Sensores e transdutores

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Universidade de Brasília - Faculdade do Gama - Área Especial 2 Lote 14 Setor Central Gama-DF Cep: 72405-610. Telefone Geral: (55 61) 3484 9719 | (Fax) 3484 9701

Sensores de Força, Torque e Pressão
Sensores e Transdutores

Daniel Canongia Furtado – 10/44184
Graduando em Engenharia Automotiva.
Universidade de Brasília Faculdade Gama, UnB, Brasil.

JoãoVictor S. Oliveira – 10/45733
Graduando em Engenharia Automotiva.
Universidade de Brasília Faculdade Gama, UnB, Brasil.

Roberto Aliandro Varella – 10/47787
Graduando em Engenharia Automotiva.
Universidade de Brasília Faculdade Gama, UnB, Brasil.

Unidade Acadêmica/Departamento:
Faculdade do Gama, UnB/Engenharia Automotiva

Gama- DF

1. Introdução:
2. Sensores de Força:

2.1. Princípio Básico de Funcionamento:
The working scheme of a force sensor consists of the direct measurement of a parameter in the equilibrium system closely correlated with the acting force. As with all sensors, the ideal condition requires that, in addition to the close correlation of the measureable parameter with the acting force,this parameter be almost independent of all influence quantities, mainly environmental conditions (temperature, atmospheric pressure, humidity, vibrations) and spurious components that may be involved in the measurement.
To give an example illustrating the concept of a parameter correlated with the acting force, we can consider the balance, in which the difference in moments with respect to thefulcrum is determined by the angle of rotation of the balance beam, so that the angle of rotation can be taken as the measuring parameter of the forces causing the moments.
Every balance of this type has a graduation of the rotation angle, calibrated in mass divisions (therefore, for the working principle of the instrument, in moment variations). This is possible because a restoring moment is alwayspresent, but it is not described in detail here because the principal aim of this article is to show how a physical quantity (mass-forcemoment) is transduced into another quantity (angular deflection) so that a sensor of angular deflection can give a measure of the mass difference.
Another example is given by a type of high-accuracy balance, based on electromagnetic compensation of force: thereference force (or a part of it) is generated by means of an electromagnetic device the purpose of which is to bring the beam back to balance. The electric current necessary to bring the beam to the zero position is measured and is taken as the parameter for determining the force.
With balances, the reference force is the weight force, which is considered to be the most accurately determinableforce available, as its value is obtained from measurements of mass, of the acceleration due to gravity, and of air buoyancy. Such measurements require, however, complex instrumentation.
Developping force sensors usually means to come back to the use of elastic forces. Consequently, an elastic element is used which has three specific tasks to carry out, often in separate zones, namely receiving theforce to be measured, transmitting it to a suitable measurement zone, and transforming it linearly, or at least reversibly, into a variation of a physical quantity measureable with a specific sensor, which will be called in the following “secondary sensor”, to keep clear the distinction from the “force sensor”.
Widely used measurable characteristics are the strain or the elastic displacementoccurring in an elastic element following force application; piezoelectricity is less commonly used, as sizable drift is involved; magnetoelasticity, acoustic wave propagation (SAW, surface acoustic waves and BAW, bulk acoustic waves), and birefringence, are still at an advanced experimental stage and their industrial applications are limited.

2.2. Alguns Tipos de Sensores de Força:
As mentioned...