Bridge Difference Three-Row Scan - Electronic Circuits II & III: Decision Networks and Interfaces Step by Step

A bridge-difference scan compares two divider node voltages, then treats the voltmeter reading as the magnitude of their difference. The rows are exact only for the declared resistor values, ideal source, unloaded bridge meter, steady DC, and no noise; real bridges add resistor tolerance, input bias, meter loading, source drift, contact resistance, temperature effects, and voltage measurement uncertainty.

A bridge voltmeter reads the exact difference between two divider node voltages. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

A bridge starts with two divider outputs

The left branch stays fixed. The right branch changes, so the bridge voltmeter reads the exact node-voltage difference.

V_{\text{bridge}}=\left|V_{\text{left}}-V_{\text{right}}\right|

The difference grows as the right node drops

Read each row as left output, right output, then absolute difference. The balanced row is allowed to be exactly zero.

\begin{array}{c|c|c}V_{\text{left}}&V_{\text{right}}&V_{\text{bridge}}\\8\ \text{V}&8\ \text{V}&0\ \text{V}\\8\ \text{V}&\tfrac{36}{5}\ \text{V}&\tfrac{4}{5}\ \text{V}\\8\ \text{V}&6\ \text{V}&2\ \text{V}\\\end{array}

The final row exceeds one volt

For the rendered row, the bridge difference is 2 volts, above a one-volt strict threshold.

2\ \text{V}>1\ \text{V}