To: Professor La Fleur From: Adrienne W., Kris S., Fernando Q. Re: ME401 Experimental Design LabSection: 10Certification: ________________

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.Control ConceptAs 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: CommandInserting 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).

Figure 1

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 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.

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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

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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.

Step 5: Validate AdjustmentAs 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 SpeedThe 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

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enough to still get an accurate reading and also not too high that the system response becomes slow.

HardwareSoftware 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

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3.Procedure of Use

Figure 9 – Front Panel Display with Desired vs. Measured Pressure Gradients Graph

Hardware startupThere 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

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.

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=PmLS×100

Where Pm is the measured pressure gradient and LS is the station limit.

The statistical mean and standard deviation of the measured pressure gradient are shown next to the Measured Pressure Gradient box.

System Shut 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).

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.