Digitization of vibrating wire type load cell for mine support systems

Abstract

In this study an attempt is made to digitise the output of load cells using electronic circuitry and microcontrollers and its loading profile has been made. The circuit used to excite internal coils of load cell is Wien Bridge Oscillator. The frequency range of each coil was determined for which optimum output is produced from the load cell. The overall frequency range observed during experiment is 60 to 160 kHz. Wien Bridge Oscillator circuit was developed which gives a frequency range of 78 to 143 kHz. Wien Bridge oscillator was interfaced with the instrument and it was loaded from 0 to 25 T using Compression Testing Machine (CTM) and changing the input frequency for a certain load within its range i.e. 78 to 143 kHz. The output rms voltage changed from 1.15 to 0.195 V for red coil, 1.17 to 0.18 V for yellow coil and 1.18 to 0.172 V for green coil. Finally the microcontroller was introduced at the output end for display of digitised load reading from the VW type load cell. The load display in microcontroller display was showing fluctuations. The experimental setup can be further improved by introducing a rectifier along with a suitable filter which would convert the AC output signal to DC. This will minimise the fluctuations of the microcontroller display. It can also be proposed to further extend the work for continuous monitoring using a wireless sensor network.