EML 3301C Strain Gage Mounting Steps: 1/4 Bridge
(Adapted from work by current/previous Instructors of the Class)
Read all instructions before starting.
Equipment:
From left to right, top to bottom: ruler, pencil masking tape, application tape, wire cutters, multimeter, sand paper, beam specimen, wood block, strain gages, wire , wipe, denatured alcohol, wire
nippers, tweezers, snap knife, solder iron, and helping hand.
I Prepare Specimen Surface
1. Use sandpaper to remove paint, surface layers and irregularities.
2. Clean surface with denatured alcohol.
3. Burnish alignment marks on surface – use a standard pencil to lightly burnish the surface
to indicate the desired gage alignment. Then clean away the graphite with an alcohol wipe
to reveal a lightly scribed alignment mark.
II Prepare Gage for Mounting
4. Clean the unmarked side of a metal ruler with denatured alcohol.
5. Carefully remove the gage from its plastic cover using a pair of tweezers.
6. Place gage --‐ with tabs up --‐ on the cleaned ruler surface.
Shiny side up
Dull side up
Correct
Incorrect
7. (Optional, DO NOT DO THIS unless the gage is prewired.) Measure the distance from
the center of the gage to the end with the tabs. Wrap masking tape around the specimen at
this distance from the alignment mark, on the side you wish the leads to land.
8. Place 3--‐5cm piece of ‘special’ adhesive tape over gage.
9. Lift tape at a shallow angle from ruler surface to remove tape & gage without bending the
gage too much.
III Mount Gage to Specimen (for each gage)
10. Align and place gage onto cleaned specimen surface and fully adhere tape at the end of
gage without tabs. Keep end with leads free from surface. (If gage is prewired: Place gage
so edge is aligned with masking tape installed in step 7.)
11. Lift tape at shallow angle until entire gage is free of surface and tape provides a ‘hinge’
for holding tape/gage on specimen.
12. Place small drop of cyanoacrylate glue at base of gage/hinge.
13. Use your finger to run the gage onto the glue and press glue evenly through the area.
(Be careful not to use so much glue that it weeps from the side of the tape and be sure
not to glue your fingers! You can create a double-wide piece of tape if you have trouble
with glue getting all over.) You do not need to adhere the tape to the specimen that has
the leads attached, just make sure the tape over the gage is fully adhered.
14. Press down with fingers over gage for about one minute as glue sets.
15. Set aside specimen.
IV Prepare Strain Gage Wire
(preheat soldering iron)
16. Obtain ~45cm length of 3 conductor strain gage wire (or length as required).
17. Strip approximately 1 cm of insulation from both ends of the wire. Place wire onto
metal ruler surface or wood block and use soldering iron to melt away insulation from both
sides of wire (2-3 seconds each side), and then remove insulation with fingers or tweezers.
18. Use knife to separate three wires at one end of wire. Should have about 3-4 cm of free
wire for each conductor. Cut on the wood block, not the table, then pull apart.
19. Twist the white and black conductors together on the other end.
20. Use soldering iron and solder to “tin” each of the exposed wires on both ends (3, 2
places). Cut the gage end conductors to approximately 1/8 in (3 mm) or less.
TURN OFF SOLDER IRON WHEN NOT IN USE
V Final Assembly and Connections
21. Remove ‘special’ adhesive tape from gage by lifting at a sharp angle and pulling tape
back over itself. Pull from side of gage without tabs. Take care when removing, you can lift
the gage and/or damage the tabs.
21. Place masking tape over active section of gage while leaving solder pads exposed.
(optional)
22. Using soldering iron and solder drop small beads of solder on each strain gage solder
pad. Directly heating the pad before applying solder will help, but do not over-heat the
gage.
23. Put a downward bend into gage end wires. Then create a strain relief “hump” about 1-2
cm from the gage end.
24. Use masking tape to fix wire to specimen with two end conductors touching the strain
gage solder pads, and tape both sides of strain relief hump. Use additional masking tape as
necessary to insure wire is not easily ripped from strain gage.
25. Use soldering iron to quickly melt each wire to a strain gage solder pad (2 places).
26. Use masking tape to fix wire to specimen. Take care not to short any wires to others or
the specimen.
VI Test and Use
27. Use Ohmmeter to test resistance of strain gage install. Check all branches. The
resistance should be approximately the gage resistance (nominally 120 Ohms ) for a single
gage, and as expected for equivalent resistances. If this is not the case, check and re-solder
connections as necessary.
28. Use your strain gage device.