De-synchronization/lag on the data

Ignition
1

Hello world,

Recently we faced to an incident on one of our production line and the electrical power has been stopped by using an emergency button. All the equipments of this station has been sudently stopped, and all the devices were stopped their mouvement in less than 5s.

On the Ignition we see the tension falls to 0 but we still get some rotation angle values coming from the main device of the line. But without any power it cannot move.
Then we looked on our old tool (Pegase) to replay the same data and in the chart we see the same parameters fall in the same time to 0.
I thought at the begining the issue on Ignition might be due to a glitch issue on the Perspective screen and I decided to look on the raw data in the DB. In the DB of Ignition, this de-synchronization is still present.

Note: all this tags are provided by the same PLC and take the same route to be streamed to the Ignition gateway.
Note 2: on the Pegase view the green curve is a temperature

I cannot explain this desynchronization/lag

Could you help me to understand ?
Anyone has already experienced this kind of lag ?

This can pose a number of problems for subsequent analysis of the incident.

Ignition lag
Ignition lag1261×617 54.3 KB

image
image1437×983 14.4 KB

2

In Ignition, the historian's deadband style "Analog", which includes "Auto" for floating point tags, delays storing data to determine trends lines, to allow space-saving interpolation in typical usage (slow-changing process values).

You will need to use deadband style "Discrete" for your case, and probably shouldn't be using the historian for this at all.

3

Hey Pturmel,
thank you for your answer. When you write "delays storing data", I can understand it may have few seconds of delay but here it is around 3min of delay. That's a lot !

4

It can be even more, depending on your tag's max time between samples. The algorithm for "analog" style is in the documentation. You should study it.

(And let me repeat: for the waveforms you show, the historian is a terrible choice. You should be using wide tables with unconditional inserts on a tight schedule--or conditioned only on a debounced line run status.)

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