Force and Fluid Pressure

5.6. Force and Fluid Pressure#

Force and fluid pressure sensors detect mechanical loads or pressure exerted by liquids and gases.

5.6.1. Strain-Gauge Load Cells#

Strain-gauge load cells are the most common devices for measuring force or weight. A load cell typically consists of a metal element that deforms slightly when subjected to a load. On this element are bonded strain gauges resistive sensors whose resistance changes with mechanical strain.

When force is applied, the metal flexes, stretching or compressing the strain gauges. This tiny change in resistance is measured using a Wheatstone bridge circuit, which converts the resistance change into a voltage signal proportional to the applied force.

Strain-gauge load cells are highly accurate and can measure forces ranging from a few grams to hundreds of tons. They are used in weighing scales, robotic grippers, industrial presses, and structural monitoring systems. However, they require precise calibration and are sensitive to temperature changes, which can introduce measurement drift.

5.6.2. Hydraulic Pressure Sensors#

Hydraulic pressure sensors measure the pressure of fluids in systems such as hydraulic actuators, braking systems, or industrial process lines. The most common type uses a diaphragm or membrane that deflects under pressure. The deflection is detected by either:

  • Strain gauges bonded to the diaphragm, or

  • Piezoresistive elements integrated into a silicon chip (MEMS).

This deflection changes an electrical property (resistance, capacitance, or piezoresistance), which is converted into a voltage or digital signal proportional to fluid pressure.

Hydraulic pressure sensors are critical in mobile machinery, industrial automation, automotive systems, and aerospace. They allow systems to monitor and regulate pressure for both safety and performance. These sensors are typically robust, sealed against contaminants, and designed to withstand harsh operating conditions.