How can I hold a value of voltage, which can be used as a numeric value

Question

Hi, I'm trying to read in a voltage value and then hold it when i press a button. This value should then be able to be used as a numerical value, e.g. I can divide it or add constants etc. I realise this is probably a totaly remedial question, but it's for my dissertation at uni and my tutor thought it would be a great idea to program part of it in Labview, which NOONE in the uni knows how to use, and we've never been taught it.
Any help would be awesome,
Grant

Answer 1

Thanks JoeLabView, but maybe I should start by describing the purpose of the program.
I'm reading the voltage going into a DC motor (max 200V) so i'm using a 10:1 voltage divider to reduce the voltage seen by my labjack since it can only measure up to 20V. I read the voltage seen at the voltage divider, e.g.  20V at 200V and then, in labview, multiply this by a multiplying factor to get it back to 'actual' voltage. e.g. 20*10 = 200. But since resistors aren't made perfect, (especially not 5A ones) my divider actually works out at something like 9.8756:1. Therefore I have to set the voltage to the motor to something known (e.g. 100V), then tell labview that value, it reads the voltage input to it through the labjack, and MultFactor = UserInputVoltage/LabjackVoltage.
Using the multiplying factor, I can then display the 'Actual' voltage over the motor.
The motor is also being controlled by LabView, but this is simply using a slider, attached to an analogue_out VI for the LabJack, so shouldn't be too consequential.
Now to answer your questions.
1) The LabJack is a USB device which 'instantaneously' reads the voltage, so as the voltage input to it changes, so does the value output by its VI in LabView. It changes in real time.
2) I will need to continue to use the input from the LabJack once I have generated the mulitplying factor, multiplying the LabJack input by the multiplying factor in real time, so I can plot a graph of the change in voltage with 'real' values.
3) Do you mean what does my program do just now when i release the button, or what i want it to do?
4) I don't know how to structure the program, but hopefully what i've said above should help.
5) The interface will include;
Numeric Control to set the 'actual' input voltage
A button to tell the program when to generate the mulitplying factor
A waveform chart displaying the 'actual' voltage (0-200V)
A slider that I can use to control the motor. (this part i can do myself, it's a reference for a PWM circuit connected to a buck converter)
Thanks again man, hope this is what you need.