Tira bimetálica – Funcionamento, vantagens e desvantagens

Bimetallic strip – Functioning, advantages and disadvantages

BIMETALLIC STRIPS

Bimetallic strip thermometers are mechanical thermometers. They are widely used in industry for temperature control due to their robustness, temperature range and simplicity. It consists of a bimetallic strip made of two different metals joined with one end fixed and the other free. A bimetallic strip is used to convert a change in temperature into mechanical displacement. The principle is that as the temperature changes, one strip expands more than the other, causing the pair to bend at the free end. Most bimetallic strips use a high thermal expansion alloy such as steel or stainless steel along with a low thermal expansion alloy such as Invar. Steel and copper or in some cases brass are also used instead of copper for bimetallic strips.

Figure 1.40 shows the configuration of a temperature-controlled bimetallic switch or thermostat. The metal with the highest coefficient of thermal expansion is on the outside of the curve when the strip is heated and is lower on the inside when cooled. When the switch temperature increases, the thermal expansion material will be higher than the other side of the low thermal expansion material. This causes the strip to bend upward when it makes contact, so the liquid can flow. By adjusting the size of the gap between the strip and the contact, the temperature can be adjusted or set.

See more: What is a temperature sensor Types of temperature sensors

bimetal strip bimetal strip

Advantages of bimetallic strips

  • Power source not required
  • The cost is low
  • It is a robust construction
  • It is easy to use and can be used up to 500°C.

Disadvantages of bimetallic strips

  • It is less accurate
  • It is limited to applications where manual reading is acceptable, for example a household thermometer.
  • It is not suitable for very low temperatures because the expansion of metals tends to be much lower. Thus, the device becomes a very insensitive thermometer.

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