Wheatstone Bridge Calculator
Calculate bridge balance resistor and output voltage for Wheatstone bridge circuits.
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How does a Wheatstone Bridge work?
A Wheatstone bridge is four resistors arranged in a diamond (or square) with a voltage source across one diagonal and a voltage measurement across the other. When the ratio R1/R2 equals R3/R4, the bridge is balanced and the output voltage is exactly zero. Even tiny imbalances produce a measurable voltage, which is what makes this circuit so useful for precision measurement.
The sensitivity of a Wheatstone bridge comes from comparing two voltage dividers. The left arm (R1, R3) forms one divider, the right arm (R2, R4) forms another. When both dividers output the same voltage, the difference is zero. Replacing one resistor with a sensor (strain gauge, RTD, thermistor) converts physical changes into tiny resistance changes, which the bridge amplifies into a measurable voltage.
In practice, the bridge output is small — millivolts or less for strain gauges. An instrumentation amplifier (like the INA125) is almost always used to amplify the signal before digitization. For the best sensitivity, the fixed resistors should be close in value to the sensor's nominal resistance.
Balance Condition
R1/R2 = R3/R4Vout
Vout = Vin × (R4/(R3+R4) − R2/(R1+R2))Key Points
- Balance: R1/R2 = R3/R4 → Vout = 0
- Very sensitive to small resistance changes (used in sensors)
- Output polarity indicates which arm has excess resistance
- Best sensitivity when all four resistors are similar in value
Applications
- Strain gauge and load cell measurement
- Temperature sensing with RTD (PT100, PT1000)
- Pressure sensor signal conditioning
- Precision resistance measurement