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Help Topics

Basic Concepts

Help - HMI Server Functions


Overview:

A web based client cannot operate on its own. It requires a server to load the client web page from, and to communicate with. This system has a special server built into it which provides both functions.


Server Features:

The HMI server provides the following features to an application.


Events and Alarms:

Events and alarms are represented as boolean conditions. An event occurs when the boolean value changes from false to true, or from true to false. An alarm occurs when the boolean value changes from false to true.

The event and alarm manager does not directly "create" events or alarms by monitoring conditions such as analogue values. Events and alarms must be created by other logic (e.g. via the soft logic or by other systems).

The addresses used for events and alarms can be anywhere in the coils area of the data table. External protocol clients, internal clients and integrated software modules can all write to the coils area to trigger and event or alarm.


Event and Alarm Buffering:

Events and alarms are "buffered" in the server. This means that when an event or alarm occurs, a copy of each message is retained in the server so that a client can retrieve all or some of them later. This means the client does not need persistent (disk based) local storage to maintain a (recent) history of events and alarms. They can be retrieved from the server at any time.

At present, the system stores the event and alarm buffers in memory. This means they do not (at present) retain a permanent event or alarm history. If the server is restarted, the existing history is lost. Permanent event and alarm storage will be addressed in a future version.


Data Scaling and Conversion:

The HMI server offers automatic scaling of numbers as part of the configuration system. Values in the data table may be automatically scaled when read from the server, with the reverse scaling being applied on writing data to the server. Scaling is user selected parameters as part of the configuration.

The server also automatically converts data types as required. Conversion is implemented as follows:

Scaling When Receiving Data

Scaling When Sending Data


Platform Data Limits:

Because all data values are mapped to data table addresses, the data must exist within the limits of that data table. These are limitations of the server platform and not HMI protocol limits.