Siuli Das, M. Sivaramakrishna, Bhaswati Goswami Department of Instrumentation & Electronics Engineering, Jadavpur University, Kolkata-700098, India e-mail: bg@iee.jusl.ac.in Abstract—In this work, a low cost automatic sensing system is proposed to detect ‘synthetic milk’, which has been reconstructed after adulterating the milk with ‘liquid-whey’. The constant-phase angle (CPA) based sensor detects the synthetic milk and a micro-controller based circuit drives a stepper motor to close the valve installed at the outlet of the milk supply line to prevent mixing. The sensor is stick type, rigid and hence it is easy to mount. The electrodes of the sensor are coated with polymethyl methacrylate (PMMA) film, which makes it bio-compatible and suitable for the application. Keywords-constant-phase-angle; milk adulteration; liquid- whey; automatic sensing system; phase detector circuit. I. INTRODUCTION Milk adulteration is a century old problem [1, 2]. The oldest and simplest method of adulterating milk is by dilution with water to increase volume [3] and then to compensate specific gravity, different types of salt or sugar [4] are used. Sometimes the color change due to adulterants are corrected by the addition of a small amount of coloring matter [5] which may cause serious health problem [6]. A similar type of milk adulteration problem is reported in this work, where the volume is increased by addition of ‘liquid-whey’ (liquid by-product of cottage cheese) to increase the volume. The liquid- whey addition makes the natural milk a little acidic and lowers its pH value which is compensated by adding NaOH. It is a well known fact that NaOH may cause health hazards to the patients suffering from heart disease and hypertension. It also deprives the body from utilizing lysine which is required for growing babies. Moreover, some greedy cheese maker uses cheap muriatic acid (a chemical composition of hydrochloric acid) to make cheese from milk, which causes more health problems. The profit of using liquid-whey, as milk adulterants is double folded. First of all it is in abundance to the cheese maker, so cheap and easily available to the milk supplier. Secondly whey retains many natural properties of milk, so preparation of synthetic milk from liquid-whey is simple and can camouflage the natural milk easily. As a result adulteration of natural milk with liquid-whey became a wide spread fraudulent activity, where huge amount of cottage cheese is used everyday to make different varieties of sweets. Hence, this becomes a serious concern to the dairy firms who buy milk from thousands of different milk suppliers and need a simple, robust and bio-compatible automated sensing system to their milk incoming line for quality control. In this work a stick type probe, whose electrodes are coated with porous film of PMMA [7], is used as a sensor for developing the sensing system. The advantage is that it can be easily dipped inside the medium and at the same time Karabi Biswas Department of Electrical Engineering, I.I.T Kharagpur, Kharagpur-721302, India e-mail: karabi@ee.iitkgp.ernet.in biocompatible due to the PMMA coating on the electrodes. More over, the detection is based on the principle of change of phase angle with the ionic property of the medium. The phase angle remains constant over a band of frequency, so measurement can be frequency independent, which is an important requirement for automated sensing system. The other advantages are - it is simple, easy to fabricate, cheap and can be replaced easily. The paper is organized as follows: Section II describes the principle of operation of constant phase angle based sensor to detect milk adulteration. Section III provides fabrication and characterization of the CPA-based sensor. Section IV details the integrated sensing system with the detector circuit. Section V discusses the experimental observations and results. Section VI presents a conclusion. II. PRINCIPLES OF CONSTANT PHSAE ANGLE –BASED MEASUREMENT In earlier works, the construction and working principle of the constant phase angle based sensor has been reported [8]. The impedance of the sensor (Fig. 2) dipped inside the medium can be represented as α - = Qs s Z ) ( (1) where Z is the impedance, Q is a constant, α is a real number and s is the Laplace operator. So, magnitude |Z| = Qω -α and phase angle θ = -απ/2, where θ is expressed in radians and independent of frequency. When α = 1, Z = Qs -1 and Z represents a capacitor. Similarly for α = 0 and -1, Z represents a resistance and inductance respectively. For the above sensing system, it has been observed experimentally that the constant phase angle θ is a function of three parameters of the measurement arrangement and expressed as ) , , ( σ θ t A f = (2) where ‘σ’ is the property (e.g., ionic, dielectric) of the medium under test, ‘A’ is the area of contact of the probe with the test medium and ‘t’ is the thickness of PMMA-film coated on the electrodes [7, 9]. In this work, the change in constant phase angle θ for pure milk, adulterated milk and synthetic milk (reconstructed after adding liquid-whey) has been observed to identify synthetic milk. For a particular measurement, area of contact of the probe with liquid medium and the thickness of film coated on the electrodes are kept constant. However the effect of these two parameters needs to be studied for standardizing the sensor and the optimum area and thickness is to be chosen for measurement [10]. It has also been observed that this Design of a Low-Cost ‘Constant Phase Angle’ Based Sensing System to Detect Natural Milk and ‘Synthetic-Milk’ Reconstructed from ‘Liquid-Whey’ 307 SENSORCOMM 2011 : The Fifth International Conference on Sensor Technologies and Applications Copyright (c) IARIA, 2011. ISBN: 978-1-61208-144-1