TN Appsvr214 How to Configure Slowly Changing Application Server Attributes to prevent gaps in Historian data

Description

How to prevent Application Server tags from showing gaps in Historian data especially for slow changing tags

• Author: Mike Viteri
• Published: 12/9/2016
• Applies to: Application Server

Details

By default when setting up Application Server tags for History the forced storage is set as 0.

If the tag you are trying to store is a slow changing tag and the communication to the PLC is somewhat unstable. You will see gaps in your trend data for this tag.

The reason you see gaps is that the first value that is received is not consider good quality once the PLC is back online. Historian waits until the second value is received and then considers it good quality.

If you set the forced storage period to 5000ms(5 seconds) this means that value must be stored even if it has not changed. This forces the value to be checked instead of waiting for the value to change. 

This will fix the gaps as you are consistently checking for the value. So if the PLC goes offline within 5 seconds the object is check again. You are not waiting until the next time the value changes.

Note: If the forced storage period is less than the scan period. Forced storage will occur every scan period.