Thermometers are not only used in homes and healthcare establishments since they are also used in industries and laboratories all over the world. Easy to read dials, rugged construction, leak proof heliarc welds and guaranteed precise temperature measurements will ensure even the most discriminating buyer of the finest thermometer. One of the accurate thermometers that have been designed is the bi-metal thermometer that operates on the principle that different metals contract and expands to certain degrees when exposed to different temperature levels.

How the bi-metal thermometer works

Two strips made from different metallic materials are fused together to form a spiral or rod. The strip will wind, unwind or bend according to temperature changes because one of the two metallic materials in the strip will contract or expand to a greater degree than the other. The free end of the strip is attached to a pointer that will indicate the temperature. Dial thermometers and thermostats often use the bi-metal thermometer technology that virtually meets every type of temperature measurement requirements. Bi-metal coils are wound to pre-determined standards and are individually trimmed and tested until they provide the exact amount of rotation required for a full scale reading.

Advantages of the bi-metal thermometer

• Clear and raised marks and numbers on the dials allow for exceptional readability with the “pointer to dial” indication.
• Due to its metal construction, the bi-metal thermometer are virtually unbreakable and can be used even in the harshest of conditions.
• The bi-metal means of reading temperature eliminates the need for gas, vapor, mercury, alcohol or capillary tubing.
• There are no parts to wear out or fail and there is no possibility for leakage or fluid column separation and no glass tube breakage.
• Stainless steel stems, plugs and mounting nuts are used to form together a moisture proof bond without possibility for corrosion or rust.
• The most precise calibration methods are in the fabrication, testing and calibration of each sensing helix coil before it goes into the bi-metal thermometers.
• The high degree of perfection by which the bi-metal thermometers are developed allows for the accuracy tolerance of within 1% of the range over the full scale.
• Long stem models can be immersed in deep vats or tanks where there is a variation between the top and bottom temperatures. It can be plunged directly into molten lead.

Safety consideration in using bi-metal thermometer

• Use of a thermowell is recommended for pressure, corrosive fluid or high velocity applications
• Thermometers must be installed in places that minimize injury or damage in the event that someone accidentally causes a breach in the stem/thermowell combination.
• Cases may be silicone filled for additional dampening of extreme vibrations and to ensure consistent performance in low process, temperature/high environmental humidity applications.
• Bi-metal thermometers should not be exposed continuously to process temperatures exceeding 800⁰F (425⁰C) to avoid damaging the bi-metal elements.
• Use of silicone fill should be avoided in bi-metal thermometers when strong oxidizing agents such as oxygen, chlorine, nitric acid and hydrogen peroxide are present.