Data View Returns to Defaults

[Britney]

Hi,

I’m using SignalExpress 2.5 to continuously monitor a couple of analog channels on a NI USB-6008.  I have set up a custom scale for each of the channels and created and saved a project for the monitoring process.  However, when I run the monitor function the Y axis label that I have specified defaults back to “Amplitude” and more importantly the X axis scale defaults back to .09 seconds (preview defaults back to 500ms).  I can not change this during the run operation so a 1/2 second is all I get for a preview.  I have tried changing all of the timing settings in the Step Setup and all of the X scale settings in the Data View dropdown.  I have tried this on different platform as well with the same result.  One thing that is odd is that the Y axis scale stays where I have set it.  Any ideas?

B.

[Seth_B.]

In order to conserve memory resources, Signal Express 2.5 only displays the data it just pulled off your USB device's buffer.  As a result, if you are acquiring continuously and your sample at a rate of 1 kHz and 100 samples to acquire, your data view will display 1/10th of a second of data each time it updates.  If you would like to display more data than this, you will need to increase your "samples to read".  This will result in a more choppy update of data, but you will see it update each time.  Also, the "Preview" pane in the Step Setup tab is not really meant for long-term viewing of the data, hence the reason your Y-axis label does not update properly.  It should be correct on the Data View screen if you update it there.

[Britney]

So does this mean that if I want to watch process changes over say a 2 hour period I have to wait 2 hours for a chart update?  I need to see data on a real time basis in order to respond to it.  A 1/2 second between updates is reasonable but being able to review only a 1/2 second worth of data will not be practical.  I’m wondering if there is a way around this.  VI Logger updated the graph as samples came in regardless of the period specified across the X axis.  If I remember correctly it wasn’t Vista compatible so I will not be able to revert back to it.

As for the Y axis label, it is on the view data tab chart that it is reverting to the default of “Amplitude”.  This happens during the first update after I press the run button.  The preview I was referring to is the bar under the data view chart that appears when you right click on the chart and choose “visible items” then “preview”.

Thanks,

B.

[Phil_J1]

Hi Britney,

Having mentioned VI Logger, it sounds like you're trying to record a signal, and view it while recording. What you are currently doing, is viewing the signal as it is being acquired, so each chunk of data is being displayed one at a time, overwriting the previous chunk of data on the viewer. This is the default SignalExpress behavior. This means that changing the x-axis scale has no effect on the data being displayed since only that amount is getting acquired each run.

Rather than press the Run button, Press the Record button. A dialog will appear with a list of signals, select the signal(s) you would like to acquire and record. Recording will start when you press the Ok button and will act as a buffer; this will provide the history you are looking for. When recording starts, in the bottom left corner of the application window is a Log folder. A new log will appear there with a dated signal group, and your signals are within that group. Drag any or all the signals (you can drag the whole group) into the viewer and that will show you the signal as it is being logged.

Once you are done Recording, press the Stop button. You can then also interact with the log once it is finished recording. Pressing the Record button again will create a new log for you and you can repeat the process.

I hope this is what you were trying to do.

Phil

[Seth_B.]

Britney,

To clarify, you will see data updated every time you pull samples from the card.  Thus, it will update every 1/2 second over the 2 hour period.  However, the data view won't store previous updates as the values in the data view's buffer are overwritten each time a new set of samples comes in.  This was intended to help reduce the RAM usage of Signal Express, but I understand how it can get very frustrating.  You will need to find a balance between how quickly you need the data to update and how much data you would like to view at a time.

Depending on your device, a potential workaround is to set your acquisition mode to "One Sample On Demand".  This will store the data in the buffer, allowing you to view all the data collected to this point.  The downside of this mode is that it is software timed, so you are more limited in how fast you can sample.  However, I was able to easily have my PC sample every 5ms with many processes running in the background, so this alternative may work for you better.  I would recommend you try this out and see if it works for you.

For the label, let's rename the axis in the Data View » Properties » Scales.  This should keep the axis named correctly.  If not, we can continue trying to track down the problem.

[Britney]

Thanks Phil and Seth,

Using the record function does provide more functionality allowing me to display samples as they come in while viewing the entire session.  Excellent!

Data View » Properties » Scales is where I have been changing the label but to no avail.

I change the label and save the project but as soon as the first samples are displayed it defaults to “amplitude”.  If I rename the label, save and close the application and then open the project again it also reverts back to “amplitude”.  This happens across projects and across platforms. It would be nice to figure this out since the chart is displaying multiple channels and there will be multiple operators using the workstaion.

B.

[Seth_B.]

Hi Britney,

I'm glad to hear that helped.

As far as the scale label is concerned, so that I understand your setup clearly, the data view contains just the voltage reading being acquired from your DAQmx Acquire Step, correct?  I'm still trying to figure out what would cause the label to reset like that.  Would it be possible for you to post a screenshot of the step you are viewing data from, as well as a screenshot of the data view itself?  Thank you.

[Britney]

This is what it looks like when I’ve set up the Data View and saved the project:

 

This is my Step Setup:

 

These are the two scales associated with the three channels I’m acquiring from:

 

Thanks,

B

[Britney]

When I press “Run”, “Run Once” or  “Record”, as soon as the Data View updates it ends up looking like this:

B

[Britney]

Notice that the Y axis scale stays where I have set it (0-1600) but the label returns to "Amplitude".

B.