Design of Portable Air Purge Level Transmitter with Built-in Calibration Feature

Abstract

In almost all the process industries level is the prominent process parameter which is being monitored and controlled. For level measurement a wide variety of level sensors are available. For level measurement of chemically corrosive liquids or liquids containing suspended solids, specific sensors are used. In such applications, the direct contact of sensor with the fluid is avoided. Air purge or bubbler pipe is the most suitable level measurement method in such cases. In this method, compressed air is forced through the bubbler pipe which is placed in the level measurement tank. This compressed air/gas emerges from the other end of the tube in the form of bubbles. The pressure in the pipe is equal to the head pressure created by the height of liquid column in the tank. The conventional air purge level measurement method has limitations like lack of portability and non-electrical output. This also consumes more power, lacks in scheduled measurement and requires recalibration for the changes in the range. To overcome these limitations a novel portable programmable air purge level transmitter is designed in this paper. The designed system consists of an on board compressor to improve the portability. The electrical output is obtained using MEMS pressure sensor which is mounted on the top of the bubbler pipe. The electrical signal given by the MEMS pressure sensor is converted to standard output using Microcontroller and Signal Conditioning Unit. The system is made programmable using keyboard and display interface to microcontroller. Due to this recalibration and scheduled measurement is possible and this results in reduced power consumption.