Easy Chart Values and Tag Historian Values Do Not Match

Ignition
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1

I am using vision 8.1 and have a motor position OPC tag that is History Enabled with the following settings:

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Here are the issues I am having:

  1. I use an easy chart to display the data, but users can select multiple tags to trace on the easy chart. When the data is exported to excel, it doesn’t actually match the data that I see in the database. Example pic below shows the database entries for the tag historian on the left for the time 11:35:05 which has 11 logged data points, and the right shows the data exported from the easy chart which contains only 4 data points. Why would the number of data points be less on the easy chart?

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  2. My tags are configured with a min time between samples of 50ms and On Change Sample Mode, yet the values on the left of the picture above that come directly from the database seem to only be logging every 100ms. Why would it be logging at double the minimum when the value has changed beyond the beyond the deadband?

Thanks in advance for any help you can offer!

2

How do you know your driver is actually sampling that fast? History cannot log faster than the data can be sampled.

3

@pturmel Fair point as I have not done any testing to ensure this, but occasionally data is captured and logged at the specified 50ms rate, so this would indicate it is possible?

4

It is definitely possible. You'd have to study your driver diagnostics.

5

Are you using a tag history binding? What do the binding settings look like?