Associated with: Points
This status attribute displays a point’s value at the time that it was Previously Updated in ClearSCADA (as opposed to its Current Value).
The Previous Update Value might be the same as the Current Value if the point’s value has not changed since the last data retrieval.
A driver typically polls and retrieves a point’s data at the rate it is configured to do so, but only sends point updates to the ClearSCADA server if that point’s value has changed. In such circumstances, the Previous Update Value and Current Value will differ. The exception to this is if another activity requires the point’s value to be passed to the server, regardless of whether that point value has changed. Such an activity would include, for example:
- A Refresh action
- A Scan Group’s interval expiring (Scan Groups apply to points on direct outstations on some advanced drivers)
- On start-up or re-establishment of communications with the device on which the point is located
- A Logged Value updating the Current Value (this applies to points that have logged (time stamped) data).
Any of the above activities can result in the point’s Previous Update Value being identical to the Current Value.