Structure & Principle
Bimetal thermometers are manufactured based on the thermal expansion and contraction principle of metals. They generally consist of a temperature sensing element, metal protection tube, transmission shaft and pointer, dial and case, and mounting fixture.
A bimetallic strip is composed of two metal sheets with significantly different thermal expansion coefficients bonded together. The bimetallic strip is cut and coiled into a spiral or other suitable shape to form the temperature sensing element.
In the production of bimetal thermometers, the sensing element is usually installed inside the metal protection tube, with one end fixed at the bottom of the tube (fixed end), and the other end connected to the pointer via the transmission shaft (including thin shaft and flexible shaft) as the free end.
When the temperature changes, the sensing element coils or uncoils, driving the free end to rotate. The transmission shaft then causes the pointer to deflect by an angle. The rotation angle of the pointer has a linear relationship with the temperature change. After calibration, the device can be used for temperature measurement.
Technical Parameters
|
Measuring range |
-80~500℃ |
|
Measuring accuracy |
Class 1.5, Class 1.0 |
|
Resolution |
1~5.0℃ |
|
Thermal response time |
≤40 s |
|
Protection tube diameter |
Φ12, 10, 8, 6, 4 |
|
Mounting thread |
M27×2 |
|
Dial diameter |
150, 100, 60, 40, 25 |
|
Protection grade |
IP55 |
|
Angle adjustment error |
Not exceeding 1.0% of the full scale |
|
Hysteresis |
Not greater than the absolute value of the basic error limit |
|
Repeatability |
Not greater than 1/2 of the absolute value of the basic error limit |
|
Applicable standards |
JB/T 8803, JJG 226 |
Classification & Application
Bimetal thermometers are classified into axial type, radial type, 135° angle type, and universal type according to the orientation between the dial and the protection tube.
According to functions, they are divided into standard type, electric contact alarm type, and remote transmission type.
According to environmental conditions, they are classified into standard type, shockproof type, explosion-proof type, and waterproof type.
Bimetal thermometers are ideal instruments for on-site temperature indication at medium and low temperatures (-80~500℃) without external power supply, serving as an alternative to liquid thermometers. They are widely used in industries such as petrochemical, shipbuilding, machinery, pharmaceuticals, etc.