A simple vibration sensor can be made from some PVC pipe components and a piezo – ceramic disc. This sensor is designed to be used with an oscilloscope. An oscilloscope is also necessary to test the operation of the completed sensor.
1.) 0.75 inch PVC pipe plug. (Actual O.D. 1.050 inch)
2.) 0.5 inch length of 0.75 inch PVC pipe. (Actual O.D. 1.050 inch)
3.) 1.5 inch length of 0.156 inch O.D. plastic tubing. Evergreen Scale Models #225.
4.) 2.75 inch length of 0.093 O.D. plastic rod. Plastruct #90272 or equv.
5.) 0.5 oz sliding lead fishing weight.
6.) 1.062 inch (27mm) diameter piezo ceramic bender disc.
7.) 2 x 6 inch length of 30 or 32 awg insulated stranded wire. (see note below).
Note: The piezo bender disc can be purchased with or without attached wires.
1.) Drill a 0.156 (5/32) inch hole in the center of the top of the pipe plug. Insert the 1.5 inch length of 0.156 inch plastic tubing into the plug until the end of the tube is about 0.5 inches above the top of the plug. Make sure the opposite end of the tube is centered in the open end of the pipe plug. Verify that the inside end of the tube does not extend past the end of the plug. Apply a small amount of cyanoacrylate glue at the joint to help hold it in place.
2.) Lightly sand the open end of the plug until it is completely flat. Remove any sanding dust. Clean the piezo bender with alcohol. Using a small amount of either cyanoacrylate or epoxie, glue the piezo bender to the bottom of the plug. Make sure that the side of the piezo with the silver-ceramic disk is on the outside.
3.) If the piezo bender does not have any wires attached, solder them on now. Use a minimum amount of heat as possible.
4.) Take the 0.5 inch length of 0.75 inch PVC pipe and file a shallow notch on one end. This is to provide clearance for the wires. Attach this piece using cyanoacrylate or epoxie to the exposed end of the piezo bender, locating the notch end over the wires.
5.) Verify that the 0.093 O.D. plastic rod slides freely inside the plastic tubing located on the top of the PVC plug. Using cyanoacrylate or epoxie, attach the lead fishing weight to one end of the 0.093 O.D. plastic rod. Once the glue has set, install the weight assembly into the plastic tubing on the top of the plug.
Construction is now complete.
The sensor can be tested by connecting it to a oscilloscope. Set the vertical volts/division to 200 mv/div or 500 mv/div.
Lightly move the lead weight up and down, allowing it to tap against the piezo bender. You should notice an output voltage being generated on the oscilloscope display.
In testing the sensor, I have found it to be very immune to electrical noise. To establish a base line output simply remove the lead weight from the sensor.
VIBRATION SENSOR AMPLIFER
Here is an adjustable gain AC coupled op amp based amplifier that can be used to amplify the output from the vibration sensor, up to about 10X. A small value capacitor, generally 1000pf or less, can be connected across Pin 1 and Pin 2 of the op amp to filter the high frequency component of the output.
Be sure to decouple the power supply input to the op amp by connecting a 0.1uF ceramic capacitor between Pin 4 and Pin 8 as close to the op amp as possible.
VIBRATION SENSOR EXAMPLES
The first two examples are of two cordless drills, a Makita Model 6041 and a much larger Black and Decker Model 2665.
The sensor was set on the handle of each drill and both drills were run at 450 RPM. The sensor amplifier was used and the gain setting was set identical for both.
The next two examples are with the sensor located on a hardwood surface. I lightly tapped the wood surface with my knuckle. In the first example, the sensor was located one inch away. In the second example, the sensor was located forty eight inches away. Note that in the second example where the sensor is located forty eight inches away, there is an apparent delay in the first waveform peak.
Ya Verks Good!