International Journal of Measurement Technologies and Instrumentation Engineering, 1(4), 1-11, October-December 2011 1
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.
Keywords:
Dielectric Constant, Level Sensor, Liquid Interface Level, Non-Contact Type, Semi Cylindrical
Capacitive Array
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
DOI: 10.4018/ijmtie.2011100101
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;
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2 International Journal of Measurement Technologies and Instrumentation Engineering, 1(4), 1-11, October-December 2011
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 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
multi-interface 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 impulse that propagates down
a thin wave guide. In this technology the
impulse velocity is primarily affected by the
permittivity of the medium through which
the pulse propagates. The present method of
semi cylindrical capacitive array type sensing,
capacitance variation has been measured with
the liquids and its interface as dielectric and
the method is very simple, accurate and cost
effective compared to TDR technique. Chiang
and Huang (2006a, 2006b, 2006c) utilized semi
cylindrical capacitive sensing techniques with
two semi cylindrical plates for different process
parameter measurement. In the present work,
semi cylindrical array consisting of 19 elemental capacitances have been designed for liquid
interface level measurement instead of two
large semi cylindrical plates. The experimental
results are found to have good repeatability
and resolution.
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Design, Development and Testing of a Semi Cylindrical Capacitive Array
Type Liquid Interface Level Sensor
Sagarika Pal, Ramtanu Mukherjee and Sharmi Ganguly (2011). International Journal
of Measurement Technologies and Instrumentation Engineering (pp. 1-11).
www.irma-international.org/article/design-development-testing-semicylindrical/68154/