Should we use wheatstone bridges nowadays?

Question

For measuring strain gauges, the Wheatstone bridge is the historical choice.

In a quarter Wheatstone brigde (\$350 \Omega \$ typically (?)), with a high input impedance amplifier, and some bridge power voltage \$V\$, the ratio between the bridge output voltage w.r.t. any resistor is 1/4, which is the same ratio in a voltage divider between the output voltage w.r.t. any resistor, compared with a stable voltage reference of \$V/2\$.

A voltage divider with a voltage reference would have a voltage noise of about 35.16 nV/rtHz (from a voltage reference of 35 nV/rtHz plus two resistors), and the Wheatstone bridge a voltage noise of 4.86 nV/rtHz (from four resistors), which should be enough (?) for most ADC systems (i.e. for 24 bit, 0-5V range: 300nV resolution).

And a voltage reference (\$0.02\%\$ initial error, \$2 \ ppm/C^\circ\$, AD, ADR4525), would be more stable and precise (?) about \$4\ ppm/C^\circ\$, than a precision resistor (\$0.005\%\$ error, \$2 \ ppm/C^\circ \$, Vishay, MR100), about \$8 \ ppm/C^\circ\$.

Hence, why bother using Wheatstone bridges?

Answer 1

What you are missing is that the common purpose of using a Wheatstone bridge is to balance two sensors. Ie. when we use a Wheatstone bridge we usually have two variable resistances or current sources that we want to balance like this;

^{simulate this circuit – Schematic created using CircuitLab}

You are right in concluding that if we only have one sensor to measure and not two that we want to balance then the Wheatstone bridge is not the ideal way to do it.

Answer 2

The problem with using a voltage reference version is that the circuit depends on the difference between two accurate voltage sources, V and Vref. In the Wheatstone bridge, there is just one voltage source, and there is some error cancelation.

Accurate voltage references are noisy and difficult to filter without losing accuracy. They have good long-term stability for voltage, but many have poor short-term stability.

The Wheatstone bridge and its variations are still widely used in the design of measurement equipment. There are many real-world measurement errors that are not just resistor noise, and a bridge circuit often helps.