What is Temperature Switch

A temperature switch is a kind of switch that uses bimetal as the temperature sensing element. When the appliance is in normal operation, the bimetal is in a free state, and the contacts are closed/broken. When the temperature rises to the action temperature value, the bimetal element is heated to produce internal stress. The contact is opened/closed, and the circuit is cut/connected, thus playing a role in thermal protection; when the temperature drops to the preset temperature, the contacts automatically close/open and return to normal operation.

I. Classification

Mechanical temperature switch

Temperature Switch

A mechanical temperature switch principle is the same as that of a pressure switch. However, the mechanical temperature switch uses a special silicone oil with a stable coefficient of thermal expansion, which undergoes thermal expansion and contraction when it senses a temperature change, resulting in deformation and displacement. The mechanical temperature switch is activated by a mechanical structure such as a bar spring, which eventually activates the uppermost microswitch and causes the electrical signal to be output.

Mechanical temperature switches can be divided structurally into two main categories. Examples are local inline mechanical temperature switches and remote capillary mechanical temperature switches.

Mechanical temperature switches are divided into two types depending on the temperature measuring elements, such as brass and stainless steel.

Electronic temperature switch

Temperature Switch

Electronic temperature switches contrast mechanical temperature switches, which do not require a power supply. The temperature sensing element of the electronic temperature switch is different from the mechanical, thermal expansion, and contraction principle but uses a high precision RTD commonly used in temperature transmitters.

It is also divided into local inline and remote electronic temperature switches. In this case, the remote split installation uses an RTD temperature sensing element. It can easily be extended by wire and is more accurate. In addition, it has a wider temperature measurement range and is a good choice in demanding situations.


  1. It has multiple switching quantities, selecting the analog signal.
  2. No dead zone for switching point adjustment. You can set it at will within the range.
  3. The output time of delayed switching can be set by itself.
  4. it has high precision, small hysteresis, fast response, stability, and reliability.
  5. We can set various parameters by pressing the key and setting it on site. It is easy to operate and more flexible.


Mechanical temperature switches

Mechanical temperature switches have a high degree of reliability.

The high output capacity of the switching signal also facilitates direct control of some simple actuators by the user.

Local inline mechanical temperature switches are easy to install and facilitate fixing the meter head. However, its proximity to the electronic micro switch does not have the same temperature resistance as the remote capillary mechanical temperature switch.

The remote capillary mechanical temperature switch is suitable for applications with no local mounting position. In addition, it has a more flexible insertion depth.

The capillary length of the mechanical temperature switch is 1.8 m as standard and can be extended up to 15 m according to customer requirements.

Electronic temperature switches

In addition to the advantages of reliability and ease of installation in various locations.

The LCD shows real-time temperature changes, conveying more accurate information about the operating conditions.

The electronic temperature switch head keypad facilitates total adjustment of the setpoint and returns the difference.

With a simple pushbutton, it is possible to display the current setpoint and deadband and the maximum temperature range at any time.

IV.Technical Parameters

  1. Electrical parameters: 1) AC 250V 50~60Hz 5A / 10A / 15A (resistive load)

2) AC 125V 50Hz 15A (resistive load)

  1. Operating temperature range: 0~240℃ (optional), temperature accuracy: ±2 ±3 ±5 ±10℃
  2. Reply and action temperature difference: 8~100℃ (optional)
  3. Wiring method: plug terminal 250# (bend 0~90° optional); plug terminal 187# (bend 0~90° optional, thickness 0.5, 0.8mm optional)
  4. Service life: ≥ 100000 times
  5. Electrical strength: AC 50Hz 1800V over 1min, no flicker, no breakdown
  6. Contact resistance: ≤ 50mΩ
  7. Insulation resistance: ≤ 100MΩ
  8. Contact form.

Usually closed type: temperature rise, the contact is broken; temperature drop, the contact is connected.

Normally open type: temperature rises, the contact is connected; temperature falls, the contact is broken.

  1. Shell protection level: IP00
  2. grounding mode: through the thermostat metal shell and device grounding metal parts connected.
  3. Temperature working range:-25℃+240℃+1℃∽2℃


The temperature switch is widely used in water and electricity, water, petroleum, chemical, machinery, and hydraulics. It provides on-site measurement display and control of media temperature in pipelines and vessels.

Mechanical temperature switches are widely installed in various pipeline tanks.

With their excellent reliability, mechanical temperature switches are used to protect crucial hazardous equipment. For example, temperature control of lubricating oil tanks or temperature control of pipelines. It is used in a wide range of industries. Such as power, petroleum refining, offshore platforms, oil pipelines, chemicals, environmental protection, metallurgy, pharmaceuticals, and many other locations in various industries.

Electronic temperature switches are widely used to control the opening and closing of pumps and valves in zones. For example, pump or compressor start/stop, lubricating oil circuit temperature monitoring, hydraulic oil temperature monitoring, and various other cooling lubricating oil circuit temperature monitoring; are convenient for actual on-site marking.

Electronic temperature switches are most often used on hydraulic systems in the metallurgical, cement, and environmental industries.


  1. When using contact temperature sensing installation, you should keep the product close to the installation surface of the controlled appliance.
  2. Do not collapse or deform the plastic or metal casing during installation to avoid performance.
  3. We can not add metal shell products with an insulating jacket to the insulation sleeve removed without use or crushed in the installation. It can avoid causing leakage and ensure safety in use.
  4. The product is used in circuits with no more than 5A. Therefore, we should connect a copper core cross-section of 0.4-0.75mm2 wire.
  5. The temperature switch is usually installed at the sensitive point where heat is generated inside the appliance or at the part where the abnormal temperature will occur. However, you can also install it at thermal measurement points where temperature control or interlocking is required.

VII.Selection Guide

The relevant parameters to focus on when purchasing a temperature switch are as follows.

  1. Specifications: setpoint/action range, high/low report, number of contact pairs.
  2. Maximum contact capacity: operating voltage/current.
  3. Installation size: We should choose the size according to the actual space available for the equipment on-site and the requirements for the speed of temperature response.
  4. Protection level: we should choose the temperature switch with the corresponding protection level according to the explosion-proof level of the site, the chemical corrosion situation, the air humidity, etc.
  5. The operating temperature point of the temperature switch is also related to the current effect of its operating current. Therefore, when selecting a temperature switch, we should consider its cut-off temperature and the impact of its operating current.


  1. 1.The product should be stored in a ventilated, clean, dry, and non-corrosive gas place with less than 90% humidity and ambient temperature below 40℃.
  2. It is essential to carry out preventive maintenance and regular inspections of components. We need to check if there is any damage to the elements and endangering property and personnel safety.
  3. We must pay attention to the range of the controller to avoid the danger of some wrong range not being able to alarm and control.


When a temperature switch is not allowed to switch points, operates abnormally, or refuses to move, we need to inspect. According to the inspection results, the faults are divided into three types such as mechanical component faults, electrical faults, and installation defects.

1. Mechanical faults.

Damage to the temperature switch enclosure or probe is caused by subsystem vibration or other external forces, system media, room chemical gases, and seawater corrosion. This type of failure has a more noticeable appearance.

Measures: We need to identify the cause of the damage and treat the temperature switch against corrosion and mechanical damage. We need to replace the temperature switch with a new one or reconfirm whether the installation position and type of the temperature switch are suitable.

2. Electrical faults.

It is mainly manifested in poor or damaged contact systems, short circuits such as burrs between terminals, and corrosion. This type of fault can be found by visual inspection and multimeter measurement.

Measures: We need to deal with poor contact and corroded parts. For more severe corrosion phenomena, develop corresponding anti-corrosion treatment measures or replace the temperature switch with a higher level of protection.

3. Installation defects.

The temperature switching point is sometimes high and sometimes low. So there is a delay, or consistency is high.

This type of failure is mainly due to the temperature switch in the measurement point not being very tightly installed. As a result, there is a gap, or the position of the measuring point is not selected correctly.

We need to take appropriate measures to replace the temperature switch with a suitable one or change the position of the measuring point.

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