The explosion-proof rating of thermometers
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The owner’s MR document states that the electrical area classification for all instruments shall be Zone 1, Group II A/II B, T3; the owner understands that \"ALL INSTRUMENTS\" includes thermometers. However, the thermometer provided by the manufacturer does not indicate any explosion-proof rating; does it lack such a rating? Looking forward to answers from experts.
It depends on the type of thermometer used: whether it is a field instrument such as a bimetallic thermometer, or a temperature transmitter based on thermal resistors or thermocouples. If it is a field instrument like a bimetallic thermometer, no explosion-proof requirements are necessary. However, in the case of temperature transmitters using thermal resistors or thermocouples, explosion-proof requirements must be taken into account when the electrical signals from the control room are fed into these instruments. When selecting instruments with explosion-proof features, it is essential to consider factors such as the level of danger present at the site, the types of materials involved, and the installation location.
Thermocouples and thermal resistors are generally flameproof and can meet the requirements of Zone 1, Group II A / II B, T3.
A thermometer should be a device that directly measures temperature and displays it on-site; in principle, it should not have a function for transmitting signals over distance. Such as bimetallic thermometers and bulb-type thermometers, as long as they are mechanical and do not rely on electricity, there is no need to consider explosion-proof issues at all, because they are inherently \"intrinsic safety\" type. If thermocouples or thermal resistors are used as temperature sensing elements and on-site display is required, power supply and signal conversion become necessary in order to transform the measured raw signals into readable analog or digital signals; in such cases, explosion protection must be taken into consideration. Depending on on-site requirements, explosion-proof or intrinsically safe instruments can be selected.