Knowledge Base

Existing invalid point management
When PcVue shuts down, for each trended variable, an invalid point is logged. This is used by the Trend Viewer to mark a trace as invalid (usually drawn as a dotted line) between the time stamp of the invalid point and that of the first valid point recorded after PcVue is re-started.

An invalid point is only NOT recorded under the following circumstances.

1. If a trend has the «Disable invalid point record on exit» option selected.
2. HDS only – If another server in the historical server association is active. In this case the acquisition and recording is done by another station and so we do not lose data once the tables are consolidated.
3. If the source of the variable supports local (at the equipment) Trend Logging. This can be the case for some of the more fully featured protocols. BACnet for example.

New invalid point management
When PcVue shuts down, for each trended variable, a record is made of the last recorded value & timestamp in a temporary file.  When PcVue re-starts the trend recording behaves as follows.

• If the first value & timestamp is the same as last value & timestamp an invalid value is not written.
• If the first value is the same but the timestamp is NOT the same, an invalid value is written with the shutdown timestamp.
• If the first value is NOT the same an invalid value is written with the shutdown timestamp.

The new behavior only has a significant effect on the trend recording of variables from equipment that supports time stamping.
The new behavior is currently only for the HDS.

Last recorded value file
The Last Recorded Value file has the name <Project Name>.inv and is located in [InstallDir]\Databases folder.

It starts with a header containing the version number of the file and the timestamp of when PcVue was shutdown.
<FILE VERSION>

Then, for each trend recorded variable, there is a record with the following format.
<TREND VAR NAME>;<ARCHIVE UNIT NAME>;<LAST CHRONO>;<VAR TYPE>;<LAST VALUE>;<LAST QUALITY>

Limitations
If the HDS or PcVue does not shut down cleanly the Last Recorded Value file may not be created.

As the decision to record an invalid value for a variable is made only after the first value is received after startup, if a Trend Viewer is displayed before this time it will not immediately display an invalid value. An invalid value will only be displayed if the Trend Viewer is refreshed after the first value is received.