Automatic Concrete Sounder Connor Murphy ELM 4702 3/24/14
Presentation Order • Background • Standard Testing Procedure • Electronic Testing Procedure • Problem • Proposed Solution • System Diagram • Time Delay (1) • Time Delay (2) • Mechanical • Timing Mechanism • Electrical • Programming (1) • Programming (2) • Project Goals Chronology • Budget • Questions?
Background • As concrete structures deteriorate, the concrete must be monitored • Some testing requires sample of the concrete but this is destructive • Non-destructive evaluation (NDE) is a more popular method to test concrete. Examples of testing techniques for concrete and other materials include • Existing Testing Technology • Ground penetrating radar • Infrared evaluation • Sounding
Standard Testing Procedure • Standard testing for bridges in Vermont is hammer and chain sounding • Hammer strike against the concrete results in a sound whose pitch and ring tell whether the concrete is good or bad • Technician sounds out “bad sections of concrete” to mark area of concrete to be replaced.
Speed of sound through materials • Sound travels at a given speed through different materials • A Person yells to two people, one person 10 ft away and one 100 ft away • The speed of sound in air is 1000 ft/s • The sound will reach the person who is 10ft away faster than the person who is 100ft away • The time it took for the sound to travel is the time delay 10ft 100ft Time delay 10ft away= (10 ft)/(1000ft/s)= .01s Time delay 100ft away= (100 ft)/(1000ft/s)= .1s
Problem • Create an automated concrete sounder • Device must be able to determine concrete depth and delaminations (cracks) • Device must be portable • Must be easy to use
Proposed Solution • Solution will use a time delay based on the pulse echo standard • Sound input will be a mechanized hammer; the start of measured time delay • MEMs microphone will record concrete sound; this marks the end of the time delay • Kinetismicro-controller will measure time delay and convert an outputted time in seconds • Hammer and microphone will both be on top side of bridge
System Diagram • Initially • Micro controls hammer • Reads, records data from microphones • Exports data to excel file on laptop Hammer Mechanism Microphones Kinetis Micro Concrete Slab Cart
Time Delay (Thickness measurement) Sound Paths -Concrete -Air only Scope Ch2 Scope Ch2 Scope Ch2 Slide Hammer Scope Ch1 Scope Ch1 Scope Ch1 Copper Plate Concrete Slab Time Delay Voltage Voltage Voltage Time (ms) Time (ms) Time (ms)
Timing Mechanism Hammer hits plate • Used for timing when hammer hits copper plate • Hammer completes circuit when contacting copper plate • Normally open contact drives circuit low upon the hammer striking the copper Energy In: Potential E=mhg E=(.7kg)(.1524m)(9.807m/s) E= 1.04 J/s h= 6in =.1524m Hammer Slug m=.7kg To Micro Voltage Copper Plate Time (ms)
Time delay (Sound speed measurement) • To determine the speed of sound through concrete a time delay between 2 mic.s will be used • That speed can then with the time delay of the concrete to determine concrete depth • The speed of sound is 10 times faster through concrete than air • Concrete carries sound 10 times the distance air does in the same time V= 1ft/ t1 Velocity = Displacement/time Can then be used: Thickness= V*t2 Displacement= Velocity * time 1 ft Distance = 1ft
Mechanical • Device tentatively to be contained on rolling cart. • Weights to improve coupling between hammer and microphone on cart and bridge surface • Specific plans to be developed for cart • Cart will be similar in size to the chain drag cart shown Weights Cart Hammer Mechanism
Electrical • MEMs microphones • Comes with amplifier built in • Requires 3Vand ground • Signal out sits at .8V when no sound acts upon mic. • Kinetis • USB, with 5V power and ground • A/D converter to read signal out of mic. • Hammer • Timing circuit will be simple switch involving hammer and copper plate External PS, to be sized Hammer Mechanism Driver 3V A/D Kinetis Micro USB Microphone
Programming • Programming is in initial stages • 4 general action concepts • Programming will be in C • Timing will be very critical so sound waves don’t interfere with one another
Programming • Where • Desired sound wave--------- • Cancelation wave------------ • Unwanted reflected/ transmitted wave------------ • Hammer------------------------ • Microphone-------------------- • Concrete Bridge Slab---------
Speed of sound through materials An evolutionary step of hammer sounding is to automate the hammer and investigate physics creating the pitch and ring variance in concrete. Four Concrete test depths • Terms • MB - Main Bang • BE – Back Echo • FE – Flaw Echo