AT THE MOST basic level, an alarm system provides information through a human-machine interface (HMI) console. Often linked to a PLC, these systems allow for a clear look at the details about historical and current alarms. When an event occurs, the alarm pops up on the console. Operators are able to acknowledge and clear the alarm once it has been fixed. The information may then be stored to create charts and graphs to assist in identifying trends or events leading up to and after alarms.
"Intermediate systems function essentially the same way as basic systems with the difference mainly in the notification of an alarm,” says Renee Brandt, product marketing manager, Wonderware. “In basic systems, an operator must be located directly in front of the display to see and respond to the alarm. Intermediate systems have the ability to send alarms to portable devices such as PDAs or other types of personal digital assistants. This ability is useful when companies share or divide resources; it allows an individual operator to attend to more than one machine.”
Alarms that provide information to keep processes running are essential, but more important is the ability to identify trends that improve machine productivity. The next level of alarm management provides the ability to analyze messages in the event history. This in turn lets the users view operational changes and identify root causes.
"Alarms based on efficiency are much more sophisticated than purely reactive alarms," says Roy Kok, senior product manager for Proficy, GE Fanuc Automation. "Current development is focused on the historization of alarms, allowing users to construct an historical database. Technologies readily available today allow users to view this database via a web interface. This type of portal technology receives notification of an alarm and allows different levels of personnel to access and look into the context of specific events.” Groups of users can be established and alarm types can be sent to specific groups. Different levels of notification can also be established. An alarm can be sent to an operator who’s responsible for correcting the situation and, at the same time, a notification can be e-mailed to the plant manager or quality department so that the occurrence can be logged and tracked, or for other remedial actions.
"Alarms are set up to be delivered based on specific values, settings or levels,” adds Brandt. “These settings are referred to as ‘tags.’ If a holding tank has a capacity of 1,000 gallons, a tag can be set such that if the level remains below 800 gallons, everything is OK. Once that tag is exceeded, an alarm is sent and an operator will be required to respond.”
Alarm events can flood operators with numerous messages that are all related to a single root cause. “The trend is to develop systems that have the ability to interpret root causes," says Eric Dorgelo, systems architect, Rockwell Automation Software Group. "The infrastructure currently exists to deliver events using Internet standards. Airlines currently use this to send flight information messages, and alarm systems can use this same technology.” These types of predictive alarming systems are still in development, says Dorgelo. “The technology will really start to take shape over the next one to three years,” he adds.
Kok agrees with the potential value. "Ultimately, these predictive systems will allow operators to make better decisions," he states.
An additional advantage for machine builders is the ability to reuse alarm design work from project to project. OEMs can build new projects based on existing programming from past projects, reducing development costs and time-to-market. The information is retained in libraries and can be re-applied in new projects.
Industry standards such as the OPC Foundation Alarms & Events specification provide the means for interfaces across different products. The OPC Foundation aims to improve interoperability in automation by creating and maintaining open specifications that standardize the communication of acquired process data, alarm and event records, historical data, and batch data to multi-vendor enterprise systems and between production devices.
It’s high time to stop thinking about alarm systems as purely reactive devices. These days, they also can be an effective tool in tracking and identifying little problems before they become big problems.