This document describes an experimental design project to create a digital control system for measuring and controlling pressure gradient using LabVIEW software. The control system uses input voltage to an electric fan to control pressure gradient. It provides details on the control concept, including using a case structure to account for different station configurations, comparing measured response to desired setpoint to calculate error and proposed voltage adjustment, and applying the adjusted voltage to stabilize the system. Procedures for starting up and operating the hardware and software are also outlined.

1. To: ProfessorLaFleur
From: AdrienneW., KrisS., FernandoQ.
Re: ME401 ExperimentalDesignLab
Section:10
Certification: ________________
1. Introduction
In this Experimental Design Project the main objective was to create a control
program that measures pressure gradient and is controlled by input voltage to an electric
fan. Our team opted to use LabView software to build the control system. Beginning with
the references provided (experimental design desktop folder) the construction and setup
of the generic digital control software code could then be formatted for the objectives
listed. Before progressing any further, a few considerations were taken, such as
accounting for the timing issues in between the modified computer code and the actual
unit. Another consideration to take into account is that the large over and undershoot in
the software, as a result of the proposed gain value coupled with time delay.
The gain value and time delay values proposed were calculated for each station.
These were found while running the program continuously and monitoring the stability of
the system. On a completely stable system (critically damped) the pressure gradient
input will match the system output value, and do so in an appropriate time frame. This
control is designed to utilize a sequence of events; beginning with a set-point
specification, measurement of system response or status, comparison of the system
status to set value, and continually adjusting until the system status matches the set
value. Once complete, it is ready to actuate the control on the physical system, which
gives us the result that we are looking for in a stable system.

2. 2. Control Concept
As stated above, the program of choice was LabVIEW. This was because LabVIEW
works as a continuously updating system, giving us better control of the system (the
same reason why all our labs use LabVIEW code). LabVIEW was also designed with the
purpose of collecting data (Data Acquisition). With this in mind, the following program
was written.
Step 1: Command
Inserting the desired pressure gradient is done
by the user. The user specifies on the front panel what
the desired value is. The pressure gradient has limits for
each station which are listed next to the input box. The
user is also asked to specify the pressure gradient as a
negative value [inches H20/inches length] (its true
value).
Step 2: Measure Response
When a value is entered for
pressure gradient, the next step is to
measure the current pressure gradient
(to later see if the values are equal).
This was done with a separate VI using
a “for” loop and providing a numerical
output which can then be compared.
We utilize two separate scenarios
(values associated with stations) to
Figure 1
Figure 2

3. account for either a grey station or silver jet station. A case structure contains the
true/false statement of whether or not a grey station is used. When true, the gain, delta
x, and # of tubes is set to a specific value. When false, they are changed to the silver jet
station values.
Figure 3
Step 3: Compare Response and Calculate Error
After the system is measured, it must be
compared to the desired value. This is simply the
difference between the two values. A graph is utilized
to better visualize the system response, where you
can clearly see the system adjusting the actual
pressure gradient (red line) to meet the desired
(white line).
Step 4: Calculate Voltage Adjustment (Proposed)
Since the input to the motor is a voltage, we must convert
the pressure gradient difference to a proposed voltage change. This
is tacked on to the current voltage value (stored by a shift register
from the previous iteration). The value for voltage adjustment is
simply the gain value (found through testing) multiplied by the
difference in pressure gradient.
Figure 4
Figure 5

4. Step 5: Validate Adjustment
As stated, this voltage must then be added to the current
voltage (from shift register). It is then compared to the limits of the
system (between 0 and 10 volts). If the adjustment is within range, it
then sends it to the next block.
Step 6: Adjust Speed
The voltage proposed is then applied to the electric fan and the total
value is stored in a shift register (for the next loop).
Step 7: Wait
It is necessary to wait a period for the system to settle before
measuring again. This is done with a wait timer. We found a wait period of 3
seconds was low enough to still get an accurate reading and also not too high
that the system response becomes slow.
Hardware
Software and hardware utilized in this experiment is the following:
- DAQ Card (0 - 10v input/output max)
- Frenic-Mega Inverter
- BBA14-11 Series - Brushless DC Blower (120V AC Input)
- 9000 Series Intelligent Pressure Scanner (Brick)
Software
- Windows XP Operating System
- RunProgram2015.vi (LabVIEW)
- MeasurePressureGradient.vi
Figure 6
Figure 7
Figure 8

5. 3. Procedure of Use
Figure 9 – Front Panel Display with Desired vs. Measured Pressure Gradients Graph
Hardware startup
There are two different stations that can be run with this program.
Step 1:
The first is the silver station. To start up the silver station, pull the lever on the
blue control box upwards.
~OR~
The second station is the grey station. To start up the grey station, flip the switch
on the backboard of the station to on.
Software startup

6. Step 2:
In order for the computer to connect with the station, the folder containing the
RunProgram2015.vi and the MeasurePressureGradient.vi must be on the desktop.
Step 3:
Open up RunProgram2015.vi
Command set point
Step 4:
If the experiment is being run at the Grey Station, click the button that asks ‘Is this
station a Grey Box?’ and then click the Run Continuously button.
~OR~
If the experiment is being run at the Silver Station, click the Run Continuously
button.
Step 5:
Click the button labeled ‘Build Graph Yes’, otherwise you will not get the plot of
the desired pressure gradient and the actual pressure gradient.
Step 6:
Input the desired pressure gradient into the box labeled ‘Desired Pressure
Gradient’. Make sure it is a negative number.

7. Observing Displays
The graph at the bottom of the screen displays the pressure gradient over time. The red
line on the graph is the plot of the actual pressure gradient and the white line is the plot
of the desired pressure gradient.
If the LED display flashes green, the pressure gradient has not reached the desired value.
When the LED display flashes red, the pressure gradient has passed the desired value.
The Percent of Station Limit is shown in the box located next to the desired pressure
gradient input box. The Percent of Station Limit can be calculated using the equation
shown below.
% 𝐿𝑖𝑚𝑖𝑡 =
𝑃𝑚
𝐿 𝑆
× 100
Where 𝑃𝑚 is the measured pressure gradient and 𝐿 𝑆 is the station limit.
The statistical mean and standard deviation of the measured pressure gradient are
shown next to the Measured Pressure Gradient box.
SystemShut Down
Step 7:
In order to shut down the system, input a value of 0 into the Desired Pressure
Gradient box.
Step 8:
Once the actual pressure gradient has returned to 0, click the Stop Running
button (you may now close LabVIEW).

8. 4. Discussion of Control Options
In this experiment, the voltage is controlled through multiplying the pressure gradient
by the gain together. The control can be changed by changing any one of the factors
shown below:
 Time delay
 Gain
 Number of tubes changes depending on which station is used and affects the
maximum pressure gradient that can be used.
 Distance between tubes
Therefore, if this control were to be applied on a new system, the parameters above
would have to be accounted for. The gain will be estimated first, and then refined with
testing. This is due to the unaccounted error found when working with any electro
mechanical system.