Wheatstone Bridge

DERIVATION INCLUDED BELOW FOR STUDENTS/EE NERDS :)) Here is a direct comparison between a Wheatstone bridge and a potential divider. Same values. Click on the potentiometer, click the spanner and vary the wiper %. A Wheatstone bridge offers superior accuracy over a potential divider for measuring resistance because it uses a null-detection method to detect when a circuit is balanced, making it insensitive to the internal resistance of the measuring device (galvanometer) and less susceptible to noise, supply voltage variations, and lead errors. This leads to highly precise measurements of small resistance changes, which is crucial in applications like strain gauges, unlike a voltage divider that has limitations in accuracy and sensitivity to loads. Due to the balancing network, the parallel resistances can be replaced with the same type of variable resistor (strain gauge, thermistor etc) to temperature-compensate "rebalance" the currents in the circuit so that it remains stable during temperature deviations. If using a potential divider, the temperature would increase the system resistance via ohmic losses (resistance increases when temperature increases) and hence shift the measured output voltage - causing inaccuracies. DERIVATION: Look at left and right sides independently. The voltmeter is infinite resistance (so 2 resistors in series times 2) Vbatt is voltage between A and B. then splits into 2 current paths. Left side, and Right Side. Total resistance through left side: R1+R2. therefore current ILeft = Vbatt/(R1+R2). Hence V(R1) = Ileft*R1. Total resistance through right side = R3+R4. therefore current right side Iright = Vbatt/(R3+R4). Hence VR3 = Iright*R3. So that: Va = Vbatt. Vc = Va-VR1. Vd=Va-VR3. HENCE: Vout = VR1-VR3. 𝑉_𝐵𝑎𝑡𝑡𝑒𝑟𝑦 [𝑅_1/((𝑅_1+𝑅_2)) −𝑅_3/((𝑅_3+𝑅_4))] Small changes in resistance = large changes in our voltmeter (Vout) Doesn’t depend of Rint, or Vbatt – ratio is always consistent so reliable, robust measurement.

published 7 months ago