adding real time to charts

[doug_O]

I have been trying to add real time to the X axis of my strip chart. I can add the time with out a problem, but as the chart scrolls, the time on the right side is not staying synced to the real time clock. It is running fast.

How can I sync the scale up and be able to look at a point on the chart and have faith that it is at 13:05:05 and not some other time. I have autoscaled, not autoscaled, used various properties.

I have looked at various examples and none seem to meet my needs.

  As a new user, I  ask why is this not a part of the charts  as much as the scaling and formating is.

[Ben]

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doug_O wrote:

I have been trying to add real time to the X axis of my strip chart. I can add the time with out a problem, but as the chart scrolls, the time on the right side is not staying synced to the real time clock. It is running fast.

How can I sync the scale up and be able to look at a point on the chart and have faith that it is at 13:05:05 and not some other time. I have autoscaled, not autoscaled, used various properties.

I have looked at various examples and none seem to meet my needs.

  As a new user, I  ask why is this not a part of the charts  as much as the scaling and formating is.

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It is!

Yes there may be a short delay between the time when the data was converted by the hardware and when it shows on the chart.

Could you share a small example that demonstrates the issue you are seeing that leads you to this conclusion. We may be able to help or explain.

Have fun!

Ben 

[Dennis_Knutson]

You also need to understand how graphs and charts work. By definition, the dt on both is a constant. The constant is something that is set when the chart/graph is first written to and is part of the Scale property (offset). If your time between iterations is varying, then you need to use an XY Graph.

[Ben]

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Dennis Knutson wrote:
You also need to understand how graphs and charts work. By definition, the dt on both is a constant. The constant is something that is set when the chart/graph is first written to and is part of the Scale property (offset). If your time between iterations is varying, then you need to use an XY Graph.

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OR

Use Waveform Data types that include the timestamp and dt in the Waveform data.

Ben

[doug_O]

It  sounds like I need to learn about charts and graphs. Any articles that I can read on how to understand the Labview way of doing it?

This what I understand about charts ... the time base is free running and when a data point is fed into it, it is printed on the chart display.

the free running time base can be referenced to the referenced real time clock of the system at time zero.

Attached is an example of using the real time clock to set the offset and using the choices in the property menu as I understand it.

Absolute and relative choices  have no use from what I can see.

I still digesting the info provided by you and Ken on charts and graphs.

Is there a guide with more detail and setup (How to)info than the Help files provide?

I am still learning the vocabulary , that is slowing me down in the search for a solution.

In a nutshell,

I am reading downhole gauges (4-20mA) from a DGH module via RS485.

The readings are converted to pressure and temps and display on a strip chart.

One of the requirements is that gauge values on the chart need to be referenced  to time not just a free running reference of tick marks.

thanks for everyone's help on this.

[Dennis_Knutson]

Sorry, I gave you misleading information. The start time is the offset but the dt is the multiplier property. Modify as shown.

 

p.s. This is what is done in the example called Real Time Chart.

Message Edited by Dennis Knutson on 04-08-2009 05:52 PM

[Ben]

This illustrates what I had in mind for plotting non-periodic data with arbitrary t0 values.

If you look closely that example is plotting at two different rates. 

Ben

Message Edited by Ben on 04-09-2009 05:54 AM

[doug_O]

Thanks for all the help. I apologize for not replying in a timely manner. I have found a solution to my problem about time stamping the waveform chart. It was a combination of your's and others that generously gave of their time.  I have attached my solution. My  problem with was the X axis was being updated constantly with the present time while graphing. My solution was to have the time update take place during the false case. The time stamp was what I expected when I was graphing.  Thanks again to everyone.