Effective process control is critical for the safe and reliable manufacture of goods. An important requirement in process control is the accurate measurement of pressure. The classic strain gauge remains a popular choice for designers due to the low cost and high reliability of the material.

The working principle of a strain gauge is straightforward. When a force is applied to a strain gauge, the physical structure is altered and a proportional change in resistance occurs. A Wheatstone bridge can be used to measure this change in resistance with high precision.

The gauge factor of a strain gauge is a measure of the sensitivity of the sensor and expresses the relative resistance change under a given force. The change in resistance can be incredibly small, and a change of only 0.1% of the nominal resistance value of the strain gauge is not uncommon. This change results in a very small signal that needs significant gain to be accurately digitized. OPAx486 devices offer exceptional precision and wide gain bandwidth product to accommodate for very high gain configurations.

The OPAx486 can be configured as a three op amp instrumentation amplifier to provide high gain, high common-mode rejection ratio, and differential to single ended conversion.

Use the following parameters for this design example:

• Single supply: 12V
• Linear output voltage range target: 0V to 5V
• Bridge excitation: 5V
• Strain gauge resistance variation: ±6%
• Nominal strain gauge resistance: 350

The following design details and equations can be used to reconfigure this design for different output voltage ranges and current loads.