Types of Force Sensors
The main types of force sensors are
· Mechanical types.
· Hydraulic types.
· Electrical strain gauge types.
Mechanical types are usually complete measuring systems involving some form of spring such as in a simple spring balance or bathroom scale. It is a basic mechanical principle that the deflection of a spring is directly proportional to the applied force so if the movement is shown on a scale, the scale represents force.
Hydraulic types are often referred to as hydraulic load cells. The cell is a capsule filled with liquid. When the capsule is squeezed, the liquid becomes pressurized. The pressure represents the force and may be indicated with a calibrated pressure gauge. The capsule is often a short cylinder with a piston and the pressure produced is given by p = F/A where F is the force and A the piston area.
Electrical strain gauge type
A typical load cell consists of a metal cylinder with strain gauges fixed to it. When the cylinder is stretched or compressed, the strain gauges convert the force into a change in resistance and hence voltage. Since the elements require a supply voltage, the cell usually has 4 wires, two for the supply and two for the output.