Strain measurements

A principal use of the four-wire full bridge is the measurement of strain gages in structural stress analysis. StrainCalc() calculates microstrain (µɛ) from the formula for the specific bridge configuration used. All strain gages supported by StrainCalc() use the full-bridge schematic. 'Quarter-bridge', 'half-bridge' and 'full-bridge' refer to the number of active elements in the bridge schematic. In other words, a quarter-bridge strain gage has one active element, a half-bridge has two, and a full-bridge has four.

StrainCalc() requires a bridge-configuration code. The following table shows the equation used by each configuration code. Each code can be preceded by a dash (-). Use a code without the dash when the bridge is configured so the output decreases with increasing strain. Use a dashed code when the bridge is configured so the output increases with increasing strain. A dashed code sets the polarity of V_r to negative.

StrainCalc() configuration codes
BrConfig code	Configuration
1	Quarter-bridge strain gage:
2	Half-bridge strain gage. One gage parallel to strain, the other at 90° to strain:
3	Half-bridge strain gage. One gage parallel to +ɛ, the other parallel to -ɛ:
4	Full-bridge strain gage. Two gages parallel to +ɛ, the other two parallel to -ɛ:
5	Full-bridge strain gage. Half the bridge has two gages parallel to +ɛ and -ɛ, and the other half to +nɛ and -nɛ
6	Full-bridge strain gage. Half the bridge has two gages parallel to +ɛ and -nɛ , and the other half to -nɛ and +ɛ:
Where: n : Poisson's Ratio (0 if not applicable). GF: Gage Factor. V_r: 0.001 (Source-Zero) if `BRConfig` code is positive (+). V_r: –0.001 (Source-Zero) if `BRConfig` code is negative (–). and where: "source": the result of the full-bridge measurement (X = 1000 • V1 / Vx) when multiplier = 1 and offset = 0. "zero": gage offset to establish an arbitrary zero.