Transducers

Dr Jahangir Ikram

What is Transducer
 In general, any device that converts one form of energy

to the other.
 For measurement systems: A transducer produces a usable electrical output signal in response to s specific physical phenomenon.
 Force, Acceleration, Light, Displacement, RPM,
Pressure, Temperature, Humidity.

Selection Considerations
 Sensitivity

 Defined as range of output / unit input

 Range
 Transducers must respond over the min and max values to be

measured

 Physical Properties
 Methods for mounting, protection

 Frequency Response
 The transducer should be able to follow the changes

 Other: Noise, Power Requirement
 Calibration, Environment, Cost

Temperature Transducers
Thermocouples
 The Thermocouple is a thermoelectric temperature

sensor which consists of two dissimilar metallic wires,
e.g., one chromel and one constantan. These two wires are connected at two different junctions, one for temperature measurement and the other for reference.
The temperature difference between the two junctions is detected by measuring the change in voltage
(electromotive force, EMF) across the dissimilar metals at the temperature measurement junction.

Thermocouple (Contd)
ISA

Material
(+ & -)

Temperature Range
°C
(°F)

Sensitivity@
25°C (77°F) µV/°C (µV/°F)

E

Chromel & Constantan
(Ni-Cr & Cu-Ni)

-270~1000
(-450~1800)

60.9
(38.3)

J

Iron & Constantan
(Fe & Cu-Ni)

-210~1200
(-350~2200)

51.7
(28.7)

K

Chromel & Alumel
(Ni-Cr & Ni-Al)

-270~1350
(-450~2500)

40.6
(22.6)

T

Copper & Constantan
(Cu & Cu-Ni)

-270~400
(-450~750)

40.6
(22.6)

R

87% Platinum/ 13% Rhodium
(Pt & Pt-Rh)

-50~1750
(-60~3200)

6
(3.3)

S

90% Platinum/ 10% Rhodium
(Pt & Pt-Rh)

-50~1750
(-60~3200)

6
(3.3)

B

70% Platinum/ 30% Rhodium &
94% Platinum/ 6% Rhodium
(Pt-Rh & Pt-Rh)

-50~1750
(-60~3200)

6
(3.3)

Thermocouple: