What is Temperature Sensor and its Working Principle?

What is Temperature Sensor?

A temperature sensor is a device that detects whether a substance is hot or cold. The device could be a thermocouple or a resistance temperature detector, which gives temperature measurement in the readable form via an electrical signal.

Temperature Sensor Working Principle

A temperature sensor is an instrument designed to detect the level of coolness or hotness of an object. This sensor’s basic operation is based on the voltage in its diode. The temperature variation is proportional to the diode’s resistance.

The resistance in the diode detects and sends the signal into readable values such as Fahrenheit, Kelvin, or Centigrade. Temperature sensors are designed to sense or detect the internal temperature of various structures, such as industries, power plants, refineries, and so on, and to provide an electrical signal as a result.

The voltage change in the MOSFET terminal is the fundamental principle of temperature sensors. The temperature and voltage are directly proportional to each other. That means if the voltage reduces the temperature also decreases and vice-versa. This happens according to the voltage drop between the MOSFET’s emitter and the base sensor’s terminals.

The basic metal of modern temperature sensor is made up of aluminum due to aluminum has a .greater coefficient of thermal than steel

Temperature Sensors Formula

The temperature-related frequency, which is also proportional to the tension “σ" in the wire, can be stated as follows:

f = 1/2 [σg/ρ] / 2l Hz


σ = tension of the wire

ρ = density of the wire

L = length of wire

g = acceleration due to gravity

Types of Temperature Sensors

The temperature sensors are mainly classified into two. They are

• Contact Type Temperature Sensors

• Non-Contact Type Temperature Sensors

Contact Type Temperature Sensors

There are some temperature sensors that can only measure the hotness or coldness of an object by being in contact with the object.

Such temperature sensors are classified as contact-type. They can detect solids, liquids, or gases at a variety of temperatures.

Non-Contact Type Temperature Sensors

Non-Contact Sensors can measure the temperature without being in contact with the object. This can be done by utilizing the radiation of the heat source. The common non-contact sensor is an infrared sensor (IR). IRs detect an object’s energy remotely and send a signal to an electrical circuit, which uses a calibration diagram to determine the object’s temperature.

The contact and non-contact temperature sensor are further classified into the following types.

  • Thermocouples
  • Thermistors
  • Resistive Temperature Detectors (RTD)
  • IR Temperature sensor
  • Optical Pyrometer.

Contact Type Temperature Sensors

Thermocouples: Due to the wide temperature operating range, reliability, accuracy, simplicity, and sensitivity thermocouples are considered as one of the most common temperature sensors.

A thermocouple is made up of two dissimilar metals, such as copper and constantan. One of these junctions, known as the Cold junction, and another junction is called Hot junction.

A cold junction is always kept at a specific (constant) temperature, while the other end, the hot junction, is the measuring junction.

A voltage drop is developed across the junction on being subjected to temperature

Thermistors: Thermistors are extremely small devices. It consists of a sensing element that can be glass or epoxy coated, as well as two wires that link to an electric circuit. Temperature is determined by measuring the change in resistance of an electric current. Thermistors are available in NTC or PTC configurations and are frequently inexpensive.

Resistive Temperature Detectors (RTD)

RTD sensor is made up of either platinum, copper, or nickel. RTDs have a reliable resistance vs. temperature relationship and operate between –200°C and +850°C. RTDs have a resistor that changes the value of the resistor according to the value of temperature changes.

Non-Contact Type Temperature Sensors


A pyrometer, often known as a radiation thermometer, is a non-contact device. The main purpose of a pyrometer is to determine an item’s surface temperature by measuring the temperature of electromagnetic radiation emitted by the object. As a result, this non-conductive device can be used to measure thermal radiation. We may use this to determine the temperature of the object’s surface. There are two types of pyrometers available on the market. They are

  • Infrared Temperature Sensor
  • Optical pyrometers

Infrared (IR) Temperature Sensors

IR temperature sensor is used to detect the temperature of a moving object. We cannot use a contact-based temperature sensor on a moving object. IR sensors are used to detect the temperature of moving objects such as tires, brakes, etc.

Optical Pyrometer

It is a temperature measurement sensor used to detect the temperature of molten metals, furnaces, and in some cases liquids too. It is a prime example of a non-contact temperature sensor.

Parameters used for selecting temperature sensors

Before selecting a temperature sensor you should keep in mind the following parameters

Temperature range – We can’t measure all the temperatures by using a single temperature sensor. Different temperature sensors are designed for different temperature ranges. Please make sure before selecting temperature sensors whether they meet your need or not. The range of sensors would be on the specification sheet of the sensor.

Accuracy and stability – This is something to keep in mind if your application requires a specific level of precision. Glass-coated NTC thermistors are the temperature sensors with the best accuracy.

Size and Package – Different sensors come in different shapes and sizes. If space is limited, then you should select only a smaller one. Package size is also an important parameter for selecting a temperature sensor. Actually, the package style describes how the temperature sensor is connected to the application and how the temperature will be sensed.

Application of Temperature Sensor

  • Used in electric motors for measuring the temperature of the motor winding, bearing, brushes, etc.
  • Used in mechanical engines for measuring the internal temperature
  • It is also used in an HVAC system
  • Used in humidity and air control conditioning equipment

Advantages of Temperature Sensor

  • Low cost
  • Can be used for both embedded and surface mount applications
  • Faster response
  • Temperature probes have precise linearity and low hysteresis.

Your introduction is very detailed and useful. Thank you for sharing.

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