12.2. Alarm

Emergency alarm system (alarm) - this alert the operator of a certain event involving a violation or threatened violation of procedural flow process.

Alarm configured by setting limits (boundaries, thresholds) individually for each of process variable. The system automatically tracks the change of process variable and compare its value with a pre-configured limits. In case of a variable for the normal boundaries, the system generates an alert and fixes it in the magazine alarm. Consider the most frequently used alarm for analog values:

Lo - lower warning limit. In the case of process variable is less than Lo, generated a warning alert.

LoLo - the lower boundary of an emergency. In the case of process variable is less LoLo, generated alarm.

Hi - the upper warning limit. In the case of process variable becomes more Hi, generates a warning alert.

HiHi - the upper limit of emergency. In the case of process variable becomes more HiHi, generated alarm.

DEV_HI (DEVIATION_HI) - upper limit of deviation (mismatch). If the difference (absolute value) between the two variables becomes more DEV_HI, is generated alarm. For example, such an alarm can be set up in block PID. In this case, the system will signal the rejection of the controlled quantity of the set value, exceeding the limit DEV_HI. By analogy, you can configure alarm DEV_LO.

ROC_HI (RATE_OF_CHANGE_HI) - upper limit of the rate of change. The system monitors the rate of change of process variable (first derivative). If the rate of increase in the variable above the ROC_HI, is generated alarm.

For discrete variables, alarms are much less. In fact, there are only two: the emergency state, the corresponding value of 1, and the accident, in case the value 0.

Fig. 1 - 57 is a diagram of the appearance of alarm on the example of a rapidly changing of process variable. It should be noted that the figure shows, not all generated alerts. For example, when returning variable back to the normal range of values than shown in the figure, an alert is generated RETURN_TO_NORMAL.

Fig. 1 - 57. Example of generating alarms and alerts

Importance (or criticality) alarm is determined by priority (integer number). Typically, the higher the priority for the alarm, the more critical it is for production, and the faster it is necessary to pay attention.

The operator, when an alarm is given two options:

1. Ignore it. Not always a good decision to put it mildly. Moreover, if the variable of process returns back to normal limits, it will display the new warning - UNACK_RETURN_TO_NORMAL, saying that the operator did not notice the emergency event, but, fortunately, all normal.

2. Confirm that the alarm seen by the operator (acknowledge). The fact that immediately after an alarm it is automatically assigned a status UNACK (not confirmed). As soon as the alarm confirm (sometimes they say - "kvitiruyut"), its status is ACK (confirmed). In this case, the return variable in the normal boundaries leads to a warning ACK_RETURN_TO_NORMAL, indicating that the operator responded to the alarm.

The alarm can be arbitrarily grouped. In practice, the group carried out by the distribution of process variables and, consequently, the corresponding alarm in various technological areas (plant areas) and facilities (plant units).

How is archived alarm? All the above alarms and alerts are recorded in a special archive immediately after their occurrence. This archive is called a log alarm (alarm journal, alarm list).

Journal alarm is a database SQL, which is deploying a carrier on station or on the server, if any management system. More about this will be discussed below.

How can display the alarm? The most comprehensible map - it is showing as sorted by the time and automatically updated spreadsheet. Examples of such tables are shown in Fig. 1 - 58 and 1 - 59.

Fig. 1 -58. Example of alarm from visualization package Wonderware Intouch

Supports filtering and sorting alarms, as well as their acknowledgment. Operations as possible with individual entries in the table, and with user groups. This standard tools offered by modern CSF, to work with the magazine alarms.

Fig. 1 - 59. Example of alarm. Package Simatic WinCC