The conflict between keeping machines running and maintaining a safe working environment alwayswill exist. Fortunately, advances in machine automation and safety systems are like having a guardian angel on your shoulder, minimizing tradeoffs between uptime and safety.
Safety can be defined as a state where risks and hazards are judged to be acceptable or in control. Although this classic definition doesnt posit control to be the same as automation, better control through automation can reduce risk to an acceptable level.
Old-school versus new
Traditional safety systems are simple, effective and proven during decades of use. Thats the good news. The bad news is that these systems can be devilishly difficult to troubleshoot and repair.
An old-school system from way back in the past century might consist of a number of e-stop pushbuttons and electromechanical interlocks connected to a fail-safe relay system. Such a system reacts quickly and reliably to shut down affected equipment.
Maintaining and repairing machines protected by an old-school system is easy if the work can be done with no time constraints and if no power needs to be applied to any part of the machine. Also, lots of time is required to find root causes, as diagnostic information is minimal or nonexistent. Another issue is that no part of the machine or line can be started up until all work is finished.
But in the real world, woe comes to those who must quickly repair old-school systems, or need to maintain these systems during short time windows. Unfortunately, these systems shut down entire production lines with no thought given to the time and effort required to get machines and lines back up and running.
However, new-school systems recognize the need to get machines back up quickly, and also make accommodations for effective maintenance. Safety controllers, digital safety networks and smart sensors provide a host of benefits to plant personnel who need to quickly and safely fix and maintain equipment.
What would you say to a vendor who tried to sell you a complex machine controlled by panels full of relays and timers? Youd probably throw the salesman out without a second thought.
What if the vendor knew nothing of digital networks, and chose to connect sensors, motor drives and other devices to the controller via hard wiring? Chances are youd look for a supplier that knew when and where to deploy digital communications to speed startup, reduce wiring errors and ease troubleshooting.
You probably also would want a technically proficient source that could provide smart sensors connected to the digital network to speed diagnostics and troubleshooting.
Move to integrated systems
Most plant personnel know enough about automation to require machine control via PLCs or other solid-state controllers, and many also want to see digital networks connected to smart sensors and drives. But, many of these same plant personnel dont know they can and should demand at least some of these automation features in their safety systems. Some dont realize the benefits, and others are reluctant to abandon the tried and true for a new solution, especially in a critical area like safety.
Lets face it, theres something reassuring about pushing a heavy-duty e-stop pushbutton or engaging an electromechanical switch, immediately hearing the satisfying clunk of a safety relay, and seeing an entire line safely and quickly shut down. Giving up this reassurance for a more advanced safety controller connected to smart sensors by digital communications is quite a leap, even when the new system meets or exceeds required safety codes and standards.
Machine builders and other suppliers recognize that getting some plants to accept newer safety systems can be difficult. The addition of modern safety devices has caused a great deal of confusion when installing new machines in a plant with lots of older equipment, reports Todd Evans, electrical engineering supervisor at Fosber America (www.fosber.com). Fosber is an OEM supplier of equipment for the corrugated paper industry (Figure 1).
The older equipment isnt usually guarded to current requirements, and its sometimes difficult for our customers to understand why all of the newer safety devices are needed, Evans says. Knowledge of device networks, how the devices work and how the devices interlock may not be ingrained into the maintenance department. This is changing, however, as every year our customers engineering departments are upgrading safety requirements for their machines.
But dealing with the newer technology has its rewards. Using safety networks instead of hard-wiring is a change culturally and in practice, says Mark Harned, vice president of controls for Astec (www.astecinc.com), which produces continuous and batch-process hot-mix asphalt facilities and soil remediation equipment. Our customers quickly found out that they didnt have to use their voltmeters to troubleshoot everything. They could actually monitor from a computer and pinpoint problems by looking at the operator interface. We programmed the operator interface so our customers could see all the functions, specifically down to which node was causing the problem down to the individual e-stop or sensor level.
As Evans and Harned say, it isnt always easy to incorporate advances in safety systems. But as with many advances in technology, the benefits are real and must eventually be adopted to avoid obsolescence. Lets take a look at how these automated safety systems, digital safety networks and smart sensors can work together to ease repairs and maintenance.
It starts with the machine
Many of the potential safety hazards in your plant can be found on or around machines purchased from OEM suppliers. Fortunately, these suppliers realize how important it is to integrate safety as part and parcel of their machines.