By Dan Hebert, PE, Senior Technical Editor
Alarm systems have progressed significantly since the days of light boxes, illuminated indicators and pushbuttons. Most advances have been due to three technologies: programmable graphics terminals, Ethernet/Internet communications and controllers with PC-like functionality.
"With modern HMIs, OEMs have a full-blown graphical interface that provides realistic representations of what's actually taking place in their machines and robots, as opposed to just an assortment of flashing lights," says Ben Orchard, application engineer, Opto 22 (www.opto22.com).
Orchard points to Opto's G4 Handler, a large machine for final assembly and testing of the company's G4 I/O modules. "We recently installed an HMI to view diagnostic and other data," he says. "Our operators clearly see if a screw gets jammed, if air cylinders move up and down as they should or if another machine malfunction has taken place."
PLCs are great relay and timer replacements, but poor data handlers. Today's programmable automation controllers (PACs) have PC-like data-handling capabilities, ideal for alarm and event handling.
"Machine and robot control system PACs contain a plethora of data points related to machine conditions, events and causes," notes John Dart, program manager of the global OEM solutions business at Rockwell Automation (www.rockwellautomation.com). "Using unmodified Ethernet with PACs enables use of standard notification tools such as email, paging, text messaging, secure remote monitoring and other technologies. Unfortunately, the task of finding this data in a custom-programmed control system is often expensive, time-consuming and prone to error."
[pullquote]Dart says, to reduce customization, machine builders should first implement standard ways of describing machine entities, conditions and events. "Once these standards are implemented, then a consistent alarm and event-handling methodology integrated with the machine's overall control system can be implemented," he concludes.
Ethernet and Internet technologies can provide many of the remote links that increase the utility of alarm and event notifications systems. "Advanced Ethernet controllers can send email to operators and supervisors about an alarm or an event," observes Charlie Norz, product manager of I/O systems at Wago (www.wago.us). "Some of our Ethernet-enabled controllers contain a file server. After events and data are logged, they can be exported into a comma-delineated file as part of an email alert. Recipients can review data leading to an error, as well as the actions occurring after the error. This tracking, handy in root-cause analysis, enables a supervisor to see who was logged on at time of error and who pressed the acknowledge button."
Time-stamping has become increasingly important in several applications, adds Norz. "We had a customer with an extensive network of controllers leading back to a main system for multi-facility supervision," he relates. "The primary concern was to ensure all clocks were synched for time-stamping events and alarms. The solution was simple network time protocol (SNTP) synchronized with a common time server via Ethernet."
Chris Vitale, senior product manager with Turck (www.turck.us), details other benefits of Ethernet. "The bandwidth and speed of an Ethernet backbone allow greater amounts of data to be collected and shared," he states. "Each device can share not only the status of an individual input or output, but also diagnostic data coupled to the same messages, all without a decrease in the performance of the network."
A combination of PAC power and Ethernet can simplify alarm and event systems and speed implementation. "Most modern automated machinery alarm and notification systems offer remote connectivity as an important option, with alarming often originating at the controller," notes Alan Cone, HMI marketing manager at Siemens Industry (www.usa.siemens.com/industry). "Many controllers now include built-in process and system diagnostic routines that automatically report on I/O and device alarms. They also report specific sensor alarms such as wire-off or under-range of analog signals, eliminating manual logic development. These alarms often have automatic connectivity to compatible HMI operator panels or to networked SCADA systems for intranet/Internet accessibility without manual configuration."
