A Homemade Wire Resistance Type Vibrometer

Abstract

For the purpose of measuring the vibrations at the handle of the power tillers in field operation, we designed and constructed a small wire resistance type vibrometer (accelerometer) which consist of a pick up, bridge, oscillator, amplifier and magnetic oscillograph.
The pick up has a cantilever pendulum with a mass attached to the free end and strain gages placed so as to measure the bending strain of the cantilever. The bending strain becomes proportional to the acceleration of the tiller when the natural frequency of the cantilever pendulum is higher than the frequency of the tiller. So we determined the natural frequency of the cantilever pendulum is 40.0cps. And to reduce the weight of the pick up, we use an acrylic resin case filled with the silicon oil to give the damping. The size of this pick up is 66×52×38 (mm) and its weight about 250g. (Fig. 1)
Fig. 2 shows the circuit used this vibrometer.
The characteristics curve of this vibrometer is shown in Fig. 3. The performance of this vibrometer shows a desirable result though the acceleration is slower, therefore, we recognized this vibrometer is enough to measure the vibration of the power tillers in the field operation.