An Outstation, or Remote Terminal Unit (RTU), gathers data from, and send commands to, plant. This plant is represented by points in the ClearSCADA database.
Some drivers support third-party devices other than outstations, such as data loggers. These devices perform some of the functions of an outstation. For the purpose of this guide, these devices are also referred to globally as ‘outstation’.
ClearSCADA can process various forms of data from an outstation, depending on the type of data that the outstation supports. For example, many outstations support current data—the present state or value of a point when the ClearSCADA server requests current data from the outstation. Many outstations also support logged data—time stamped data that is stored in the outstation.
Outstations communicate with the ClearSCADA server using one of two types of connection:
Direct outstations communicate with the ClearSCADA server using a connection, such as a cable or network. Direct outstations may be in Direct, Shared, or Switched outstation sets, depending what the outstation type supports (see Direct Outstations).
The ClearSCADA server retrieves data from direct outstations using timed scans. Where a Direct outstation has a large amount of logged data, several scans may be required to retrieve the data.
Where supported by the outstation type, operators with the required privileges can send commands to the outstation to, for example, control plant, or retrieve data.
For further information, see Scanning Direct Outstations, and refer to the driver-specific documentation for the types of outstation and communication that are supported by individual drivers.
PSTN outstations communicate with the ClearSCADA server using a telephone line (see PSTN Outstations and Communications). This type of outstation is not in continuous contact with the server. Instead, the circumstances surrounding when the server and outstation are in contact differs depending on the type of outstation, but may include:
- When an alarm is raised on the outstation—The outstation dials in to report an alarm. On some types of outstation, you can inhibit dial-ins using a Disable Dial In pick action.
- A Scheduled One Shot—The server dials out to the outstation to retrieve its data on a scheduled basis, for example once a day.
- An operator initiates a One Shot or Open Line call—The server dials out to the outstation and retrieves its data.
- An operator initiates a Promoted Dial Out—The server dials out to the outstation to retrieve its data at a more frequent rate than usual, for the length of the promotion period.
Where a PSTN outstation has a very large amount of logged data, more than one call may be required in order to retrieve the logged data.
Where supported by the outstation type, operators with the required privileges can send other commands to the outstation to, for example, control plant, or extend a call to retrieve further data.
Some direct outstations can use PSTN as a fallback means of communication should ClearSCADA detect that the direct connection has failed (see Direct - PSTN Fallback). To use PSTN fallback, an outstation has to have a dial-up modem. Additionally, at least one PSTN Channel for the same driver and with the same Connection Type as the outstation, has to exist in the ClearSCADA database (see PSTN Connection Types).
Where a PSTN outstation has a very large amount of logged data, more than one call may be required in order to retrieve the logged data.
Where supported by the outstation type, operators with the required privileges can send other commands to the outstation to, for example, control plant, or extend a call to retrieve further data.
Some direct outstations can use PSTN as a fallback means of communication should ClearSCADA detect that the direct connection has failed (see Direct - PSTN Fallback). To use PSTN fallback, an outstation has to have a dial-up modem. Additionally, at least one PSTN Channel for the same driver and with the same Connection Type as the outstation, has to exist in the ClearSCADA database (see PSTN Connection Types).
For further information on PSTN outstations, see Retrieving Data from PSTN Outstations, and refer to the driver-specific documentation for the types of outstation and communication that are supported by individual drivers.
Use the fields on the appropriate Outstation Form to configure the properties of each outstation on your system. The Form has several tabs (see Tabs on Outstation Forms).
If required, a Queue feature can be enabled on your system to allow users to optionally queue certain pick action requests on PSTN and ‘On Demand’ outstations. For more information, see Define whether the Queue Parameter is Available, and see Optionally Queue Pick Action Requests on PSTN and ‘On Demand’Outstations.