Specify the Polling Interval and Offset for Logged Data

WITS allows Field Devices to store time-stamped point data and events (see WITS Data Logging - Logged Data Retrieval). This logged data can be retrieved by Geo SCADA Expert at specified intervals, for example, you could set Geo SCADA Expert to poll for logged data every 15 minutes. However, periodic logged data retrieval can only take place on:

• Connections that are permanent (direct)
• Connections that are open at the time of the scheduled logged data retrieval (on demand).

Geo SCADA Expert will not initiate a connection to retrieve logged data; it will only retrieve logged data on a connection that is already open.

To configure Geo SCADA Expert to poll a WITS Field Device for logged data, you need to enable Logged Data and configure the Polling Interval and Polling Offset. These settings are located on the WITS tab of the WITS Outstation Form.

When specifying the Logged Data Polling Interval and Polling Offset, you need to consider:

• Whether your Field Device is going to be used to store logged data (if not, you can disable Logged Data for the Outstation in Geo SCADA Expert).
• When you need the Field Device's logged data to be available in Geo SCADA Expert. For example, you may only need to use the logged data during the day, and so can configure Geo SCADA Expert to retrieve the data at night.By using the Polling Offset setting, you can define the time of each poll, for example, the time of day at which a daily poll will occur.
• How often you want the Field Device's points to log data
• The size of each record (each value or state logged by a point is stored in a separate record). Different Field Devices store records in different ways, so please refer to your Field Device manufacturer for more details.
• How often you expect events to be logged and the size of each event record
• The storage capacity of the Field Device. Again, please refer to your Field Device manufacturer for more details.
• The speed and bandwidth of the communications link between the Field Device and Geo SCADA Expert. You should also consider how many Field Devices share the communications link and the potential load when communications are taking place. By using the Polling Offset setting, you can set Geo SCADA Expert to stagger polls on a multi-drop connection, rather than poll all Field Devices at the same time (this will help to even the load on the communication channel).

Ideally, you want Geo SCADA Expert to be able to poll each Field Device efficiently, without causing a high load on the communications channel. You should also aim to poll each Field Device regularly so that it does not lose data due to an overflowing data store.

To enable polling for logged data, you need to use the Logged Data settings on the WITS tab of the WITS Outstation Form:

1. Log on to ViewX via a user account that has the Configure permission, and then display the Form for the Outstation that represents your Field Device (see Display a Form).
2. Select the WITS tab.

3. In the Logged Data section, use the Enabled check box to define whether Geo SCADA Expert retrieves logged data from the Field Device.

   If you want Geo SCADA Expert to retrieve logged data from the Field Device, select the check box. You can then use the Polling Interval and Polling Offset to specify when the logged data will be retrieved (see step 4).

   If you do not want Geo SCADA Expert to retrieve logged data from the Field Device, clear the check box. You should clear the check box if you do not want your Field Device to log data or if it does not support logged data (as defined in its Device Profile, see Display a WITS Device Profile).

   

   If the Field Device signals logging is filling or has overflowed, the logged data is retrieved automatically, irrespective of the Enabled setting.

4. Use the Polling settings to define when Geo SCADA Expert will poll the WITS Outstation for logged data.

   • Polling Interval—Use to specify how often Geo SCADA Expert will poll the WITS Outstation.

     If you want Geo SCADA Expert to retrieve logged data only when a connection is established or Refresh (WITS Outstation) is selected, set this field to 0 (zero). A Polling Interval of 0 is often used for on-demand connections such as PSTN.

     If you want Geo SCADA Expert to retrieve logged data regularly, specify how often the polling should occur (in the OPC Time Format). You can enter the value directly in the field, or use the Interval Window (accessed via the field’s browse button) to specify the required value. For more details, see OPC Time Format.

   • Polling Offset—Use to specify the start time for the poll in the OPC Time Format. You can enter the value directly in the field, or use the Offset Window (accessed via the field’s browse button) to specify the required value.

    

   To set Geo SCADA Expert to poll a WITS Field Device every fifteen minutes:

   Interval: 15M

   Offset: 0

   To set Geo SCADA Expert to poll a WITS Field Device every hour at half past the hour:

   Interval: 1H

   Offset: 30M

   To set Geo SCADA Expert to poll a WITS Field Device every day at 06:00 (UTC):

   Interval: 1D

   Offset: 6H

5. Save the configuration.

If Logged Data is enabled and your Field Devices start to overflow, you should consider:

• Reducing how often the Field Device's points log values (defined on the Point Form, see Periodic Logging of Data for WITS Database Points)

• Reducing the number of events logged. For example, you could increase Persistence, increase Hysteresis, and/or change the severity of actions for state changes or DNP3 Object Flag changes.

  • Persistence: see Persistence for WITS Database Points
  • Hysteresis: see Hysteresis for WITS Analog Points
  • DNP3 Object Flag changes: see DNP3 Object Flag Actions.

• Increasing how often Geo SCADA Expert polls a Field Device.

  For Field Devices with permanent communications, you will need to reduce the Polling Interval.

  For Field Devices with on-demand connections, such as PSTN, you can disable periodic polling by setting the Polling Interval to zero. To retrieve the logged data more frequently, you need change the schedule for connecting to the Field Device. For example, for a Field Device using PSTN, you could increase the frequency of scheduled dial-out, or you could reduce the interval for a scheduled dial-in (see Scheduled PSTN Dial In for a WITS Outstation).

  Typically, the Polling Interval is not used for on-demand connections. However, it does apply if the on-demand connection is open at the time of the scheduled poll. For this reason, if your Field Device uses an on-demand connection:

  • The Refresh action needs to be triggered more frequently (network connections).
  • The One Shot action needs to be triggered more frequently (PSTN connections)
• Upgrading your communications infrastructure, so that more bandwidth is available.