Temperature Sensors what are they? Comparison between Thermocouples, Themisters, RTD's and IC Sensors.

Hey friends,

Today we are going to discuss about Thermistors, Thermocouples, TRD (Resistance Temperature Detectors) and IC Sensor which are all in the category of temperature sensors.

Thermocouples.

A thermocouple is a temperature sensor with two junctions and what it does is that it gives a voltage as an output for a particular temperature change.

When 2 dissimilar metals are joined together to form a junction, an emf is produced which is proportional to the temperature being sensed.

           

The generation of current in a circuit comprising of two wires of dissimilar metals in the presence of temperature difference.

Advantages

•  Self-Powered
•  Simple
•   Inexpensive
•  Wide Temperature Range (0-750 C)

Disadvantages

• Non-Linear
• Output Voltage is Low
• Reference Required.

Thermistors.

Thermistor, a word formed by combining thermal with resistor, is a temperature-sensitive resistor fabricated from semiconducting materials.

The resistance of thermistors decreases proportionally with

increases in temperature.

The operating range can be -200°C to + 1000°C.

Disc       Thermistor

                                     

The thermistors can be in the shape of a rod, bead or disc. Manufactured from oxides of nickel, manganese, iron, cobalt, magnesium, titanium and other metals

Thermistors come in two varieties; NTC, negative thermal coefficient, and PTC, positive thermal coefficient.

•  The resistance of NTC thermistors decreases proportionally with increases in temperature.
• PTC thermistors have increasing resistance with increasing temperature.

Thermistor resistance-temperature relationship can be approximated by,

                         

T-Temperature in Kelvin.

Tref-Referance temperature usually the room temperature.(25 Degree or 298.15K)

R-This is the resistance of the thermistor.

Rref-This id the resistance at Tref.

Bita is the calibration constant depending on the thermistor material usually between 3000K and 5000K.

Advantages

•      Very Sensitive.
•      Quick Response’
•      More Accurate.

Disadvantages

•      Output is a nonlinear Function.
•      Limited Temperature Range.
•      Require a current source
•      Self-heating.
•      Easily Broken.

Resistance Temperature Detector-RTD.

It is a positive temperature coefficient device, which means that

the resistance increases with temperature. The resistive property of the metal is called its resistivity.

The industry standard is the platinum wire RTD (Pt100) whose base resistance is exactly 100.00 ohms at 0.0°C.

Platinum Wire RTDs (PRTs)

PRTs have established themselves as the de-facto industry standard for

temperature measurement, and for many reasons,

•      linear temperature sensors
•      Resistance vs temperature characteristics are stable and reproduceable
•      linear positive temperature coefficient (-200 to 800 °C)
•      Very accurate and suitable for use as a secondary standard

Electrical Resistance Change (RTD)

•      10 ohms Copper RTD - .00427 coefficients
•      100 ohms Platinum RTD - .00385 coefficients (new IEC)
•      100 ohms Platinum RTD - .00392 coefficients (old)
•      120 ohms Nickel RTD - .00672 coefficient
•      604 ohms Nickel-Iron RTD - .00518 coefficient

Advantages

•      Very Accurate
•      Change in Resistance is Linear

Disadvantage

• Expensive
• Current Source Required.
• Small change in Resistance
• Self-Heating.

Comparison of Temperature Sensors

For more details on sensors please take a look at https://www.theory2learn.com/2020/03/what-is-sensor-what-are-parameters-that.html

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