Issue
When points show Old Data some processes may cause equipment to shut down.
Product Line
TAC INET
Environment
I/NET
Cause
When a value is out of range in I/NET, any control referencing it will also be out of range. For systems with communications issues this can be a problem for indirect points such as Outside Air Temp.
DDC modules contain a Failsafe Output Control Point which can also over come this obstacle.
Resolution
Refer to What does it mean when a point goes "OLD" in I/NET? with information on how to prevent points from going "Old". If the point continues to go old you can use this process to account for the old point:
For this example assume that you are monitoring OAT with an indirect point
- Connect to the controller with the indirect point that is going old. (OAT)
- Create a duplicate of this point that is internal. Call it "OAT_mirror" ensure that it has a relatively short scan interval
- Add a Calculation to OAT_mirror
- Use this expression: AV(P0,P1)
- Set P0 as OAT
- Set P1 as OAT_mirror
- Click okay
- Change any control logic referencing OAT so that it references OAT_mirror
Results:
- The AVG calc function will ignore any old value. This means that while the OAT point is valid the OAT_mirror will quickly change to equal to it.
- When the OAT point goes old the OAT_mirror point will retain it's current value until the OAT point is no longer old.
For information about triggering an alarm when a point goes old, view Triggering an alarm or message if a point goes old in I/NET
For further Indirect Point "Old Data" Filtering Techniques read I/NET Indirect Point "Old Data" Filtering Techniques
