This article examines the construction of sensor for measuring the sagging. It is the frame, which consists of four rods. One of the rods (stock) of is mobile and is found in the contact with the model. Another rod (beam) of is the elastic element, whose deformations are measured with the aid of the strain gage resistors. Remaining two rods lock the kinematics chain, transferring the measured displacement from the stock to the beam. The special feature of sensor is protection from damage, if model will be destroyed or will occur the uncontrollable motion of stock. For this connection of stock and beam it is executed by mobile. As a result this during the uncontrollable motion of stock, which exceeds the range of the measurement of sensor, connection is uncoupled without the destruction. The connection between the displacements of stock and free end of the beam is examined. The relationships between the sizes of rods, which ensure the correct work of sensor, are obtained on this base