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  • Author Author: rscasny
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Beyond the PLC: A Primer on Automation Panels

In the early days of automation, original equipment manufacturers (OEMs) shipped control systems with rack-mounted PLC’s, pilot lights, gauges, and push buttons. Over the years, the vast majority have simplified their systems by migrating to operator interface (OI) panels in place of other panel mount components. To reduce wiring costs and to make it easier to ship their equipment in modular sections, many have also moved to distributed IO.

 

And, in an effort to further reduce the cost associated with reactive maintenance, many OEMs are now adding secure remote connectivity to access end user networks to perform remote program modifications and analyze equipment performance. Typically, an OEM machine would utilize an automation panel consisting of a programmable automation controller (PAC) with distributed IO, a touchscreen operator interface with data logging, and an industrial security router. The PAC, OI, and router each have their own processor, their own installation requirements, and their own unique software configuration. Automation panels combine the programmable controller functionality and the operator interface into a single unit.

 

Backgrounder

Automation panels entered the market about 15 years ago. Many of these early units were simply operator interface panels with some local IO, ladder logic, and a flat database.  Modern automation panels like the GE QuickPanel+ include the full IEC61131 programming languages (Ladder, Structured Text, Function Block Diagram, Sequential Function Chart, and Instruction List), as well as user-defined data structures and user-defined function blocks.image

 

It may be more accurate to describe these automation panels as PAC controllers with a built-in operator interface, rather than just an operator interface that performs control. In the case of the QuickPanel+, OEMs can purchase a remote security software package from SecomeaTm that will allow the OEM to securely connect to the QuickPanel+ over the Internet using the customer’s existing network, eliminating the need for a separate security router. The advantages of this simplified architecture include cost savings, simplified maintenance, and improved performance.

 

Benefits

Automation panels can significantly reduce software development costs. Many automation suppliers tout the benefits of a shared database between the PAC and the OI panel, but if these are separate devices, then they still have separate databases at run time. This means that each time you add a variable, you need to download to both devices. If the controller and OI get out of sync, you end up with communication errors and possibly unexpected operation. Automation panels truly use a single database with a single development environment and a single library for reusable objects. Hardware costs are also reduced. Combining the controller, operator interface, and remote connectivity into a single device means only one device to purchase, install, and configure. This saves money on both production time and on panel space.

 

Maintaining one device is less work than maintaining three, especially when you have shipped a system to an end user that may be hundreds or thousands of miles away. With an automation panel, you can back up the operator interface and logic program on a single memory card or USB stick. If the end user has separate files for the operator interface and controller and needs to restore one or both programs, they might load different revisions and end up with a non-working system. Having a single program to restore is easier and eliminates version compatibility issues. A single device means a single point of connect. There is no need to connect to multiple ports to monitor or upgrade the system.

 

Performance

It may sound counter-intuitive, but combining the PLC and OI into a single device can actually improve the update times for the operator interface in many applications. This is because one of the main CPU tasks for a traditional operator interface is communications with the controller. When today’s operators press a button on the OI screen, they expect an immediate response for the equipment and immediate feedback on the graphic screen. The biggest reason for delays in that response is the communication driver between the OI panel and the PLC. With an automation panel, this communication is much faster, because it is internal to the device. There is no need to rely on serial or Ethernet communication links for updating operator screens.

 

Automation panels offer the same deterministic real-time control as traditional programmable controllers. Programmable controllers are a better fit for extremely fast scan times, very large IO counts, or high performance redundancy. For low- to mid-range applications that require a dedicated operator interface, automation panels like the QuickPanel+ provide a simplified architecture with easy remote connectivity options and lower total cost of ownership.

 

To learn more about Automation Panels, please download the attached document by GE Intelligent Platforms called "Automation Panels vs PLC in System Control," which was the source of information for this document.

Attachments:
imageautomation-panels-vs-plc-in-system-control-wp-gft886.pdf
  • in reply to rscasny

    Thanks for the great explanation. It seems that I have already worked with PLCs on a small scale. What you described is exactly what a main board in a dental chair does. It controls the movement and position of 2 or 3 motors which in turn raise/lower, recline/incline, and tilt the dental chair. Position is often monitored with sensors so preferred settings can be memorized and returned to with a single push of a button. Motors are usually bidirectional AC with a gear box or more recently hydraulics have been used to replace the motors in which case there is a hydraulic pump and a bank of solenoids that direct the flow of oil.

     

    Here is a PLC for a Pelton Crane Chairman 5000 Dental Chair.

     

    image

     

    Thanks again it is always fun to learn new things.

     

    John

  • Wow, that's interesting. 500?

     

    Well, I'm not surprised about the your not seeing a reference to PLC. The site does have a big following in the hobbyist and maker community. Someone interested in PLCs would not really be a maker; rather, someone who does is a field engineer in the industrial sector, a manufacturing engineer, a process control engineer in the chem or pharma or food processing industries. Not a great fit for the toy robot crowd. Plus, PLCs have a specific application -- controlling some type of machinery or equipment. Prior to PLCs, electromechanical relays were used to produce the control logic -- star, stop, reversing, ramp up down, etc sequences -- as wired up according to is ladder logic diagram:

     

    image

     

    The above is a logic control for a motor . As we see here, M1 and M2 are relays that are powered by L1-L2, say, 120V.   To Energize M1 (normally open), someone has to push the "forward" switch. which pulls in the M1 coil and closes the M1 (normall open) contact which locks in the M1 coil and at the same time opens the M1 (normally closed) to prevent the M2 coil from energizing -- in essence preventing the motor or compressor or whatever equipment from going into reverse while it is in forward. In the event that the motor becomes overloaded, the OL (normally closed) contact will open, which deenergizes the M1 coil and the motor coasts to a stop since the OL contact is upstream preventing the M1 or M2 coils from energizing.

     

    As you can imagine, creating all the control logic of a simple motor would require a lot of hardwiring and is not easily changed. Plus, electromechanical relays have their own set of reliable problems (coils burn out, contacts get welded together, etc)

     

    So, to get around the inherent problems of hardwired logic, as computer control was introduced into manufacturing decades ago, the PLC was created to do in software what was previously done with hardwired control. Plus, you can change the logic via a keypad that was easy to program since maintenance engineers didn't know a lot of fancy code. It saved some maintenance problems as well.

     

    Today, PLCs are the mainstay of manufacturing process control and machine design -- that is the mechatronics revolution.

     

    In the months ahead I will be writing contant that goes into much more depth on PLCs, if there is interest in the community.

     

    Cheers!

  • in reply to rscasny

    Thanks for the Info and the picture. I have been collecting the Initialisms used on the site for the last 4 years and have over 500 to date. This is the first time I came across PLC so I have added it to the list.

    Thanks John

  • in reply to jw0752

    Hi John. PLC stands for Programmable Logic Controller. Here's a pic:

     

    image

     

    But this isn't an automationa panel. It's just the PLC. Like the article stated, Automation panels have a lot more than a PLC.

     

    Thanks for reading.

  • Thanks for the good information.  One Question:  What does PLC stand for?

    John