Everything You Need To Know About Temperature Switches

Temperature switches are used in a wide range of industrial and technical processes.  When a preselected temperature is reached, a respective switch contact is opened or closed by the temperature switch. Mechanical or electronic switches can be used depending on the requirements. In this article, we’ll look at what temperature switches are and how they work and some of the other features that make them useful.

What Is a Temperature Switch?

Temperature switches are devices  used to open and close switch contacts. The condition of the temperature switch varies based on input temperature. This feature provides anti-overheating and anti-overcooling protection. Thermal switches are temperature limiters and temperature monitors for machinery and equipment.

How does a Temperature Switch Work?

In a broad sense, a temperature switch is a device that measures temperature and performs a specific function (opening or closing a switch) at a set temperature.

A thermostat switch in an electric radiator is one of the most popular temperature switches. If the temperature in the room is lower than the desired temperature,  the thermostat will turn on the radiator; if the room temperature is higher than the specified temperature, the thermostat will turn off the heating.

Practically, the set & reset points are slightly different so that the control does not begin to swing when the temperature reaches the specified point. Hysteresis, or deadband, refers to this difference. When the thermostat is set to 20 degrees Celsius, the radiator will start heating when the temperature drops below 19 degrees Celsius and stop when the temperature climbs to 21 degrees Celsius, resulting in a 2-degree deadband.

Temperature switches are used in various industries, and they have a wide range of applications.

Specifications of the temperature switch

Adjustable Range

The temperature range between the temperature switch’s actuation or deactivation range is between the upper and lower limits. It is used to express a desire to raise the temperature.

Set Point

The discrete temperature where the temperature switch is set to actuate/deactivate when the temperature rises or falls. It must be within the adjustable range and labeled as rising or falling temperature.

Dead Band

The temperature differential between set points that are growing and decreasing.  It’s expressed as “typical,” which is an average of the increasing set point at the mid-adjustable range using the standard K switch element. Usually, it is fixed or not adjustable.

Hermetically Sealed

The electrical switching element(s) are isolated from the environment by a welded capsule with glass-to-metal, factory secured electrical leads.

Over-range

The temperature to which the sensing bulb can be exposed continuously without distortion sufficient to cause leakage or cause a permanent change in set point or significant degradation of the fill fluid is referred to as the over-range temperature. Temperatures that are too high may permanently damage the device and render it useless.

Repeatability

A temperature switch should be able to operate at a set point that is approached in the same direction from an initial point and returns to the starting point over successive cycles in order to establish a temperature profile. The degree to which the measured set point values are close to each other is usually expressed as a maximum adjustable range temperature.

SPDT Switching Element

SPDTs have three connections: NO or Normally Open, C or Common, and NO or Normally Closed, allowing the switch to be electrically connected to the circuit in either NC or NO state.

DPDT Switching Element

DPDT comprises two synchronized SPDT switching elements that actuate and deactivate together as the set point increases. Two separate circuits, one AC and one DC can be switched using discrete SPDT switching elements. The synchronization linkage is not fielded adjustable and is factory set.

Synchronization can be confirmed by attaching test lamps to the switching elements and watching them simultaneously turn “On” and “Off” during actuation and deactivation.

What Types of Temperature Switches Are There?

Electronic and Mechanical switches are generally distinguished. Gas-actuated temperature switches and Bimetal temperature switches are two types of mechanical temperature switches. An electronic temperature switch should only be used when high precision is required.

The user can adjust the limit value and set multiple switch points here. On the other hand, Bimetal temperature switches have a low level of precision but are inexpensive and small. The gas-actuated temperature switch is another switch type that is commonly used in safety-critical applications.

What makes a temperature switch different from a temperature controller?

The actual temperature can be determined by a temperature probe and compared to the set point by a temperature controller. An actuator is used to alter the desired set point. The temperature controller handles temperature display, control, and monitoring. Temperature switches, however, are used to open and close circuits by triggering a switching operation based on the temperature.

What Is a Bimetal Temperature Switch?

A bimetal disc is used in bimetal temperature switches to determine temperature. These are made up of two metals used as platelets or strips and have different thermal coefficients. Steel and Zinc, or steel and brass, are the most common metal combinations. The bimetal disc reverses when the nominal switching temperature is reached due to rising ambient temperature.

After cooling down to the restart switching temperature, the temperature switch pulls back to its previous state. The power supply is disrupted before switching back on for temperature switches that have electrical latching. The discs are mostly concave-shaped everytime when open to attain higher clearance from each other. Due to the heat effect, the bimetal deforms within the convex position, allowing the contact surfaces to touch securely. Bimetal temperature switches can also be used as a thermal fuse or overtemperature protection device.

How Does a Bimetal Switch Work?

Two strips of various metals make up bimetallic switches. The bimetal strips are permanently bonded together. A strip comprises a fixed contact and a second contact on the bimetal strip. Bending the strips on a snap-action switch allows the circuit to be opened or closed and the process to start or stop. In some cases, snap-action switches are not required because the platelets are curved and have a snap action. Coffee machines,  automatic circuit breakers, irons, and fan heaters utilize bimetal switches as thermostats.

What Are The Benefits Of A Temperature Switch That Is Activated By Gas?

Gas-actuated temperature switches are reliable and high-quality, explicitly designed for safety-critical applications.

What Is The Best Way To Calibrate Temperature Switches?

Before calibration

• Before beginning, remove the measurement from the process, stay in touch with the control room, & ensure that the calibration will not cause any alarms or undesired repercussions, as with any process instrument calibration.
• Visually inspect the switch to guarantee it is not damaged and that all connections appear to be in good working order.
• Clean the sensor before placing it into the temperature block if it is dirty.

Generate some Slow Temperature Ramp As Input

• If you’re readjusting the temperature sensor and its switch simultaneously, ensure the temperature source where the switch’s temperature sensor is installed has a slow enough temperature ramp.
• This necessitates using a temperature source capable of producing a controlled temperature ramp at a steady rate, as slow as the application needs.
• In practice, you can easily reach a temperature set point near the calibration range, let it stabilize, and then gradually ramp the temperature across the calibration range. You can quickly return to room temperature after the calibration is finished.
• The most common way to generate a temperature ramp is to use a dry temperature block. Not all dry blocks can produce a slow enough ramp. You must also be able to accurately measure both the generated temperature and the switch output signal. Furthermore, the calibration system should be able to capture the input temperature automatically when the switch output changes state.

Use An External Temperature Reference Sensor Instead Of The Internal One.

• The internal reference sensor in dry temperature blocks is always present, but do not use it when readjusting temperature switches!
• The internal reference sensor is positioned at the bottom of the heated and cooled temperature block. The internal reference sensor is often located near the heating and cooling elements and reacts quickly to temperature changes.
• The temperature will be transferred to the insert and the actual temperature sensor from that temperature block. This implies that there is always a significant lag (delay) between both the sensor calibrated and the internal reference sensor, which is located in the insert’s hole.
• This delay isn’t as significant because standard sensor calibration is mostly done at fixed temperature levels  since its possible to wait for temperatures get stable. However, in the case of temperature switch calibration, this delay has a significant impact and will result in a significant calibration error.
• Rather than using the internal reference sensor, an external reference sensor should be used, which is installed in the insert alongside the switch’s sensor to be calibrated. For the external reference sensor and the temperature switch sensor to behave in the same way and with the same lag, they should have similar characteristics.
• At the very least, ensure that the dimensions of the temperature switch sensor and the reference sensor are as close as possible. If the sensors are the same length, they will go the same depth into the insert and have the same immersion depth. Various immersion depths will result in calibration errors and uncertainty.
• Naturally, an accurate measurement device is required for the reference temperature sensor.

Measuring the Switch Output

• After you’ve determined the input temperature ramp, you’ll need to assess the state of the switch output terminals.
• A device that can measure whether the switch contacts are open or closed is required when using a traditional open/close switch.
• You’ll need to be able to measure the electrical output if the switch is more modern. For an mA signal, this could be current measurement, or for a voltage signal, it could be voltage measurement.
• Because the switch output has two states, you’ll need a device that can detect and measure both.

Capturing the Operation Points

To manually calibrate, initiate the temperature ramp and keep an eye on the output of the switch. You must read the input temperature; the reference temperature sensor reads when the switch’s status changes. The temperature switch’s operating point is here. The hysteresis is usually measured by calibrating both operation points with increasing or decreasing temperatures.

If you don’t want to do it manually, you’ll need a system that can do everything for you, including:

• Create a temperature ramp that rises and falls at the needed rate while remaining within the switch’s temperature range.
• The output state of the switch (open/closed, on/off) should be measured.
• Measure the temperature of the reference temperature sensor inserted into the temperature source.
• Capture the temperature when the switch is turned on or off.

Temperature switches FAQ

Thermostats and Temperature switches are common in many industrial automation processes. They are helpful temperature regulators because they monitor and limit the object’s temperature and can switch off the heating or cooling when a predetermined temperature is reached.

Although it may appear simple at first, there are some questions to which you should have answers to select and operate a thermostat or temperature switch properly. We’ve compiled a list of the most commonly asked questions and found solutions for you.

What are temperature switches?

Temperature switches are electromechanical devices that are used to control and monitor the temperature in manufacturing and industrial processes, with the power to switch on and off if a certain temperature is achieved.

What is the operation of a temperature switch?

Temperature switches can be programmed to act in response to a specific temperature. The electric contacts are opened when the switch’s sensing probe detects a rise in temperature. The electrical contacts close when the temperature decreases.

Where do temperature switches come in handy?

Temperature switches are commonly used in a variety of industries, but they are particularly important in the pharmaceutical, food and beverage, and automotive engineering industries. Temperature switches are commonly found in water boilers, heating systems, air conditioners, circulation pumps, and other similar equipment.

Conclusion

Temperature switches are used to control specific functions in a variety of industrial applications. They, like any other measuring instrument, need to be calibrated on a regular basis to ensure that they are operating correctly and consistently; failure to calibrate, or imprecise calibration, can have serious repercussions. Calibration of a temperature switch differs from, — for example, calibration of a transmitter or temperature sensor.

If you are planning to purchase temperature switches or any other electrical components, contact us at ICRFQ. We manufacture the best electrical components in China.

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