Graph XY Offset

[Joe_John]

Hi,

I am working on an press force monitoring application. Right not I am plotting diplacement vs. force. I am looking to create an upper and lower limit for this plot that can be x and y axis adjustable. It sounds easy enough but I'm racking my brain trying to figure it out. On the up slope of the data the limit x offset id negative and on the down slope of the graph the x offset is positive. Is there a function in Labview to help me create a limit line identical to the plot but is x y adjustable. The limit line must move positively if the data slop is negative. Its hard to explain but I hope someone can help. If you dont understand me let me know, I'll try again.

Thanks

[MikeS81]

Hi Joe John,

shows your attached image what you need?

Mike

[jpaul]

Hi Joe John,

You can use a property node for the graph to programmatically set the maximum and minimum for your X and Y scales dynamically. See the attached example VI (while the VI is running change the X & Y max/mins and see the graph display update). Hopefully this points you in the right direction!

Cheers,

Jonah
Applications Engineer

National Instruments

[Dennis_Knutson]

It sounds to me that what you want to use is the Limit Testing functions (Signal Processing>Waveform Measurements>Waveform Monitoring palette).

[Joe_John]

Let me try and explain this application a little better.

What I am currently doing is trying to create upper and lower limits based on a master profile. The operator takes a master part and runs it through the test cell. At the end of the test a xy graph is created of displacement in (mm) vs. Force (N). At this point, upper and lower profile tolerences can be adjusted. I need help trying to manipulate the "Master" profile to create an upper and lower limit. If the operator increases the force limit (y axis) then the upper limit basically moves higher up the graph. When the operator adjust the displacment limit (x axis) then the upper profile must manipulated. This must be manipulated so that when the operator increases the displacement limits any point that has a negative slope moves to the right (Increase displacement) and any point with a positive slope moves to the left (decrease displacement). So I I am trying to look for a force spike of 350 N at 10 mm I want to create a window of  375 to 325and between 5 mm and 15 mm. I want to show the limits and the master profile on the same grap.

I am trying to look for a specific profile with a tolerence on both x and y axis.

I hope this explains it a bit better.

[Dennis_Knutson]

Then you do need to look at the Limit functions I mentioned. There are some shipping examples. One is called Limit Testing Measurement. If you have a 'master' profile, then adjusting the limits up or down is simply a matter of adding/subtracting a constant to the y rray of the specification cluster in the Limit Specification function. Shifting left/right requires you to add/subtract from the x array.

[craigc]

Hi,

If i understand correctly you run a master through the system first a sort of "Calibration" from this you then need to create an upper and lower limit from this data.  In order to do that you just need to add the limits onto your original data. and name them upper and lower.  If you then want to move these limits around you do the same again, just add or subract x and y data as approprite.  Then if you want to see if your measured result is within these specified limits then you need to look at the tools that Dennis mentioned above.

Craig

[craigc]

Hi,

I have written a quick example to get you started, however the Limit testing vi, says that the result is a pass when it blatently should not be.  I have had a quick look into why this might be, however have not got the time to debug.  If anyone else can see why this is going wrong could you let me know.

Cheers

Craig

[Dennis_Knutson]

If you connect a graph to the Output Values output of the Limit Testing function, you'll see that with the timestamps aligned, the signal is within the limits. I was bit unclear about shifting the x axis. Unlike the Y axis where you add/substract a constant, with the x array, you add remove elements to the array. At least, that is the way I used to do it. I would capture a signal at a certain trigger level and take x number or pre-trigger samples and make the beginning of the entire waveform t0=0. If, for example, I changed the number of pre-trigger points, I would append new y values to the beginning of the x arrays.

[craigc]

Thanks Dennis,

As you pointed out the X axis offset does not seem to shift the limits on the axis (or the limits vi ignores t0).  As you say it looks like some array manipulation will sort that out.

Craig

Message Edited by craigc on 08-22-2008 05:24 AM