How a bimetallic strip works in a fire alarm?

When the strip is heated by fire, the high-expansion side bends the strip toward an electrical contact. When the strip touches that contact, it completes a circuit that triggers the alarm to sound. The width of the gap between the contacts determines the temperature that will set off the alarm.

How does a bimetallic strip work?

The bimetallic strip consists of two thin strips of different metals, each having different coefficients of thermal expansion. … Due to this property, when the temperature changes, the metal strip at one side expands and the other does not, which creates a bending effect.

How does a bimetallic heat detector work?

Bimetallic Heat Detectors: These detectors contain a metallic strip with two different metals. As the heat reaches the strip, the metal warps and the contact is closed and the alarm is activated. … This causes pressure to be applied on the contacts and an electrical connection is completed, which sounds the alarm.

Why does a bimetallic strip bend when heated?

Such as thermometers, clocks, and other electrical devices. The strip of bimetal comprises two metals with different coefficients of thermal expansion. … When the bimetallic strip is heated, the metal with higher thermal expansion will bend more. Thus they bend towards the metal having a lower thermal expansion.

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What happens to bimetallic strip when heated?

When this bimetallic strip is heated, the brass expands more than the steel and the strip curves with the brass on the outside. If the strip is cooled, it curves with the steel on the outside. Bimetallic strips are used as switches in thermostats.

What is the working principle of heat detector?

Heat detectors work on a similar principle used by smoke detectors, by tracking the temperature instead of smoke. Heat detectors generally detect the heat that comes as a result of combustion. The devices trigger an alarm when they sense a rapid rise in temperature or when a certain temperature is reached.

Which type of detectors uses bimetallic strip to detect a fire?

Bimetallic strip is used in fire alarms. >>Bimetallic strip is used in fire alarms.

How does a flame detector work?

Infrared flame detectors – These sensors operate by using an infrared band. A small thermal imaging camera in these detectors can instantly detect the presence of hot gasses released anywhere near the infrared detector. … Infrared waves can penetrate dust, smoke, fuel particles and oil films.

Why does the strip bend during heating?

Brass and Iron together form the bimetallic strip. The rate of expansion and contraction of brass is more when compared to Iron, that is, brass expands more than Iron when heated and contracts faster than iron when cooled. As a result, the bimetallic strip bends with the change in temperature.

Why does a bimetallic strip of brass and iron bend on heating?

When the bimetallic strip is heated, brass expands more than steel due to higher thermal coefficient than steel. … And hence due to this phenomenon brass side shows higher expansion especially linear expansion than iron and hence forcing the whole bimetallic strip to bend.

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How is a bimetal strip made?

The strip consists of two strips of different metals which expand at different rates as they are heated, usually steel and copper, or in some cases steel and brass. The strips are joined together throughout their length by riveting, brazing or welding.

When a strip made of iron and copper is heated?

Since the linear expansion coefficient of copper is higher than iron. So when heated, copper will expand more than iron. So the length of copper will become more than iron after heating. Now since they are combined in a strip and have different length, the strip will bend such that iron is on concave side.

Why bimetallic strip is used in thermostat?

Bimetallic strips are used in thermostats for measuring and controlling temperature. The strip is connected to a switch and as the temperature changes the strip flexes and opens or closes a contact. They are also used in ovens for measuring temperature.