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A low cost instrumentation system to analyze different types

of milk adulteration

Siuli Das a,n, Mulinti Sivaramakrishna b, Karabi Biswas c, Bhaswati Goswami d

a Department of Instrumentation Engineering, RAIT, Nerul, Navi Mumbai, Indiab Department of ECE, Polytechnic College, Pillaripattu, Andhra Pradesh, Indiac Department of Electrical Engineering, IIT Kharagpur, Indiad Department of Instrumentation and Electronics Engineering, Jadavpur University, Kolkata, India

a r t i c l e i n f o

Article history:

Received 25 January 2014

Received in revised form

17 September 2014

Accepted 30 November 2014Available online 20 December 2014

This paper was recommended for publica-

tion by Dr. Didier Theilliol

Keywords:

Milk adulteration

Instrumentation system

Synthetic milk

Liquid-whey

PMMA-lm

a b s t r a c t

In this paper, the design of a complete instrumentation system to detect different types of milk

adulteration has been reported. A simple to use indicator type readout device is reported which can be

used by milk community people. A low cost microcontroller based automatic sensing system is also

reported to detect ‘synthetic milk’, which has been reconstructed after adulterating the milk with ‘liquid-

whey’.

& 2014 ISA. Published by Elsevier Ltd. All rights reserved.

1. Introduction

Food quality monitoring is a serious issue and addressed by

different researchers [1–4]. Among these milk is one of the most

vulnerable food which is adulterated very easily. Adulteration

achieved with low value ingredients like water and whey into natural

milk is known as ‘economic adulteration’. It is a very common

practice by the milk community people to add water or ‘liquid-

whey’ [5,6] to increase the volume, this in turn reduces the milk

quality. Additionally whey retains many natural properties of milk, so

preparation of synthetic milk from liquid-whey is simple and can

camouage the natural milk easily. Hence, this becomes a serious

concern to the dairy rms who buy milk from thousands of different

milk suppliers and need a simple, robust and bio-compatible auto-

mated sensing system for quality control.There are several methods [7–9] available in the literature to

detect different types of adulterants in milk. Methods to determine

additional water present in the milk are explained in [10–12]. The

volume of water mixed in milk is detected by electrical conduc-

tivity (EC) method. In this method [11], quantity of ions decreases

so the resistance is higher and the EC is changed. To detect fat and

water content present in milk, electrical admittance spectroscopy

[7,10] method has been used. Another method used to determinethe additional water content in milk is freezing point osmometry

[12]. In [13–16], different methods are proposed for determination

of whey as an adulterant. Low priced whey [14,16] and rennet

whey solid [13,15] are often mixed with liquid milk and milk

powder. To detect the fraudulent addition of rennet (enzymes for

curdling of milk) whey solid in ultra high temperature (UHT) milk

[13], capillary electrophoresis is used. Sometimes urea [17–21] is

added to milk to increase the shelf life. In [17] a potentiometric

biosensor method is reported to detect urea adulteration in milk.

Measure of change of pH [19,21] is another method of urea

detection in milk. Enzyme based piezoelectric sensor [18] is also

used to detect urea in milk by measuring the pressure of the gas

evolved in the milk sample. Addition of urea in milk is also

detected by near infrared spectroscopy method [20]. But most of these methods are expensive and time consuming and need

skilled manpower. It is, therefore, necessary to develop a new

and easy to use instrumentation system for the rapid and reliable

detection of this kind of fraud.

So the aim of this paper is to develop a low cost, user friendly

instrumentation system for measurement of these kinds of adul-

teration and can be easily installed in dairy industry.

In this paper a constant phase element (CPE) sensor is used to

detect the adulteration in milk. The sensor is a stick type two

terminal device and when dipped inside a medium the phase

Contents lists available at ScienceDirect

journal homepage: www.elsevier.com/locate/isatrans

ISA Transactions

http://dx.doi.org/10.1016/j.isatra.2014.11.021

0019-0578/& 2014 ISA. Published by Elsevier Ltd. All rights reserved.

n Corresponding author. Tel.: þ 91 022 27709574; fax: þ 91 022 27709573.

E-mail address: [email protected] (S. Das).

ISA Transactions 56 (2015) 268–275

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angle between the two terminals remains constant (hence, the

name constant phase element (CPE)). But if the property of the

measuring medium is changed the phase angle also changes [22].

This means that the phase angle of the sensor will be different for

plain milk and the milk with some impurity [9]. The change of

phase angle is then detected with the help of a phase detector

circuit [23]. Indicator LEDs are used to display the type of

adulteration. An automatic detection system for synthetic milk is

also developed and studied. The advantages of using such sensorare that the electrodes are coated with the poly-methylmetaha-

crylate(PMMA), which makes it bio-compatible and the milk

property does not get changed when the sensor is dipped in.

Moreover, it is a stick type rigid probe and can be easily dipped

inside the measuring medium, an essential requirement for auto-

matic detection.

The paper is organized as follows: Section 2 describes the

building blocks of the instrumentation system which includes

sensor design, signal processing block with the detector circuit and

display unit. Section 3 presents the automatic detection system

and conclusion is given in Section 4.

2. Design of the instrumentation system

Fig. 1 shows the block diagram of the developed instrumenta-

tion system to detect the adulteration of pure milk with different

types of adulterants. It includes sensor, signal conditioning circuit

and display circuit.

2.1. Development of the sensor

The sensor, shown in Fig. 1 [9], is a copper cladded printed

circuit board, cut into a suitable dimensions and coated with a thin

lm of Polymethyl-methacrylate (PMMA) by using spin coating

technique [24]. For determination of different adulteration of milk

the sensor has to be dipped inside the test medium as it has been

observed that its impedance changes with the interaction of the

sensor with the test medium [9]. In particular, the phase angle

changes when milk sample is adulterated with different materials

[9,24,25]. Hence in this measurement “change of phase angle” is

considered as the sensor output. Moreover, this sensor has the

property that for a particular measurement the phase angle remains

constant over almost one decade of frequency which is an essential

requirement for sensing system where change of signal frequency

for interference or other effect will not hamper the measurement.

The sensor with coating thickness 13 μm, named as FOE13, isselected for designing the instrumentation system for detection of

tap water and urea as an adulterant in pure milk in the frequency

range 5–12 kHz. It will be worth to mention that the phase angle

of the FOE13 sensor remains constant in this frequency range at a

particular test medium. Other sensors with different lm coatingcan be fabricated which gives constant phase angle in different

frequency zones [9].

FOE13 sensor is considered for development of the instrumen-

tation system because the circuit elements used are suitable for

the frequency range 5–12 kHz. So, here for development of the

instrumentation system, measurements are performed at 7 kHz

which is almost at the middle of the bandwidth of the sensor.

Hence the choice of frequency depends on the bandwidth of the

circuit element and the range of frequency where phase angle

remains constant. This value is chosen because due to environ-

mental or other effect, if the frequency of the detector circuit

shifts, the output of the sensor will remain the same.

2.1.1. CalibrationBefore calibrating the instrumentation system, each block has

to be characterized. For that purpose, the resolution, sensitivity,

repeatability and reproducibility of the sensor block are checked

with 7 kHz signal frequency.

The phase angle of FOE13 sensor is measured with LCR meter

(Agilent Precision Impedance Analyser 4294A), after dipping 2 cm

of the sensor separately in different test mediums. Four different

buffer pH solutions (pH 2.0, pH 4.0, pH 7.0 and pH 9.2), pure milk,

milk adulterated with different % of tap water and milk adulter-

ated with different concentration of urea are the testing mediums.

For measurement purpose, the frequency of the sinusoidal signal is

varied from 100 Hz to 4 MHz with a peak to peak voltage of 1 V.

The readings are repeated 5 times to check the repeatability and

the average values are considered for analysis. It is observed that

the deviation from its average values are negligibly small.

FOE13 sensor is characterized by standard buffer solutions of

pH 2.0, pH 4.0, pH 7.0 and pH 9.2. The graph of phase angle with

respect to pH value is shown in Fig. 2 and the average values are

tabulated in Table 1. A line t, y ¼mx þ c yields ‘m’, ‘c ’ and t factor

Fig. 1. Block diagram of the instrumentation system.

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R2 values which are shown as

y ¼ 3:760 x 2:594 with R2 ¼ 0:995 ð1Þ

From Eq. (1) it is observed that R2 value is close to 1 which

indicates that the relation of phase angle and pH values of FOE13

sensor (Fig. 2) is almost linear, slope is negative that is the phase

angle value decreases with an increase of the pH value.

2.1.2. Sensing adulterated milk

FOE13 sensor is tested by dipping into milk and milk adulter-

ated with different percentages of tap water and urea for three

consecutive days. The outputs are shown in Figs. 3 and 4 and the

average values of the sensor are tabulated in Tables 2 and 4

respectively.

2.1.3. Tap water

From Fig. 3, it is evident that sensor FOE13 has the capability of

identifying the presence of tap water when at least 5 ml of tap wateradded in 50 ml of milk. There is approximately 21 change of phase

angle with pure milk and milk adulterated with 10% tap water.

It has been found from Table 2 that FOE13 sensor is showing

reproducibility in consecutive three days. It is also observed from

Table 3 that the t factors in all the 3 days are approximately 0.8. The

slopes and intercept are almost the same (for all the 3 days) and the

values are negative ( 0.06 and 25.5), that is with an increase of %

of tap water, phase angle decreases. From Table 2, the threshold value

of phase with 10% tap water adulteration is almost 1.61.

2.1.4. Urea

To prepare synthetic milk and to increase the SNF (Solid Not Fat)

value, urea added to natural milk is 0.2–

0.7 mg/ml [26,27]. In our

2 4 6 8 10−40

−35

−30

−25

−20

−15

−10

pH value

P h a s e a n g l e ( d e g r e e )

y = −3.760x − 2.594

R 2 = 0.995

Fig. 2. Phase angle behavior of FOE13 sensor in different ionizing medium.

Table 1

Phase angle in different buffer solutions of FOE13 sensor at 7 kHz.

pH Avg θ (deg)

2.0 10.86

4.0 16.52

7.0 29.13

9.2 37.36

0 10 20 30 40−29

−28

−27

−26

−25

−24

Different % of tap water adulteration

P h a s e a n g l e ( d e g

r e e )

1st day

2nd day

3rd day

y(1st day) = −0.065x−25.50

y(2nd day) = −0.060x−25.76

y(3rd day) = −0.055x−26.51

Fig. 3. Phase angle versus % of tap water adulteration.

0 0.2 0.4 0.6 0.8 1 1.2−27

−26

−25

−24

−23

−22

−21

−20

−19

−18

−17

Different concentration of urea adulteration (mg)

P h a s e

a n g l e ( d e g r e e )

1st day

2nd day

3rd day

y(1st day) = 5.974x − 24.33

y(2nd day) = 5.858x − 24.65

y(3rd day) = 5.769x − 25.41

Fig. 4. Phase angle versus % of urea adulteration.

Table 2

Phase angle in milk and milk adulterated with tap water of FOE13 sensor at 7 kHz.

Day Test medium pH value Avg θ

(deg)

1 Pure milk 6.82 24.96

Added 10% tap water 6.90 26.73



Tap water 7.34 28.91

2 Pure milk 6.85 25.30




Tap water 7.86 29.01

3 Pure milk 6.83 26.11



Added 40% tap water 7.09 28.53Tap water 7.46 28.95

Table 3

Slope, zero error and residuals with tap water adulteration.

Day Slope (m) Zero error (c ) R2

1st 0.065 25.50 0.831

2nd 0.060 25.76 0.854

3rd 0.055 26.51 0.867

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study, milk is adulterated with different concentration of urea and

change of phase angle is tabulated in Table 4. From Table 4, it is found

that the sensor is showing reproducibility and there is approximately

51 change of phase angle with pure milk and milk adulterated with

0.6 mg urea per ml milk. Hence the threshold value of phase with

0.6 mg urea per ml milk is almost 51. In this case the t factor is

approximately 0.9 which is close to 1 that means the relationship is

almost linear and shown in Table 5. The slopes are also the same for

3 consecutive days and are positive, so phase angle increases with an

increase of adulteration.

It is worth to mention that addition of urea has a reverse

response compared to the addition of water. The reason may be

that milk is a biological substance and it decomposes urea into

different ions [17] and makes the milk more acidic, as a result the

output phase angle decreases whereas, addition of water makes

the milk more alkaline and phase angle increases.

2.2. Phase detector circuit

The phase angle change with different adulterations of milk can be

tracked if the output signal from the sensor is converted into voltageby some signal conditioning circuit, so the second block of the

instrumentation system is a phase detector circuit [23]. The principle

of operation of the circuit is that output square pulse will be obtained

whose width depends upon the zero crossing of the voltage signal and

phase angle can be measured with respect to the zero crossing of a

reference voltage signal. Fig. 5 shows the phase detector circuit [23]

used for the sensing system. A low pass lter is added to this circuit to

get a dc voltage equivalent to the difference in the width of the pulse.

The milk samples are now tested by connecting the output of

the sensor with a phase detector circuit and it has been observed

that voltage also remains constant, in the frequency range of

5–12 kHz. The voltage obtained from signal conditioning block is

tabulated in Table 6 and plotted in Fig. 6 at frequency 7 kHz when

the sensor is dipped into milk and milk adulterated with tap water.

From Table 6, it is observed that as the % of adulteration increases;

voltage reading from phase detector circuit also increases.

Then milk is adulterated with different concentration of urea

and the voltage of the phase detector circuit is noted. It has been

observed that for a particular adulteration, circuit is giving con-

stant voltage in the frequency range 5–12 kHz. The voltage

obtained for consecutive three days from phase detector circuit

is tabulated in Table 7 and plotted in Fig. 7. From Table 7 it is found

that as the concentration of urea adulteration increases, voltagevalue decreases. Also phase angle and pH value decrease for the

same urea adulteration and are shown in Tables 7 and 4.

2.2.1. Sensitivity evaluation

The sensitivity of the sensor in phase detector circuit was calcu-

lated from the difference of pH between 10% tap water and pure milk

(Table 2) and it was found to be 0.08 only. Again from Table 6, it is

found that difference of voltage from phase detector circuit between

10% tap water and pure milk is 0.15 V. Hence, the sensitivity of the

phase detector circuit when FOE13 sensor dipped in tap water

adulterated milk is 1.875 V/pH. Similarly from Tables 4 and 7 it is

clear that the sensitivity of FOE13 sensor is 12.5 V/pH when dipped in

urea adulterated milk.

2.3. Display unit

In the nal prototype of the sensing system, a display circuit shown

in Fig. 8 has been used to display a different color LED array for

different types of milk adulteration. Three LEDs are used to indicate

three different voltage levels. The ORANGE LED turns on when the

input voltage is within the high voltage and low voltage limit. The RED

LED will glow when the input voltage is above the high voltage limit

and GREEN LED will glow when the input voltage is below the low

voltage limit. The combination of resistance values (R1 and R2) will set

the high and low limit of voltage values.

2.3.1. LED display for different percentages of tap water adulteration

The voltage obtained for pure milk is r4:28 V and milk adulter-ated with tap water lies between 4.28 V and 5.17 V as observed from

Table 8. Hence the high voltage limit and low voltage limit as shown in

Fig. 8 are 5.17 V and 4.28 V respectively. The proper resistance values of

the display circuit have been chosen so that the voltage of pure milk is

less than low voltage range, addition of 40% tap water is above the high

voltage range and milk adulterated with 10–40% tap water is in

between these two. The LED indication and the voltages obtained for

different types of adulteration are shown in Table 8. To keep the voltage

range within 5.17 V and 4.28 V of display circuit, the calculated R1 and

R2 values are 6.8 kΩ and 16.54 kΩ respectively. With these combina-tion of resistance values, the display unit (Fig. 8) is connected to the

output of the phase detector circuit. It is found that when the sensor

FOE13 is dipped in pure milk, GREEN LED turns on. When milk is

adulterated with 10–

40% tap water, ORANGE LED is glowing and whenmilk is adulterated with more than 40% tap water, RED LED turns on.

From Table 8, it can be said that the display circuit shown in

Fig. 8 is able to indicate different percentages of tap water

adulteration by using different colored LED.

2.3.2. LED display for different concentration of urea adulteration

Similar tests were performed with milk adulterated with urea.

From Table 9, it has been observed that the voltage obtained for pure

milk and milk adulterated with different concentration of urea lies

between 4.31 V and 3.09 V respectively. To keep the voltage range

within 4.31 V and 3.09 V of display circuit, the calculated R1 and R2

values are 16.32 kΩ and 28.68 kΩ respectively. With these resistancevalues connecting in display circuit and FOE13 sensor dipping in pure

milk, it is found that RED LED turns on. FOE13 sensor is next dipped in

Table 4

Phase angle in milk and milk adulterated with urea of FOE13 sensor at 7 kHz.

Day Test medium pH value Avg θ (deg)

1 Pure milk 6.82 24.96

Added 0.6 mg/ml urea 6.78 19.77




2 Pure milk 6.85 25.29





3 Pure milk 6.83 26.10





Table 5

Slope, zero error and residual with urea adulteration.

Day Slope (m) Zero error (c ) R2

1st 5.974 24.33 0.935

2nd 5.858 24.65 0.932

3rd 5.769 25.41 0.919


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milk adulterated with 0.6 mg urea to 1.2 mg urea and ORANGE LED

glows. Again FOE13 sensor dipped in milk which is adulterated with

more than 1.2 mg urea and found GREEN LED turns on (Fig. 8). It is to

be noted that in case of pure milk RED LED turns on. But a switching

arrangement can be made so that GREEN LED turns on when FOE13

sensor is dipped in pure milk and RED LED turns on when dipped in

milk which is adulterated with more than 1.2 mg urea.

From Tables 8 and 9 it may be said that if we design two LED

circuits which can identify either tap water adulteration or urea

adulteration the two blocks together may be able to give an

indication. So using this LED circuit it may be possible to

differentiate among pure milk and milk adulterated with tap

water or urea.

Fig. 5. Phase detector circuit.

Table 6

Output voltage in milk and milk adulterated with tap water at 7 kHz.

Test medium Output voltage at

day 1 (V)

Output voltage at

day 2 (V)

Output voltage at

day 3 (V)

Pure milk 4 .28 4.31 4.43

Added 10% tap

water

4.43 5.00 5.15

Added 20% tap

water

4.66 5.23 5.22

Added 40% tap

water

5.17 5.69 5.73

0 10 20 30 404

4.5

5

5.5

6

Different % of tap water adulteration

V o l t a g e ( V )

1st day

2nd day

3rd day

Fig. 6. Output voltage versus % of tap water adulteration.

Table 7

Output voltage in milk and milk adulterated with urea at 7 kHz.

Test medium Output voltage at

day 1 (V)

Output voltage at

day 2 (V)

Output voltage at

day 3 (V)

Pure milk 4.31 4.43 4.29

Added

0.6 mg

urea

3.81 3.72 3.71

Added

0.8 mg

urea

3.55 3.45 3.49

Added

1.0 mg

urea

3.27 3.29 3.26

Added1.2 mg

urea

3.09 3.10 3.01

0 0.2 0.4 0.6 0.8 1 1.23

3.5

4

4.5

5

Different concentration of urea adulteration (mg)

V o l t a g e ( V )

1st day

2nd day

3rd day

Fig. 7. Output voltage versus concentration of urea adulteration.


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3. Automatic detection system

A low cost automated sensing system is designed in which the

sensor detects the adulterated milk and a micro-controller based

circuit closes the valve installed at the outlet of the milk supply

line to prevent mixing. The block diagram is shown in Fig. 9. As acase study ‘the results with the synthetic milk (reconstructed after

adulterating with liquid-whey)' is presented in the paper.

3.1. Design of the automated sensing system

The rst block of Fig. 9 consists of the FOE sensor dipped inside

the test sample. The second block is the phase detector circuit. The

output of the sensor is used as an input to the phase detector

circuit as shown in Fig. 5, which converts the phase angle into its

corresponding voltage output. The next is the microcontroller

block. The output voltage from phase detector circuit is fed into

microcontroller. The voltage corresponding to the pure milk is

stored in the micro-controller and whenever a deviation occurs

with respect to this stored voltage an error signal is generated and

the driver circuit drives the control valve (solenoid valve). So,

whenever adulteration is detected, the control valve at the outlet

of the milk line shuts off the ow of milk to prevent mixing. The

display unit consists of LCD display and a LED array system. The

output voltage can be read from the LCD and a comparator based

LED driver system is used to glow the ‘RED’ or ‘GREEN’ LED to

indicate the status of the milk.

3.1.1. Controller block

The heart of the control block is an 8 bit microcontroller (ATMEGA 8)

as shown in Fig. 10. It has an inbuilt ADC which is connected to Port C.There are 3 ports in this microcontroller. Port C is used to collect the

analog signal from phase detector circuit. Port D gives the control signal

to the solenoid valve. Port B and Port D are used to interface LCD

display.

ATMEGA 8 microcontroller does the following functions:

Converts the output voltage from phase detector circuit to itscorresponding digital form.

It compares the output from the sensor with the referencesignal which corresponds to pure milk. A tolerance level of 5%

is allowed for the comparison. This is 0 :95 V ref oV ino1:05 V ref . Generates an error signal to activate the solenoid valve. When

the voltage exceeds the desired limits, sends that to the

control valve. Sends the corresponding voltage value to be displayed in the

LCD display. Sends the signal to glow the corresponding LED. If exceeds the desired limit after sending the error signal waits

for starting fresh.

The microcontroller is programmed accordingly. Output signal

from PD.4, either 0 or 1, is fed to the solenoid valve through a relay.

3.1.2. Working of solenoid valve

The output of ATMEGA 8 microcontroller is used to energize a

24 V relay via ampliers. These relays have been used for switch-

ing the solenoid valve. Separate signal conditioning has been

designed by using a bridge rectier circuit for conversion from

Fig. 8. Display circuit used to indicate different adulterants.

Table 8

LED indication for different types of tap water adulteration and their corresponding

voltages.

Test medium LED ON Voltage

Pure milk GREEN Less than or equal to 4.28 V

Added 10–40% tap water ORANGE Within 5.17 V and 4.28 V

Added Z40% tap water RED Greater than or equal to 5.17 V

Table 9

LED indication for different concentration of urea adulteration and their corre-

sponding voltages.

Test medium LED ON Voltage

Pure milk RED Greater than or equal to 4.31 V

Added 0.6–1.2 mg/ml urea ORANGE Within 4.31 V and 3.09 V

Added Z1:2 mg=ml urea GREEN Less than or equal to 3.09 V


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220 V supply. Normally solenoid valve remains open. The voltage

from the phase detector circuit is kept within the specied

allowable range 0:95 V ref oV ino1:05 V ref , to keep the valve in

open condition. The microcontroller output gives a low output i.e.,

0 to the solenoid circuitry and remaining same state of ow in

pipe, i.e., valve remains open and allows the milk ow. When the

voltage from phase detector circuit is out of the allowable range

0:95 V ref oV ino1:05 V ref , the output of the pin PD4 of microcon-

troller will change from 0 to 1. The valve will be actuated and will

be closed and will block the ow of adulterated milk.

3.2. Results

Table 10 shows the pH value of the test samples and the

corresponding phase angle and voltage obtained by the FOE13 sensor

at 7 kHz.

It is to be noted from Table 10 that after adding NaOH to the

whey adulterated milk though the pH value is brought to the same

value of the pure-milk, the sensor could identify between these

two test samples and show different phase angles. This is also

reected in the voltage output.

Fig. 9. Block diagram of the automatic sensing system.

Fig. 10. ATMEGA8 microcontroller conguration.


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From Table 10, it is also observed that the voltage obtainedfrom pure milk is 4.38 V so the stored value in the microcontroller

i.e., V ref is 4.38 V. So the allowable range of voltage is 4.16–4.59 V.

From Table 10, the output voltage of the synthetic milk, V in, is

3.70 V, which is out of the limit, so the valve closes and shuts off

the ow of milk.

4. Conclusion

In this paper, a simple and inexpensive instrumentation system

has been reported to detect milk adulteration. The system is

capable to differentiate between pure milk and milk adulterated

with water and urea. For water adulteration, it has been noted that

the change is signicant between pure milk and milk adulterated

with 10% water, though for higher concentration of adulterationthe change is not that signicant. Further research work is

required in this direction to increase the sensitivity of the sensor

by different polymer coating. This is also true for urea adulteration

where 0.6 mg/ml shows maximum slope but decreases for higher

adulteration.

It is to be noted that phase detector circuit faithfully reproduces

the change in phase angle and gives output voltage. The sensor

output is noted at 7 kHz as this is in the middle of the frequency

range (5–12 kHz) where the opamp works properly and the sensor

behaves as a CPE.

A low cost automatic sensing system is also designed to detect

synthetic milk. The synthetic milk is reconstructed after adulter-

ating pure milk with ‘liquid-whey’. The main difference between

the pure milk and the synthetic milk is the presence of differentions which the sensor is capable to detect. The phase angle

remains constant over a band of frequency, so measurement can

be frequency independent, which is an added advantage for such

automatic sensing system.

Acknowledgments

The authors are thankful to UGC-DAE Consortium for Scientic

Research, Kolkata, India and also to PURSE project, JU. The authors

are also thankful to the Department of Science and Technology,

West Bengal, India, for their nancial support. The authors also

like to thank Prof. S.K. Gangopadhaya of Mohanpur Dairy Institute,

WB, for his help and suggestions.

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Table 10

Performance of the sensing system in the test medium at 7 kHz frequency.

Test samples pH value Phase angle Voltage

Pure milk 6.87 25.08 4.38

Synt heti c mi lk (r econ structed a fter a ddi ng 3 0% whey a nd N aO H) 6 .8 7 20.17 3.70

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