Does a thermometer just need a protective tube? Why bring a protective case then? I don’t quite understand; please help!

Protective tubes are used to safeguard thermal resistance wires or thermocouple wires; however, in equipment with stirring or severe material erosion, protective sleeves are needed to provide additional protection

The sensing elements of temperature measuring instruments are usually placed inside protective sleeves, which are then inserted into process pipelines or equipment. The anti-corrosion measures involve using materials with appropriate corrosion resistance; the choice of such materials depends on the corrosive properties of the medium: ① Metal or alloy materials with good corrosion resistance are used for the protective sleeves, such as titanium, tantalum, aluminum, acid-resistant steel, nickel-based alloys, etc； For high-temperature resistance to sulfur corrosion, 1Cr5Mo or 316L can be used. ② If the temperature sensing element is a thermocouple or thermal resistor, and noble metals are used as anti-corrosion materials, an armored version can be created to save material ； 　　③When metals or alloys are not resistant to high-temperature corrosive media, quartz glass can be used as a protective sleeve, capable of withstanding temperatures above 1000°C. Corundum sleeves can also be used, typically in sulfur furnaces. 　　④It is also possible to apply electroplating, spraying, lining with rubber, etc., on the outside of ordinary metal protective sleeves. At temperatures below 200°C, trichloroethylene or polytetrafluoroethylene can be used for coating. When applying coatings made of non-metallic materials, the coating should not be too thick, so as not to affect heat transfer. 　　When applying anti-corrosion measures, the following points should be noted: ① The temperature sensing protection tube and the equipment or pipes should be connected using flanges, to facilitate anti-corrosion treatment as well as installation and removal ； 　　②Try to avoid using protective sleeves made of non-metallic materials with poor heat transfer properties, in order to prevent an increase in the inert time of the temperature sensing element ； 　　③When measuring media containing particulate impurities in pipelines, to prevent the protective sleeve from being damaged by prolonged erosion, a baffle can be placed in front of the thermometer; this is particularly useful for protective sleeves coated with anti-corrosion materials using spraying methods. This type of protection works well in catalytic units; adding baffles to the riser temperature measurement and reducing the flow rate helps to prevent direct erosion of the casing.

Today’s armored thermocouples and thermal resistors both come with a protective layer, known as a protective tube. However, this protective tube is not strong enough and tends to get damaged, so a protective sleeve is installed to facilitate the replacement of the thermometer.

First, to protect against corrosion; second, for easy disassembly

Whether a thermometer requires a protective tube depends mainly on the process conditions of the medium. Protective tubes should generally be installed in the following situations: 1. When the volume of the equipment to be measured is very large, and a particularly long thermometer is used to measure its core temperature, along with high relative flow velocities of the process medium; in such cases, protective tubes should be installed (this is to prevent the thermometer from being damaged due to vibrations) ； The temperatures measured were very high, and the thermometers used were close to the upper limit of the measurable temperature range; therefore, a protective tube was necessary to prevent the thermometers from deforming due to being exposed to such high temperatures for extended periods – this is done to avoid the situation where the thermometers become too damaged to be removed ； 3 The process medium is highly corrosive; the thermometer only needs to have its measuring tip exposed.

1. Increase strength! 2. Valves cannot be installed at the location where the thermometer is inserted; using a protective tube allows the thermometer to be replaced without shutting down the system

It’s so as not to have to stop the vehicle to replace the thermometer!:lol

It is best for the casing to be of the type with holes drilled throughout the entire rod, as this is more reliable. Generally, in the case of a fully drilled design, the wall thickness should be at least 3.5 mm; a thinner thickness makes drilling difficult. Re-welding a floor to a steel pipe is unreliable and prone to accidents. A lesson indeed~~ This post was last edited by Changfeng Jiwanli on 2009-2-11 09:22.]

1 is to protect the measuring components, 2 is to facilitate replacement

The protective tube is used to protect the mechanical properties of the thermometer. The sheath is used to protect the physical properties.