last data point dsc

[viScience]

I am trying to retreive setpoint changes that are being logged into a citadel DB using the DSC read trace vi.  I find that I do not get back the last logged point for a

channel that contains infrequently changing setpoint values.  In Hypertrend I can see the last transition to the final setpoint value (after that the graph is blank) but even though my time span

encompasses this last point, it does not appear in the trace dataset.  I suppose I could turn off deadbanding on these types of setpoint channels but

that would be quite inefficient.  Since Hypertrend can display the data, I have to presume that there is a way to get the DB to cough up the last value?

[Joachim082]

sachsm,

i don't know if i understand you correct. Hypertrend displays only the ghost point which will be overwritten on every value change (you can verify by setting a dot for every datapoint in the hypertrend control. For your Read Trace.vi which options have you set? Maintain Trending info or interpolation?

Regards,

-- 

Joachim

[Ben]

Extrapolate to now ?

Remove Data Breaks ?

Ben

[viScience]

Been there done that...I have enabled both interpolate and extrapolate.  All my regularly changing traces come out correctly, but as I said the setpoint traces

do not contain the last setpoint change made.

[Ben]

As I understand it the deadband determines what get logged.

You are saying that the changes are within the deadband.

So it sounds this is working as I understand the design of DSC and your options are to reduce the deadband.

I think I used to be able to force an DB write in the old version of BridgeVIEW but don't know how to do that with DSC.

Ben

[viScience]

Actually what I was suggesting was to turn the deadband off so that it would force the last setpoint value to get logged at each sample interval (100ms in my case).  I would still probably not get the last data point but I would at least see the last setpoint value since it would be repeated n times.

[Joachim082]

have you read my previous post about the ghost-point. Maybe you read the Citadel whitepaper to get more information about this.

[Ben]

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Joachim082 wrote:

have you read my previous post about the ghost-point. Maybe you read the Citadel whitepaper to get more information about this.

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I had read your post but had never heard of the ghost points or the whitepaper. That paper did not exist the last time I updated a DSC app and it would have been handy.

So I read about the Ghost points but did not find a way to get at it.

Is it just a simple tag read or is there more to getting at the value?

Ben

[Joachim082]

the ghost point is part of the citadel database mangement system. I will find tomorrow if I find it on my office machine. Fact is that the ghost point is a virtual data point which will be overwritten on every refresh (green traffic light). This ghost point will be written persistently after a value update.

[Ben]

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Joachim082 wrote:

the ghost point is part of the citadel database mangement system. I will find tomorrow if I find it on my office machine. Fact is that the ghost point is a virtual data point which will be overwritten on every refresh (green traffic light). This ghost point will be written persistently after a value update.

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I got that part.

And if I follow you farther, that ghost point does not get returned with the historical trends and there is some other mechanism used to get the ghost point?

Ben