A low-cost noncontact capacitance-type level transducer for a conducting liquid

• Published in: IEEE transactions on instrumentation and measurement 2006-06, Vol.55 (3), p.778-786
• Main Authors: Bera, S.C., Ray, J.K., Chattopadhyay, S.
• Format: Article
• Language: English
• Subjects: Adjustable; Bridge circuits; Capacitance; Conducting materials; Conduction; Cylindrical capacitor; Electrodes; error capacitance; Glass; glass tube level sensors; high-density polyethylene (HDPE) tube level sensors; Level control; Linearity; liquid level measurement; Liquids; modified De' Sauty bridge; noncontact capacitive level sensor; Plastic insulation; Sensors; Storage tanks; Studies; Transducers; Water storage
• ISSN: 0018-9456; 1557-9662
• DOI: 10.1109/TIM.2006.873785

In this paper, an attempt has been made to design a low-cost noncontact capacitance-type level sensor for a conducting liquid. The sensor is in the form of a uniform circular cylinder made of insulating material like glass, ceramic, plastic, etc. The sensor is connected with the metallic- or nonmetallic-type liquid storage tank, in which the conducting liquid column is taken as one electrode, and a noninductively wound short-circuited outside coil is taken as the other electrode of a variable capacitor. The change in capacitance due to the change of liquid level is measured by a modified linear operational-amplifier-based De' Sauty bridge network with adjustable bridge sensitivity. The bridge output after amplification and rectification may be used to drive a direct current indicator calibrated in level. The studies have been made with high-density polyethylene and glass tube sensors separately in both metallic and nonmetallic storage tanks with tap water as the conducting liquid, and the experimental results of the static characteristics of the level sensors with percentage error from linearity are presented in the paper. These results are found to have good linearity and repeatability within acceptable limits