Frequency Response of Sensors

For most force measurement applications, the strain gage based transducer can be relied upon to faithfully convert a mechanical input into a proportional electrical analog output signal. However, when the mechanical input is either applied or changes at a rapid rate, the sensor may distort the conversion and the user should be aware of the possible consequences of this distortion. This article will explore the sources of these distortions, the possible problems created, and the normally applied corrections. A force sensor (which also includes torque sensors), consists of a structure which deforms upon the application of force and a system which senses this deformation, producing a proportional output signal. While these articles concentrate on strain gage based sensors, it should be noted that the above definitions are extremely broad and define many other force sensing systems as well. A spring is also a structure which deforms under an applied load, and the structures of transducers may be considered as stiff springs for analysis purposes. When a mass is connected to one end of a spring, and the mass is deflected and then released suddenly, the mass will be observed to oscillate and eventually return to its undisturbed position. The frequency at which the mass will oscillate is determined by the magnitude of the mass and the stiffness (or spring constant) of the spring. The equation which describes this NATURAL FREQUENCY is given below: