14CH406/CH 226 Hall Ticket Number:

II/IV B.Tech (Regular/Supplementary) DEGREE EXAMINATION

April, 2017 Chemical Engineering

Fourth Semester Process Instrumentation Time: Three Hours Maximum : 60 Marks

Answer Question No.1 compulsorily. (1X12 = 12 Marks)

Answer ONE question from each unit. (4X12=48 Marks)

1 Answer all questions (1X12=12 Marks) a) What is the purpose of measurement?

b) What are Static Characteristics?

c) Explain Peltier effect.

d) What is the working principles involved in the floating level measuring instruments?

e) Name some Composition measuring instruments.

f) Explain the principle involved in gas chromatography.

g) Explain the principle involved in refractometer.

h) What are the sections of the control center layout?

i) Explain the working principle of area flow meters.

j) Give relation between head, density and specific gravity.

k) What is pitot tube?

l) What is meant by time constant?

UNIT I

2. a) Discuss about dynamics response of first order systems. 6M

b) Discuss about the elements of Instrument. 6M

(OR)

3. a) Discuss in detail about indicating and signaling instruments. 6M

b) Explain in brief about control center. 6M

UNIT II

4. a) With a neat sketch ,describe the working of pressure-spring thermometer. 6M

b) Discuss about industrial thermocouples. 6M

(OR)

5. a) Write temperature scales? Discuss in detail response of mercury thermometers. 6M

b) With neat sketch, describe radiation pyrometers. 6M

UNIT III 6. a) Describe the measurement of pressure in corrosive fluids. 6M

b) Discuss the methods of density measurements. 6M

(OR)

7. a) Describe the principle and working of pitot tube. 6M

b) Discuss any two methods for direct measurement of liquid level. 6M

UNIT IV

8. a) Write a short note on Absorption Spectroscopy. 6M

b) Discuss Rayleigh Interferometer. 6M

(OR)

9. a) Explain the gas analysis through thermal conductivity measurement . 6M

b) Discuss pH Ion concentration measurement. 6M

II/IV B.Tech (Supplementary) DEGREE EXAMINATION

April, 2017 Chemical Engineering

Fourth Semester Process Instrumentation (14CH 406)

Subject Coordinator- N.Sudha Rani

1. Each question carry equal marks (1X12=12 Marks)

a) What is the purpose of measurement?

Measurement is done to improve the quality of the product by monitoring, controlling and

analyzing the process.

b) What are Static Characteristics?

Static characteristics are considered when instrument is used to measure a quantity not varying

with time. Accuracy, Static error, Reproducibility, Drift, Sensitivity, Dead zone.

c) Explain Peltier effect.

Peltier effect is the phenomenon that explains the potential difference applied across a

thermocouple causes a temperature difference between the junctions of the different materials.

d) What is the working principles involved in the floating level measuring instruments?

Floats work on the Archimedes' principle of buoyant force.

e) Name some Composition measuring instruments.

Spectrometers, X-ray diffraction, Thermal conductivity cell, Psychrometer, Verigraph etc.

f) Explain the principle involved in gas chromatography.

The principle in gas chromatography involves separation of components of the sample under test

due to partition in between gaseous mobile phase and stationary liquid phase.

g) Explain the principle involved in refractometer.

Refractometers work on the principle of light refraction through liquids. As light passes from air

into a liquid it slows down.

h) What are the sections of the control center layout?

Unit layout, central layout

i) Explain the working principle of area flow meters.

Variable area flow meters operate on the principle that the variation in area of flow stream required

to produce a constant pressure differential is proportional to the flow rate.

j) Give relation between head, density and specific gravity.

P2-P1 = ρgh

k) What is pitot tube?

The pitot tube is used to measure the local flow velocity at a given point in the flow stream in the

pipe or conduit.

l) What is meant by time constant?

Time constant is the product of resistance and capacitance (τ=RC). In first order systems, it is the

time taken by the response to reach 63.2% of its ultimate value to a step change in input. It has

units of time.

UNIT I

2. a) Discuss about dynamics response of first order systems. 6M

The transfer function of first order system is: 𝐺(𝑠) =𝑌(𝑠)

𝑋(𝑠)=

1

𝜏𝑠+1

The dynamic response is the behavior of the output variable (response or reading of the instrument)

with time with a change given in input. The common input forcing functions are: Step change,

Linear change, Sinusoidal change and Impulse change.

Step function:It represents sudden change of value of the input.

The step function of magnitude ‘A’ is mathematically described by the equation

x(t) = 0 for t < 0;

= A for t > 0;

The Laplace transform of the step function: L{x(t)} = L {A} =A/s.

Step response: 𝑌(𝑡) = 𝐴(1 − 𝑒−𝑡𝜏⁄ )

Linear function: It is represented by

X(t) = 0; t < 0

X(t) = kt; t > 0 k is constant and is rate of change of true value of input.

The transfer function is L{x(t)} = K/s2

The change in response with time is: 𝑌(𝑡) = 𝐾(−𝜏 + 𝑡 + 𝜏𝑒1𝜏⁄ )

Sinusoidal input : A mercury thermometer is in equilibrium with a temperature bath at temperature

xs. At time t=0, the bath temperature begins to vary according to the relationship X(t) = A sin ω t;

t > 0, Where x-Temperature of bath, xS–Temperature of bath before sinusoidal disturbance is

applied, A-Amplitude of variation in temperature, ω-Radian frequency.

The Laplace transform of this function is X(s) = Aω/ s2 +ω2

The change in response: 𝑌(𝑡) =𝐴

√𝜔2𝜏2+1𝑠𝑖𝑛(𝜔𝑡 + 𝜙)

Scheme:

Expression for input and output laplace forms-3*2=6M

b) Discuss about the elements of Instrument. 6M

Primary Element

•This element first receives the energy from the measured medium and utilizes it to produce a

condition representing the value of the measured variable.

•In a pressure–spring thermometer the ‘bulb’ represents the ‘Primary Element’. It receives the heat

energy from the hot bath that causes the expansion of the mercury inside the bulb and the capillary.

The bulb is converting the heat energy into fluid displacement.

Secondary Element

Scale corrector

Primary Element

Secondary Element

Manipulating Element

Functioning Element

Thermometer bulb

Bourdon

tube

Pointer

Scale

•This element coverts the condition produced by the primary element into a condition useful for

the functioning of the instrument.

•In a pressure –spring thermometer, Bourdon tube represents secondary element. In this, fluid

displacement into mechanical displacement of the free end of the Bourdon Spring is taking place.

This is necessary for functioning of the instrument.

Manipulating Element

•This element performs certain operations on the condition produced by the secondary element.

•In a pressure spring thermometer, the adjustable link, sector, pinion combinely act as the

manipulation element. They convert the linear motion of the free end of the Bourdon tube into the

circular motion of the pointer

Functioning Element

•This element represents the parts used for indicating, recording, signaling, registering or

transmitting the measured quantity.

Scheme:

Definition of each element with explanation -4M, Diagram-1M, Example-1M

(OR)

3. a) Discuss in detail about indicating and signaling instruments. 6M

An indicating instrument is used when only the present value of the variable has meaning and

the past record is of no consequence. Indicating scales are of three types: the eccentric scale, the

concentric scale, and the linear scale.

The eccentric scale is commonly used on mechanical instruments such as pressure thermometers,

flow meters, and pressure gages. The scale length is usually about 8 in. but may be much smaller.

The concentric scale is used for nearly all kinds of instruments. The scale length is usually about

25 in. in the precision-type instrument. For readability the concentric scale generally offers the

greatest scale length in the smallest space.

The linear scale is commonly used only on the potentiometer-resistance-thermometer-type in-

strument. Galvanometer type milli voltmeters employ a linear scale in a curved form.

The use of the various indicating instruments is generally restricted, because a free choice of scale

types is not possible.

Signaling instruments are very effective when it is only necessary to indicate that the variable is

within certain limits. This is accomplished by electric contacts or switches suitably operated from

a measuring means such as a thermometer pressure spring, liquid-level float, or thermocouple

pyrometer. Signal lights or horns are used for visual or audible signal. Signaling systems should

be positive; that is, a system should require an operator to look for a specific combination of signals

before performing an operation. An example of poor signaling is to permit process operation to

proceed only when no signal is evident. This procedure is unsafe, because no signal may simply

mean that the power is off. The common signaling systems are: The “hi-low” system, which is

useful for indicating when a variable has passed a given point; The “hi-low-neutral” system, which

is widely used to indicate that a process operation may proceed only when the amber light is on;

The "5-position" system, which provides more information on the value of the variable. Some

process operations may proceed when the amber light only is on, and some operations may proceed

when the amber and either red or green lights are on.

Scheme: Purpose, working and diagram-3*2=3M

b) Explain in brief about control center. 6M

Instrumentation equipment are generally grouped at one location near the processing unit or

manufacturing operation which they serve. This group of instrumentation equipment may be

termed a control center since it controls or aids an operator in controlling the process operation.

The control center may include only a single instrument “hung” on the process equipment, or it

may consist of hundreds of instruments and controllers housed in a separate building. The control

center then becomes the operating center of the plant. At the control center the instrumentation

equipment is conveniently grouped on panel boards around the control-center room. This room is

completely enclosed, air-conditioned, properly lighted, and clean.

Because of the physical size of some plants, it is necessary to consider two types of plant and

instrumentation layout: central layout, unit layout.

Central Layout

• The advantages of central layout are that the coordination of all plant operations is greatly

facilitated and service and maintenance of instrumentation equipment are quickly and

easily accomplished.

• Separate control centers for each operation may be used because of the physical size of the

whole plant or because the operations require no coordination.

• The control centers in this case may be located in separate enclosures, or, as is common

when the plant is inside a building, open panel boards are set up near each unit.

Unit Layout

• Unit layout has the advantages that the control center is close to the processing unit and

coordination between processing unit and control center is improved.

Scheme:

Control center definition and explanation-3M, unit and central layout explanation-2M,

diagrams-1M

UNIT II

4. a) With a neat sketch describe the working of pressure-spring thermometer. 6M

The Pressure spring thermometers are classified into three categories according to the filled

material:

• Liquid filled thermometer. These thermometers utilize volumetric expansion of liquid with

rise in temperature for indicating temperature of liquid.

• Gas filled thermometers: Pressure of certain fixed volume of gas varies with temperature

of the gas. Thus any change in temperature of gas can be measured in terms of change in

its pressure.

• Vapor – actuated thermometers: Vapor pressure of volatile liquid varies with the

temperature existing at the free surface of liquid. Hence any change in temperature of a

volatile liquid can be measured in terms of change in its vapor pressure.

Construction: The thermal system for all pressure spring thermometers consists of: Bulb,

Capillary, Thermal well, Extension neck and receiving element (pressure spring), Pen arm or a

pointer.

Working: When the bulb is sufficiently inserted in the bath whose temperature is to be measured,

the bulb’s liquid receives heat from the bath and its temperature rises until it equals the bath

temperature, thus developing a pressure or displacement of the liquid. The capillary transmits the

pressure to the receiving element that causes winding or unwinding of bourdon tube. The free end

deflection of the bourdon is coupled with the pointer that moves on a calibrated scale.

Scheme:

Diagram-1M, Principle-2M, construction-1M,working-2M

b) Discuss about industrial thermocouples. 6M

A Thermocouple is a sensor used to measure temperature. There are many types of thermocouples,

each with its own unique characteristics in terms of temperature range, durability, vibration

resistance, chemical resistance, and application compatibility. Type J, K, T, & E are “Base Metal”

thermocouples, the most common types of thermocouples. Type R, S, and B thermocouples are

“Noble Metal” thermocouples, which are used in high temperature applications.

1. Type K Thermocouple (Nickel-Chromium / Nickel-Alumel): The type K is the most common

type of thermocouple. It’s inexpensive, accurate, reliable, and has a wide temperature range.

Temperature Range: –270 to 1260C

2. Type J Thermocouple (Iron/Constantan): The type J is also very common. It has a smaller

temperature range and a shorter lifespan at higher temperatures than the Type K. It is equivalent

to the Type K in terms of expense and reliability. Temperature Range: (-210 to 760C)

3. Type T Thermocouple (Copper/Constantan): The Type T is a very stable thermocouple and

is often used in extremely low temperature applications such as cryogenics or ultra-low freezers.

Temperature Range: (-270 to 370C)

4. Type E Thermocouple (Nickel-Chromium/Constantan): The Type E has a stronger signal &

higher accuracy than the Type K or Type J at moderate temperature ranges of 1,000F and lower.

See temperature chart (linked) for details. Temperature Range: (-270 to 870C)

5. Type N Thermocouple (Nicrosil / Nisil): The Type N shares the same accuracy and

temperature limits as the Type K. The type N is slightly more expensive. Temperature Range: (-

270 to 392C)

NOBLE METAL THERMOCOUPLES (Type S,R, & B): Noble Metal Thermocouples are

selected for their ability to withstand extremely high temperatures while maintaining their

accuracy and lifespan. They are considerably more expensive than Base Metal Thermocouples.

6. Type S Thermocouple (Platinum Rhodium - 10% / Platinum): The Type S is used in very

high temperature applications. It is commonly found in the BioTech and Pharmaceutical industries.

It is sometimes used in lower temperature applications because of its high accuracy and stability.

Temperature Range:(-50 to 1480C)

7. Type R Thermocouple (Platinum Rhodium -13% / Platinum): The Type R is used in very

high temperature applications. It has a higher percentage of Rhodium than the Type S, which

makes it more expensive. The Type R is very similar to the Type S in terms of performance. It is

sometimes used in lower temperature applications because of its high accuracy and stability.

Temperature Range: (-50 to 1480C)

8. Type B Thermocouple (Platinum Rhodium – 30% / Platinum Rhodium – 6%): The Type

B thermocouple is used in extremely high temperature applications. It has the highest temperature

limit of all of the thermocouples listed above. It maintains a high level of accuracy and stability at

very high temperatures. Temperature Range: (0 to 1700C)

Scheme:

Thermocouple definition-1M, any 5 types of thermocouple-5M

(OR)

5. a) Write temperature scales? Discuss in detail response of mercury thermometers. 6M

The important scales based on the ideal thermodynamic scale but using different units are:

• Fahrenheit Scale (0F): Ice-point at 32 0F and steam point at 212 0F. The zero point or starting

point temperature is 0 0F that represents temperature of salt- ice mixture.

• Centigrade Scale (0C): Ice- point is 00C and steam - point at 1000C. This scale depends upon

the selection of working substance.

• Kelvin or Absolute Scale (0K): Also called centigrade absolute scale. Used in Technical

literature. Ice-point 273.16 0K and steam-point 373.160K

• Rankine scale (0R): Also called Fahrenheit Absolute scale, used in engineering literature. Ice-

point 491.690R’ and steam-point 671.690R’.

• Reaumur Scale (0Re): Ice-point 00Re and steam-point 800Re. Used in the alcohol industries.

Mercury in glass thermometer

The working substances that are used in liquid in glass thermometers: Alcohol (-80 to 700C),

Toluene (-80 to 1000C), Pentane (-200 to 300C), Cresols (-5 to 2000C).

Working

To measure the temperature, the ‘bulb’ of the mercury –in- glass thermometer is immersed in the

measured medium to a sufficient depth. Heat energy from the hot bath is transferred to the working

substance (like mercury) through thermal well, stem & bulb mainly by conduction. On receiving

heat, mercury expands more than glass because co-efficient of cubical expansion of mercury is

much greater than that of glass. The thermal expansion of mercury causes the rise in mercury level

inside the capillary Thus the mercury level inside the capillary changes with the change in the

temperature of the hot bath. The top of the mercury column read against the scale gives the bath

temperature

Scheme: Temperature scales-3M; Mercury thermometer: Principle-1M, Working-2M.

b) With neat sketch, describe radiation pyrometers. 6M

According to Stefan- Boltzmann’s law the intensity of radiant energy emitted by hot target varies

as the fourth power of its absolute temperature. In radiation pyrometer, the visible and IR energy

is focused on radiation detector which converts it into proportional electrical signal that indicates

the target temperature. It consists of a diaphragm, radiation receiving element, sighting hole and

indicator or recorder. Radiations at all possible wavelengths from a hot body are focused by lens

or mirror on the radiation receiving element. In lens type radiation receiver, a lens is used to

concentrate the radiant energy from the source on the diaphragm to the thermopile (or vacuum

thermocouple. In mirror type radiation receiver, a diaphragm system together with a mirror is used

to focus the radiation on a thermopile. The mirror to thermopile distance is adjustable for proper

focus. This unit has an advantage of not having lens, since lens absorption and reflection are

avoided. When thermopile or vacuum thermocouple is used as radiation receiving elements, then

radiant energy is focused on blackened measuring junction. Due to absorption of radiant energy

the measuring junction temperature rises According to Seebeck effect emf develops between

measuring junction and reference junction. When this element is connected with mill voltmeter

type instrument, the emf developed can be calibrated in terms of the target temperature. If

bolometer is used as a receiving element, then resistance of the foil changes with temperature.

Hence bolometer can be calibrated in terms of target temperature with wheat stone bridge circuit.

Lens - type radiation pyrometers

Mirror-type radiation pyrometers

Scheme: Principle-1M, Construction-2M, Working-1M, Diagram-2M

UNIT- III

6. a) Describe the measurement of pressure in corrosive fluids. 6M

In nearly all pressure gages, the fluid in which the pressure is measured is conducted to the inside

of the pressure-measuring element and is in direct contact with the element. This creates a problem

of handling high temperature, corrosive, sludgy, or semisolid materials. The metallic materials

used in the pressure- measuring element are, variously, brass, bronze, phosphor bronze, copper,

beryllium—copper, steel, chrome—molybdenum steel, stain less steels, monel, silver, and

tantalum. The nonmetallic materials are leather, neoprene, rubber, and glass.

The single-coil siphon is effective in protecting a pressure-gage element from the high

temperatures of steam. The brass coil traps condensed steam and limits the temperature rise in

the gage. A siphon is necessary on all steam-pressure gages.

The diaphragm seal is usually made of bronze or cast iron with a neoprene or thin-metal

diaphragm. The system is solidly filled with a liquid such as glycerin or oil. The area of the

diaphragm is made sufficiently large that the required motion is almost negligible to produce

the required volume change.

The liquid seal has a sealing chamber, usually of bronze or cast iron, is interposed in the gage

line between the pressure gage and the point of measurement. The pressure-gage element, line,

and sealing chamber are filled with a suitable liquid.

The purge system is useful when a small and continuous flow of air or other gas through the

measuring line is sufficient to maintain the line free from sludge. Air is supplied at the necessary

pressure through a constant-flow regulator, which contains an orifice and a differential-

pressure-controlling means.

Scheme: Working of each equipment-4M, Diagram-2M

b) Discuss the methods of density measurements. 6M

The measurement of density or specific gravity may be accomplished by two methods: (1) the

pressure at the bottom of a column of liquid (or gas) is proportional to the density; (2) the weight

of a given volume of liquid (or gas) is proportional to density.

In the measurement of liquid density using the pressure method, the head h1 is held constant in the

measuring tank or vessel by an overflow arrangement. The head h0 in the reference chamber is

constant, providing the reference liquid is nonvolatile. Therefore the differential pressure measured

by the manometer is that due to the difference in densities of the two liquids. The pressure in each

chamber is measured by means of the bubbler system.

In the measurement of liquid density, using the weight method, the liquid flows continuously in

and out of the displacer chamber at a rate of about 3 gpm. The upward force on the balance beam

is due to the displaced volume of liquid. This force is balanced by the pneumatic servomechanism

previously described. As a result, the pressure transmitted to the receiver is proportional to the

density of the liquid.

The hydrometer method can be used for continuously measuring specific gravity of liquids. The

level of liquid is maintained constant at the overflow tube. The hydrometer sinks or rises in the

liquid as the specific gravity varies (the action of the hydrometer depends on buoyancy effect of

liquid dis placed). The lower end of the hydrometer supports an armature in an inductance coil,

and the specific gravity can be remotely indicated.

Scheme: Working of each equipment for density measurement-4M, Diagram-2M

(OR)

7. a) Describe the principle and working of pitot tube. 6M

Pitot tube is a convenient, inexpensive method for measuring velocity at a point in a flowing fluid.

They are used to make airflow measurements in HVAC applications and for aircraft airspeed

measurements. In a concentric pitot tube, the inner tube has a stagnation pressure opening

(perpendicular to the fluid flow) and the outer tube has a static pressure opening (parallel with the

fluid flow).

For pitot tube measurements and calculations, the reference plane is taken to be at the height of

the pitot tube measurements, so the equation for stagnation pressure becomes:

Pstag = P + ½ ρV2, which can be rearranged to: V = (2ΔP/ρ)1/2, Where ΔP is pressure difference

(Pstag – P).

Scheme: Definition of Pitot tube -1M, Working-2M, Velocity equation-2M, Diagram-1M

b) Discuss any two methods for direct measurement of liquid level. 6M

(i)Float-and-Tape Liquid-Level Gage This method is employed in open vessels only. The float, usually of nickel-plated copper, rests on

the surface of the liquid, supported by buoyant force. The float is made with a sloping top in order

to avoid building up of solid material on top of the float, thereby changing its weight. The float is

connected to the drum by a thin light weight, flexible tape or cable. Slipping of the tape on the

drum is prevented by a direct connection of the tape to the drum. By a suitable reduction in motion

the pointer indicates on a scale calibrated in feet or other units.

(ii) Float-and-Shaft Liquid-Level Gage The float rests on the surface of the liquid and the motion of the float is taken through the shifting

box by the shaft. The counterweight is adjustable, so that the float can be made to ride half-

submerged. This is important since floats are usually spherical, and this is the point of maximum

area. The float cage may be obtained in steel or cast iron, and the float in copper, stainless steel,

nickel or aluminum. The rotation of the shaft may be converted into a change of pneumatic

pressure by the use of a pneumatic transmission system. The movement of the float causes a

displacement of a metallic bellows which is filled with oil.

Scheme:

Any two instruments: diagram-2*1=2M, working 2*2=4M

UNIT-IV

8. a) Write a short note on Absorption Spectroscopy. 6M

Absorption Spectroscopy: Absorption spectroscopy is a technique used to find out what makes

up a sample of a substance, i.e, chemical analysis. When infrared, ultraviolet or x-ray radiation is

passed through the sample of unknown material certain frequencies of the radiation are absorbed.

This is determined by separating the radiation into a spectrum and measuring the intensity of

radiation at each frequency. Absorption lines are dark lines on a light background on a

photographic negative. These dark lines are called absorption lines, and every element has its

characteristic pattern of absorption lines. On an atomic scale, this happens because of the electrons

in the atoms of the sample - an electron can absorb light to gain energy. Electrons only ever absorb

certain amounts of energy, suggesting an electron's energy must fit onto set, quantized, discrete

energy levels. The process of an electron going to a higher energy level is called excitation. For

any atom of a particular element, the energy needed to excite an electron from one specific energy

level to another will be the same. The missing colors give us information about the energy of the

photons that cause excitation. Since a color can be described as a specific frequency of light, this

is why the black breaks can be used to identify element(s) which the light is passing through.

Scheme:

Diagram-2M, working -4M

b) Discuss Rayleigh Interferometer. 6M

The Rayleigh interferometer employs two beams of light from a single source, and determines the

difference in optical path length between the two paths using interference between the two beams

when they are recombined following traversal of the paths. As shown in the figure, light from a

source (top) is collimated by a lens and split into two beams using slits. The beams are sent through

two different paths and pass through compensating plates. They are brought to a focus by a second

lens (bottom) where an interference pattern is observed to determine the optical path difference in

terms of wavelengths of the light. The advantage of the Rayleigh interferometer is its simple

construction. Its drawbacks are (i) it requires a point or line source of light for good fringe

visibility, and (ii) the fringes must be viewed with high magnification.

Scheme:

Prinicple-1M, working -4M, Diagram-2M

(OR)

9. a) Explain the gas analysis through thermal conductivity measurement . 6M

Thermal conductivity measurement is a very simple means of analyzing certain gas mixtures.

Thermal conductivity of the mixture of two gases can be related to the concentration of each

component. A thermal conductivity cell is constructed of glass. The right hand tube contains a

platinum filament held under constant tension by a spring. The filament and spring are glass

coated. The gas flow occurs at a constant rate by natural convection through the filament cell.

When a current flows through the filament the heating and consequent temperature rise of the

filament depend on the rate at which heat is conducted away from the filament. This depends

mainly on the thermal conductivity of the gas. It is important that both cells be subjected to the

same ambient-temperature conditions so that the only difference measured in the bridge is that due

to the differing thermal conductivity of the reference gas and the measured gas.

Scheme:

Diagrams-2M, working -4M

b) Discuss pH Ion concentration measurement. 6M

pH is defined as the negative logarithm of the hydrogen ion concentration.

𝑝𝐻 = − log[𝐻+] where: [H+] is hydrogen ion concentration in mol/L.

A pH Meter is a scientific instrument that measures the hydrogen-ion activity in water-based

solutions, indicating its acidity or alkalinity expressed as pH. The pH meter measures the

difference in electrical potential between a pH electrode and a reference electrode. The difference

in electrical potential relates to the acidity or pH of the solution. They comprise a simple electronic

amplifier and a pair of electrodes, or alternatively a combination electrode, and some form of

display calibrated in pH units. The electrodes, or probes, are inserted into the solution to be tested.

When the probe is placed in a solution to measure the pH, hydrogen ions accumulate around the

bulb and replace the metal ions from the bulb. This exchange of ions generates some electric flow

that is captured by the silver wire. The voltage of this electric flow is measured by the pH meter

by converting it into pH value by comparing the generated voltage with the reference electrode.

Scheme:

Definition of pH-1M, working -4M, Diagrams-1M