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									THRILL RIDE ENHANCEMENT: SEAT SENSORS


                    By


              Rachel Adaniya
               Kristin Jones
               Jason Witek




     ECE 445, SENIOR DESIGN PROJECT

              SPRING 2005




              TA: Mo Zhou



               May 3, 2005


               Project No. 6
                                               ABSTRACT

The Thrill Ride Enhancement: Seat Sensor system is designed to enhance the safety features of theme
park rides by providing an electronic means of checking occupant safety before ride dispatch. The
system detects the occupancy and state of the seat belt of any seat on the ride vehicle, and reports the
current state of the seat to the ride operator. It uses capacitance sensors to detect occupancy and Hall-
effect sensors to detect the state of the seat belts. The system reports faults in the seat sensors and
counts the number of guests passing through the ride.

The main goal of this project is to expand the safety features of a ride system by adding seat occupancy
detection to the current seatbelt and vehicle control systems. This paper describes construction of the
seat sensor system, including the design process, the finished design, verification results, and cost.




                                                     ii
                                                         TABLE OF CONTENTS


1.   INTRODUCTION ....................................................................................................................1
     1.1 Purpose ...............................................................................................................................1
     1.2 List of Acronyms ................................................................................................................1
     1.3 Review and Update .............................................................................................................1
     1.4 Specifications ......................................................................................................................1
     1.5 Subprojects .........................................................................................................................2

2.   DESIGN PROCEDURE ...........................................................................................................3
     2.1 Power ..................................................................................................................................3
     2.2 Seat Belt Sensors ................................................................................................................3
     2.3 Programmable Logic Controller (PLC) ..............................................................................3
     2.4 Fault Signal .........................................................................................................................4
     2.5 Seat Sensors ........................................................................................................................4
     2.6 LED Display .......................................................................................................................5

3.   DESIGN DETAILS ..................................................................................................................6
     3.1 Capacitance Seat Sensor .....................................................................................................6
     3.2 Magnetic Seat Belt Sensor ..................................................................................................7
     3.3 PCB Circuit Design ............................................................................................................8
     3.4 PLC Program ......................................................................................................................9
     3.5 PLC and LED Display ......................................................................................................13
     3.6 Finished Seat Sensor System ............................................................................................15

4.   DESIGN VERIFICATION .....................................................................................................16
     4.1 Seat Sensors ......................................................................................................................16
     4.2 Seat Belt Sensors ..............................................................................................................16
     4.3 PLC Control Signals .........................................................................................................17
     4.4 Power Conversions ...........................................................................................................17
     4.5 Water Tolerance................................................................................................................18
     4.6 Testing Conclusions` ........................................................................................................18

5.   COST ......................................................................................................................................19
     5.1 Parts ..................................................................................................................................19
     5.2 Labor .................................................................................................................................19
     5.3 Total Cost..........................................................................................................................19

6.   CONCLUSIONS ....................................................................................................................20

     REFERENCES .......................................................................................................................21




                                                                            iii
                                                           1. INTRODUCTION

Walt Disney Imagineering proposed a seat sensor system as an added safety feature in two Disney ride
systems, including Dinosaur in Disney’s Animal Kingdom and The Indiana Jones Adventure in
Disneyland.

1.1 Purpose
Currently, ride operators must manually check the state of each seat and seat belt before the ride vehicle
leaves the station to verify occupant safety. Thrill Ride Enhancement: Seat Sensors automatically
detects the occupancy of each seat on the ride vehicle and the state of each seat belt. Adding the seat
sensor system will eliminate the need for a manual safety check. The seat sensor system enhances safety
features, reduces the time required for a manual safety check, and increases hourly ride capacity. The
goal of the seat sensor system is to create a prototype that checks seat occupancy and seatbelt state at the
load station, and convey this information via LED to ride operators so that a decision to dispatch a ride
can be made.

1.2 List of Acronyms
WDI......................................................................................................... Walt Disney Imagineering
PLC ................................................................................................ Programmable Logic Controller
PCB ................................................................................................................. Printed Circuit Board
CPU ............................................................................................................. Central Processing Unit
IC ....................................................................................................................... Integrated Circuit
EEPROM ........................................... Electronically Erasable Programmable Read-Only Memory
EM ........................................................................................................................Electro-Magnetic

1.3 Review and Update
This system prototype was successfully built according to the specifications outlined in the proposal. It
examines the occupancy of two seats and the state of two corresponding seat belts and then transmits
that data to an LED display. A system fault signal detects problems in the system and reports them to
the LED display. A seat counter was added to count the number of guests that frequent a seat on a given
day. Counter results are displayed on the DV-1000 display on the PLC case. Sensor outputs are sent to
a PLC to output the data on LED's, which indicate four states for each seat. This system involved the
design and placement of sensors and electrodes on each seat to detect capacitance as well as sensors to
indicate that the seat belt is buckled. The PLC program was written to interface all components, and the
system was packaged to meet all specifications.

1.4 Specifications
The seat sensor system must be capable of monitoring the state of the seat sensors and seat belts. An
LED indicator alerts the operators of the following states:
     Seat is unoccupied and unlatched
     Seat is occupied and unlatched
     Seat is latched and locked with no faults
     Fault
The seat sensor system must be an affordable safety enhancement with no additional attraction operators
needed once device is installed. It must make use of off-the shelf parts whenever possible. It must be
designed to function on or around the existing attraction vehicle with a minimal amount of additional
equipment. It also must have the potential for system expansion, such as detecting seat occupancy and
seat belt position while the ride is in motion. It must be 99.99% reliable, durable to withstand the
physical stress of the ride, and be waterproof.

                                                                           1
1.5 Subprojects


                                                                       Vehicle Control System
                         Seat                  Control
       Guest
                         Sensors               Logic
                                               and PLC               Operator LED
                                                                     Display


                                                                           PLC
                                               Seat belt                   Display
                     Power Supply              Sensors




                            Figure 1.5 Seat Sensor System Block Diagram

Figure 1.5 shows the seat sensor system block diagram. The seat sensors interact with the guest to
detect the state of occupancy of each seat. Seat sensor design includes circuit design surrounding a
QT310 capacitance chip, electrode selection, and calibration of seventeen parameters in the QT310’s
onboard EEPROM. The power supply powers all components. The control logic and PLC takes sensor,
fault and reset inputs for each seat and translates them into corresponding output states. The control
logic must convert 24 VDC from the power supply to 5 VDC to supply the sensors, and then must raise
all 5V sensor logic signals to 24V logic to properly trigger the PLC. The PLC software implements the
state decoder, fault detection, and seat counters. The LED’s display four states for each seat, and the
PLC display and the DV-1000 displays PLC status and seat counters respectively. In the design process,
work was broken down according to the blocks in Figure 1.5.




                                                  2
                                      2. DESIGN PROCEDURE

The design procedure began by reviewing the design specifications provided by the Walt Disney
Company as specified in section 1.4. Disney graciously supplied a PLC and accompanying software to
implement the state decoder. Disney further suggested the use of Quantum QT310 chips for use in the
seats to detect the capacitance of a person. With these considerations in mind, the design process began.
The following sections describe design alternatives and decisions made for each system component.

2.1 Power:
To eliminate the need for additional equipment, the 24 V power supply packaged with the PLC was used
to supply power to all components. 24 V is readily available on the ride vehicle so the seat sensor
system need not use a supplementary supply. Originally the power conversions were designed for a 24V
power supply, as the power supply used was specified to be 24 V as per the industry standard. In
testing, the power supply was found to output 28V and recalculations were made to accommodate the
higher voltage. The QT310 capacitance sensor, the MP1301 magnetic hall sensor, and the switch are
rated at a maximum input voltage of 5 V each. This posed as a problem since only 28 V was available.
A LM317 voltage regulator was used to drop 28 V to 4.87 V, creating a sensor power supply. To
determine the output voltage of the voltage regulator, the following equations were used:

                                   Vout = Vref(1+R2/Ra)+Iadj*R2                                         (1)

                                   Iout = Vref/R1 + Iadj = 1.25/R1                                      (2)

Sensor outputs needed to be stepped up since the PLC requires a minimum input of 16.5 V. A transistor
was used to raise the output voltage of the onboard circuitry to trigger the PLC. A 28 V input was
placed on the drain and the sensor output that varied from 0 V to 5 V was used at the gate to produce an
output of about 16.67 V. Sedra [1] states that the output voltage of a transistor is determined from:

                                     Vout = Vcc –ic*Rc                                                  (3)

A resistance of 3.3k was used at the gate and drain of each transistor to minimize power and avoid
overheating. How the 3.3 k resistor was chosen can be found in the testing and verification section.

2.2 Seat Belt Sensors:
There were several design alternatives for seat belt sensors, including force sensors and mechanical
switches. Hall-effect sensors were selected because they are relatively inexpensive and can easily be
mounted on an off-the-shelf seatbelt. The Hall effect sensors are activated with a minimum of 300
Gauss and carry a rated voltage input of 4.75-24V. The magnets generate a magnetic field that acts
perpendicularly to the direction of current and generates the Hall voltage. Magnet selection and
placement played a large role in the seat belt sensor design as described in section 4.2.2. To determine
the field strength, the following equation was used.

                                          H = m*                                                      (4)

2.3 Programmable Logic Controller (PLC)
A PLC was used as a state decoder according to Disney’s specification. The PLC takes four inputs from
each seat: the capacitance sensor output, seat belt sensor output, fault and reset signals. It decodes the
inputs and produces four outputs for each seat: occupied latched, occupied unlatched, unoccupied
unlatched, and fault. The PLC program was written with DirectSoft32 programming software. It
implements the state decoder, fault detection and seat counters with ladder logic. Designing the PLC
circuit proceeded with general wiring, programming and compilation, debugging and recoding. The
                                                      3
inputs and outputs were tested independently of the sensors to ensure functionality before the entire
system was integrated together.

2.4 Fault Signal
Specifications required a fault signal to determine the status of the capacitance sensor and any PLC
faults. Design alternatives included a mechanical test of the seat sensors, applying a controlled signal to
the seat sensors to test functionality, or using the Heartbeat on the QT310 chip. The seat sensor system
used utilizes the Heartbeat signal on the output of the QT310 chip, because this allows for continuous
monitoring of the system. The Heartbeat consists of 15us floats superimposed on the sensor output and
indicated a healthy working chip. The floats occur once per burst cycle, or roughly 20ms. The time
between burst cycles can be altered by changing the parameter settings on the QT310. The fault signal
is described in sections 3.3 and 3.4. The fault signal will detect PLC faults and problems with the
QT310 chip including a PCB power outage and a fried chip.

2.5 Seat Sensors
Seat sensor design included the construction of the circuit utilizing the QT310 sensor chip, and the
construction of a suitable electrode. The basic circuit was taken from the QT310 data sheet [2]. A
resistor was added between the electrode and sampling capacitor (RE1) to ensure that no static charges
can be absorbed through the electrode and into the device, thus eliminating electrostatic discharge. The
value of this resistor was chosen to keep the resulting time constant between the resistor and the
capacitance from the electrode below 1/6th the transfer time of the chip. The formula for the time
constant is:

                                                      t=(RE1)(Cx)                                        (5)

RE1 represents the value chosen for the resistor and Cx represents the capacitance from the electrode.
Knowing the chip transfer time of 833ns and the range of human capacitances between 60-250pF, a
range of resistances was available for selection. A midline value for the resistance was chosen to
represent a median capacitance at a value of 560 ohms.

The construction of the electrode alleviated the concern that passengers in adjacent seats might cause a
false detection, and also to ensured that a guest could move in the seat without fooling the sensor .
Various sizes and shapes of electrodes were tested to determine the maximum distance to trigger an
occupied state. The results can be seen in Table 2.5.

                                         Table 2.5 Electrode Sensitivity
   Electrode Description                                  Max Distance to Activate Sensor
   1” Diameter thin metal circular disc with holes        1.25”
   2”x3” Thick metal square with holes                    .63”
   3.5”x3” Metal mesh screen                              2”

An analysis of these results shows that regardless of the electrode chosen, a false trigger from an
adjacent seat is unlikely, so the electrode that has the largest activation distance was chosen. This gave
the largest amount of leeway for passenger movement in the seat. Since the width of an average theme
park ride seat is approximately 16-18 inches, it could be advantageous to use an electrode with an even
larger range. Having a range of up to 6 inches in each direction provide for a person centered in any
portion of the seat to be detected, and still would not have sensed outside of the intended seat. This
modification proved unnecessary because the system as implemented was very accurate and reliable.


2.6 LED Display
                                                      4
The display was designed solely for the demonstration to give a clear representation of the PLC output
states. The display needed to show all four of the possible states of the device, and make clear the state
of the system. LED’s were used because they provide bright, easy to see indicators of output. The
LED’s available were yellow, green, and a red/green multicolor LED. Since four states needed to be
shown and easily differentiated, the decision was made to mix the red/green multicolor LED to produce
a fourth orange color. For each single-input LED used, a 2.2 kΩ resistor was placed between the output
from the PLC and the LED’s input to lower the voltage from 28 V to 3.8 V according to the following
equation.
                                   28 V – (11 mA)(2.2kΩ) = 3.8 V                                         (6)

For dual input LED’s, 4.4 kΩ resistors were placed before each lead to lower the total input voltage to V
as in the following equation.

                                  28 V – (5.5 mA)(5.1kΩ) = 3.8 V                                         (7)

This was done to ensure that the voltage rating of the LED was not exceeded. To mix the multicolor
LED, resistors were put on both the red and green inputs of the LED, and the output voltage from one
state was applied to both inputs. This caused the red and green colors to be activated simultaneously,
causing an orange color to be displayed. Each color was then assigned to a state, the LED’s and
resistors were mounted onto a PCB board, and a printout showing which state each LED corresponded
to was put onto the board under the LED’s. In actual implementation, more durable LED’s would be
chosen, however inexpensive LED’s proved adequate for demonstration purposes.




                                                     5
                                                         3. DESIGN DETAILS

3.1 Capacitance Seat Sensor
                                                                          VDD 5V

                                                                                                                                  28Vdc
                                                                                            C1

                                                                                            100n
                                               SS1                     R2             R4
      Calibration Switch            R1                                 10k            10k                                                  R10
                                                                                                           0
                                    10k        QT310-D                                                                                     3.3k

          SWITCH
          76PSB08
                                                1
                                                /CAL
                                                     8
                                                     VDD
                                                                                                                                                         SS1 to TB-1
                                                                                                                   R9
  0
                                       X
                           Not Connected
                                                2      7
                                                /SYNC_OOUT
                                                                                                                                          Q2
                                                                                                                                          Q2N2222
                                                                                                                   3.3k
                                                     6
                                                3 /SYNC_I
                                                SNS1
                                                                                                                                      0
                                                4
                                                VSS
                                                         5
                                                         SNS2
                                                                                                   Electrode


                                                                             Cs      RE1
                                           0                                 4.7n    560                                         Cx

                                                                                                                                 60-250pF
                                                             RE1 Value Experimentally Determined
                                                                                                                                                  0



                                                                                                               Not phy sically implemented. Results
                                                                                                               f rom human interaction with electrode.
                                                Figure 3.1 Capacitance Seat Sensors

Figure 3.1 shows the capacitance seat sensor chip. The QT310 is a digital burst mode charge-transfer
sensor. The IC acts as a capacitance-to-digital converter. Cs is a sampling capacitor and is treated by
the chip as a floating store of accumulated charge. Cs undergoes bursts where charge builds, is stored
on the capacitor and read into the device. Cx denotes the capacitance induced from human interaction.
Resistors R1 and R2 protect against short-circuiting of the /CAL and /SYNC_I pins. The calibration
switch sends a low signal to /CAL when switched, and allows Cx to be normalized. The transistor
amplifies the output voltage from 4.87 V to 16.7 V to be read by the PLC.

Several of the seventeen chip parameter settings in onboard EEPROM were altered to ensure proper
operation. The Max On Duration (MOD) timer was altered from its default value of 10.44s to 177.43s to
give the operator enough time to see the output. The chip recalibrates itself after the MOD period.
MOD was then varied and set to infinite. An infinite timeout indicates that the chip never recalibrates.
Although giving an operator the maximum amount of time possible to view the output of the sensor was
optimal, setting MOD to infinite posed a problem. It caused the device to stay on inadvertently even
when human capacitance was not present near the electrode. The greatest calibrated value of 177.43s
was chosen to optimize viewing time for an operator. The output polarity was also altered. An Output
of high was set using the cloning process. An active high output polarity indicates that the normal
inactive polarity of OUT is low. After the QT310’s parameters were set accordingly, the seat sensors
were arranged to give a voltage output of 0V when capacitance was placed in close proximity to the
electrode. When capacitance is not placed near the electrode, the output voltage was 4.8V. All QT310
parameters not listed remain at their default values as listed in the QT310 data sheet [2].




                                                                             6
3.2 Magnetic Seat Belt Sensor
                                                                         1
                                                                                   VCC (Red)
                                                                                                     28 Vdc f rom PLC




 Magnet

                                                                                  Pull-up Resistor
                                                                                     2.2k




                                                                         4       Output (Green)
                            +                                                                        Output

                                OUT

                            -   OPAMP                      Transisitor

                                                                         3   Ground (Black)




                                                                                  0


                     Housing denoted by dotted block
                                  Figure 3.2 Magnetic Seat Belt Sensor

Figure 3.2 shows the Hall-Effect magnetic sensor. When a magnetic field is present, a current and
voltage are induced pulling the voltage low. While there is no field, VCC is connected straight to the
output. The pull-up resistor present between VCC and the output protects against short-circuiting.




                                                       7
3.3 PCB Circuit Design




                                                                                                     Figure 3.3 PCB Circuit Design



Figure 3.3 shows the complete circuit design that was implemented onto the PCB board. The major
blocks of the circuit are enclosed in dotted lines. The seat sensor and magnetic sensor are outlined in
green and orange, and were referred to in 3.1 and 3.2 respectively. The power conversion outlined in
blue converts 28V to 5V for powering the sensors. The fault detection block outlined in red shows the
fault detection input to the PLC. The fault signal uses the periodic voltage drop created by a pull-up
resistor connected to the QT310 output as the clock input to a D-latch. The D latch inverts every clock
cycle, resulting in a square wave with a 40ms period. The square wave serves as the fault input to the
PLC, which uses it to reset timers in the PLC program as described in section 3.4. If the PLC timer

                                                   8
passes five seconds without reading a transition in the fault input, it triggers a fault output in the system.
The four transistors amplify the 5V sensor, fault and reset signals to 16.7V to trigger the PLC inputs.

3.4 PLC Program
The PLC program was written using DirectSoft32 programming software. The program is written in
ladder logic using relays, timers and counters as programming tools. The PLC takes four inputs for each
seat: the seat capacitance sensor, seat belt sensor, fault signal and reset. It generates four outputs for
each seat corresponding to each of the four states as outlined in section 1.4. The program implements
the state decoder, fault detection, seat counters, and DV-1000 display interface as described below. A
list of component designations, nicknames and descriptions is provided in Table 3.4. “X” denotes an
input, “Y” denotes an output, “C” denotes a control relay, “T” denotes a timer, “CT” denotes a counter,
and “V” denotes a location in PLC memory. Background in PLC coding can be found in the PLC
manual and DirectSoft32 programming manual [3], [4].

       Table 3.4 DirectSoft32 PLC program component designations, nicknames and descriptions
                     Designation   Nickname               Description
                     X0            SS1                    Seat Sensor 1
                     X1            SS2                    Seat Sensor 2
                     X2            BS1                    Belt Sensor 1
                     X3            BS2                    Belt Sensor 2
                     X4            FAULT1                 Fault Input 1
                     X5            FAULT2                 Fault Input 2
                     X6            RESET1                 Seat 1 Reset
                     X7            RESET2                 Seat 2 Reset
                     Y10           OccupiedLatched1       Seat 1 Occupied, Latched
                     Y11           OccupiedUnlatch1       Seat 1 Occupied, Unlatched
                     Y12           UnoccUnlatch1          Seat 1 Unoccupied, Unlatched
                     Y13           FaultOut1              Seat 1 Fault
                     Y14           OccupiedLatched2       Seat 2 Occupied, Latched
                     Y15           OccupiedUnlatch2       Seat 2 Occupied, Unlatched
                     Y16           UnoccUnlatch2          Seat 2 Unoccupied, Unlatched
                     Y17           FaultOut2              Seat 2 Fault
                     C0            FaultControl           Fault Control Relay
                     C3            ResetControl1          Seat1 Reset
                     C4            ResetControl2          Seat 2 Reset
                     T0            Seat1TimerLo           Seat 1 Low State Fault Timer
                     T1            Seat1TimerHi           Seat 1 High State Fault Timer
                     T2            Seat2TimerLo           Seat 2 Low State Fault Timer
                     T3            Seat2TimerHi           Seat 2 High State Fault Timer
                     CT1           Seat 1 Counter         Seat 1 Counter
                     CT2           Seat 2 Counter         Seat 2 Counter
                     V7626         DispMode               DV1000 Display Mode




                                                      9
In figure 3.4a, line one indicates to the DV-1000 display to load in message mode upon the first PLC
program scan. Lines two through seven serve as the seat state decoder, translating combinations of the
seat sensor input and belt sensor input for each seat into the corresponding output. Line eight
implements fault detection as described below.




           Figure 3.4a PLC program page 1 (Taken from a screen capture in DirectSoft32.)




                                                  10
In figure 3.4b, lines eight and nine implement fault detection for seat one, while lines ten and eleven
implement fault detection for seat two. In line nine, if the seat sensor output is low, the reset input is not
triggered, and the fault input signal is high, timer T1 will begin timing. When the fault signal transitions
to low, timer T1 will reset. If timer T1 can reach five seconds without resetting, then control relay T1
will turn on in line thirteen, causing Seat 1 Fault to turn on. The timer in line eight operates similarly,
except it will begin timing when the fault signal is high. Line twelve turns on the fault control relay C0
if the PLC detects an internal error. Line thirteen turns on the Seat 1 Fault output if T0, T1, or C0 are
high. The fault output from T1 or T0 will turn off when the reset button is pressed. Line fourteen in
figure 3.4c operates similarly to line thirteen for seat two.




           Figure 3.4b PLC program page 2. (Taken from a screen capture in DirectSoft32.)




                                                     11
In figure 3.4c, lines fifteen and sixteen turn on control relays C3 and C4 when RESET1 and RESET2 are
turned on, respectively. Line seventeen implements the Seat 1 Counter. While Seat 1 Reset is off, when
Seat Sensor 1 input transitions from low to high, Seat 1 Counter will increment. The counter resets to
zero when the Seat 1 Reset is turned on. Line eighteen implements the counter for seat 2. Lines
nineteen and twenty load the counter values to the DV-1000 display.




           Figure 3.4c PLC program page 3. (Taken from a screen capture in DirectSoft32.)

The seat sensor system uses the DV-1000 display on the front of the PLC case to display the counts on
the seat timers. The DV-1000 was setup using DirectSoft32. In DirectSoft, clicking on “PLC” on the
menu bar, then “Setup”, “DV1000”, and the “Messages” tab will display the following screen. The


                                                  12
“Active Text Location” and “Screen editor” sections were set as in figure 3.4d to display the states of
the counters on the DV-1000. Further instructions in DV-1000 setup can be found in the manual [5].




            Figure 3.4d DV-1000 setup screen taken from a screen capture in DirectSoft32.

3.5 PLC and LED display
Figure 3.5 shows the PLC connections to the sensors and the output LED display. All inputs and
outputs are routed through terminal blocks denoted “TB” in the diagram. The PLC consists of several
modules, including the CPU, input module and output module. Each module has an independent LED
display and display mode switch. The PLC takes eight inputs, and gives eight corresponding state
outputs displayed on eight LED’s.




                                                    13
14
     Figure 3.5 PLC and LED output display schematic
3.6 Finished Seat Sensor System
Figure 3.6 shows the complete seat sensor system, including the two seats and seat belts constructed,
and the PLC. A PCB was made for each seat, and packaged in a plastic container so that the system
would be waterproof. The plastic tubs were slid under each seat so they would not be accessible to the
guest. In actual implementation, the PLC and PCB’s would be attached to the underside of the seat
bench, inaccessible to the guest.




                            Figure 3.6 Photo of finished seat sensor system.




                                                  15
                                     4. DESIGN VERIFICATION

4.1 Seat Sensors
While the design of the seat sensor system is challenging, most of the difficulty arises in the testing
portion of the project. The capacitance sensors needed to be meticulously configured to reliably detect a
person, eliminate detection of inanimate objects, and cancel out the effects of water. Sensor
functionality was tested and the appropriate chip parameter settings were determined by connecting the
seat sensor chip to the manufacturer’s evaluation board. Functionality of its various parameters was
observed. A cloning process was used to program and permit unique combinations of sensing and
processing. The cloning process was performed though the use of the manufacturer’s evaluation board.

4.1.1 Electrode
Electrode sensitivity was tested using various sizes and a variety of electrodes, including a metal square,
wire mesh and coiled metal. The minimum distance required to activate the sensor was recorded.
Results were documented and can be found in section 2.5. The electrode was also required to have a
sensitivity range such that a person would not have to be in one specific place to activate the sensor. For
this reason, the electrode was chosen such that it produced the largest range from our test results. A 3
1/2”*3” wire mesh electrode with a high space to conductor ratio produced the best results, as seen in
table 2.5. Sensitivity was found to decrease with a smaller sized electrode. It was desired that a person
outside of the designated seat area not activate the electrode. In testing, the electrode range proved to be
limited to a few inches, eliminating that concern.

4.1.2 Sensing
A seat sensor reliability test documenting output due to persons of various weights was performed.
Persons weighing 45, 55, and 90 kg tested the sensitivity over a period of fifty trials each, and the sensor
was found to correctly trigger each time. The seat sensor’s imperviousness to inanimate objects was
also tested and documented over a period of fifty trials. Objects commonly found in a theme park were
tested. These include a water bottle, Ipod, jacket, backpack, stuffed animal, snow globe, and camera.
No false detections were recorded for any object. Sensitivity of the electrode was important to ensure
that the sensor would not trigger when an inanimate object was placed in close proximity of the
electrode. Testing various weights was also necessary to ensure that the sensor was not dependant on
weight and was only triggered when capacitance was present.

4.2 Seat Belt Sensors

4.2.1 Reliability
Seat belt sensor reliability was tested and documented over a period of fifty trials per seat belt by
latching the belt repeatedly. The seat belt sensors were tested to ensure that they were accurately set up.
When triggered, the seat belt sensor outputted 4.87 V and triggered correctly every time.

4.2.2 Magnet Placement
Magnet placement was important to ensure proper function of the seat belt sensor. Four different types
of magnets were purchased, which varied by width, length and thickness. Field strength of 300 Gauss
was required to activate the sensor. Field strength per distance from the magnet was considered to allow
for the maximum strength of necessary to trigger the seat belt sensor. Figure 4.2.2 indicates the total
field strength of magnet per distance away from seat belt sensor. The seat belt sensors yielded a total
field strength of 430 Gauss when a magnet of 0.25”*0.25”*0.25” was placed at a distance of about 0.25”
away from the seat belt sensor. This configuration yielded field strength greater than the sensor
threshold of 300 Gauss and was used in the final design.


                                                    16
                                                                      Field Strength of Nd-Fe-B Magnet

                                                1000




                          Field Magnitude (G)
                                                800

                                                600

                                                400

                                                200

                                                  0




                                                                                                                                                            1
                                                                                                            0.2
                                                                                                                  0.3
                                                                                                                        0.4
                                                                                                                              0.5
                                                                                                                                    0.6
                                                                                                                                          0.7
                                                                                                                                                0.8

                                                                                                                                                      0.9
                                                       0.13
                                                               0.14
                                                                       0.15
                                                                              0.16
                                                                                      0.17
                                                                                              0.18

                                                                                                     0.19
                                                                                                      Position (in)


                                                 Figure 4.2.2 Total Field Strength of Nd-Fe-B Magnet

4.3 PLC Control Signals
Giving test inputs to the system and comparing outputs tested the PLC output signals as described in
section 1.4. After some debugging, the PLC was found to output states correctly. Table 4.3 indicates
the inputs and outputs that correspond to the LED’s on the front of the PLC that were used in debugging.
These are separate from the LED output display used for the demonstration.

                                                       Table 4.3 Corresponding PLC LED’s
              INPUTS    PLC LED                                                      OUTPUTS                PLC LED
                 0      Seat Sensor 1                                                   0                   Seat 1 Occupied, Latched
                 1      Seat Sensor 2                                                   1                   Seat 1 Occupied, Unlatched
                 2      Belt Sensor 1                                                   2                   Seat 1 Unoccupied, Unlatched
                 3      Belt Sensor 2                                                   3                   Seat 1 Fault
                 4      Seat 1 Fault                                                    4                   Seat 2 Occupied, Latched
                 5      Seat 2 Fault                                                    5                   Seat 2 Occupied, Unlatched
                 6      Seat 1 Reset                                                    6                   Seat 2 Unoccupied, Unlatched
                 7      Seat 2 Reset                                                    7                   Seat 2 Fault

4.4 Power Conversions
Power conversions were tested independently to ensure proper voltage supplied to each component.
After initial simulation in Pspice, the power conversions from 28 V to 5 V and 5 V to 28 V were tested
by connecting the power conversion portion of the circuit only and observing its voltage and current
with a voltmeter. Results were documented, can be found in Table 4.4, and proved successful. The
actual voltage that triggered the sensors was 4.87 V. The actual voltage that triggered the PLC was
16.67 V.

                                                              Table 4.4 Voltage Conversion
                                                                      Voltage Regulator
                                                              Vin (V)    Vout (V)   Iout (mA)
                                                                 28        4.87         10

                                                                                 Transistor
                                                              Vin (V)           Vout (V)    Iout (mA)
                                                                4.87              16.67        8.0


                                                                                             17
The transistor resistances were altered and tested by increasing the resistance value with common
resistances found in the lab to eliminate overheating. The power per resistance can be found in Figure
4.4. At 3.3k, the resistors no longer overheated, with 0.24W flowing through each. This eliminates
the overheating problem, and 3.3k resistors were used in the finished system.


                                                    Power per Resistance

                                        1

                                       0.8
                       Power (Watts)
                                       0.6

                                       0.4

                                       0.2

                                        0
                                               5


                                                     5


                                                           3




                                                                              5


                                                                                       5


                                                                                             5
                                                                 4


                                                                       6
                                             1.


                                                   2.


                                                         3.




                                                                            5.


                                                                                     6.


                                                                                           7.
                                                         Resistance Value (K-Ohms)


                                               Figure 4.4: Power per Resistance

4.5 Water Tolerance
The presence of water on the seat greatly affects the ability to detect the presence of a person sitting
down, since water alters the dielectric constant of the environment near the sensor similarly to that of a
human. The seat was covered with Saran wrap so that it would not be damaged, and the system still
accurately detected the presence of a person with the plastic coating. Introducing 100 ml of water
absorbed by several cotton balls tested system water tolerance. The cotton was placed directly on the
seat. The amount of water and cotton balls was gradually increased from 0ml to 1000 ml in 100 ml
increments, as specified in the design review. The wet cotton never triggered the seat sensor. The test
was continued by adding water in 100 ml increments until 3 liters of water covered the seat, and still no
false detections were recorded. The wet cotton was then placed in a plastic tub on the seat and water
was added up to 5 L. No false detections were recorded, and the system passed the water tolerance test.

4.6 Testing Conclusions
In conclusion, the seat sensor system passed all tests specified in the design review. The seat sensor
passed reliability tests including repeated sensing, sensing persons of different weights, and filtering out
inanimate objects. The magnetic sensors proved to be reliable over fifty trials, and magnet placement
testing was completed. PLC control signals and power conversions were tested independently for
functionality and passed all tests. The system passed the water tolerance test with up to 5 L of water on
the seat with no false detections.




                                                                18
                                                        5. COST

5.1 Parts
                                                 Table 5.1 Parts List
                Parts List
                Part                   MFR           Value          Part Number Qty. Price ($) Total
                Pull-Up Resistor                     2.2k Ohm                      7     0.16     1.12
                RE1                                  560 Ohm                       1     0.23     0.23
                Resistor                             10k Ohm                       3     0.16     0.48
                Capacitor                            100nF                         5     0.16      0.8
                Cs Capacitor                         4.7nF                         1     0.49     0.49
                Calibration Sw itch    ITT Industries               KT11P3SM       1     2.27     2.27
                Magnetic Sensor        Cherry Corp.                 MP101301       3     6.08 18.24
                Capacitance Sensor     Quantum                      QT310-D       10     1.87     18.7
                Eval Board             Quantum                      E3B            1       20        20
                Cloning Board          Quantum                      QTM300CA       1       49        49
                Seat Belt              OEM                          SB2PRBG        2 24.15        48.3
                PLC*                   Direct Logic                                1    1500     1500
                LED (Bi-color)         Fairchild Op.                HLMP-4000      4     0.35      1.4
                LED (Green)            Fairchild Op.                HLMP-500       2     0.35      0.7
                LED (Yellow )          Fairchild Op.                HLMP-3300      2     0.35      0.7
                Magnet                 K&J Mag.       .25x.25x.0625 B441           3     0.17     0.51
                Magnet                 K&J Mag.       .25x.25x.125 B442            3     0.25     0.75
                Magnet                 K&J Mag.       .25x.25x.25   B444           3     0.28     0.84
                Magnet                 K&J Mag.       .25x.25x.50   B448           3     0.85     2.55
                Voltage Regulator      National Semi.               LM317          3     0.68     2.04
                Resistor                              710 Ohm                      4     0.16     0.64
                Resistor                              240 Ohm                      4     0.16     0.64
                Capacitor                             1uF                          4     0.16     0.64
                Portable Computer      Compaq                                      1    1500     1500
                Chair                                                              2 19.99 39.98
                Aluminum Screen Kit    Do It Best                                  1     2.99     2.99
                D-Latch                Texas Inst.                  SN74LS74       3      0.5      1.5
                Transistor                                          2N2222A        8     0.86     6.88
                Dip Sw itch (16 Pin)                                76PSB08        2      1.4      2.8
                PCB Board                                                          2        5        10
                Resistor                              5100 Ohm                     4     0.16     0.64
                Resistor                              3300 Ohm                    16     0.16     2.56
                Total                                                                          3238.4




5.2 Labor
Each person worked a total of 10 hours a week for 12 weeks. Each person charged a total of $40 per
hour.

Total Cost of Labor=$40/hour * 2.5 * 12 weeks * 10 hours/week * 3 engineers = $36,000

5.3 Total Cost
Summing the cost of all parts plus the total cost of labor as found in sections 5.1 and 5.2 respectively,
the total cost is $39,238.40.




                                                            19
                                          6. CONCLUSIONS

In conclusion, the seat sensor system design was successfully build. It met all specifications and passed
all tests specified in the design review. While the system passed all tests, further testing is
recommended to fully verify reliability before implementing the system in a theme park. While testing
was thorough for the time allotted in the semester, fully ensuring 99.99% reliability requires many more
trials of all tests performed. Further testing in seat sensor reliability and water tolerance is
recommended to ensure the system will function under the demanding requirements in a ride setting.
While the seat sensor system performed very well in the senior design classroom, modifications must be
made to integrate the system with Disney’s current proprietary seat belt system. The design will be
given to Disney’s engineers for review and possible implementation. The seat sensor system has great
potential for expansion. In the future, it could be modified to detect guests while the ride is in motion,
and to verify seat occupancy upon restart of the ride. Both of these modifications would help ensure
guest safety.




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                                          REFERENCES

[1]   Adel S. Sedra and Kenneth C. Smith, Microelectronic Circuits. New York: Oxford University
      Press, 2004.

[2]   Quantum Research Group Technical Staff, Qprox QT310 Capacitance Sensor IC, Quantum
      Research Group, 2002, http://www.qprox.com/downloads/datasheets/qt310_103.pdf

[3]   Automationdirect.com Technical Staff, D2-USER-M, Automationdirect.com Incorporated, 2003,
      http://web3.automationdirect.com/static/manuals/d2user/d2uservol1.pdf.

[4]   Automationdirect.com Technical Staff, DirectSoft32 Programming Software Users Manual,
      Automationdirect.com Incorporated, 1999.

[5]   PLCDirect Technical Staff, D-24VIEW-M, PLCDirect Incorporated, 1998.




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