Underground Utility Detection

1. Underground Utility Detection John Bertram Joseph Rutherford ECE 345 – Senior Design

2. Introduction • Improperly marked utility lines can be damaged by construction equipment, leading to costly repairs • Traditionally, marking services such as JULIE are used to obtain the location of underground utility lines • Accuracy is usually within two feet (0.61 m) of desired location

3. Objective • We wanted to construct a system capable of detecting buried lines that provided several features: • Identification of line location/orientation • Distance approximation within 0.25 meters • Line proximity warning • Portable packaging • Convenient interface • Automated

4. Original Design

5. Design Considerations • Initial focus was on development of the signal generator and control unit • After the Design Review, focus was redirected towards accurate detection and reliable amplification of the signal • Our revised design consisted of several subprojects: • Signal generation and reception • Amplification of received signal • Quantification of magnetic field • Antenna rotation control • Distance approximation

6. Signal Generation and Reception • A function generator was used to drive a 20 mA, 100 kHz sinusoidal signal • 100 coils of magnet wire were used for the antenna • Yielded a base amplification of 100 • Used a variable capacitor network in parallel with antenna to attain an additional gain of 37.8 • A voltage follower was used to transform high impedance to low impedance for connection with amplifier

7. Signal Reception • Measured unfiltered voltage • Decays approximately as expected • Noticed significant noise when observing unfiltered signal

8. Amplification of Received Signal • Amplification was needed to amplify the signal from antenna to readable values • A voltage follower was used to buffer the signal from the antenna • Amplification was performed using bandpass filters • AC to DC conversion of the signal was attained using a full-wave rectifier, peak detector, and low-pass filter • Quantification of the DC signal was accomplished using an A/D converter

9. Amplifier Design • Band-Pass Amplifier • Low-mode Specifications • Measured Gain at 100 kHz = 16-17 • Quality Factor=4.975 • High-mode Specifications • Measured Gain at 100 kHz = 325-350 • Quality Factor=4.975 • Switching between modes was accomplished using an analog multiplexer

10. Quantification of Magnetic Field • The full-wave rectifier used was found to perform inadequately at 100 kHz • To correct this problem, a peak detector was used to smooth the output • A low-pass filter removed any irregular peaks and minimized the ripple voltage • Gain=1, cut-off frequency=10 Hz, time constant=19.5 ms

11. A/D Converter • After rectification, the DC signal was quantified using an A/D converter • Operated in free-running mode • Safeguarded using voltage protection • Output 8-bit binary representation of magnetic field intensity

12. Antenna Rotation Control • A gimbal was used to rotate the antenna on two axes and hold the center constant • Stepper motors provided accurate control of orientation • Stepper motor drivers were built to interface the motors with a BASIC Stamp • Motors require current beyond maximum supplied by microcontroller • Provided voltage protection for microcontroller

13. The BASIC Stamp • Used to provide controlled sequential pulses to stepper motors • Antenna was moved through a Raster Scan • Upon completion, antenna was moved back to point of maximum intensity • Program estimated the distance from the wire

14. Distance Approximation • The BASIC Stamp was found to have many mathematical limitations • Accomplished using a series of mathematical functions to approximate the measured exponential decay

15. Distance Approximation • The estimated distance was close to actual measured distances • Error = -4.14±4.90 cm • Error was found to be mainly due to variable external noise sources

16. Challenges • Amplifiers became unstable when presented with high impedance sources and loads • Microcontroller lacked robust mathematical functionality • Abundant external noise sources made it difficult to control testing environment • Mass of the gimbal made it difficult to rotate using stepper motors

17. Successes • Reliably detected magnetic field • Accurately quantified magnetic field intensity • Controlled antenna orientation • Estimated distance from wire to within 10 cm in most cases

18. Future Development • Better developed User Interface • More tightly integrated and better enclosed structure for portability • More robust microcontroller to improve distance approximation

19. Conclusion • Achieved primary goals • Accurately located wire based on antenna position/orientation • Attained distance approximation within 0.25 m • Used raster scan for automated data acquisition • Remaining challenges can be overcome using better hardware • Successfully prototyped an economically viable and reliable system for wire detection

20. Acknowledgements • We would like to thank those who helped contribute to the success of this project: • Prof. Steven Franke • Prof. Gary Swenson • Chirantan Mukhopadhyay • Robert Rutherford