Refresh

Associated with: Advanced OPC Groups and Advanced OPC Points

Security permission required to access this pick action: Retrieve Data

ClearSCADA typically reads items for data on a scheduled basis. If required, you can use the Refresh pick action to read items on demand. Select the Refresh pick action to request a current data update of the points associated with the group,the following dialog is displayed:

• Source—Use to select the source of the data, the options are:
  • Cache—Use to select the Cache as the source of data. Access to the Cache data is expected to be 'fast' and should contain the latest value of the data (this depends on the polling interval (update rate) and deadband optimizations) as well as the quality and time stamp. The time stamp should indicate the time that the value and quality was obtained by the device (if this is available) or the time the server updated or validated the value and quality in its Cache.
  • Device—Use to select the Device as the source of data. Accessing data from the Device is usually slower than from the Cache and is expected to be used primarily for diagnostics or for particularly critical operations.
  • Maximum Age—This option is only available with OPC DA 3.0.When you use this option the server makes a determination whether the data is obtained from the Cache or the Device. If you select this option you need to complete the Maximum Age interval field.
• Maximum Age—When you select the Maximum Age as the source you need to enter the Maximum Age interval in milliseconds. Enter the required interval value directly in the field in OPC Time Format.

  The server checks the time stamp on each item. Where the data for an item has been updated within the Maximum age interval the data is obtained from the cache. If the time stamp is not within the Maximum age interval the data is obtained from the device.