How can you acquire a XY-graph from two signals?

[AK87]

Greetings,

I am a part of a team that is working on a school project which involves making a machine that pulls material apart to test its durability. It’s basically a hydraulic cylinder that does the work. We are at a point in our project where we need to display a curve that shows force in relation to length. To do this, we are using two analog sensors; a force sensor and a position sensor. We have purchase the LabView 8.2 and are using a DAQ-module to acquire the signals. Our problem is that when we try to connect the signals to an XY-graph (X being the position, and Y being the force), we only get a ‘dot’ that displays the exact values of our sensors. We cannot get it to display a curve.

Basically, what we’re trying to do is to get the program to draw a curve for us using these two signals, and not just a mere dot that updates real-time. The curve should then be writeable to an excel-sheet for an instance for future studies of the material.    

We think that we should be able to achieve this by logging values from the signal and then drawing a curve using those logged values. Unfortunatly, we have not succeeded due to our limited knowledge of Labview. The deadline for the project is approaching fast and we need to finish soon, which is why we are asking for help here. If anybody can help, please do so as soon as possible.

I’ve attached a picture of the machine to give you a better clue of what we’re doing.

/Alex

[Dennis_Knutson]

A picture of your equipment really doesn't help. It would have been better if you had posted an image of your code (or even better, the actual program). If you program is only acquiring a single point, then a single point is all that will be displayed on a graph. If you have a loop in your program and you are acquiring multiple values over time, then the XY graph should display them as long as you providing the correct data. If you are using the Express XY Grpah, then make sure that the 'Reset' input has a False wired to it. Otherwise the old data will be deleted with each write to the graph. If you are using the regular XY graph, then you have to build an x array and a y array to wire to the graph. You would use a shift register to keep the old data. Below is an image of a simple way to build an XY graph one point at a time. It is not very efficient at memory usage and should only be used if you are acquiring a fairly small amount of data. Best for you would be to use the Express XY Graph with the correct inputs.

[AK87]

Hi, again.

You didn't post a picture of the graph.

By the way, I looked at the XY-chart example that was shipped with Labview. I experimented a bit, and got this (look at the program I sent).
I'm using a signal simulation, and I wonder if you can use a signal from DAQ-assistant. I use DAQ-assistant to capture my signals, thar are Continous and are RNE.
Can I do so, or how can I do it?

Thanks
//Alex

[AK87]

FIXED!

I took your advice on Express XY-grapg with a loop and false reset and did a program with only numeric controllers. Those will be replaced with our signals, DAQ-assistant.
Now I wonder how you can print or store this graph, in example Excel or a picture?
And I can't get the calibration function in DAQ-assistant. Could you explain how it works?

PS: I've attached the new program

Thanks!

//Alex

[Dennis_Knutson]

What DAQ card are you using. I don't think the calibrate function works with all of them (i.e. USB600x) though I I'm not positive. I never really use the assistant and I don't have the low cost boards.

If you just want to save or print the graph, then you can use the Report Functions. You can create a report and then use the Append Control Image to Report. Pass it a reference of the graph (right click and select Create>Reference). You have the option of creating an HTML report. If you look at the block diagram of Append Control Image to Report, you will see a Get Image property node and a Write JPG file function. You could use just these two to save a .jpg of the graph.