Analytical Instrumentation Lecture Notes

Irradiance vs intensity vs luminance

2023-05-09T02:59:00.004-07:00

Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls within a given solid angle.

Illuminance is the total luminous flux incident on a surface, per unit area.[1] It is a measure of how much the incident light illuminates the surface, wavelength-weighted by the luminosity function to correlate with human brightness perception.[2] Similarly, luminous emittance is the luminous flux per unit area emitted from a surface. Luminous emittance is also known as luminous exitance.[3][4]

Irradiance: The amount of energy incident on a given area of a surface in a given amount of time (W/m2).

Irradiance is the radiometry term for the power per unit area of electromagnetic radiation incident on a surface. The SI unit for irradiance is watts per square meter [W/m2], or milliwatts per square millimeter [mW/mm2]. (Irradiance is sometimes called intensity, but this usage leads to confusion with another standard, but infrequently used, radiometry unit —Radiant Intensity — which is measured in watts per steradian.)

If a point radiation source emits radiation uniformly in all directions and there is no absorption, then the irradiance drops off in proportion to the distance squared from the source, since the total power is constant and it is spread over an area that increases with the distance squared from the radiation source. To compare the irradiance of different sources, one must take into account the distance from the source. A 50 cm distance is often used for such measurements.

Irradiance is a useful measure for applications where power must be delivered to large areas. For example, illuminating a classroom or a football field is primarily a question of delivering a certain number of watts per square meter. This can be achieved by using a single high power source. However, since irradiance does not depend on solid angle, multiple sources can be combined, illuminating the walls or the field from different angles.

The irradiance of a source is not the most useful measure when designing an efficient optical coupling system that collects radiation from a source, and then delivers the radiation into an optical instrument. Such optical instruments will have a limited entrance aperture and a limited acceptance solid angle. In such cases it is the radiance of the source (its ‘brightness’) that is most useful.

Radiance: The amount of energy scattered in a particular direction (W/m2/sr).

The SI unit of radiance is watts per square meter per steradian [W/m2-sr]. Since many radiation sources used in laboratories have emitting area in the square millimeters range, the unit of milliwatts per square millimeter per steradian [mW/mm2-sr] is often used for radiance. As shown in Figure 1, the radiance (R) of the source emitting area (A) equals the radiation power (P), which is emitted from A and propagates in solid angle Ω, divided by the area A and the solid angle Ω: R = P / (A x Ω).

Tech-understanding-radiance-image

Figure 1. (left) Radiance (R) of source is the Power (P) emitted from the source emitting Area (A) and propagated in the Solid Angle (Ω).

The steradian [sr] is the SI unit for measuring solid angles, defined by the solid angle (Ω) that projects on the surface of a sphere with a radius of r, having an area (A) equal to r2 (Ω = A/r2 = r2/r2 = 1 [sr]). It describes angular spans in three-dimensional space, analogous to the way in which the radian [rad] describes angles in a two-dimensional plane. The total solid angle for a point in space is 4π steradians.

Steradian

Figure 2. (left) Steradian [sr] is a unit for measuring solid angles (Ω) defined by the solid angle that projects on the surface of a sphere, with a radius of r, having an area of A = r2 (Ω = A/r2 = r2/r2 = 1 [sr]).

The radiance of a source is increased by increasing its emitted power, by making the emitting area of the source smaller or by emitting the radiation into a smaller solid angle. Strictly speaking, radiance is defined at every point on the emitting surface, as a function of position, and as a function of the angle of observation. Often, as in the example above we use radiance of a source to mean the radiance averaged over a finite sized aperture and over some solid angle of interest.

Radiance is a conserved quantity in an optical system so that radiance measured as watts per unit area per unit solid angle incident on a detector will not exceed the radiance at the emitter. In practice, for any bundle of rays mapping an emitter to a detector, the radiance seen at the detector will be diminished by the light which is absorbed along the way or scattered out of the solid angle of the bundle of rays reaching the detector.

Let us consider an example. Suppose one observes with the eye a 35W Xenon (Xe) short-arc lamp, and then a 60W straight tube fluorescent lamp, both at a similar distance of a few meters. (As background information, the 35W arc lamp emits significantly less visible power than the 60W fluorescent tube.) Which light source is perceived to be brighter, or in radiometric terms, has higher radiance? The Xe short-arc lamp is perceived to be much brighter, although the 35W arc lamp emits less power than the 60W fluorescent lamp. This is as a result of the much smaller emitting area (A) of the short-arc lamp compared to the very large emitting area of the fluorescent lamp, while the eye is receiving the radiation at more or less the same solid angle (Ω) when the distance between the eye and the source is the same. The eye’s lens forms a bright image of the Xe arc on a very small area of the retina and the eye does not feel comfortable. The larger area fluorescent lamp will form an image over a much larger area on the retina, which the eye can tolerate more comfortably. The arc-lamp has a much higher radiance than the fluorescent lamp, even though it emits less power.

By way of a further example, imagine using the Xe and fluorescent lamps to illuminate a small area such as the end of a 200 μm diameter optical fiber. As a result of the higher source radiance the radiation from the 35W Xe arc-lamp can be much more efficiently collected and focused into the fiber. In contrast, the low radiance 60W fluorescent lamp will be ineffective in coupling its radiation energy into the fiber, no matter what type of focusing optic is used.

Energetiq’s Laser-Driven Light Sources have ultrahigh radiance from their small emitting area (~ 100 μm diameter). Radiation from such a high radiance and small emitting area source can be even more efficiently coupled into the 200 μm diameter optical fiber described above. This is also true for other optical systems with small apertures and a limited accepting solid angle - optical systems with small ‘étendue’ - such as the narrow slits of a monochromator. (For further discussion of étendue, see Application Note #002-2-14-2011, Etendue and Optical Throughput Calculations.)

Radiant flux is radiant energy per unit time, also called radiant power [W, mW or μW]. Radiant flux is often used to describe the radiation power output of a radiation source, or the radiation power received by an optical instrument. Examples of radiant flux are: the radiation power passing through a pinhole; the radiation power emerging from the optical fiber of a fiber-coupled laser; the radiation power received by a power detector.

Non-standard terms such as brightness, radiant power, flux, and intensity

Radiance, Irradiance and Radiant Flux,

1. NonStandard

2. Photometry terms

3. Radiometry terms

SI photometry quantities
v
t
e
Quantity		Unit		Dimension	Notes
Name	Symbol^{[nb 1]}	Name	Symbol	Symbol^{[nb 2]}	Notes
Luminous energy	Q_v^{[nb 3]}	lumen second	lm⋅s	T J	The lumen second is sometimes called the talbot.
Luminous flux, luminous power	Φ_v^{[nb 3]}	lumen (= candela steradian)	lm (= cd⋅sr)	J	Luminous energy per unit time
Luminous intensity	I_v	candela (= lumen per steradian)	cd (= lm/sr)	J	Luminous flux per unit solid angle
Luminance	L_v	candela per square metre	cd/m² (= lm/(sr⋅m²))	L⁻²J	Luminous flux per unit solid angle per unit projected source area. The candela per square metre is sometimes called the nit.
Illuminance	E_v	lux (= lumen per square metre)	lx (= lm/m²)	L⁻²J	Luminous flux incident on a surface
Luminous exitance, luminous emittance	M_v	lumen per square metre	lm/m²	L⁻²J	Luminous flux emitted from a surface
Luminous exposure	H_v	lux second	lx⋅s	L⁻²T J	Time-integrated illuminance
Luminous energy density	ω_v	lumen second per cubic metre	lm⋅s/m³	L⁻³T J
Luminous efficacy (of radiation)	K	lumen per watt	lm/W	M⁻¹L⁻²T³J	Ratio of luminous flux to radiant flux
Luminous efficacy (of a source)	η^{[nb 3]}	lumen per watt	lm/W	M⁻¹L⁻²T³J	Ratio of luminous flux to power consumption
Luminous efficiency, luminous coefficient	V			1	Luminous efficacy normalized by the maximum possible efficacy
See also: SI · Photometry · Radiometry

References:

https://www.energetiq.com/technote-understanding-radiance-brightness-irradiance-radiant-flux

What makes a object Transparent ?

2023-04-27T02:38:00.009-07:00

When a light beam passes through an object it goes through various light matter interactions.

1. Refraction

2. Absorption

3. Remission

And these processes explain why speed of light is slower in other mediums except vaccum

NDIR Revisited

2015-12-23T02:07:00.003-08:00

Long ago i had written a article on NDIR, that was a know how from the text books only now am working for last 3 years on High accuracy NDIR sensors. Now i have a lot to describe the same.

External links
NDIR Gas Sensors Explained, The Gas Detector Encyclopedia, Edaphic Scientific Knowledge Base
NDIR Gas Sensor Lamp Selection Application Notes
NDIR Technology for gasoline exhaust
NDIR detectors for CO&CO2 in internal combustion engine exhaust

MRI

2014-03-04T01:07:00.001-08:00

Oxygen Sensor (C)

2013-10-20T23:39:00.001-07:00

X-Ray Diffraction (XRD)

2013-09-22T06:23:00.001-07:00

Diffraction is

AUGER ELECTRON SPECTROSCOPY (AES)

2013-01-03T23:45:00.000-08:00

AUGER Electron Spectroscopy Should not be confused with Atomic emission Spectroscopy. AES is a popular method in material analysis.

The Auger effect is an electronic process at the heart of AES resulting from the inter- and intrastate transitions of electrons in an excited atom. When an atom is probed by an external mechanism, such as a photon or a beam of electrons with energies in the range of 2 KeV to 50 KeV, a core state electron can be removed leaving behind a hole. As this is an unstable state, the core hole can be filled by an outer shell electron, whereby the electron moving to the lower energy level loses an amount of energy equal to the difference in orbital energies. The transition energy can be coupled to a second outer shell electron which will be emitted from the atom if the transferred energy is greater than the orbital binding energy.An emitted electron will have a kinetic energy of:

where , , are respectively the core level, first outer shell, and second outer shell electron energies, measured from the vacuum level. The apostrophe (tic) denotes a slight modification to the binding energy of the outer shell electrons due to the ionized nature of the atom; often however, this energy modification is ignored in order to ease calculations.Since orbital energies are unique to an atom of a specific element, analysis of the ejected electrons can yield information about the chemical composition of a surface. Figure 1 illustrates two schematic views of the Auger process.

Figure 1. Two views of the Auger process. (a) illustrates sequentially the steps involved in Auger deexcitation. An incident electron creates a core hole in the 1s level. An electron from the 2s level fills in the 1s hole and the transition energy is imparted to a 2p electron which is emitted. The final atomic state thus has two holes, one in the 2s orbital and the other in the 2p orbital. (b) illustrates the same process using spectroscopic notation, .

Difference MRI NMR and ESR

2013-01-03T22:57:00.001-08:00

NMR = Nuclear Magnetic Resonance is the resonance that occurs when a nucleus (usually hydrogen, but any nucleus that has non-zero spin will work) is placed in a magnetic field and is 'swept' by a radio frequency that causes the nuclei to 'flip'. This causes the radio frequency to be absorbed, which is what is measured.

MRI = Magnetic Resonance Imaging is a more complex application of NMR in which the geometric source of the resonances are detected and deconvoluted by Fourier transform analysis.

ESR = Electron Spin Resonance is also a resonance phenomenon, except in this case it is the spin of an unpaired electron that is in resonance, rather than a nuclear spin.

So if you are NMR then it is only the resonance effect no imaging involved, NMR some times used in material analysis.

MRI is a imaging technique where as NMR and ESR both are methods used for material analysis, but NMRI (Nuclear Magnetic Resonance Imaging) is same as MRI the medical people just deleted the first word as it scares the patients.

Introduction to Chromatography

2012-03-13T02:14:00.003-07:00

Chromatography, ohh the editor showing me this as a error !! But i am sure u must be known to aleast to this word that u can say such a word exist. This is a common and simple instrument in analytical instrumentation.

The technique is used for analysis of available chemical components in a fluid(gas or liquid) mixture. The technique adopt several methods to separate the components and then detecting the concentration of each component.

A Sample Chromatogram

The output is graph with time in x-axis and concentarion of different components on the Y-axis

What is the Principle and the method ?

when a fluid is allowed to pass through some another fluid or solid tunnel, the rate of flow for the components of mixture will be different. So at the other end of the tunnel the components will reach at different time.(the medium or the column called separator).

OK now our job turned easy becoz we know which component will come out at which time( its called retention time). we have to detect the gas coming out at different time.

Why different retention time?

Now the questions is why these components(our analyte is a mixture of different molecules and ions). The prime cause is the average speed. Acording to kinetic theory the average speed of gas molecules will depend upon its molecular mass.

except this there are different processes invloved in side the chromatography column/channel. The molecules may be adsorbed on the columns inner surface temporarily and then released. this stick and release may happen many times before it comes out of the column.

The terminology

Now its time to get some terminology things. i hate these from the begining as these may confuse the reader.

The gas (or liquid) is passed through the tunnel(chromatography column) which contains some material called the stationary phase. Again the analyte mixture may not pass through itself so we need some truck(we call it carrier gas) it acts as the mobile phase.

Simply we may say the mobile phase+analyte mixture is passed through the stationary phase which causes the separation of components. Separation caused by differntial partiotioning, selective adsorption, selective ion exchange...etc.

Scintillation, luminescence, Fluorescence & Phosphorescence

2012-03-04T22:22:00.003-08:00

All these three are used in instrumentation engineering. But is this all are the same, what is the relation, similarity or difference between these processes.

florescence means absorbing energy in some higher energy or higher frequency band end emit in lower band.

luminescence is the type radiation from a cold body. here the excitation of the molecules must be by some other method than heating.

Scintillation is when the material is excited by some radiation and give out some emission in lower band(visible range)

X-Ray Detectors

2012-03-01T19:31:00.004-08:00

These Detectors are categorised into two main classes depending on their application 1) Imaging, 2) Dose measurement, except this some Analytical instruments use these detectors.
Photographics plates are the simplest type of detector. Plates Coated with photosensitive chemical (silver halides) when exposed to Xray decomposes to form silver Metal. Now photographic plate type detectors replaced by semiconductor detectors both for imaging and analytical instruments (XRD).

X-Ray Gas Detectors are same as the radiation detectors used for detection of neutral (chargeless particle) radiation detectors.

These are categorised as following

Gas Ionization Chamber
Solid State detectors
Scintillators
Scintillator Solid state Detectors

Gas Filled Detectors / Gas Ionization Chamber
Gas ionisation chambers are generally a tubular structure in which a gas placed between two electrons allowed to be exposed to the radiation. which in turn ejects out an electron from the gas atoms shells giving a charge particle (ionised gas atom). This ion can now be drifted by the electric field. The ion is collected at the anode(+ve) so producing a pulse of current in circuit.

Geiger Muller Tube

Ionisation Chamber, proptional Counter and Geiger Muller Couter are usable for Xray detection.

X-Ray Methods in Analytical instruments

2012-03-01T07:12:00.007-08:00

What is X-Ray ?

X-Ray is an electromagnetic wave with frequency 3x10E16Hz to 3x10E19 Hz or in wavelength scale 0.01 to 10 nano meters i.e. shorter than UV and longer than gamma radiation. In energy scale 120eV to 120 KeV. these are em waves with High penetrating Power.

What are the Properties useful for Us?

Penetration power: this ray can penetrate deep into metals atteneuting throughout. So can used probe into solid blocks.

optical Resolution: as per raleigh criterion the resloution of an optical microscope increases with decrease in wavelength and these are em waves with lowest wavelength.

Diffraction:Wavelength suitable for crystalography. The planes of crystals produce a diffraction pattern when radiation of suitable wavelength target on it. the xray wavelength suitable for this.

as pern barggs equation

2dsin(theta)=n x Lambada

Spectroscopic Analysis: The emission / absorption is not just a single line or just a single band. It is a set of quantized bands. Now you can say then sodium(Na) has only two lines 589.0 and 589.6 nm , yes it is true if you are looking only at the visible spectra.

there are more spectras which belongs to transition other than 3p1/2->3s1/2(589nm) and 3p3/2->3s1/2(589.6nm).

We have more no of spectra for most of the elements in X-ray region.

What are the classes ?

These rays are categorised according to penetrability through matter. Hard Xrays (12ev to 120Kev)/0.1 to 0.01nm wavelength. and soft xrays (0.12 to 12KeV)/(10->0.1nm).

These are sometimes also classified as per the method of generation or its spectrum.

Continuous / white X-ray

Discrete / Characteristic X-ray

Generation Methods:

There are two methods two generate x-ray based on two physics processes.

Flouroscence: when a high energy photon stikes a electron it ejects out the electron from the shell leaving a blank space. That blank space filled by a electron from upper shell which means dexcitation of the electron so there is a emission of a photon.

Bremhallstrahlung: This is radiation given off by the electrons as they are scattered by the strong electric field near the high-Z (proton number) nuclei. These X-rays have a continuous spectrum. The intensity of the X-rays increases linearly with decreasing frequency, from zero at the energy of the incident electrons, the voltage on the X-ray tube.

So the resulting output of a tube consists of a continuous bremsstrahlung spectrum falling off to zero at the tube voltage, plus several spikes at the characteristic lines.

X-ray Generation Techniques:

X-ray is generated by X-ray tubes. I have diagram of the two oldest tubes and the commercial tube. The basic design is same as we have to achieve the process "bombardment of high eneergy electron beam over some metal surface". The enhancements in this tube is

1) Enhancement of the cathode (use of filaments, use of isolated filament)

2) Use of cooling systems for anode.

3) Replaceable anode as the anode is continuously corroded.

4) Rotating anode tube

The output of the X-Ray tube is dependent on the enrgy of the electron beam, which in turn dependent on the electric field provided by the applied potential.

So the applied potential will be one key parameter for the output energy.

Another Key factor is the anode temperature, how much heat the anode can sustain,

only 0.05% of the electron beam is converted to x-Ray then what happen to rest part is converted to heat. So this amount of heat should be dissipiated in anyway otherwise our anode will melt down.

Figure 1. Schematic of an X-ray tube for X-ray diffraction analysis: (1) metallic anode block (usually grounded); (2) beryllium window for exit of X-radiation; (3) hot cathode; (4) glass envelope insulating the anode part of the tube from the cathode part; (5) cathode leads, to which the filament voltage and high (with respect to the anode) voltage are supplied; (6) electrostatic electron-focusing system; (7) anode (anticathode); (8) inlet and outlet pipes for the flowing water that cools the anode block

Do We Use Thorium The Radioactive Carcinogen

2012-02-26T20:54:00.002-08:00

Here in berhampur we have a Plant of DAE extracting rare earth materials from sea beach mud. The prime element is Thorium a radioactive element can be used as a nuclear fuel.

But the intresting fact is we are using it in home also. Yes that is inside the picture tube, in gas lamp mantels. In lab its with the Photo MultiPlier Tube (PMT), PMT is are inside almost every analytical instruments.

Why is it used in picture tube ?

Filaments in electronic tubes and television picture tubes have be coated in thorium oxides to produce electrons more easily

Radioactivity:

Thorium oxide coated gas lamp mantles used in ornamental gas lanterns and gas burning camping lamps are radioactive. The thorium oxide is chosen because it can be raised to white heat without decomposing. However, the mantle does become extremely fragile and will powder into a fine ash which can potentially be inhaled or ingested. Thorium is a natural alpha emitter with the potential for increasing lung tumors. Thorium disintegrates to produce radon-220, an alpha particle emitting radioactive gas.

A number of substances have been used as positive contrast agents: silver, bismuth, caesium, thorium, tin, zirconium, tantalum, tungsten and lanthanide compounds have been used as contrast agents. The use of thoria (thorium dioxide) as an agent was rapidly stopped as thorium causes liver cancer.

For conventional dynode materials, such as BeO and MgO, a multiplication factor of 10 can normally be achieved by each dynode stage.

Microchannel plate detector

Scanning Tunneling Microscope(STM) & Atomic Force Microscope (AFM)

2012-02-24T02:51:00.005-08:00

STM & AFM

Scanning Tunneling Microscope (STM)

These are devices 2D & 3D Surface analysis of Materials at micrometer resolution. Scanning Tunneling Microscopic is based upon the tunneling theory i.e. an electron may tunnel (or jump) through a barrier when the barrier is thin enough. So produces

an elctric current at the surface. If we can use a microtip probe. we can monitor the tunneling current profile in a 2D surface. Which will give a 2D picture of the atomic structure. But the necessary condition for the probe to get image at atomic scale is that the probe shou

ld be moved at such resolution.

Here comes the role of Piezo transducers, we have used steppers Servos for precison positioning but when the precison we need is of micrometer level we have the only option Piezo Transducers.

As we know Piezo materials produce Structurals change (expand or compress) in the axis of applied field. So for an X Y scan we can use two piezo plates or a single block and the probe at a corner. Commonly we use two piezo plates at two sides.

Some more PIC of AFM

References:

http://www.siint.com/en/products/spm/tec_descriptions/descriptions2_e.html

http://www.ieap.uni-kiel.de/surface/ag-kipp/stm/stm.htm

http://www.quasi.iastate.edu/hot.html

http://sxm4.uni-muenster.de/stm-en/STMElectronics.html (Making DIY STM)

http://www.stm.phas.ubc.ca/Science/Introduction-to-STM.html

http://www.foresight.org/UTF/Unbound_LBW/chapt_4.html

http://www.tutorialsweb.com/nanotech/page-6.htm

http://www.phys.ttu.edu/~tlmde/thesis/DESIGN_AND_CONSTRUCTION.html

http://www.physics.leidenuniv.nl/sections/cm/ip/Onderwijs/Scanning-Probe-Microscopy/Chapters/CHEN%20Chapter%209%20Piezoelectric%20scanner%20213-235.pdf

http://www.nanodic.com/Nanocharacterization/Atomic_Force_Microscopy.htm

http://chemwiki.ucdavis.edu/Wikitexts/UCD_Chem_205%3A_Larsen/ChemWiki_Module_Topics/How_an_FTIR_Spectrometer_Operates

ParaMagnetic Gas Analyser GA-2

2012-02-21T21:46:00.003-08:00

This method is primarily for oxygen content analysis. As the method described is suitable for paramagnetic gases its usable for few industrial gases.

Block Diagram Paramagnetic Gas Analyzer

This method is primarily for oxygen content analysis. As the method described is suitable for paramagnetic gases its usable for few industrial gases.

Relative volume magnetic Susceptibilty at 20deg celcius(Zero ref:Nitrogen, 100 ref O2)
Oxygen 100.00
Nitric Oxide 43.00
Air 23.50
Hydrogen 0.24
Carbon monoxide 0.01
Nitrogen 00.00
Nitrogen Oxide -0.20

References:
http://www.habmigern2003.info/suggestions/Problems/oxygen/Oxygen-sensors.html
http://www.fujielectric.com.cn/products/airanalyze/pdf/EDS3-125a.pdf
http://www.systechillinois.com/media/296bae86/paramag_98.PDF
http://www.systechillinois.com/en/paramagnetic-cells_54.html

GAS Analyser -1 (Thermal Conductivity Type)

2012-02-19T21:10:00.003-08:00

Thermal Conductivity of Gases different and unique for all. So this property can be used to distinguish gas concentrations in a mixture of gases.

Thermal conductivity of a mixture of gas

where is the thermal conductivity of jth gas whose concentration is ,

so that

from the above equations its confirmed that concentration of a gas in a mixture of gases can be determined from the change in thermal conductivity.

Now we have to make out some way to measure the change in thermal conductivity by addition of the gas in the mixture. So how to measure thermal conductivity of a gas.

Simple, let it conduct heat and see how fast is it conducting. So the arrangement is a hot body surrounded by cold wall and between the hot n cold bodies the media is the "gas mixture". The gas mixture will conduct heat from the hot body(an electrically heated filament) to the surrounding relatively cool walls.

Heat Gained by hot body=

Heat Lost By hot body= Convection Loss+Conduction Loss+ Radiation Loss

At thermal equilibrium heat loss=heat gained

Now we have to monitor temperature at thermal equilibrium

References:

http://www.systechillinois.com/en/thermal-conductivity_52.html

http://www.hitech-inst.co.uk/thermal_conductivity_sensors.php

GAS Analyser

2012-02-19T20:36:00.000-08:00

Gas Analysers are of different types based upon different techniques

1. Thermal Conductivity

2. Heat of Reaction

3. Para-magnetic

4. Selective Absorption

5. Electrochemical

6. Optical Spectroscopy(Emission, Absorption, Diffraction)

7. Opacity

8. Humidity & moisture

I will start with the Thermal Conductive Type Gas Analysers