Measurement of Non-Electrical Quantities Short notes | Sensor & Industrial Instrumentation - Electronics and Communication Engineering (ECE) PDF Download

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1 Measuremen t of Non-Electrical Quan tities
1.1 In tro duction
Non-electrical quan tities, suc h as temp erature, pressure, flo w, and displacemen t, are crit-
ical in industrial pro cesses. Sensors and transducers con v ert these quan tities in to measur-
able electrical signals for monitoring and con trol in industrial instrumen tation systems.
1.2 Key Non-Electrical Quan tities and Measuremen t T ec hniques
1.2.1 1. T emp erature Measuremen t
T emp erature is measured using sensors lik e thermo couples, resistance temp erature detec-
tors (R TDs), and thermistors.
• Thermo couple: Op erates on the Seeb ec k effect, generating a v oltage prop ortional
to the t emp erature difference b et w een t w o junctions.
– F orm ula: V = a(T
1
-T
2
) , whereV is the v oltage, a is the Seeb ec k co e?icien t,
and T
1
,T
2
are junction temp eratures.
• R TD: Resistance c hanges linearly with temp erature, t ypically using platin um (Pt100).
– F orm ula: R
t
= R
0
[1+a(T-T
0
)] , whereR
t
is resistance at temp eratureT , R
0
is resistance at reference temp erature T
0
, and a is the temp erature co e?icien t.
• Thermistor: Non-linear resistance c hange with temp erature, suitable for narro w
ranges.
– F orm ula: R
T
= R
T
0
e
ß
(
1
T
-
1
T
0
)
, where ß is the material constan t, and T,T
0
are
temp eratures in Kelvin.
1.2.2 2. Pressure Measuremen t
Pressure sensors include strain gauges, piezo electric sensors, and capacitiv e sensors.
• Strain Gauge: Measures pressure-induced strain via resistance c hange.
– F orm ula:
?R
R
= GF·? , where
?R
R
is the fractional resistance c hange, GF is the
gauge factor, and ? is the strain.
• Piezo electric Sensor: Generates v oltage prop ortional to applied pressure.
– F orm ula: V = g·P·t , where V is v oltage, g is the piezo electric co e?icien t, P
is pressure, and t is the thic kness of the material.
• Capacitiv e Sensor: Detects pressure b y c hanges in capacitance due to diaphragm
deflection.
– F orm ula: C =
?
0
?
r
A
d
, whereC is capacitance, ?
0
is p ermittivit y of free space, ?
r
is relativ e p ermittivit y , A is plate area, and d is the distance b et w een plates.
1.2.3 3. Flo w Measuremen t
Flo w rate is measured using differen tial pressure devices, turbine flo w meters, or electro-
magnetic flo w meters.
1
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1 Measuremen t of Non-Electrical Quan tities
1.1 In tro duction
Non-electrical quan tities, suc h as temp erature, pressure, flo w, and displacemen t, are crit-
ical in industrial pro cesses. Sensors and transducers con v ert these quan tities in to measur-
able electrical signals for monitoring and con trol in industrial instrumen tation systems.
1.2 Key Non-Electrical Quan tities and Measuremen t T ec hniques
1.2.1 1. T emp erature Measuremen t
T emp erature is measured using sensors lik e thermo couples, resistance temp erature detec-
tors (R TDs), and thermistors.
• Thermo couple: Op erates on the Seeb ec k effect, generating a v oltage prop ortional
to the t emp erature difference b et w een t w o junctions.
– F orm ula: V = a(T
1
-T
2
) , whereV is the v oltage, a is the Seeb ec k co e?icien t,
and T
1
,T
2
are junction temp eratures.
• R TD: Resistance c hanges linearly with temp erature, t ypically using platin um (Pt100).
– F orm ula: R
t
= R
0
[1+a(T-T
0
)] , whereR
t
is resistance at temp eratureT , R
0
is resistance at reference temp erature T
0
, and a is the temp erature co e?icien t.
• Thermistor: Non-linear resistance c hange with temp erature, suitable for narro w
ranges.
– F orm ula: R
T
= R
T
0
e
ß
(
1
T
-
1
T
0
)
, where ß is the material constan t, and T,T
0
are
temp eratures in Kelvin.
1.2.2 2. Pressure Measuremen t
Pressure sensors include strain gauges, piezo electric sensors, and capacitiv e sensors.
• Strain Gauge: Measures pressure-induced strain via resistance c hange.
– F orm ula:
?R
R
= GF·? , where
?R
R
is the fractional resistance c hange, GF is the
gauge factor, and ? is the strain.
• Piezo electric Sensor: Generates v oltage prop ortional to applied pressure.
– F orm ula: V = g·P·t , where V is v oltage, g is the piezo electric co e?icien t, P
is pressure, and t is the thic kness of the material.
• Capacitiv e Sensor: Detects pressure b y c hanges in capacitance due to diaphragm
deflection.
– F orm ula: C =
?
0
?
r
A
d
, whereC is capacitance, ?
0
is p ermittivit y of free space, ?
r
is relativ e p ermittivit y , A is plate area, and d is the distance b et w een plates.
1.2.3 3. Flo w Measuremen t
Flo w rate is measured using differen tial pressure devices, turbine flo w meters, or electro-
magnetic flo w meters.
1
• Differen tial Pressure (Orifice Plate): Flo w causes a pressure drop across a restric-
tion.
– F orm ula: Q = C
d
A
v
2?P
?
, where Q is flo w rate, C
d
is disc harge co e?icien t, A
is orifice area, ?P is pr essure drop, and ? is fluid densit y .
• Electromagnetic Flo w Meter: Measures flo w of conductiv e fluids using F arada y’s
la w.
– F orm ula: E = B·v·d , whereE is induced v oltage, B is magnetic field strength,
v is fluid v elo cit y , and d is pip e diameter.
1.2.4 4. Displacemen t Measuremen t
Displacemen t is measured using linear v ariable differen tial transformers (L VDT) or ca-
pacitiv e sensors.
• L VDT: Pro duces a v oltage prop ortional to the displacemen t of a core within a coil.
– F orm ula: V
out
= k·x , where V
out
is output v oltage, k is sensitivit y , and x is
displacemen t.
• Capacitiv e Sensor: Detects displacemen t via c hanges in capacitance.
– F orm ula: Same as pressure capacitiv e sensor, adjusted for displacemen t af-
fecting d .
1.3 Sensor Characteristics
• Sensitivit y: Change in output p er unit c hange in input (e.g.,?V/?T for temp era-
ture).
• Linearit y: Degree to whic h output is prop ortional to input.
• Range: Minim um to maxim um measurable v alues.
• A ccuracy: Closeness of measured v alue to true v alue.
1.4 Industrial Applications
• T emp erature: Used in HV A C, man ufacturing, and c hemical pro cesses.
• Pressure: Applied in h ydraulic systems and gas pip elines.
• Flo w: Critical in w ater treatmen t and oil refineries.
• Displacemen t: Used in rob otics and structural monitoring.
1.5 Conclusion
A ccurate measuremen t of non-electrical quan tities relies on selecting appropriate sensors
and understanding their principles. Calibration and en vironmen tal considerations ensure
reliable p erformance in industrial instrumen tation.
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