Design and Analysis of an Electro-Optic Type Pressure Transmitter Using Bellows as Primary Sensor

Abstract

In process industries, an optical transmitting system has a great impact especially for long distance transmission through inflammable and hazardous areas. A combination of bellows and Mach-Zehnder Interferometer (MZI)-based pressure transmitting system has been proposed in this paper. This novel approach is capable to transmit pressure reading to a remote location using an electro-optic modulation in the MZI. The proposed system is the hybrid type and consists of two sections. First part is the electrical type which is responsible for transmission of measured information in an electrical domain (primary) and a second section is designed for transmission of measured information in an optical domain (secondary). Primary part is the combination of bellows, a Hall probe sensor, and a signal conditioning circuit, and the second part consists of the MZI with three electrodes. The pressure is directly applied to the bellows. The magnet is placed at the top of the Bellows and the variation of the magnet positions is sensed by the Hall probe sensor. The response of the Hall probe sensor, in terms of millivolt range, is not capable to perform the electro-optic modulation in the MZI, so it is further amplified by an instrumentation amplifier and a calibrating circuit. The output from the signal conditioning circuit is fed to the MZI so that the intensity of light which is propagating in the MZI is modulated due to the electro-optic effect. Transmission of the optical signal is very much beneficial for the inflammable industry to prevent the sparking like situation. The operation of the system has been explained with the help of derived theoretical equations. The experiment has been done and the performance of the system along with the experimental results is reported in this paper. The proposed system is linear and provides good repeatability with the applied pressure.