CCD Based Constant Deviation Spectrometer

(For Arc Emission & Absorption Measurements)

The apparatus uses CCD imaging instead of photographic silver halide films. It has become difficult to carry out silver halide film based spectroscopic experiments in class rooms due to the unavailability of consumables and hurdles in its processing. CCD imaging of the spectrum is a timely solution. Data acquisition is easy and fast. As most of the commercial spectroscopes are based on digital imaging, students get an exposure to the latest trends in spectroscopy.

Mercury is used as a standard element in most cases. Knowing the wavelength, corresponding to different spectral lines, elements can be judged. Hartmann's method is employed to determine the unknown wavelength.

If a transparent substance is placed between a continuous source and a spectrometer, the substance absorbs a certain part of the spectrum. Hence in the continuous spectrum of the source, a few dark lines or bands appear. This spectrum is called absorption spectrum of the substance. This method is useful for manufacturing as well as for academic experiments. Constant Deviation Spectrometer (Model No: HO-ED-S-0203) can be used for the study of spectral series viz. emission spectra of elements, absorption spectra of compounds, quantitative spectrum analysis etc.

When a substance is heated, electrons first absorb energy, go to a higher energy level and eventually fall to a lower level, by emitting photons. Every element emits a characteristic spectrum of its own. There are certain important and prominent spectral lines associated with each element. These lines are used to distinguish one element from another. In the experiment to determine an element, spectrum of standard known source is pictured first.

Experiment:

   To measure the wavelength of absorption bands of KMnO₄ and calculate it’s Hartmann's constant.

The positions of spectral lines are usually measured in the direction of increasing wavelength. The constant d depends on scale setting, C on the range of spectrum and is a constant for the instrument. To determine these constant, we take three prominent lines of standard spectrum and equations are,

A    =    (λ₂ – λ₁) / (λ₃ – λ₁)

B    =    (d₂ – d₁) / (d₃ – d₁)

C    =    [ (λ₂- λ₁) (d₀ – d₁) (d₀ – ₂) ] / (d₂ - d₁)

d₀    =    (B d₃ - A d₂) / (B - A)

λ₀    =    (Aλ₃ - B λ₂) / (A- B)

Where, A, B, C, λ₀, d₀ are called Hartmann’s constants.
Using these Hartmann’s constants, we can calculate the absorption band wavelength as

λ    =    λ₀ + [C / (d₀ - d)]

   To find wavelength of prominent lines of the emission spectra of copper, iron and brass.

The wave length of the corresponding lines of the arc spectrum can be calculated using the equation;

 

λ    =    λ₀ + [C / (d₀ - d)]

Specifications:

Optical Platform	Constant Deviation Spectrometer
Prism	Pellin Broca
Prism Material	N-SF1
Effective Spectral Range	380 nm to 750 nm
Spectral Resolution	0.1 nm
Accuracy	0.5 nm
Slit Options	Micrometer Controlled, Variable Slit (0 - 3 mm)
Stray Light	< 0.06 % @ 532 nm (< 0.1% overall )
Detector	Toshiba Linear CCD Array
Total Pixel Number	3648
Pixel Size	8 µm x 200 µm
Pixel Well Depth	100,000 electrons
Signal-to-Noise Ratio	1,000 : 1 (at full scale)
A/D Resolution	16 bit
Exposure Time	1.0 to 6,500 ms
Frame Rate	Upto 138 fps
Trigger Input	Yes (Optional)
PC Interface	USB 2.0
Software	Spectra QSR V2.26
Compatibility	Windows 7 or higher

Features: