Strain Gage Activity

In this activity you will learn how to apply strain gages to an object of your choice. It could be a rock, a ceramic mug, or anything else you think would have an interesting strain signal when squeezed, bent, or twisted by hand. We will build on this activity for several classes when learning how to condition, amplify, and record signals from transducers.

Materials

  • Item to instrument (rock, metal plate, etc.)
  • Strain gages (4x)
  • Small gauge hookup wire
  • Superglue
  • Cellophane tape
  • Acetone and cloth
  • Square
  • Marker
  • Soldering iron/solder
  • Tweezers

Procedure

  1. Clean the surface you’ll use with acetone. It the surface is very smooth, roughen it first with some emery cloth to help adhesion.
  2. We will be creating a full bridge circuit using four gages. Layout a square pattern on your test object that lets you place a gage on each side of the square. Mark the center of each side as well. The needs to be really square and relatively accurately measured distances - use good technique!
  3. Place the strain gauge right side up on a clean surface. Get a short piece of cellophane tape and place it over the gage, taking care to not cover the solder pad area of the gages.
  4. Using the superglue and tweezers, place one gage centered on each side of the square you just laid out. Place a small amount of glue beneath each gage. Any glue that gets onto the contacts will make soldering much more difficult later! Stick the gage in place with the tape. In an instrumentation for research setting, using the manufacturers gage bonding chemicals is recommended.
  5. After all of the glue has dried, hookup the strain gages in a full bridge configuration – pay attention the orientation of the gages when hooking them up or you could get no signal.
  6. Hookup your bridge to a bi-polar power supply (two 9V batteries for example) and to a DMM set to read DC Voltage. The output under no-strain should be near zero volts. When you squeeze or deform your test object, you should observe a change in the output voltage. Be sure you are using the lowest range on the meter as this signal will likely be a few millivolts. We need to amplify the signal, but that is a future activity.

Deliverables

Show us your strain gaged object and the output voltage change when you stress your object.