Capturing Data Point

Question

I have written a program that constantly monitors the pressure from a transducer.  Once the pressure has stabilized the user can begin the record process which essentially records the data to an excel spreadsheet at different rates depending on whether or not the even has been triggered.  The event is determined by the pressure at the point when the record process began + a user defined slope, so when the initial pressure increases by this much begin recording at a faster rate.  To capture the initial pressure I'm using a for loop with an iteration count of 1 reading from the continuous pressure reading.  That value is then used in a formula node.  I'm getting an error saying that the left brace for the formula node is needed.  Is this because of the way I'm capturing that initial pressure value?  Thanks.....
LabVIEW 2012 - Windows 7
CLAD
Attachments:
PressureScanv1.vi ‏89 KB

Answer 1

Hi MeCoOp,
I don't know if I fully understand what you are trying to accomplish,
but it sounds like you want the first (initial pressure) value to be
used in all calculations, once it's acquired the first time. With your
current code that will never happen since you are continuously writing
new values to "Initial Pressure" when the "Begin Pressure Monitor" is
TRUE. If you use "Highlight Execution" (the small light bulb) while
your VI is running, you will get a good idea of your dataflow - you
should see that the "Initial Pressure" keeps getting new values from
outside the Case Structure.
To store the initial value and use it for the subsequent iterations,
you could use a couple of Shift Registers on the edge of the While Loop
to store the value. The reason that you need a couple of Shift
Registers and not just one, is to keep track of if it is the first time
the "Begin Pressure Monitor" has been pressed and if it's the first
iteration of the loop. Here's a simplified example:
If this example doesn't relate to what you are trying to accomplish, please let me know why, thanks.
Have fun!
Message Edited by Philip C. on 08-03-2005 12:40 AM
- Philip Courtois, Thinkbot Solutions
Attachments:
InitialValue.PNG ‏6 KB
InitialValue.vi ‏22 KB