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MUSCLE STRENGTH CIRCUIT

MUSCLE STRENGTH CIRCUIT. Siddharth Lohia Group 2 ECE 445 Summer 07. Introduction. A Circuit to measure applied force and convert the force into meaningful output Two main features of the circuit are current output and output display The current output is stable across a range of load

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MUSCLE STRENGTH CIRCUIT

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  1. MUSCLE STRENGTH CIRCUIT Siddharth Lohia Group 2 ECE 445 Summer 07

  2. Introduction • A Circuit to measure applied force and convert the force into meaningful output • Two main features of the circuit are current output and output display • The current output is stable across a range of load • The amount of current per amount of force is easily adjustable by just a screwdriver

  3. Additional Features • Display • The user can define the minimum and maximum range of input force • The Screen shows the current force and also holds the maximum force until the user resets it • The input force can be linearly scaled to the output value by any factor • The Output can be in any dimension

  4. Hardware • Load Cell • Filter • Voltage Amplifier • Current Transmitter

  5. Load Cell • Dinamica Generale DG-SP1 • 88 lbs Capacity • 2mV/V output • For 12 V power supply the output is in the range of 0-24 mV

  6. Filter The frequency of noise from the Load cell output is 215.52 kHz

  7. Filter Schematic

  8. Filter Equations Calculation of Cutoff Frequency • 1 / ( 2pi * RC) = 1/ ( 2 * 3.14 * 1000 * .001u ) = 159,154.94 Hz • 160 kHz • 1 / ( 2pi * RC) = 1/ ( 2 * 3.14 * 1000 * .002u ) = 318,309.88 Hz • 320 kHz • Zeroes in on the 215 kHz noise frequency • Improvement in signal stability observed

  9. Voltage Amplifier • AD708 Ultra low Offset Voltage Dual Op Amp • Differential amplification of Load Cell Output • Gain Controlled by potentiometer knob • The gain is between 30 and 100 • Although the gain can be adjusted to be up till 350, the current transmitter will burn out at such high input voltages

  10. Amplifier Schematic

  11. Op Amp Equation and Data • Gain = 1 + 2*10k/ ( 56 + R4) • For R4 = 163.2 Ω , Gain= 91.24 • Actual Data collected for R4 = 163.2 Ω

  12. Current Transmitter • AD 694 4- 20 mA current range • Converts input voltage into a current over desired range • The current output is independent over resistor range of 20 Ω to 400 Ω • Calculated from the equation ( Vsrc – 2.5) / 20m, where Vsrc is 12 V • An easy way to increase the value of load resistance is to increase the Vsrc of Current Transmitter

  13. Transmitter Schematic

  14. Configuration of the transmitter • The V ( A-B ) output from AD 708 is buffered by a 20k resistor, and fed into the + signal and – signal inputs respectively.

  15. Current Output Voltage Input For Load 19.8 Ω For load 384 Ω

  16. Force Input to Current Output

  17. Software • HIO 010 Prizm V.3 software used for programming the HIO device • GUI for screen displays • Ladder Structure Programming for storing and displaying the maximum value

  18. GUI Screenshot

  19. A/D conversion

  20. Partial Code for Displaying max. Force

  21. Equation For Display • Slope [ lbs/mA]= Load Range / Current range (In the application zone for max. accuracy) • Hi Set [lbs]= Slope * 16 • Lo Set [lbs] = 0 for max. range • (since the max input is 20 mA and the min input is 4 mA) • now 4 mA corresponds to 0 force and 20 mA corresponds to Hi Set.

  22. Current Output For Display Configuration

  23. Uses With Display • Measure Push & Pull Strength. • Two Such Devices can be used to detect muscle imbalances in a Chiropractor Clinic setting. • Measure and record maximum force applied when working in a gym.

  24. Uses Without Display • The Force can be calibrated to output any desired current in the 4-20 mA range. • The Current Loop can be used for operations like prosthetic devices. • It can be used for devices that require a stable power supply over a broad range of application of load.

  25. SWOT Analysis

  26. Credits • Mr. Craig Zeilenga from the Machine Shop • Prof. Gary Swenson • Mr. Tony Mangognia

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