Safety First Inc.

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Safety First Inc.
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Team Members
Sheref Edwards ( team leader) se4_at_msstate.edu Leo
nard S Walker ( project administrator
) Lsw7_at_.msstate.edu Jay Knight ( senior design
engineer ) jkk4_at_msstate.edu Kenneth Douglas (
senior design engineer ) kid2_at_msstate.edu Rockell
Ingram ( senior design engineer ) rdi_at_msstate.edu
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Goals

• Produce a testable printed circuit board for ESP
• Verify operation in field and laboratory
• Construct working, packaged device by end of
  semester

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Design Constraints 1-5

• Detection- The ESP shall be designed to detect a
  magnetic field of Bgt10uT emanating from a current
  carrying power line.
• Reliability- signal originating from the source
  is received regardless of the angle between the
  antenna and the power line.
• Frequency range- The target frequency is 50 to 60
  Hz.
• Working Distance- The device will be sensitive
  within a distance of 2m at 100 amps from the high
  current power lines.
• Size- The safety pin will be about 1/3 the size
  of a large watch(1.5" X 1.5" X .25").

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Constraints 6-10

• Power Consumption- The product will consume less
  than 500mW when fully activated.
• User control Volume/on - off switch.
• Decibel Output- Increase in volume, as the
  magnetic field intensity grows stronger, no more
  than 80dB.
• Durability- Operate under elements such rain,
  snow and dusty conditions, shock impact from a
  height of 4 meters, temperature range from 0-70
  C.
• Cost- Produce a device that is under 40.00

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Design Block Diagram
Receiver antenna
Filter
Amplifier
Audio Out
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Present Detection Device Hall Sensor

• Small and cheap
• No construction required
• Provides linear output proportional to magnetic
  field normal to chip surface.
• Excellent route for field detection at all
  frequencies

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Updated Bread Board Design
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Performance Input vs. Output
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Output Characteristics

• Input form Hall sensors
  Fluke reads 5.7mv AC RMS
• Output from second stage amp
  Fluke reads 0.7 v AC RMS
• Rectifier Fluke reads 1.3v DC
• Current draw is (24-26)mA
• Power consumption 135mW ( constant)

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Pspice Capture Layout
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PCB (Home Grown)
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Filter Specs

• We choose C12.5nF,
• Quality Q5, DC Gain K40
• Then R1 5/(402?60Hz2.5nF)132.6KO.
• R2 25/(120?2.5nF) 10.6MO
• R3 25/(120?2.5nF(252-40))1.061MO
• Band pass was chosen due to its low component
  count, size, and cost.

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Differential Amplifier

• Gain R2/R1(Vhall-Vdiff)
• Set to 100 initially
• V(hall) Typically 2.5Vdc
• V(diff) created by a voltage divider (ideally
  2.5Vdc)
• Used to eliminate DC offset voltage created by
  Hall sensor

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A3515LUA Linear hall sensor test results
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Hardware Updates

• Single Rail Dual-Operational Amplifier reduces
  chip and battery count.
• Eliminates the need for a voltage divider circuit
  on the differential Amplifier further reducing
  component count.
• Delivers lower gain as opposed to the two rail
  amplifiers

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Hardware Updates

• Smaller battery pack consisting of two 3v coin
  cell batteries.
• DC piezoelectric rated at 1V vs 3.0 volt
  currently in use to allow a lower alert.

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Problem Low Gain

• 3 volt audio alert is presently activated at 5mV
  from hall sensorneed to bias audio at 0.5mV
  (need higher gain)
• 2-stage gain capped to about 120 due to
  limitations of single rail opamps
• Alternative reduce voltage needed to bias buzzer
  (down from 3 to 1 volts DC)

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Field Testing

• 7.5 kV
• 3 Phase
• A239A
• B279A
• C259

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Field Testing
C
B
A
y
x
z
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Field Testing
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Field Testing
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Field Testing
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Electromagnetic Field Strength
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Audio

• Preliminary testing complete.
• Output candidate is a DC Audio Piezoelectric
  Buzzer (1-15VDC).

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Tentative Pricingunit price per 1000

• Linear Hall Sensor (3) ...... 1.52ea
• Opamp Dual (TLV 4113 ) .. 1.196ea
• Resistors ( 7 ) .. 0.05148
• Capacitor ( 3 ) . 0.0286
• Rectifier (1) ... 0.79
• Piezoelectric Buzzer (1) .. 1.08
• Coin cell Battery Holder (1) 1.02
• Total per unit .. 9.00
• Estimated unit sale price.. 36.00
• Battery not included

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Future Plans

• Intense testing of PCB circuit in lab and in the
  field.
• Distance
• Angular position
• Gain
• Audio reliability
• Field measurements for the presence of field
  nulls.

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Summary

• Verify functionality through testing
• Buzzers and battery packs on order
• Product casing needs to be constructed

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Special Thanks to

• Dr. Ray Winton advisor
• Dr. Patrick Donohoe
• Starkville Electric Department (SED)

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Questions Answers
Hold this Sheref !!!
Lord Just Spare Me!!!!