Instrumentos de medição
Autor | Tuffi Messias Saliba |
Ocupação do Autor | Engenheiro Mecânico |
Páginas | 57-62 |
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A medição da vibração é feita por meio de instrumento ligado a um transdutor ou acelerômetro. O acelerômetro é o elemento que capta o movimento vibratório transformando-o em grandeza mensurável, ou seja, fornece um sinal de saída elétrico, mecânico ou óptico proporcional ao deslocamento (aceleração). Os tipos mais comuns de acelerômetro são: piezoelétricos com eletrônica integrada (ICP); piezorresistivo; capacitância variável; servo-acelerômetro4. O transdutor (acelerômetro) piezoelétrico é usado universalmente para a medição de aceleração absoluta de vibrações e tem características gerais superiores às de qualquer outro tipo de transdutor de vibrações, com as seguintes vantagens:
— grande faixa dinâmica 1:30 106;
— resposta plana em larga banda de frequência;
— linear, robusto e estável ao longo do tempo;
— compacto, pequeno e leve;
— não necessita de uma fonte de energia externa, já que o material piezoelétrico é autogerador;
— saída proporcional à aceleração, podendo ser integrada para fornecer sinal proporcional à velocidade ou ao deslocamento de vibrações5.
Na avaliação ocupacional de vibração, é utilizado o acelerômetro triaxial, que permite captar as acelerações nos eixos x, y e z. Esse acelerômetro é montado em adaptadores, de acordo com o tipo de vibração a ser avaliada: corpo inteiro ou mão e braço.
O medidor de vibração é o instrumento responsável pelo processamento dos dados captados pelo acelerômetro. Na avaliação ocupacional
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normalmente se utiliza instrumento portátil, que atenda as especificações da norma ISO 8041:2005, devendo esse equipamento ser do tipo 1 ou 2.
Esse medidor é ligado ao acelerômetro por meio de cabo, devendo possuir recurso de ponderação da aceleração nas frequências em função da resposta do corpo humano, conforme explicado nas partes III e IV. Desse modo, o instrumento fornecerá a aceleração r.m.s ponderada nas frequências — aw, separadamente em cada eixo, além da aceleração da soma vetorial dos três eixos — xyz. Outro dado processado e fornecido pelos instrumentos de medição é a dose de vibração prevista nos limites de normas internacionais, NHO 09 e anexo 8 da NR-15.
Há medidores no mercado que possuem filtros de frequência em terça de oitava, permitindo a avaliação detalhada dos valores das acelerações nas respectivas frequências.
Cabe destacar também que os medidores de vibração modernos possuem programas específicos...
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