![Thermistors with epoxy coatings are available for use at lower temperatures [typically -50 to
150°C (-58 to 316°F)]; thermistors are also available with glass coatings for use at higher
temperatures [typically -50 to 300°C (-58 to 572°F)]. These coatings protect the thermistor and
its connecting wires from humidity, corrosion and mechanical stress.
Surface-mounted thermistors come with adhesive exteriors that can easily be stuck in place
on flat or curved surfaces.
Temperature Range, Accuracy and Stability
Thermistors are highly accurate (ranging from ± 0.05°C to ± 1.5°C), but only over a limited
temperature range that is within about 50°C of a base temperature. The working temperature
range for most thermistors is between 0°C and 100°C. Class A thermistors offer the greatest
accuracy, while Class B thermistors can be used in scenarios where there’s less need for exact
measurement. Once the manufacturing process is complete, thermistors are chemically stable and
their accuracy does not change significantly with age.
Applications of thermistors
Thermodiodes and transistors
LM35 Temperature sensor
Temperature change
a) Liquid in glass bulb thermometers](https://image.slidesharecdn.com/emt4103sensorsandtransducerson27thmay2020lesson2-250325053625-4411e3ae/85/EMT-4103-SENSORS-AND-TRANSDUCERS-ON-27TH-MAY-2020-LESSON-2-pdf-7-320.jpg)
EMT 4103 SENSORS AND TRANSDUCERS ON 27TH MAY 2020 LESSON 2.pdf
- 1. EMT 4103 ON 27TH MAY 2020 TEMPERATURE SENSORS AND TRANSDUCERS Instruments to measure temperature can be divided into separate classes according to the physical principle on which they operate. The main principles used are: 1. The thermoelectric effect 2. Resistance change 3. Sensitivity of semiconductor device 4. Radiative heat emission 5. Thermography 6. Thermal expansion 7. Resonant frequency change 8. Sensitivity of fibre optic devices 9. Acoustic thermometry 10. Colour change 11. Change of state of material. Thermoelectric effect
- 2. Figure: schematic of a thermocouple circuit Resistance change
- 3. Figure 4.2 Figure: Behavior of some RTD materials
- 4. Figure: Constructon of an RTD It has a resistor element connected to a Wheatstone bridge. The element and the connection leads are insulated and protected by a sheath. A small amount of current is continuously passing though the coil. As the temperature changes the resistance of the coil changes which is detected at the Wheatstone bridge. Bridge circuit
- 6. Thermistors or thermal resistors or thermally sensitive resistors sensors Are made from semiconductors. Thermistors are composed of materials with known resistance. As the temperature increases, an NTC thermistor’s resistance will increase in a non-linear fashion, following a particular “curve.” The shape of this resistance vs. temperature curve is determined by the properties of the materials that make up the thermistor. Thermistors are often selected for applications where ruggedness, reliability and stability are important. They’re well suited for use in environments with extreme conditions, or where electronic noise is present. They’re available in a variety of shapes: the ideal shape for a particular application depends on whether the thermistor will be surface-mounted or embedded in a system, and on the type of material being measured. Figure: Schematic of a thermistor
- 7. Thermistors with epoxy coatings are available for use at lower temperatures [typically -50 to 150°C (-58 to 316°F)]; thermistors are also available with glass coatings for use at higher temperatures [typically -50 to 300°C (-58 to 572°F)]. These coatings protect the thermistor and its connecting wires from humidity, corrosion and mechanical stress. Surface-mounted thermistors come with adhesive exteriors that can easily be stuck in place on flat or curved surfaces. Temperature Range, Accuracy and Stability Thermistors are highly accurate (ranging from ± 0.05°C to ± 1.5°C), but only over a limited temperature range that is within about 50°C of a base temperature. The working temperature range for most thermistors is between 0°C and 100°C. Class A thermistors offer the greatest accuracy, while Class B thermistors can be used in scenarios where there’s less need for exact measurement. Once the manufacturing process is complete, thermistors are chemically stable and their accuracy does not change significantly with age. Applications of thermistors Thermodiodes and transistors LM35 Temperature sensor Temperature change a) Liquid in glass bulb thermometers
- 8. b) Bimetallic strips As temperature rises, bimetallic strips bend and make soft iron make contact with the small magnet, where the alarm is trigered and avoids overheating. Radiation temperature sensors and transducers a) Optical pyrometers or disappearing filament pyrometers
- 9. Figure: Disappearing filament pyrometer b) Total radiation pyrometers Figure: Total radiation pyrometer In ceramic, food and assembly industries 1. 2. 3. For Newtonian Fluids, viscosity Cv is
- 11. Humidity sensors and transducers Humidity Capacitive sensors