Introduction to Strain Gauge Measurements

CLEVELAND - June 20, 2024 - PRLog -- easuring Material Deformation with Electrical Signals

1. Strain Gauge Measurement

• What is Strain?  Strain is a dimensionless quantity that describes the deformation of a material. It represents the relative change in length (or dimension) due to an applied force and is typically expressed in microstrain (μεm/m).
• How Does a Strain Gauge Work?  A strain gauge is a sensor that turns strain into an electrical signal by using a thin wire or foil. It measures strain along different axes.
• Gauge Factor (GF): This is a measure of the gauge's sensitivity to strain. It's the ratio of the fractional change in resistance to the fractional change in length (strain).
• Wheatstone Bridge:  Because it is not practical to measure such small changes in resistance directly, strain gauges are often used in a Wheatstone bridge circuit.

2. Temperature Effects

Fluctuating temperature can alter strain gauge measurements by affecting gauge material resistance. This makes accurate measurements tough. Multiple solutions exist to tackle this issue.

a. To measure strain gauge resistance, use a Wheatstone bridge with matching completion resistors or dummy gauges. This keeps the bridge balanced during temperature changes.

b. Temperature-compensated strain gauges cancel out their own thermal expansion effects, minimizing resistance changes due to temperature alone. This design ensures accurate measurements.

3. Excitation

The strain gauge bridge circuit needs an electrical current or voltage source for excitation and is a ratio-metric device, meaning the output voltage changes with the excitation. The type of excitation depends on specific factors. Factors to consider include:

• To use voltage excitation, you need a stable, low-noise source to avoid errors from cable runs. Use 5 or 10 VDC, but watch out for self-heating in the strain gauge.
  
  
• Current excitation is better when there are long cable runs and it can offer better noise immunity. However, a constant current source can be more complex, and interpreting the results may be more complex.

4. Measurement System

The Wheatstone bridge output voltage is influenced by strain gauge resistance change. It's amplified, digitized for accuracy, and filtered for noise reduction. Cycle filtering removes EMI effects.

Conclusion

Strain gauges are a versatile way to measure mechanical strain. Understanding gauge operation, temperature effects, excitation methods, and system requirements is essential for accurate measurements. Careful selection is crucial.

To find the ideal solution for your application-specific needs, contact a CAS DataLogger Application Specialist at (800) 956-4437 or visit us at https://www.dataloggerinc.com.