A Balanced Resistance Bridge: Ratios Can Match Without Equal Individual Resistances

Name the two divider nodes

NI describes a Wheatstone bridge as two voltage dividers whose midpoint difference is the output. Balance occurs when the appropriate resistance ratios match. Primary reference: bridge configuration.

Preserve the chosen top and bottom arm labels. Reversing one ratio silently changes the comparison. A zero midpoint difference under the model says something about relative divider proportions, rather than identifying the absolute value of every arm.

An invented balanced pair

Assume one ideal divider has top resistance 100 Ω and bottom resistance 200 Ω. A second has top 300 Ω and bottom 600 Ω. With the same fictional 6 V excitation, both midpoint voltages are 6×2/3 = 4 V. Their difference is zero although none of the corresponding arms has equal resistance.

If the second bottom arm becomes 630 Ω while its top remains 300 Ω, that midpoint becomes approximately 4.0645 V. The output magnitude is approximately 0.0645 V. Output sign depends on which midpoint the stated measurement subtracts.

Keep balance separate from performance

Create fields for arm names, actual values, excitation, midpoint voltages and subtraction direction. List any source or input-loading assumptions beside the calculation.

An observed zero could also involve instrument resolution, offsets or an actual circuit problem; the ideal balance calculation does not diagnose them. It gives a reviewer a coherent ratio question before interpreting bridge evidence or requesting a sensor-specific assessment.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• Primary reference: bridge configuration