Hi All,
I am having some anomalies that are causing me problems in my pressure test cell simulator project. Probably due to my lack of Ignition knowledge etc. This is in Vision 8.1, test VM with trial license.
To simulate pressure rising and falling in tags I have created 2 Gateway scripts; one for incrementing a value and one for decreasing a value, both at @ 200ms.
In my project I am using expression tags for pump and product pressure, which on page load I am scripting the change of the expression to be a float of 0.0.
These two tags have history in the default SQLdb.
When we start the test I take a stamped value of the current increasing tag value and write it to a tag, to effectively make a zero point.
I then change the pump pressure tag's expression to
pumpExpression = "{[.]gwTimerInc}-{[.]gwTimerStamp}"
This works well and simulates rising pressure with a pump, which is plotted in an Easy Chart. When the test is finished I write the tag's expression back to "0.0".
However, after a simulated test I am noticing that the value of the product pressure tag bounces around, even with the expression firmly locked at "0.0"? I just cannot see what is driving this as the expression does not change? Any help would be appreciated.