A strain gauge is used to measure an alteration due to external force through the use of electrical resistance in a Wheatstone-bridge configuration. The Wheatstone bridge is used to precisely measure very low values of resistances down in the mΩ range. An excitation voltage is applied to the bridge, and the output voltage across the middle of the bridge is measured. The total change in output voltage is relatively small, typically in the mV range. Therefore, an op amp is used to amplify the signal. The OPA2182 is designed to construct high-precision amplification.

Use the following parameters for this design example:

• Use the op-amp linear output operating range, which is usually specified under the AOL test conditions. The common-mode voltage is equal to the input signal.
• Use an op amp that does not add significant noise to the system or else the small output voltage from the Wheatstone bridge will be lost.
• The input signal must be gained; therefore, use an op amp with low input offset voltage (V_OS)
• The input signal must be gained; therefore, use an op amp with enough open-loop gain to provide the required amplification