Aren’t we all gadget-dependant? Life without appliances and devices, run by electricity or battery, is unimaginable. Therefore, we look out for ways to increase the longevity of these devices. The prime factor that can lead to damage of machines is excessive amount of heat generation. Are you facing such problems with your device as well? Then this article will indeed help you a lot. This article tells you why thermal protection is important and also about the thermal protectors that can save your appliances. Let us learn about them.
Why Is Thermal Protection Necessary?
Thermal protection is a method of controlling the excessive heat produced within a machine or gadget. It protects a device from fires or other damages, which may arise from excess amount of heat generated in the power supplies.
The temperature of machines or devices rises because of the heat generated from their components. The rise in temperature depends on power supply, size of the device and type of components used. In smaller equipment, the heat problem is not much of a danger as the heat easily gets released into the atmosphere. But in case of larger machines, forced cooling is required.
Forced cooling might cause dysfunction of the machines. Therefore, industries try to install internal thermal protection into their machines or motors that shuts it down when the temperature exceeds the safe limit. Apart from this, there are other thermal protectors like thermal fuses and thermal switches that serve the same purpose. Let us take a look at these thermal protectors.
A thermal protector is a thermal-actuated circuit that protects a device from heat damage due to excess rise in temperature. There are two kinds of thermal protectors:
Thermal fuse is a single-use circuit that cuts off or shuts off the working of a device as soon as it detects rise in temperature. It is a one-time fusible link that cannot reset itself.
A thermal fuse consists of three parts; the melted part, the electrode part and the bracket. The melted part (generally made of lead-antimony alloy), as the name suggests, melts when temperature exceeds the minimum and cuts off the circuit. The electrode part acts as a connecting medium between the melt and the circuit. The bracket holds together all the three components rigidly.
When current flows through the electrode, heat is generated because of its resistance. The amount of heat generated depends on the current and the resistance of the electrode. When the heat generated is more i.e. the temperature rises above the melting point, the fuse blows.
There are mainly three kinds of thermal fuse.
- Organic Type (Consisting of a sliding contact, a spring and a thermal pellet)
- Square-shell Type (A fusible alloy wire covered with a resin connected between two thermal fuse pins)
- Porcelain Type (Consisting of a fusible alloy, a special resin compound and a ceramic insulator)
- Cut off temperature is the temperature at which the thermal fuse blows or we can say, it is the minimum temperature at which the circuit opens.
- Holding temperature is the highest temperature that a fuse can hold without melting, for several hours.
- Functioning temperature rate is the rate at which the thermal fuse adjusts itself with the changing current or temperature.
- Rated current is the maximum current load the fuse can bear before it melts.
- Rated voltage is the maximum potential difference allowed across the ends of the fuse.
They are generally used in heat-producing electrical devices like blow dryers, clothes dryers, coffee makers, etc. They are also used in devices like electric cookers, laminators and space heaters.
Thermal switches are reusable electro-mechanical on/off switches that opens the circuit when temperature is high and closes when the temperature falls or is back to normal.
Snap Action Switch:
It is also known as bimetallic disc switch. This operates on the principle of thermal expansion. Two metallic discs expand when the temperature rises and snaps when the temperature crosses the threshold line, thus, opening the circuit.
A glass envelope filled with mercury is mounted on a metal coil. When temperature increases, the liquid mercury starts to expand resulting in tilting of the envelope. This tilting or change in angle of inclination actuates the switch.
Rod and Tube thermal switch:
This consists of rod fitted inside a tube and they have different coefficients of thermal expansion. The difference in the expansion coefficients results in rapid response and high temperature sensing feature that triggers the switch.
Thermal reed switches:
This type of switches consist of two ferrous contacts that changes state from NO (normally open) to closed and NC (normally closed) to open, when there is rise in temperature. When temperature rises above the curie point of the contacts, magnetic field around the switch changes and that actuates it.
The phenomenon of thermal expansion is applied to gases within a sensing bulb. The temperature rise results in expansion of the gas which puts pressure on a certain diaphragm and this actuates the switching element.
- Thermal switches have a set point temperature. This means that the device can change its actions whenever there is a certain change in the contacts. In this case, change in contacts depends on the temperature rise.
- Different kinds of switches have different ‘maximum current rate’, i.e. the maximum current load a switch can bear.
- Thermal switches have a finite temperature at which the switch changes its action. The path of temperature differential is known as hysteresis.
- Maximum voltage rate is the figure that informs about the maximum potential difference a switch can hold across its ends.
- Controlling temperatures in an oil refinery plays a vital role in preventing fire hazards. Thermal switches are a good option for that.
- In military aircrafts, thermal switches are used to trigger cooling systems when the temperature in the avionics bay rises, because of the heat produced by the components.
- Thermal switches are used in Navy ships. These switches are helpful to raise an alarm or turn of the gas supply whenever a risk of galley fire arises.
- Some devices have cooling fans built inside them. These fans are triggered by using thermal switches.
- In steel manufacturing industries, thermal switches are of essential use as they gauge the temperatures within the factory and actuate accordingly.
Your continuous and rigorous usage of appliances and machines can damage them. After this brief explanation on the benefits of using thermal protectors for different kinds of devices, you can now give your appliances a longer life.