Measuring the liquid temperature sensor selection
1, when the life of the system than the estimated useful life of the probe looks for a long time.
2, is expected to be fairly frequent disassembly of the probe to calibrate or repair, But can not open a mouth in the container, A thermocouple can be installed on the wall of the container.
Thermocouple (sleeve) can significantly increase the time constant measurements. When the temperature change is very slow and the thermal conductivity error is very small, The thermowell does not affect the accuracy of the measurement. But if the temperature changes very quickly, Sensitive components can not track the rapid changes in temperature, And the thermal error may increase, Measurement accuracy will be affected. So we must weigh the consideration of maintainability and measurement accuracy of these two factors.
Thermocouple or thermal resistance of the probe all the material should be contacted by the fluid to adapt. When using a bare element probe, It is necessary to take into account the adaptability of the components (the sensing element, the connecting lead, the support, the local protective cover, etc.) in contact with the fluid to be measured. When using a thermowell, Only need to consider the casing material.
Resistive thermal elements in the immersion liquid and most of the gas,Usually sealed, At least to be coated. The exposed resistive element can not be immersed in a conductive or contaminated fluid. When it needs its quick response, They can be used for dry air and a limited number of gases and certain liquids. Resistive elements such as in stagnant or slow flow of fluid, There is usually a shell cover for mechanical protection.
When the catheter or container can not open or prohibit the opening of a hole, And therefore can not use the probe or thermocouple casing, Can be measured by means of a method of clamping or fixing a surface temperature sensor in the outer wall. In order to ensure a reasonable measurement accuracy, The sensor must be isolated from ambient air and isolated from the heat source. And must be through the appropriate design and installation of the sensor so that the wall of the sensitive components of the heat transfer to achieve the best condition.