Submitted to Prof. Y. J. Morabiya Prepared by: Solanki Akshay N. Enrollment No

1. Liquid-in-glass thermometres 2. Bimaterial thermometres 3. Electrical thermometres 4. IR-thermometres 5. Pyrometres 6. Summary 7. Other measurement methods

 The “traditional” thermometres  Measurement scale from -190 °C to +600 °C  Used mainly in calibration  Mercury: -39 °C … +357 °C  Spirit: -14 °C … +78 °C

 Method is based on the expansion of a liquid with temperature The liquid in the bulb is forced up the capillary stem  Thermal expansion:

 Temperature differences in the liquid  Glass temperature also affects  The amount of immersion (vs. calibration)

 Method based on different thermal expansions of different metals  Other metal expands more than other: twisting  Inaccurary ± 1 ° C  Industry, sauna thermometres

 Resistive thermometres  Resistivity is temperature dependent  Materials: Platinum, nickel

 Semiconductor materials  Based on the temperature dependence of resistance  Thermal coefficient non-linear, 10 times bigger than for metal resistor  NTC, (PTC): temperature coefficient’s sign

 Sensor cable’s resistance and its temperature dependency  Junction resistances  Thermal voltages  Thermal noise in resistors  Measurement current  Non-linear temperature dependencies  Electrical perturbations  Inaccuracy at least ± 0.1 °C

 Every atom and molecule exists in perpetual motion  A moving charge is associated with an electric field and thus becomes a radiator  This radiation can be used to determine object's temperature

 Waves can be characterized by their intensities and wavelengths  The hotter the object: the shorter the wavelength the more emitted light  Wien's law:

Magnitude of radiation at particular wavelength (λ) and particular temperature (T). h is Planck’s constant and c speed of light.

 An ideal emitter of electromagnetic radiation  opaque  non-reflective  for practical blackbodies ε = 0.9  Cavity effect  em-radiation measured from a cavity of an object

 Emissivity of the cavity increases and approaches unity  According to Stefan-Boltzmann’s law, the ideal emitter’s photon flux from area a is  In practice:

 For a single reflection, effective emissivity is  Every reflection increases the emyssivity by a factor (1-ε)

 Copper most common material  The shape of the cavity defines the number of reflections  Emissivity can be increased

 Quantum detectors  interaction of individual photons and crystalline lattice  photon striking the surface can result to the generation of free electron  free electron is pushed from valency to conduction band

 hole in a valence band serves as a current carrier  Reduction of resistance Photon’s energy

 Thermal detectors  Response to heat resulting from absorption of the sensing surface  The radiation to opposite direction (from cold detector to measured object) must be taken into account

 Disappearing filament pyrometer  Radiation from and object in known temperature is balanced against an unknown target  The image of the known object (=filament) is superimposed on the image of target

 The measurer adjusts the current of the filament to make it glow and then disappear  Disappearing means the filament and object having the same temperature

 Two-color pyrometer  Since emissivities are not usually known, the measurement with disappearing filament pyrometer becomes impractical  In two-color pyrometers, radiation is detected at two separate wavelengths, for which the emissivity is approximately equal

 The corresponding optical transmission coefficients are γ x and γ y Displayed temperature

 Stefan-Boltzmann’s law with manipulation:  Magnitude of thermal radiation flux, sensor surface’s temperature and emissivity must be known before calculation  Other variables can be considered as constants in calibration

 Errors in detection of the radiant flux or reference temperature  Spurious heat sources  Heat directly of by reflaction into the optical system  Reflectance of the object (e.g. 0.1) But does not require contact to surface measured!

 Generate electric charce in response to heat flux  Crystal materials  Comparable to piezoelectric effect: the polarity of crystals is re-oriented

 Only some temperature measurement methods presented  Examples of phenomenons used: thermal expansion, resistance’s thermal dependency, radiation  The type of meter depends on  Measurement object’s properties  Temperature

 Thermocouples  Semiconductor thermometres  Temperature indicators  Crayons etc.  Manometric (gas pressure) sensors