Measurement of Temperature & Flow Short notes | Sensor & Industrial Instrumentation - Electronics and Communication Engineering (ECE) PDF Download

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Measuremen t of T emp erature
T emp erature measuremen t is critical in industrial pro cesses, relying on v arious sensors
and principles to ensure accuracy . Common metho ds include:
• Thermo couples : Op erate on the Seeb ec k effect, where a v oltage is generated due
to a temp erature difference b et w een t w o dissimilar metals. F orm ula : E = a?T ,
where E is t he electromotiv e force, a is t he Seeb ec k co e?icien t, and ?T is the
temp era ture difference.
– A dvantages : Wide range, rugged, cost-effectiv e.
– Limitations : Nonlinear output, requires reference junction comp ensation.
• Resistance T emp erature Detectors (R TDs) : Use the principle that a metal’s
resistance c hanges with temp erature. Platin um (Pt100) is common. F orm ula :
R
t
= R
0
(1+a?T) , where R
t
is resistance at temp erature T , R
0
is resistance at
reference temp erature, and a is the temp erature co e?icien t.
– A dvantages : High accuracy , stable.
– Limitations : Higher cost, slo w er resp onse.
• Thermistors : Semiconductor-based, with resistance v arying significan tly with
temp erature. F orm ula : R = R
0
e
ß(1/T-1/T
0
)
, where ß is the material constan t,
T is absolute temp erature (Kelvin), and R
0
is resistance at reference temp erature
T
0
.
– A dvantages : High sensitivit y , compact.
– Limitations : Nonlinear, limited range.
• Infrared Pyrometers : Measure temp erature remotely b y detecting thermal radi-
ation. F orm ula : Stefan-Boltzmann La w, P =?sAT
4
, where P is radiated p o w er,
? is emissivit y , s is the Stefan-Boltzmann constan t, A is surface area, and T is
absolute temp erature.
– A dvantages : Non-con tact, suitable for mo ving ob jects.
– Limitations : Affected b y emissivit y and en vironmen tal factors.
Measuremen t of Flo w
Flo w measuremen t is essen tial for monitoring fluid mo v emen t in industrial systems. Com-
mon tec hniques include:
• Differen tial Pressure Flo w Meters : Measure flo w b y creating a pressure drop
across a constriction (e.g., orifice plate, v en turi). F orm ula : Q=C
d
A
v
2?P
?
, where
Q is v olumetric flo w rate, C
d
is the disc harge co e?icien t, A is the cross-sectional
area, ?P is the pressure drop, and ? is fluid densit y .
– A dvantages : Simple, widely used.
– Limitations : Pressure loss, main tenance required.
1
Page 2


Measuremen t of T emp erature
T emp erature measuremen t is critical in industrial pro cesses, relying on v arious sensors
and principles to ensure accuracy . Common metho ds include:
• Thermo couples : Op erate on the Seeb ec k effect, where a v oltage is generated due
to a temp erature difference b et w een t w o dissimilar metals. F orm ula : E = a?T ,
where E is t he electromotiv e force, a is t he Seeb ec k co e?icien t, and ?T is the
temp era ture difference.
– A dvantages : Wide range, rugged, cost-effectiv e.
– Limitations : Nonlinear output, requires reference junction comp ensation.
• Resistance T emp erature Detectors (R TDs) : Use the principle that a metal’s
resistance c hanges with temp erature. Platin um (Pt100) is common. F orm ula :
R
t
= R
0
(1+a?T) , where R
t
is resistance at temp erature T , R
0
is resistance at
reference temp erature, and a is the temp erature co e?icien t.
– A dvantages : High accuracy , stable.
– Limitations : Higher cost, slo w er resp onse.
• Thermistors : Semiconductor-based, with resistance v arying significan tly with
temp erature. F orm ula : R = R
0
e
ß(1/T-1/T
0
)
, where ß is the material constan t,
T is absolute temp erature (Kelvin), and R
0
is resistance at reference temp erature
T
0
.
– A dvantages : High sensitivit y , compact.
– Limitations : Nonlinear, limited range.
• Infrared Pyrometers : Measure temp erature remotely b y detecting thermal radi-
ation. F orm ula : Stefan-Boltzmann La w, P =?sAT
4
, where P is radiated p o w er,
? is emissivit y , s is the Stefan-Boltzmann constan t, A is surface area, and T is
absolute temp erature.
– A dvantages : Non-con tact, suitable for mo ving ob jects.
– Limitations : Affected b y emissivit y and en vironmen tal factors.
Measuremen t of Flo w
Flo w measuremen t is essen tial for monitoring fluid mo v emen t in industrial systems. Com-
mon tec hniques include:
• Differen tial Pressure Flo w Meters : Measure flo w b y creating a pressure drop
across a constriction (e.g., orifice plate, v en turi). F orm ula : Q=C
d
A
v
2?P
?
, where
Q is v olumetric flo w rate, C
d
is the disc harge co e?icien t, A is the cross-sectional
area, ?P is the pressure drop, and ? is fluid densit y .
– A dvantages : Simple, widely used.
– Limitations : Pressure loss, main tenance required.
1
• Electromagnetic Flo w Meters : Based on F arada y’s La w, where a v oltage is
induced b y a conductiv e fluid mo ving through a magnetic field. F orm ula : E =
BvD , whereE is the induced v oltage,B is magnetic field strength, v is fluid v elo cit y ,
and D is pip e diameter.
– A dvantages : No mo ving parts, suitable for conductiv e fluids.
– Limitations : Not for non-conductiv e fluids.
• Ultrasonic Flo w Meters : Use sound w a v es to measure flo w v elo cit y . T ransit-
time or Doppler metho ds are common. F orm ula (T ransit-Time) : v =
L(t
2
-t
1
)
2t
1
t
2
cos?
,
where v is flo w v elo cit y , L is path length, t
1
and t
2
are upstream and do wnstream
transit times, and ? is the angle of the sound path.
– A dvantages : Non-in v asiv e, accurate.
– Limitations : Sensitiv e to fluid prop erties.
• T urbine Flo w Meters : Measure flo w b y coun ting the rotations of a turbine
placed in the fluid stream. F orm ula : Q=kf , where Q is flo w r ate, k is the meter
constan t, and f is the frequency of turbine rotations.
– A dvantages : High accuracy for clean fluids.
– Limitations : W ear in mo ving parts, not for viscous fluids.
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