routine Structure

It is up to the programmer to decide the layout and scan order of logic routines. Our own guidelines require logic to have a basic organization that separates process related logic from device control logic.

Alarm logic is to be grouped depending on the type of alarm. Device related alarms should be in the logic area of the device. Process related alarms should be in the logic area of the process control logic. Miscellaneous alarms are to be in a separate routine.

Alarm logic

In-line Documentation

As with any programming language, documentation in the form of commenting throughout the code is an expectation. Having the ability to read the intentions of a logic section helps to understand the importance of what the program is doing.

This not only helps with diagnostics, but it provides a clear path for understanding the best way to approach future modifications.

Change Management / Logging

Comments outside of the logic file in a dedicated change log is an important tool in understanding the evolution of a control system. When changes are requested, it’s not always understood what the complete effect of the change will be. 

Some changes can involve ripping away logic that took hours to build. This is why it’s important to archive versions of a project file that can be tracked with a list of modifications that have been made. Some manufacturers provide software utilities to examine differences between logic files. These can be very useful but do not replace the need for a change tracking document. 

These are just a few of the guidelines we have built into our workflow to guarantee our systems will perform as designed and allow our team to easily support our systems in the field for years down the road. This is not an exhaustive list, and we expect that as technology keeps moving forward with new logic control software and hardware solutions, our procedures will evolve along with them as necessary.

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