Selection method of armored thermal resistor

When wiring the armored thermal resistor, first open the junction box and then connect the wires. There are generally two wiring methods: two-wire and three-wire. The advantage of the three-wire connection is that it can prevent the indication error of the display instrument caused by the resistance value of the connecting wire of the bimetallic thermometer. The connecting wire between the armored thermal resistor and the display instrument should be insulated copper wire, and the compensation wire of the thermocouple shall not be used. The resistance value of the copper wire should be selected according to the data specified in the technical conditions of the display instrument, generally 2-50, and the resistance value of the wire can be adjusted by a DC balancing bridge. An armored thermal resistor cannot be used in parallel with two display instruments. Only a double-branch thermal resistor can be used with two display instruments. When not in use, the armored thermal resistor and its accessories must be kept in a place where the tungsten-rhenium thermocouple is not subject to vibration and collision. The most suitable storage conditions are: ambient temperature 10-35gc; relative humidity not more than 80%; the surrounding air should not contain substances that may cause corrosion of thermal resistor parts.
Armored thermal resistors have many advantages, such as small size, bendability, good mechanical properties, and long service life, so they play a greater role in people's lives. Their excellent characteristics make them popular with people, but everyone must pay attention to the method when choosing them.

Characteristics of armored thermal resistors

Armored thermal resistors have low thermal inertia and rapid response. For example, ordinary platinum resistors with a protective tube diameter of 2mm have a time constant of 25s; while armored thermal resistors with a metal casing diameter of -2mm have a time constant of only about 5. The armored element and the bottom of the protective tube are elastically compressed structures, which shorten the thermal response time and further improve the seismic resistance. Armored thermal resistors have bendable properties. Except for the head, armored thermal resistors can be bent in any direction, so they are suitable for temperature measurement of equipment with complex structures and small volumes.

Armored thermal resistors have a long service life. The resistor body of the armored thermal resistor is protected by the twist cover and metal sleeve of the iron insulation material. The thermal resistor wire is not easily corroded by harmful media. Therefore, its thermal resistor life is longer than that of ordinary thermal resistors, and it has good vibration and impact resistance. The selection method of armored thermal resistors is based on the temperature measurement range. Generally, thermocouples are selected for temperatures above 500℃, and thermal resistors are generally selected for temperatures below 500℃; selection is based on measurement accuracy: thermal resistors are selected for higher accuracy requirements, and thermocouples are selected for lower accuracy requirements. According to the measurement range, the temperature measured by thermocouples generally refers to the "point" temperature, and the temperature measured by thermal resistors generally refers to the average temperature of the space; the wiring of the 2-wire thermal resistor is simple, but the additional error of the lead resistance is brought in. Therefore, it is not suitable for manufacturing a-level precision thermal resistors, and the lead wires and wires should not be too long when used. The wire system can eliminate the influence of the lead resistance, and the measurement accuracy is higher than the 2-wire system. As a process detection element, it is the most widely used. The wire system can not only eliminate the influence of the lead resistance, but also eliminate the influence of the resistance when the resistance of the connecting wires is the same. When making high-precision measurements, a 4-wire system should be used.