What is Temperature Switch : Working, Types & Its Applications

In every electrical and electronic application, at least one switch is used to control the device. So these are the most significant elements in the control system to achieve control operation. In the industrial sector, there are different types of switches used for different purposes like toggle, slide, push button, rotary, liquid level, temperature, pressure, and many more. From them, a temperature switch is most frequently used in industries for monitoring and controlling the temperature of different machinery. So this article discusses one type of switch namely temperature switch – working with applications.


What is a Temperature Switch?

A mechanical device that is used to monitor and control the temperature in manufacturing and industrial processes by turning ON & OFF switch contacts once a fixed temperature range is reached is known as a temperature switch. This switch is a small and cost-effective solution to measure temperature within moveable & space-constrained applications. The temperature switch symbol is shown below.

Symbols
Temperature Switch Symbols   

The switching condition of these switches mainly changes based on the input temperature. So this function is used as protection from overheating. So, these switches are mainly responsible for monitoring the temperature of equipment & machinery.

Temperature Switch Construction

The different components used in this switch mainly include switch case, range nut, range spring, main spindle, bollows, capillary, and temperature sensing bulb. The construction diagram of the temperature switch is shown below.

Construction
Construction

As shown in the above diagram, the fluid within the temperature sensing bulb responds to variations in temperature. Once temperature increases, the pressure within the bellows increases. So the increase in the temperature sensing bulb will compress the bellows & moves the spindle up until the force of spring as well as the pressure of bellows are in equilibrium. The spindle movement is moved toward the switch & causes ON & OFF action based on the set point of the switch.

Working Principle

The working of a temperature switch mainly depends on the variations of temperature taking place within an enclosed space. The function of a temperature switch is to trigger when changes in temperature occur.

Once the sensing probe in this switch detects an increase in temperature, then it opens the electric contacts. Similarly, if the switch detects a decrease in temperature then electrical contacts will be closed. So these variations in temperature can be used to activate a switching mechanism.

Specifications

The temperature switch specifications include the following.

  • Voltage supply ranges from12 to 30VDC.
  • Its accuracy is ±0.1%FS ±0.3%FS ±0.5%FS.
  • Pressure resistance typically min 40bar to maxi 300bar.
  • Long-term stability (1 year): ±0.1%FS
  • Response time T=90°C at 5.4s and T=50°C at 2.3s.

Temperature Switch Types

These switches are categorized into two types mechanical temperature switches and electronics temperature switches.

Mechanical Temperature Switches

Mechanical temperature switches are available in two types bimetallic and liquid expansion temperature switches which are used for measuring or detecting the change in temperature.

Bimetallic Temperature Switch

The bimetallic temperature switch or bimetallic thermometer uses the bimetallic strip, which is used to change the temperature into mechanical displacement. Here, the bimetallic strip mainly uses the principle of metal expansion on heating. So when the temperature changes then the volume of metal will be changed.

Bimetallic

The temperature coefficient of each and every metal is different, so it shows the main relationship between the change within the metal’s physical dimension & the temperature that causes it. Here, the expansion of metal or its contraction mainly depends on the temperature coefficient which means, the metals at a similar temperature have different changes within the physical dimension.

The advantages of bimetallic temperature switch mainly include compact size and less cost whereas its disadvantages mainly include; less accuracy, prone to vibrations & shocks, not handling high temperatures and its performance will get affected when the ambient temperature changes.

Liquid Expansion Thermometer

The liquid-filled temperature switch or liquid-filled expansion thermometer includes a brass bulb that is filled with a gas or chemical fluid. It includes a fluid-filled bulb system. So at the thermometer bulb, a large amount of fluid is kept which has the maximum sensitivity. This enclosed fluid will expand once the bulb gets heated. So this liquid expansion will increase the fluid pressure within the bulb. The increase in fluid pressure will result in the activation of the pressure switch which is connected to the bulb.

Liquid Expansion Thermometer
Liquid Expansion Thermometer

The advantages of a liquid expansion thermometer include less cost, compact size, and more accurate whereas the disadvantages are; that response time is high, leakage occurs, resistant to temperature & shock, etc.

Electronic Temperature Switch

This temperature switch mainly includes a power supply source, measuring element, and electronic circuit. This switch is used to measure temperature by changing it into a switching signal through the change in temperature of the measuring element. This switching signal changes in proportion to the temperature & can be calculated accordingly. Electronic temperature switches are applicable where high accuracy is necessary.

Electronic Temperature Switch
Electronic Temperature Switch

Temperature Switch Circuit Diagram

The temperature switch circuit diagram is shown below. The main function of this circuit is to control a cooling fan. Generally, these switches are mainly designed for providing automatic control for temperature regulating equipment automatically.

Temperature Switch for Controlling Cooling Fan
Temperature Switch for Controlling Cooling Fan

The circuit is connected as per the above-shown diagram; So this diagram illustrates a 2-wire temperature switch for controlling a cooling fan motor. The working of this circuit is, that when a high temperature shuts the switch, then it immediately activated ‘F”. This coil closes two ‘F’ contacts for activating the motor.

Temperature Switch Vs Thermostat

The difference between a temperature switch and a thermostat includes the following.

Temperature Switch

Thermostat

The temperature switch is also known as a thermal switch. The thermostat is also known as an indicator or thermometer.
The main function of this switch is to measure temperature. A thermostat device’s function is to regulate temperature,
This switch is a bi-stable electromechanical device. This is a closed-loop control device.
Generally, these switches are classified into two types electronic and mechanical. Thermostats are classified into three types programmable, non-programmable and smart.
This switch includes two main parts like sensing part and snap-action contacts. The thermostat includes different parts like flange, frame, housing, and wax element.

Temperature Switch Hs Code

HS code is a Harmonized Commodity Description & Coding System. This code includes a list of numbers (at least 6 digits) that are used by customs to categorize a product being shipped. So that it can calculate taxes, and duties precisely & apply any required restrictions. If the HS code is not included on the commercial invoice, the shipment will be delayed. This is the standard code worldwide to describe the kind of commodity. Every commodity that crosses international borders must be acknowledged by customs through an HS code.

Here Temperature switch with HSN Code import shipment data is shown in the following table.

HS Code Product Source Destination
90328990 The opener of Temperature Switch 150 C – 125961 – Germany India
90328990 Intelligent, Programmable – TTR31- Thermophant TTTR31-Temperature Switch -, A1C12WAE1XYB P.O.1023282298

S.O.3016344852

Germany India
90328990 Temperature Switch – TS-SNA/SNK-PT100 – 1920000266 Germany India
90328990 ETS or Electronic Temperature Switch 7246-A-137 Germany India
90321090 Temperature Limit Switch (TLS) 200 C Injection Moulding Machinery Parts. Germany India

Applications

The applications of temperature switches include the following.

  • Temperature switches are mainly designed to use in heating systems, boilers, circulation pumps, air heaters, burners, etc.
  • They are particularly used in different industries like pharmaceuticals, automotive engineering, foodstuffs, etc.
  • These switches can be used with pumps, boilers, and heating systems.
  • Thermal switches are mainly used in kitchens, and restaurants to check the food temperature that is being cooked.
  • These switches play a key role in processing information & protecting equipment.
  • These types of switches are used in a wide range of applications like RF power amplifiers, motor drives, power supplies, etc.

What is the Purpose of Temperature Switch?

The main purpose of the temperature switch is to monitor the temperature of machinery & equipment. These are used to limit temperature in industries and protect machinery from overheating.

What is the Deadband of Temperature Switch?

The deadband of the temperature switch is the difference within temperature between the increased set point & decreased set point.

Are Temperature Switches Normally Open or Closed?

When the temperature switch is Normally Open (NO), then the switch contacts are NO normally open at minimum temperature. Similarly, Normally Closed (NC) means that the switch contacts are NC at minimal temperature.

This switch gets activated by a change in temperature & changes its condition from NO to close or from NC to open. The NO thermal switch contacts usually stay open which will close with the increase in temperature.

What is Temperature Differential on Thermostat?

The temperature differential on the thermostat is the setting at which point the thermostat activates once the room temperature drops under the set temperature.

Thus, this is brief information on temperature switch – types, working with applications. This is a bi-stable electromechanical device used to activate or deactivate a minimum of one or above electrical switching elements at a set point on increasing or decreasing temperature. Here is a question for you, what is a temperature sensor?

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