The Basic principle of the S-sensor is that the natural frequency of a vibrating strip varies according to the tension in the strip.The heart of the S-sensor is an S-shaped metal strip fixed at both ends to a metal ring. When the ring is deformed, the natural frequency of vibration of the strip changes.
This frequency is detected as an A.C voltage in a coil positioned close to the strip. The deformation of the ring is by means of two angle brackets welded to the ring and to the stressed steelwork. The ring, the S-shaped strip and the coil are hermetically sealed inside a stainless steel housing.The forced vibration of the strip is excited by regular short pulses in the coil.
The same coil is used for detecting the frequency of the strip which is excited by regular short pulses in the coil.