CIRCUTOR OPC Server PS/PSS - Manual (Page 5)

PS/PSS OPC Server -5-
3.3.- Basic concepts
In order to better understand this manual and the operation of the PowerStudio /
PowerStudio Scada OPC server, it is necessary to define some concepts:
• Available configurations: The set of all of the different created configurations, which
are saved in *.xml files in the “profiles” folder located in the main application
directory.
• Active configuration: Among all created configurations, one of them must be set as
the active. This will be the one that will determine the OPC server behaviour. The
setup utility allows you to select the active configuration. Whenever the active
configuration is changed, the OPC server is restarted so that it begins to operate
using the new parameters.
• OPC server status: The server can be in any one of the following four different
states: activated, deactivated, started or stopped. We can activate and deactivate
the server from the setup utility, thereby either making it accessible or inaccessible
to OPC clients. If at any moment the server does not detect the presence of the
required dongle in the USB port, it will remain activated but will stop updating the
monitored variables. When the server is active - when it is accessible from any OPC
client - it can either be started or stopped. When a client connects to the server, it
starts up and handles the incoming requests. When there are no clients connected,
the server stops.
• PowerStudio devices: This is the set of all the devices and variables availables on
the PowerStudio server specified in the active configuration.
• OPC devices: This is the set of all the devices and variables accessibles from an
OPC client.
• Update frequency: This is the minimum amount of time that the server will wait
before changing the value of a variable available on it. However, it will always
depend on the update frequency of that particular variable in PowerStudio itself.
• Buffer and buffer expiration time: The server has an intermediate memory that
stores the values requested from PowerStudio, arranged by device. These devices
have an associated expiry time. When the value of a device variable is requested
and the values in the buffer for this device have not expired, the value stored in the
buffer is returned. If the buffer values have expired, a request is made to
PowerStudio, updating the values of all the variables in this device. Using the buffer
considerably reduces the number of XML requests carried out. Increasing the
buffer's expiry time is a good way to reduce the strain on system resources.
• Request management method: It determines the way in which the OPC server
makes the XML requests to PowerStudio, according to the OPC client requests it
receives. This is one of the most important configuration parameters since it directly
affects the performance of the OPC server. Selecting the management method that
best suits your needs is essential in order to obtain good results and minimise the
use of system resources. There are 2 available methods: