The conventional capacitance-type liquid level sensor consists of an insulated solid metallic rod electrode immersed in the liquid contained in a metallic storage tank, or two such identical electrodes in a nonmetallic storage tank. Such metallic rods may suffer from the self-inductance effect which varies nonlinearly with the level. In this paper, we present a modified capacitance-type level sensor in which effect of self-inductance of the metallic rod has been eliminated. The theoretical equations describing the operation of the sensor are derived. The sensor is designed and tested experimentally and is found to follow the theoretical equations. The experimental results are also presented. A very good linearity of the sensor is observed. © 2013 IEEE.

S C BERA

H MANDAL

S SAHA

A DUTTA

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Study of a Modified Capacitance-Type Level Transducer for Any Type of Liquid

IEEE Transactions on Instrumentation and Measurement

A new Switched Capacitor (SC) Capacitance-to-Digital Converter (CDC) is presented in this paper. Its output exhibits a high-level of insensitivity to interference, by virtue of the conversion mechanism itself. The proposed scheme is a combination of an SC relaxation oscillator and an integrating type analog-to-digital converter (ADC). Its conversion time is independent of the measurand and hence can be set, such that it is an integral multiple of the interference period, unlike in a dual-slope ADC where the de-integration time is a function of the measurand. The final output is proportional to the number of transitions in the oscillator output, which is directly proportional to the value of the sensor capacitance and has negligible sensitivity to the presence of the interference signal. The proposed scheme has been realized and tested as a hardware prototype unit. The non-linearity of the scheme was found to be 0.4%, and the resolution, in terms of the effective number of bits (ENOB), was 11.13, when tested, with sensor capacitance varied from 10 to 32.5 pF. The studies conducted to evaluate the effect of capacitively coupled interference to the sensitive node on the CDC showed that it is negligible for a wide range of magnitude. © 2001-2012 IEEE.

IEEE Sensors Journal

An Extended Study on an Interference-Insensitive Switched Capacitor CDC

A new interference-insensitive Switched Capacitor (SC) Capacitance-to-Digital Converter (CDC) is presented in this paper. The insensitivity is achieved by the conversion mechanism itself. It is a combination of a SC relaxation oscillator and an integrating type analog-to-digital converter whose integration time is made an integer multiple of the time period, Tintr, of the interfering signal. Although in a typical dual-slope converter, the integration time can be set as a suitable multiple of Tintr, the deintegration time is a function of the measurand. Thus, the extent of interference rejection that can be achieved, using such converters, is limited. The SC relaxation oscillator in the proposed CDC is operated for a fixed duration to make a measurement. This duration is set as a multiple of the Tintr. In this scheme, the final output is proportional to the number of transitions in the output of the SC relaxation oscillator which is directly proportional to the value of the sensor capacitance and has negligible sensitivity to the presence of the interference signal. The proposed scheme has been realized and tested using a SPICE tool. The non-linearity of the scheme is found to be less than 0.1% for a sensor capacitance, varied from 15 pF to 25 pF. The study conducted, to evaluate the effect of coupled interference from a distribution power line, showed that the sensitivity of the output to the interference is negligible for a large range. This paper also proposes a method to further increase this range and to improve the resolution of the proposed conversion method. The proposed converter is suitable for capacitive sensors that are used in the consumer applications. © 2017 IEEE.

Proceedings of the International Conference on Sensing Technology, ICST

An interference-insensitive switched-capacitor CDC

In this paper, a new digitizer, which accurately provides the values of the change in the capacitor Cx and resistor Rx of a parallel R-C sensor, is presented. Conventional measurement schemes for parallel R-C sensors require a precision sinusoidal excitation, followed by a signal conditioner, a demodulator and an ADC. This increases the cost and complexity of the scheme. Hence, a dc excitation and an ADC modified to measure Rx and Cx directly is preferred, by the design engineers. But, such a scheme has not been reported. Another challenge is the low-modulation nature of such sensors, i.e., the change in resistance ΔR and capacitance ΔC can be very small compared with the nominal values R0 and C0 of the sensor. This introduces a large offset in the digital output, leading to an inefficient conversion. The proposed digitizer employs a dc excitation and provides accurate digital values of change ΔR in Rx and ΔC in Cx of the sensor. The digitizer employs a simple, but effective automatic calibration, with the help of an improved switched capacitor controlled voltage and obtains an output independent of the nominal values (R0 and C0) of the sensor leading to an efficient conversion compared with the existing schemes. A detailed analysis of the sources of errors affecting the output of the digitizer has been conducted. A prototype of the proposed digitizer has been developed and tested in the laboratory for a wide range of R0 and C0. The results show that the output of the proposed digitizer is independent of the R0 and C0 and can accurately measure the ΔR and ΔC without any cross-sensitivity. © 2017 IEEE.

A Switched-Capacitor Circuit-Based Digitizer for Efficient Interfacing of Parallel R-C Sensors

In this paper, a new and high accuracy, dual-purpose Direct-Digital Converter (DDC) is presented. The proposed Switched-Capacitor (SC) DDC can be used to interface sensors whose electrical equivalent is (a) a capacitor Cx or (b) a resistor Rx or (c) Cx and Rx in parallel. Irrespective of (a)-(c), the DDC gives digital outputs proportional to Cx and Rx of the sensor. Capacitance-to-Digital Converters (CDC) and Resistance-to-Digital Converters (RDC) have been reported earlier, but no accurate dual-purpose DDC has been reported. In comparison with most of the CDCs/RDCs, the DDC presented uses no noticeable additional hardware. In the DDC, the conversion is obtained based on a SC dual-slope technique, which guarantees high immunity to interference. The DDC uses a dc reference voltage for excitation and helps to achieve high accuracy. A prototype of the proposed DDC has been developed. The prototype was tested for Rx from 50 kΩ to 1 MΩ and Cx from 50 pF to 250 pF. The results obtained from the DDC confirmed its usefulness. © 2016 IEEE.

Conference Record - IEEE Instrumentation and Measurement Technology Conference

A direct-digital interface circuit for sensors representable using parallel R-C model

This paper presents a capacitance-to-digital converter (CDC) that employs a novel approach to perform an accurate measurement of capacitance of a leaky capacitive sensor. This CDC employs a sinusoidal source for excitation, which is advantageous for various sensing applications, including ice detection, liquid level measurement, humidity measurement, proximity sensing, and so on. Recently, an impedance-to-digital converter (IDC) based on the dual-slope conversion technique has been reported. It can measure the value of capacitance even when a parallel resistance is present, but requires a large number of sinusoidal excitation cycles to complete a conversion, leading to poor update rate. The CDC proposed in this paper gives much higher (about 125 times) update rate compared with the IDC as it requires only a few excitation cycles for the conversion, but still gives an accurate output due to the use of a specially designed clock, which helps to count the number of charge packets received by the integrator capacitor during the deintegration. Other than the operation of the CDC, this paper also describes an outcome of a thorough analysis conducted to quantify the effect of various circuit parameters on the output of the new CDC. A prototype of the improved CDC has been developed, and its performance parameters, such as accuracy (±0.27%), conversion time (24 ms), effect of parallel resistance, and so on, have been tested, and the results are reported in this paper. © 2015 IEEE.

An improved capacitance-to-digital converter for leaky capacitive sensors

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. © 2006 IEEE.

Journal	Data powered by TypesetIEEE Transactions on Instrumentation and Measurement
Publisher	Data powered by TypesetInstitute of Electrical and Electronics Engineers Inc.
ISSN	0018-9456