Interdependence of strain, resistance and signal upon load. A steady state model simplifies calculation and understanding. The mathematical model shows minimum and maximum change.
MECHANICS
Load can be: force, weigh, torque for: shear, bending, or torsion. Compressive and tensile load have slightly different physical change.
ELECTRICAL
Molecular displacement produces a piezoresistive effect. This effect produces a “linear” response to the load. Signal response can be correlated to a measurement.
MATH
We can consider this idealized mathematical correlation.
ε = Rg/(2 Rg + Gf) ((From VPG Tech note)
CALCULATIONS
Capacity can be any value, here it has been portrayed as a 10,000 divisions.
Capacity mV Strain Gauge Ω ΔΩ µε
10,000 30.000 348.951 572 641 1.048 427 359 1,497.753 370 7
1 00.003 349.999 895 000 105 µ* 0.105 000 173
*perhaps the limit of computational power at 12 digits
INSTRUMENTATION
Digital multimeter resolution vs signal and division size
8 DMM ==> 0.285 72 µV ==> +100,000 div
7 DMM ==> 2.857 148 µV ==> ≈ 10,000 div
6 DMM ==> 28.571 48 µV ==> 1,000 div
CONCLUSION
Yes you can measure the resistance change on applied load. You need at least a 7 DMM or better to read 10,000 divisions. Otherwise, you can’t read resistance change with 3½ DMM.
