Contents

o Introduction

o Objectives

o Different types of Oxygen Analyzer

- Paramagnetic Method

- Thermomagnetic Method

- Zirconia Cell type

- Dissolved Oxygen analysis

o Advantages & Disadvantages

o Conclusion

INTRODUCTION

FACTS ABOUT OXYGEN

Oxygen is one of the most important elements without which life on earth would not be able to exist. Here are a few interesting oxygen facts that you can mull over.

All life on earth is based on 5 basic elements: sulphur, nitrogen, hydrogen, carbon, and oxygen. Amongst these, the element that is most abundant is oxygen. Oxygen makes up about 65% of the human body, 47% of dry soil, 46% of igneous rocks, 85% of sea water, 42% of all the vegetation, and 50% of the crust of the earth by weight. Odourless, tasteless, and colourless, oxygen is one of the most important substances without which life would not be able to exist. For example, we can go without food for a number of weeks and survive, we can even go without water for 3-7 days, but we cannot survive without oxygen beyond 5 minutes. Given the importance of this 'breath of life' here are some interesting facts about oxygen.

Oxygen provides us with 90% of our nutritional energy, with just 10% coming from the food we eat. The more our cells are saturated with stabilized oxygen the lower is the wear and tear that occurs in the body. Hence, oxygen is one of the most important anti-aging substances.

Oxygen's natural ability to oxidize or catabolise viruses, fungi, and bacteria is vitally important in order to sustain the cells' natural immortality factor and to prevent degenerative diseases.

Oxygen is also an essential factor for burning up the body's toxins - those that are generated by us internally as well as those that we get from external sources such as the environment, water, and food - particularly junk food. The lower the content of oxygen, the less ability we have to burn up toxins, to heal, and to fight disease.

In fact, diseases can actually occur when there is a deficiency of oxygen. Without enough oxygen, cells lose the ability to function properly, which leads to disease setting in. All kinds of diseases are basically linked to oxygen starvation, also known as hypoxia, or low oxygen levels.

The concentration of oxygen in our blood is about 60-70% on an average, at which level we function well, with average brain activity and energy. However, if the levels of oxygen drops lower than 60%, the cells are overwhelmed with pathogens, leading to diseases taking over. The lowest concentration of oxygen required to maintain life is around 52%, however, at this level, one is hardly alive.

Studies have also revealed that the oxygen levels in the atmosphere was about 36-38% about 200 years back, however when recent measurements were done, it was discovered that at present the earth's atmosphere just comprises 19% concentration levels of oxygen. In some areas that are heavily industrialized, which have high levels of pollution, the oxygen level is often as low as 9%.

The level of oxygen in the earth's atmosphere has been seriously depleted due to various factors, such as: the industrial revolution; the carbon-based fuels we use; and the depletion of large tracts of oxygen generating forest areas. According to scientific studies, it has been shown that the concentration level of oxygen in the atmosphere is being depleted by 0.8% about every fifteen years or thereabouts.

It is quite evident why it is essential to keep our body oxygenated. Oxygen is the sole element that has the capability of combining with practically all other elements in order to form the essential ingredients that are required for building and maintaining our body. For instance: water is made up of oxygen and hydrogen; carbohydrates are made up of oxygen, hydrogen, and carbon; proteins are made up of oxygen, hydrogen, carbon, and nitrogen.

The list of crucial roles played by oxygen is quite endless. It is necessary for oxidization, or combustion, and also acts as a preserver, sanitizer, deodorizer, and disinfectant. Our cells are energized by oxygen, which helps them to regenerate. Oxygen regulates all the functions of the body. Our ability to talk, sleep, eats; move, feel, and think are all

dependent on the energy that is generated by oxygen. Our body uses oxygen for the metabolism of food and the elimination of waste and toxins via oxidation. Oxygen is used by the brain to process information.

WHAT IS OXYGEN ANALYZER?

It is a device that measures the level of oxygen in a system therefore determines if the level needs to be increased or not. Oxygen analyzers in turn use a kind of oxygen sensor for their functioning. An analyzer uses a sensor cell constructed of ceramic materials to measure the oxygen level. Recently since industrial, vehicular, or rather all types of emissions are given more emphasis so as to decrease pollution, industrial users want the analyzers to be more accurate in the measurements and repeatable in terms of usage. Regular users of oxygen analyzers also want it to be more calibrated and in need of less maintenance.

Features Of Oxygen Analyzers ............

Oxygen Analyzers have advanced solid-state sensors, which help to get a very high precision measurement of oxygen. It also measures the part of oxygen per billion to hundred percent, thus there is no need to get another instrument to do that. With the help of one instrument only all the information can be received. Oxygen analyzers have the ability to respond very quickly, in fact in milliseconds, which not only saves time and increases efficiency but also provides the facility to track the process conditions competently and methodically. The oxygen analyzers have a non depleting sensor most of the time which performs well for a long period of time thus saving you the time and energy to research on a new analyzer sensor and money to invest in a new one. The outputs provided by the analyzer are user scalable and analogous, which have the ability to define the concentration range of interest in a better way. There are dual user adjustable alarms, which set critical process limits. A

Microprocessor Controller is also present which helps in ensuring dependable and accurate readings. There is also a built in sample by-pass gas which helps to promote rapid transport of the sample gas. Most of the analyzers are very compact and durable. They are easy to operate, splash proof, they have a built in flow restrictor and the sensor and battery replacement are also easy to do. The battery time is expected to be two years. AAA batteries are used which are inexpensive and easy to use. With some of the cases a deluxe carrying and storage case also comes which makes it convenient to carry if you have opted for a portable oxygen analyzer.

THE OXYGEN SENSOR

Oxygen sensors are devices which measure the amount of oxygen in the gas or liquid that is being analyzed.

Today, oxygen sensors are being used mainly in cars. They sense the amount of oxygen in the exhaust gas being emitted from the car and determine if the air to fuel ratio is at an optimum. The ideal or optimum air-fuel ratio is said to be 14.7:1.

When the amount of air in the exhaust is greater, then the mixture is said to be a lean mixture. In this case, the exhaust fumes will be full of nitrogen oxides. Such a mixture may often cause an increase in the fuel efficiency of the car, but it may lead to an eventual damage to the engine.

When the amount of fuel in the exhaust is greater, then the mixture is said to be a rich mixture. In this case, the exhaust fumes will be full of unburnt fuel vapors that are full of hydrocarbons. This may cause an increase in the power of the car, and a decrease in the car’s fuel economy. However, this can eventually lead to damage of the catalytic converter of the car.

The engine management computer or ECU checks the data supplied by the oxygen sensor against look-up tables and adjusts the air-fuel ratio in order to have complete combustion occurring in the engine.

The oxygen sensor and the engine computer play a major role in maintaining the lowest air and fuel mixture, which in turn, lowers the fuel consumption. In this process, the oxygen sensor reacts with the unburned oxygen and generates a low-voltage signal (usually 0-1.1 volts) that determines the level of fuel content in the exhaust. When the air and fuel mixture is rich (too much fuel), the oxygen sensor signal increases and vice versa.

TYPES OF OXYGEN ANALYZER There are various types of oxygen analyzers and users have a wide range of choice. Some of them measure the quantity of oxygen in gas-mixture and some of them measure the quantity of oxygen in liquid. Here I will discuss only about four types of analyzer. These are:-

-Paramagnetic Method

- Thermo-magnetic Method

- Zirconia Cell type

- Dissolved Oxygen analysis

Paramagnetic Oxygen Analyzer

BASIC MEASURING PRINCIPLE:

The principle of this method depends upon the force by which a paramagnetic substance is attracted towards a field of higher magnetic intensity.

Oxygen is one of the few gases with very strong paramagnetic properties, i.e.it does not have strong magnetism as permanent magnet, but it is attracted towards the magnetic field. Nitric-oxide, nitrogen-di-oxide are other two gases showing paramagnetic property.

CONSTRUCTION:- -It consists of a glass dumbbell suspended by quartz fiber between

the two poles of permanent magnet.

-Magnetic pole pieces are in shape of wedge so that the field

between them is non-uniform.

-The dumbbell is filled with a diamagnetic gas like nitrogen.

-The dumbbell is designed to move freely as it is suspended from the wire.

OPERATION:-

-The system is enclosed in a chamber through which the process Gas is flushed at a specific rate.

-When a sample gas containing oxygen is in, the oxygen molecules are attracted to the stronger of the two magnetic fields.-This causes a displacement of the dumbbell which results in the dumbbell rotating.-A precision optical system consisting of a light source, photodiode, and amplifier circuit is used to measure the degree of rotation of the dumbbell.-An opposing current is applied to restore the dumbbell to its normal position.-The current required to maintain the dumbbell in it normal state is directly proportional to the partial pressure of oxygen, i.e. percent of oxygen.

ADVANTAGES:-

1) In general, it offers very good response time characteristic.

2) It also offers excellent precision over a range of 1% to 100% oxygen.

DISADVANTAGES: -

1) It is quite delicate and is sensitive to vibration and/or position.

2) Other gases that exhibit a magnetic susceptibility can produce sizeable measurement errors

MEASURING DATA .

Measurement range: freely settable by input of parameters

Response time 90% (T90): ≤ 10 s (gas flow dependent)

Measured value characteristic: linear

Repeatability: ≤ ± 0.03 % O2

Zero point drift: ≤ ± 0.05 % O2 / week (offset)

Sensitivity drift: < 0.5 % of measured value per week

Temperature influence

Zero point < ± 0.01 % O2 /°C

Sensitivity < ± 0.025 % of measured value / °C

Detection threshold: 0.01 % O2 Air pressure effect: 1% air pressure change causes 1% change in reading

AMBIENT CONDITIONS

Ambient temperature: +5 °C to +45 °C

Transport and storage temp.: -25 °C to +65 °C

Relative humidity: ≤ 75% as annual average

THERMO MAGNETIC OXYGEN ANALYZEr

Basic Principle: -

The instrument utilizes the effect called Currie’s law according to which the magnetic susceptibility decreases with increasing temperature. The relevant Currie’s law is given by-

XP= k/(T-θ)

Where, XP = Paramagnetic susceptibility

T = Absolute Temperature

K & θ are constants

CONSTRUCTION:-

-It consists of a ring, middle of which lies a horizontal glass tube.-This horizontal glass tube tube houses two wound resistors which form two arms of a bridge.-One of the wound resistor is placed between the two pole pieces of magnet and current flow through the resistors so that they produced heat.-in absence of oxygen the wound resistors are heated to some extent and the bridge to which they are connected remains balanced.

OPERATION:-

In absence of oxygen, the wound resistors are heated to some extent

& the bridge remains balanced.

When sample gas enters, it is attracted towards pole-pieces.

In consequence, it gets heated& loses its paramagnetic property.

Then nearest cold gas on the left pushing the hot gas to the right.

Thus the left resistor becomes colder than right one & bridge becomes unbalanced.

The bridge unbalanced current will be proportional to the % of oxygen in the sample gas.

APPLICATION:-

Thermo magnetic oxygen analyzer , used for continuous analyzing oxygen concentration automatically, It not only applied in the power plant, cement workshop, chemical plant ,metallurgy etc whereas the process control system, also applied as monitoring instrument for the hospital.

ADVANTAGES: - 1) Scale is almost linear.

2) In comparison to paramagnetic method, it is rugged in design. 3) The construction of hot wire is also critical.

DISADVANTAGES :-1) the measurement is generally affected by the ambient temperature change, pressure, viscosity,

Thermal conductivity of the constituent gases. 2) High temperature can also cause stability & reliability problems.

3) The construction of hot wire is also critical.

The sample Gas should meet the following conditions---

a. Humidity :< 85%.

b. Dust:<=0.01g/m3

c. Causticity:(SO2,H2S,NH3...)< 0.005%

d. Temperature: +5-50 C

e. Flow: 0.5-1L/min

ZIRCONIA OXYGEN ANALYZER

BASIC MEASURING PRINCIPLE:

The type of oxygen analyzer that uses this type of oxygen sensor is occasionally referred to as the “high temperature” electrochemical sensor and is based on the Nernst principle [W. H. Nernst (1864-1941)].

The Nernst equation:-

Cell output = 2.303RT/nF(log P1/ P2)

Where:-

R = molar gas constant

T = absolute temperature of cell in Kelvin

F = Faraday constant

P1 = partial pressure of oxygen in the reference gas (air in most cases)

P2 = partial pressure of oxygen in the sample

n=no. Of electrons involved in the reaction

. CONSTRUCTION:-

-This is an electrochemical method and potential is derived from a pair of electrode across a zirconia cell gives a measure of oxygen when the two sides of the cell are flushed with a measuring gas and a reference gas respectively.-The electrolyte is a solid zirconium oxide ceramic material which is a sandwiched between two porous Platinum Electrodes.-The cell is housed in a furnace that is maintained at about 750- 800 degree cecious.

OPERATION:-

-At 746 deg temperature, on a molecular basis, the zirconium lattice becomes porous, allowing the movement of oxygen ions from a higher concentration of oxygen to a lower one, based on the partial pressure of oxygen.-To create this partial pressure differential, one electrode is usually exposed to air (20.9% oxygen) while the other electrode is exposed to the sample gas. -The movement of oxygen ions across the zirconium oxide produces a voltage between the two electrodes, the magnitude

of which is based on the oxygen partial pressure differential created by the reference gas and sample gas.

-The electrode in contact with gas which has higher partial pressure of O2 acts as a ‘–ve’ electrode (Pr) & lower partial pressure of O2 acts as a ‘+ve’ electrode (Pm).-In ‘ –ve’ electrode, O2 molecules in the gas acquires electrons & becomes ions.-Moving in the zirconia element, they arrive at the positive electrode & the electrons are released & the ions are return to the O2 molecules.-This reaction is indicated as follows:

Negative Electrode: O2+4e 2O2-

Positive Electrode: 2O2- O2 + 4e

- As a result an emf generates between two electrode. This emf is inversely proportional to % of O2 present in the flue gas .

ADVANTAGES: -

1) It does not require sampler.

2) It has relatively much fast response.

3) Warm-time is also less than paramagnetic & Zirconia type.

4) Operating temperature range is very wide.

DISADVANTAGES:-

1) A major limitation of the zirconium oxide oxygen analyzer is their unsuitability for trace oxygen measurements when reducing gases (hydrocarbons of any species, hydrogen, and carbon monoxide) are present in the sample gas

2) Operation is affected due to presence of combustible gases like H2, CH4, CO.

3) Scale is not linear.

GENERAL PRECAUTIONS FOR USE

Zirconia oxygen analyzers ordinarily operate at a high temperature close

to 800°C (700°C, in the case of Toray). Therefore, please be aware that

measurement may be impossible, or there may be adverse effects on

sensor service life, in the following situations.

1. Oxygen analyzers cannot be used if the set-up atmosphere is an

explosion-proof zone.

2. If the measured gas contains flammable gas (i.e. methane,

alcohol, carbon monoxide), it will cause a combustion reaction, and

result in measurement error.

3. Organic silica (used in sealing compounds etc.) will cause sensor

degradation. (Our company's findings indicate that this is the leading

cause of degradation.)

4. The sensor may degrade if the measured gas contains corrosive

gas (i.e. fluorine-based gases, chlorine-based gases, sulfate-based

gases) or poisonous substances (i.e. Si, Pb, P, Zn, Sn).

5. If the measured gas intermittently contains a substance such as

carbon monoxide with a high calorific value, the sensor will accumulate a

heat history, and this will cause sensor malfunction due to problems

such as platinum electrode peeling.

6. If the measured gas contains large amounts of NOX, SOX or other

corrosive gas, this will cause sensor malfunction due to problems such

as platinum electrode peeling.

7. At high temperatures, Freon gas will cause an unpredictable

reaction with oxygen, and this may result in measurement error.

8. Water droplets, dust and mist will damage the sensor, shorten its

service life, and cause errors.

9. In general, these analyzers cannot be used with closed loops

(circulating systems) unless they are specially designed for that purpose.

The sensor may be damaged by excess pressure.

DISSOLVED OXYGEN GALVANIC CELL

While some gases like Nitrogen and Ammonia chemically react with water, other gases like Oxygen do not react with water at all. Dissolved Oxygen can be defined as physical distribution of oxygen in water. The main sources of dissolved oxygen in water are the atmosphere and

photosynthesis. Waves and flowing water mix the air and water while aquatic plants produce oxygen as a by-product during photosynthesis.

The amount of dissolved oxygen that can be present mainly depends on the water temperature, salinity and atmospheric pressure. Additionally, the amount of dissolved oxygen can increase with a decrease in temperature of the water and can increase with an increase in atmospheric pressure.

WHAT IS DISSOLVED OXYGEN (DO) METER?

A dissolved oxygen meter is used to measure the amount of oxygen present in a unit volume of water. Now the next question that arises is, why do I need to measure the quantity of oxygen in water? This is because it indicates if the water is useful for a specific application like water treatment plants, sewage treatment works, river monitoring and

Importance of this-

The life of animals and plants is dependent on their energy, which is obtained when their food is oxidized and decomposed with atmospheric oxygen. Thus, oxygen is indispensable to life. The life of aquatic animals and plants is similarly dependent on dissolved oxygen. Thus, dissolved oxygen is critical for living organisms. This means that the life of aquatic animals and plants is greatly affected by the concentration of dissolved oxygen. Therefore, water with a low concentration of dissolved oxygen is considered to be dirty.

MEMBRANE-TYPE DISSOLVED OXYGEN ELECTRODES USING A GALVANIC CELL

The theory of operation of the dissolved oxygen galvanic cell is the same for gaseous samples. The main area of difference is in the nature of applications. The majority of the dissolved oxygen analyzer are placed in dirty water and therefore they require special cleaners, agitators & specialized sample system.

CONSTRUCTION & WORKING:-

The membrane-type dissolved oxygen electrodes using a galvanic cell are configured as illustrated below-

- The working electrode uses a noble metal (Pt), and the opposite electrode uses Ag. For the electrolyte, a potassium chloride solution is used, and for the membrane, a Teflon membrane is used.

- In this case, no external voltage is applied, the reaction is spontaneous.

-The oxygen which has passed through the membrane is reduced with the working electrode.

- A reduction current in proportion to the dissolved oxygen is generated, and then the dissolved oxygen is measured.

• Oxygen diffusing into the sensor is reduced to hydroxyl ions at the cathode:

O2 + 2H2O + 4e- ----> OH- 

• Hydroxyl ions in turn oxidize the lead (or zinc) anode:

2Pb + 4OH ----> 2PbO + 2H2O +4e-

• This yields an overall cell reaction of:

2Pb + O2 ----> 2PbO

USES OF DISSOLVED OXYGEN METER

Some of the industrial uses of a dissolved oxygen meter are:

• Analysis of boiler feed water for industries • Waste water treatment plants • Pollution control in rivers and lakes • Ionic concentration measurement for pharmaceutical companies

Uses of Oxygen Analyzer

Oxygen analyzers are used for combustion monitoring and keeping a control over it in a range of applications and help the industries to achieve considerably in saving energy. The applications of oxygen analyzers vary from energy-consuming industries to various combustion facilities. It is used in industries such as iron and steel, electric power, oil and petrochemicals, ceramics, pulp and paper, food and textiles and in facilities such as incinerators and small or medium-sized boilers. Besides, monitoring and controlling the analyzer also helps in lowering the amount of carbon dioxide, Sulfur dioxide and Nitrogen oxides in the emissions by resisting the incomplete combustion of fuel, therefore preventing the world from global warming and air pollution.

CONCLUSION

REFERENCES

Introduction to Measurements & Instrumentation – A.K Ghosh

Industrial Instrumentation- D Patranabis

Process Measurement & Analysis – B.G. Liptak