Controllers and drives set the pace of change

System design from as little as 8 years ago seems antiquated

By Rick Rice

It wasn’t that long ago that designing a control system, particularly PLC- or PAC-based, was a simple decision. One picked your favorite processor and built your design around it.

These days, the simple decision is no longer simple. Technology advances at such a rapid pace that there is no such thing as a base platform any more.

I have been with my current employer for eight years now. As with any employment situation, some things move faster than others. Closer to the start of my tenure, I spent some time coming up with the design to replace the controls on a horizontal packaging machine.

The machine was built in 1969 and is still in use today, but it seemed like a good idea to update the controls to something at least in a PLC-based platform as this machine was all relays and contactors.

As things would transpire, I didn’t get to do that controls upgrade. The life of a co-packer is always in flux, and the project just never rose to the top of the pile.

Fast forward to 2019 and that project is now in focus as part of a determined effort to improve workplace safety. Let’s face it a machine made in the late 1960s wasn’t manufactured with safety as a forefront concern.

After pulling my eight-year-old design out of what I now call my archives, I was surprised to learn how far our company has advanced in these past eight years as far as what type of control designs we are comfortable working with.

My design, sound for when I designed it back in 2011, was seriously out of date, from a technology standpoint. The base approach to control systems for me hasn’t changed much in the 30-odd years I have been playing in this wonderful field of automation. But the components and the technology behind them have little semblance to the devices I once called “standard.

Designs for me have always been about power and control with the e-stop, reset, stop and start circuit snuggled comfortably between the two. Holding the two or three parts together was the network platform so we humans could interact with the bits inside the box.

The first decision needs to be the network, as pretty much all of the other components that make up a control system depend on some aspect of that network architecture. For most people, at least in North America, that choice is Ethernet I/P. Other popular architectures are built around Profibus or Modbus. No matter what name we give to that network protocol, it forms the backbone of a modern controls design.

Components on the power side take on a whole different aspect when network connectivity is the base of the design. Traditionally, a variable-frequency drive (VFD) would be controlled by digital signals with contactors before and/or after the drive to isolate the power for safety.

The same goes for a servo or stepper drive. With the advent of networks, the control of drives has shifted to network messaging. Early drives would have just status and command registers that were sent to and from the programmable controller. Status bits, such as ready, running, forward, reverse, accelerating/decelerating and velocity feedback, would incorporate the information coming from the drive while bits such as stop/start, jog, forward/reverse direction and command reference, would comprise the information going to the drive from the PLC.

These early data exchanges mimicked the digital signals that were traditionally used to control the drive. Drives utilize an expanded data structure to send far more than just command and status bits. Important information such as torque, temperature and bus voltage are available to the programmer to better manage the use and care of the drive.

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On the control side, components have had an enormous growth in technology, also based on network connectivity. PLCs and remote I/O or field I/O have been talking to each other on networks for many years, but recently the number of types of devices has expanded dramatically.

On-machine blocks that contain not only digital and analog control points but whole valve banks are commonplace in control systems. Joining those are heater controls that house both the control voltage and the thermo-couple feedback to close the loop, linear and rotary actuators with closed-loop feedback and other advanced technology.

The best part of this development is that the same advanced data exchange that happens on the power side happens here on the controls side.

Straddling the bridge between power and control, the safety circuit is the most important component in the control design. With the advanced features that both power and control components now possess, it just makes sense that hardware manufacturers would bring that same technology to safety devices.

Recent advances in safety circuits leverage the convenience of networking on this heart of the control system. Multiple safety relays, each with traditional wiring and control standards, can be connected to a master device via wireless technology.

Each relay is treated as a node on the master. Individual safety relays can each contain up to 32 smart devices on each of two channels for a total of 64 safety devices. This technology is very similar to IO-Link where a four-wire connection carries both power and communications/control to the 32 nodes on each channel.

Devices can be swapped out and assume both the node number and configuration of the previous device. When used with a PLC or PAC from the same manufacturer, the master safety device automatically populates a tag profile and provides programming access to both input and output functions, right down to individual devices on each safety channel.

As with the power and control devices, these new-generation safety devices have value-added information, such as temperature, current and voltage levels, that can be accessed via the master device.

One of the greatest developments has been the use of these smart safety components to improve the implementation of variable-frequency and servo drives. Gone are the days of upstream and downstream power contactors to safely remove power from motive devices.

Drives have electrically operated power circuits that render a drive safe by incorporating a safe-torque-off (STO) safety function that is operated by the dual circuits from an associated safety relay. This technology ensures that no torque-generating energy can act upon a motor that is connected to the drive.

The net result of all of these advancements in technology is a dramatically reduced footprint in the control cabinet. The control design that I alluded to previously seems archaic when looked upon eight years later. That design was planned for an enclosure that measured 48 inches high by 60 inches long with a great deal of on machine wiring required to complete the controls upgrade.

With new technology, we are able to split the power and control into separate enclosures and introduce protection from arc flash. The resultant enclosures are 30 x 24 inches with most of the field I/O located on-machine. Wiring time will be less than a third of what it would have been with the old design.

The footprint is just a part of the story as the wealth of value-added information can be used to create a much-enhanced operator interface that puts diagnostics tools in the hands of operators where a maintenance technician would normally be needed to interpret. This machine-level empowerment results in reduced downtime and enhanced performance.

Machine commissioning time is also reduced as the simplicity of just a power connection with a network cable reduces wiring issues. Many control components now come with Web interfaces that also enhance the implementing and troubleshooting process.

Simply typing in the network address of the device, such as 192.168.1.10 for a private network, in a Web browser when connected to the machine network will bring up the manufacturer’s Web-page interface for the device. Diagnostics and configuration pages are common on this interface and eliminate the need to purchase costly software to separately achieve this purpose.

With all of this technology at our finger tips, controls design has taken on a whole new look. Shorter design time, reduced build times, enhanced diagnostic tools and safer control circuits are the landscape of the future.

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