equation node

[ashmex]

Hi all

i am quite newbie to labview and i need to input a first order differential equation in an equation node. My problem is that, i am feeding back a signal to an input of the equation node which is of integer type while the initial input is a floating point number, this is leading to an error. Plz help me out of it.

Also any vi concerning process control, would be most welcome. i am finding it difficult to draw standard items like pumps, valves... any hints how to customize these items. thanx

[Louis Manfredi]

Hi Ashmex:

I can't duplicate your problem, or perhaps I don't quite understand the problem you are having. If you can post a simple vi showing the problem, or even a screen-shot of your diagram, we might be better able to help.

LabView is pretty tolerant of doing type conversions automatically for you when it needs to do so, Maybe the problem is something other than the type conversion. (It is better programming style to avoid unnecessary type conversions, they cost time and memory, but usually type conversions won't make a program crash.)

Hope to be able to help, & Best Luck, Louis

[didierj]

am quite newbie to labview and i need to input a first order differential equation in an equation node. My problem is that, i am feeding back a signal to an input of the equation node which is of integer type while the initial input is a floating point number, this is leading to an error. Plz help me out of it.

4087[/snapback]

Tell me if I'm wrong, but do you try to wire an output of the node directly to an input? If yes, then it won't work. This breakes the dataflow paradigm, If no, jump over this section:

A operation in LV is only performed when all its inputs got a value (turn on debug mode, with bulb in the icon-bar, this is true when on every single input of your node a wandering dot reached it. When you try to wire an output to an input of the same operation/node/vi, then it won't ever work, because the output can only be set when your node has run, but to run your node all inputs have to be set (like when a dog chases his own tail).

Also any vi concerning process control, would be most welcome. i am finding it difficult to draw standard items like pumps, valves... any hints how to customize these items. thanx

4087[/snapback]

Customizing controls is quite something painful (I suppose you know how to do it).

If you own the Datalogging and Supervisory toolbox, then you have quite a lot of items (pumps, valves,...).

Alternatively you can put a background picture (drawn with your favourite paint program) to your frontpanel. To add a (static) picture to your frontpanel select in the menu Edit>>Import Picture from File..., choose your picture (gif, jpg, png, bmp), go to the frontpanel and make a paste (<Ctrl>+<V> or menu Edit>>Paste).

Didier

[ashmex]

Hi all

i need to input a first order differential equation in an equation node. My problem is that, while integrating the output signal with an integratore express vi,i am feeding back a dynamic type signal to another input of the equation node. the initial input is a floating point number, which is leading to an error. Plz help me out of it.

Plz find the vi attached.

Thanks a lot

[Louis Manfredi]

Hi Ashmex:

Good to see you've got attachments to bulliten board posts worked out! It is a little confusing, since they don't seem to appear for me in message preview either. :question: Is there something we are both doing wrong? (also got your Email, but, as I said, the bulliten board is better.)

The problem is that the inegrate operation returns an array, while the formula node wants a scalar. I'm guessing that what you want for the formula node is the most recent value of the integral-- If that's what you want, the following change to your vi should work. If not, it should at least give you a clue for how to get what you want.

Hope I've been of some help.

Best regards, Louis