247
Chapter 18
Design, Development and
Testing of a Semi Cylindrical
Capacitive Array Type Liquid
Interface Level Sensor
Sagarika Pal
National Institute of Technical Teachers’ Training and Research, Kolkata, India
Ramtanu Mukherjee
National Institute of Technical Teachers’ Training and Research, Kolkata, India
Sharmi Ganguly
National Institute of Technical Teachers’ Training and Research, Kolkata, India
ABSTRACT
In this study, a semi cylindrical capacitive array type liquid interface level measuring sensor is described.
The sensor consists of a continuous large semi cylindrical thin metallic plate acting as a common plate
of the capacitor and an array of small semi cylindrical thin metallic plates, separated by very small gap
distance. All plates are mounted along the outer wall of a cylindrical non conducting vertical storage
tank. The detection of liquid interface is based on the measurement of capacitance of the array of plates
which varies with the dielectric constant of the liquid within the tank. The measured capacitance has been
obtained in nano farad range. Since the sensor is non contact type, it can be used for both conducting
and non conducting type of liquid contained within a non conducting tank. Experimental results confirm
the satisfactory performance of the sensor for liquid interface level measurement.
DOI: 10.4018/978-1-4666-4165-5.ch018
Copyright © 2013, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited.
Design, Development and Testing of a Semi Cylindrical Capacitive Array Type
1. INTRODUCTION
The interface level detection of two heterogeneous
mixtures is too much necessary for an immiscible
liquid extraction plant, particularly within primary
separation systems. Generally, heterogeneous
mixtures of multiple phases or components are
a common occurrence within many industrial
processes such as chemical, petrochemical, oil
and gas extraction, pharmaceutical, food, drink
and water treatment plants.
Capacitive type level detecting technique
is very popular for its reliability, low cost, low
power consumption, good linearity, robustness
and easy to use. Various researchers (Brasseur,
2003; Seliskar, Waterbury, & Kearney, 2005;
Reverter, Li, & Meijer, 2007) have introduced
various techniques for sensing liquid level using
capacitive technique. Previously, a lot of effort had
been made on semi cylindrical capacitive sensing
technique. Baxter (1997) designed a capacitive
sensor and classified its various applications.
He established that liquid level in a reservoir or
container can be monitored by measuring the
electrical capacitance between two electrodes
immersed in a liquid. As the conventional contact
type level sensing techniques may suffer from the
corrosion effect due to the contact with corrosive
liquid, Bera, Ray, and Chattopadhyay (2003)
have designed a novel non-contact capacitance
type drum level measurement technique. Latter,
they modified this system for conducting type of
liquid (Bera, Ray, & Chattopadhyay, 2006). Pal
and Barik (2010) designed a non contact type
semi cylindrical capacitive sensor for liquid level
measurement.
Chiang and Huang (2006b) described a Semi
cylindrical capacitive sensor with interface circuit
which has been used for flow rate measurement.
Jaworek and Krupa (2004) implemented a ratio
measurement technique for Gas/liquid using
rf resonance capacitance sensor. Khalifa, Ali,
Alam, Islam, Khalifa and Khan (2008), invented
a non-contact capacitance type level transducer
248
for liquid characterization, such as buoyancy,
pressure at a depth, relative electrical permittivity, electrical conductivity, etc. Dyakowski, Hale,
Jaworski, White, Nowakowski, Meng, and Rwifa
(2005) also developed a dual-modality probe for
characterization of heterogeneous mixtures.
Bukhari and Yang (2006) developed a multiinterface level sensors and a newly developed
system for monitoring and control of oil separators. Jaworski, Dyakowski, and Davies (1999)
designed a portable capacitance probe for detection
of interface levels in multi-phase flows. But the
limitations of these inventions for liquid interface
detection are that the sensors are coming in contact with the measuring liquid. Lu, Hu, He, and
Chen (2009) developed a sensor for monitoring
oil-water interface level and oil level. This sensor
can realize two sensing functions, namely, inductive and capacitive sensing. Thomsen, Hansen,
and Schelde (2000) and Nemarich (2001) applied
Time Domain Reflectometry (TDR) technique
for water level measurement. Chiang and Huang
(2006a, 2006c) utilized semi cylindrical capacitive sensor along with signal conditioning for both
fluidic measuring and flow meter application.
In the present experiment, differing from the
structures of all conventional capacitive sensors,
a novel semi cylindrical capacitive array type
sensor has been investigated for liquid interface
level detection. This sensor consists of a common
continuous large semi cylindrical metal plate and
an array of small semi cylindrical metal plates
which are separated by a gap distance. All these
semi cylindrical metal plates are mounted around
a polyvinyl chloride (PVC) type liquid container.
Heterogeneous mixtures of two or more relatively
immiscible liquids such as water, vegetable oil,
crude oil, etc have been used as dielectric medium
of the capacitor. The variation in capacitance due
to variation of dielectric property of liquids and
their interfaces within the container have been
converted into voltage variation using ICL 7660.
In Time Domain Reflectometry (TDR) based
level measurement device, the device generates an
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