Alarm Management Challenge 4: Quality of Values and String Processing
It’s a matter of fact that the communication quality to the PLC very much influences the alarm generation in the SCADA system. If the communication is bad, interrupted, or even lost, the system generates a flood of alarms which might lead to false conclusions. Therefore, the quality of values is essential. Another common challenge is the monitoring of string values via alarming features.
zenon’s Alarm Management Solution 4: Reaction Matrix
The most powerful tool for a global alarm definition, status supervision and string monitoring in zenon is the Reaction Matrix, known by zenon users by its abbreviated name ReMa. The Reaction Matrix differs from variable and datatype limits in a few ways, but most notably in its linking. Where limits are defined directly on the variable or datatype, the Reaction Matrix makes it possible to define a global alarm condition and reuse it for multiple variables. For example, in an automation system using zenon, there could be 300 valves and all valve statuses are read in as an integer for the defined states. Since all valves have a common value reading for their states, the Reaction Matrix is perfectly suited. The engineer must create only one reaction matrix with this configuration and it is then simply linked to all instances of the valve.
In addition to the global aspect of the Reaction Matrix, zenon also offers the ability to use a Numerical Reaction Matrix, a Binary Reaction Matrix, or a String Reaction Matrix. The Numeric Reaction Matrix gives the user the option to define the alarm set points in terms of less than, greater than, or equal to a specific numeric value. It also has a unique feature to “treat any value change as a limit violation”. The Binary Reaction Matrix gives the engineer the ability to define alarm conditions based on the state of individual bits of a word. The String Reaction Matrix can be linked with any string variables being read from the PLC to generate an alarm. Value monitoring can be achieved with static values or even with wildcards.
In zenon Runtime a variable always consists of the following three things: (1) the variable value, (2) the variable timestamp, and (3) the variable status. The variable status is maintained for every zenon variable and is composed of 64 individual status bits to always give a clear indication of the real-time or recorded variable status, whether it was a good status, communication fault status, alarm suppressed status, etc.
The main benefit of the Reaction Matrix is that not only can it analyze the value of a variable, it can also generate alarms or event conditions based upon a specific status bit. Or sometimes even more important: it can suppress alarms if the status information does not fit. For example, if there is a communication problem no alarm will be triggered. This makes it quite easy to avoid thousands of alarms during a communication problem with the PLC.
See “Alarm Management Challenge 3: Multiple Points of Configuration” here.