LabVIEW projects - RTD Pressure Measurements

Pressure measurements on Residence Time Distribution equipment

Dana Christensen (ChemE)

Introduction

The goal of the program is to execute an automated series of pressure measurements on the Residence Time Distribution - RTD - setup of Dana Christensen (ChemE, The Netherlands).

Dana operates a setup where the normal procedure is to switch valves so a tracer gas can enter a fluidized bed and where gas analysis is used to establish the residence time distribution.
The alternative procedure, to measure the pressure (fluctuations) over the fluidized bed, only allows to change the inlet flows whithout the disturbances of switching valves.

The vi presented in this publication loads a recipe and allows the user to adapt and use the recipe.

Once the vi is started it will present a table where values can be entered for each consecutive step. The table can be pre-loaded with the table that was used the last time.

The panel

The front panel of this vi is based on three screens: Settings, Recipe, Main.

Settings

The 'Settings' screen displays some system variables and allows the users to set the following settings:

• Autosave recipe
• Hide STOP button
• Use simulation mode
• Filename for the next datafile (actually the basic name, runnumber and file extension)

Recipe

The 'Recipe' screen has a spreadsheet like table. This is the screen that the vi starts with. The spreadsheet can be altered as long as the 'EXECUTE' button remains untouched. Once you hit the 'EXECUTE' button the 'Main' screen will be displayed and the recipe will be executed.

Main

The 'Main' screen displays:

• a graphical representation of the last measurement
• the setting belonging to that measurement
• the setings for the measurement in progress

The diagram

The LabVIEW diagram consists of two sequences: one to execute the recipe and one to abort normal operation.

Sequence 1 - 'Main Sequence' (Frames 0..10)

Frame 0: Initialization 1
Enable the 'STOP' button.
Clear selection form the table.
Set all values to their defaults.

Frame 1: Initialization 2
Create the headers for the table.

Frame 2: Initialization 3
Read the configuration (.ini) file.

Frame 3: Initialization 4
Read a previously recorded recipe.
Set the digital ouputs to all zero.

Frame 4: Preparations 1
Select the 'Recipe' tab.
Wait until the 'EXECUTE' button is pressed.

Frame 5: Preparations 2
Name and open the next data file.

Frame 6: Preparations 3
Select the 'Main' tab.
Calculate the number of steps in the recipe.
Select the first row (or line) of the recipe.
Hide the 'STOP' button if the 'Hide STOP button' was selected.

Frame 7: Main loop
Run the main loop reading each consecutive line of the recipe.

Frame 8: Termination 1
Close the data file.
Write the recipe if the 'Autosave recipe' option was selected.

Frame 9: Termination 2
Save the configuration (.ini) file.

Frame 10: Termination 3
Set the analog outputs to zero.
Set the digital outputs to zero.
Stop the program.

Sequence 2 - 'Stop Sequence' (Frames 0..2)

Frame 0: Main loop
Run the main loop until the STOP button is pressed.

Frame 1: Termination 1
Put the 'STOP' button in it's original state.

Frame 2: Termination 2
Run (a copy of) the same sequence as frame 10 of the 'Main Sequence'.

The close observer will notice that the main loop from the 'Main Sequence' could interfere with the 'Stop Sequence', e.g. if the 'Stop Sequence' sets an analog output to zero the 'Main Sequence' could set in to the next value.

Downloads

pressure-measurements.llb
The pressure-measurements.vi was created to run with National Instruments hardware, but the library also contain simulation routines. So the vi can be used without the actual hardware.

pressure-measurements.ini
This is the initialization file which contains the variables:
- to construct the name of the next datafile
- to save the recipe at (normal) exit
- to hide the 'STOP' button during recipe execution
- to enable the use of simulation routines

pressure-measurments.rcp
Sample of a previously saved recipe

Remarks

At the time the department of chemical technology of the Delft University of Technology ChemE was named DelftChemTech.

---