System composition and installation requirements of explosion-proof thermal resistors

Explosion-proof thermal resistor is a sensor used to measure temperature, which can be used safely in explosive environments. Its working principle is to use the gap explosion-proof principle to seal all parts that will produce sparks, arcs and dangerous temperatures in a junction box cavity with sufficient strength. When an explosion occurs in the cavity, the flame can be extinguished and cooled through the gap of the joint surface, so that the flame and temperature after the explosion cannot be transmitted to the outside of the cavity, thereby realizing temperature measurement.
Composition of explosion-proof thermal resistor system

The explosion-proof thermal resistor temperature measurement system is generally composed of thermal resistors, connecting wires and display instruments. The following two points must be noted:
① The graduation numbers of the thermal resistor and the display instrument must be consistent
② In order to eliminate the influence of the resistance change of the connecting wire, a three-wire connection method must be adopted.

The explosion-proof thermal resistor uses a junction box with a special structure to isolate the explosive mixed gas inside its shell from the sparks or arcs. The short-circuit repair of the resistor body will inevitably change the length of the resistor wire and affect the resistance value. For this reason, it is better to replace the resistor body. If welding is used for repair, it must be calibrated and qualified before it can be used.
Installation requirements for explosion-proof thermal resistors
When installing thermal resistors, attention should be paid to ensuring accurate temperature measurement, safety, reliability, and easy maintenance, and not affecting equipment operation and production operations. To meet the above requirements, the following points should be noted when selecting the installation location and insertion depth of the thermal resistor:
1. In order to ensure sufficient heat exchange between the measuring end of the thermal resistor and the measured medium, the measuring point location should be reasonably selected, and thermal resistors should be installed near valves, elbows, and dead corners of pipelines and equipment as much as possible.
2. Thermal resistors with protective sleeves have heat transfer and heat dissipation losses. In order to reduce measurement errors, thermocouples and thermal resistors should have sufficient insertion depth:
(1) For thermal resistors that measure the temperature of the fluid in the center of the pipeline, generally The measuring end should be inserted into the center of the pipe (vertically or obliquely installed). If the pipe diameter of the measured fluid is 200 mm, the insertion depth of the thermal resistor should be 100 mm;
(2) For the temperature measurement of high-temperature, high-pressure and high-speed fluids (such as main steam temperature), in order to reduce the resistance of the protective sleeve to the fluid and prevent the protective sleeve from breaking under the action of the fluid, the protective tube can be shallowly inserted or a heat sleeve thermal resistor can be used. The shallow insertion thermal resistor protective sleeve should be inserted into the main steam pipe to a depth of not less than 75 mm; the standard insertion depth of the heat sleeve thermal resistor is 100 mm;
(3) If the temperature of the flue gas in the flue needs to be measured, even if the flue diameter is 4 m, the insertion depth of the thermal resistor is 1 m.
(4) When the insertion depth of the measuring element exceeds 1 m, it should be installed vertically as much as possible, or a support frame and protective sleeve should be installed.