SU368518A1 - METHOD FOR AUTOMATIC FIXATION OF THE LIMIT OF TENSION TENSION - Google Patents

Description

one

This invention relates to the testing of tissue properties.

A known method for determining the stress-elongation extensibility, consisting in the Graphic solution of the curves obtained, which is produced manually.

The known method has a low measurement accuracy, since it depends on the skills of the experimenter.

To improve the measurement accuracy of the proposed method, the signal from the force sensor differentiates three times successively in time and records the moment when the third derivative passes through the zero with a comparison device.

FIG. Figure 1 shows a structural block diagram for implementing a method for automatically fixing extensibility; in fig. 2- arising in the circuit electrical sitnaly.

The clamp / through test piece 2 and clamp 3 acts on the coisol beam 4.

The signal from the bridge from the strain resistance 5 through the amplifier 6, the differentiating link 7 falls on the comparison circuit 5. The switching device 9 includes a dynamometer and triggers the trigger 10, which passes the time signals from the generator 11 through the KEY1CH 12 into the counter 13.

The method is carried out as follows.

The clamp of the dynamometer is lowered and stretches the test sample 2, which through the upper clamp 3 bends the cantilever beam 4. In the electric bridge of strain gauges 5 a voltage appears proportional to the tensile force in the form of a graph P-f {e). The output voltage is amplified by amplifier 6 and 1 is supplied to differentiating element 7, at the output of which

0 is a voltage proportional to the third derivative of the input voltage.

In the .moment of the transition of this voltage through zero, which corresponds to the limit of stretchability of the test tissue sample, the output voltage of the comparison circuit abruptly changes and overturns the trigger 10 to its original position. The trigger closes the electronic key} 2 and thereby stops the flow of time stamps from the signal generator to the electronic counter 13. With the appropriate agreement of the circuit constants, the electronic counter automatically records the percentage stretch.

25

Subject invention

The way to automatically fix the limit

tissue extensibility by obtaining a curve

30 deformations of the test specimen using a force sensor, characterized in that, in order to improve the measurement accuracy, the signal from the force sensor is fed to a differentiating device, three times differentiated successively in time and by means of a comparative device, the moment is fixed (Zero third derivative transition).

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