Commonly used common industrial thermal resistors mainly include:
1. Platinum thermal resistance: widely used to measure the temperature in the range of (-200 ~ 850) °C. In a few cases, the low temperature can be measured to 1K, and the high temperature can be measured to 1000°C. Its physical and chemical properties are stable and its reproducibility is good, but it is expensive. Platinum thermal resistance is approximately linear with temperature. Its index number is mainly Pt10 and Pt100.
2. Copper thermal resistance: widely used to measure the temperature in the range of (-50 ~ 150) °C. The advantage is that the high purity copper wire is easy to obtain, the price is cheap, the interchangeability is good, but it is easy to oxidize. Copper thermal resistance is linear with temperature. The index number is mainly Cu50 and Cu100.
Armored thermal resistors are developed on the basis of armored thermocouples and are manufactured from a combination of thermal resistors, insulating materials, and metal sleeves. They are characterized by a small form factor (up to a diameter of 20 Millimeters), so the reaction speed, has good mechanical properties, resistance to shock and vibration, has good flexibility, and is not susceptible to the erosion of harmful media.
Before using a thermal resistor, it must be checked for good loops. A simple check method is to pull the thermal resistor out of the protective tube and measure its resistance with a multimeter. If the multimeter reads “0†or the multimeter reading is less than the R0 value, the thermal resistor is short-circuited and a short circuit must be found to repair it; if the multimeter reads “∞â€, the thermal resistor has been disconnected and cannot be used; if the multimeter reads The resistance value is higher than R0, indicating that the thermal resistance is normal.
When the resistance value of the thermal resistance is incorrect, the resistance wire should be increased or decreased from the intersection of the lower end points and should not be adjusted from other places. After completely adjusting, the resistance wire should be arranged neatly and cannot be touched, and it is still wrapped as it is.
The repaired thermal resistance must be qualified before being used.
When the thermal resistance is installed, the insertion depth is not less than 8 to 10 times the outer diameter of the thermal resistance protection tube, and the thermal resistance of the thermal resistance is increased as much as possible. The thermal resistance is mounted as vertically as possible to prevent bending at high temperatures. In order to reduce the error caused by radiant heat and heat conduction during use, the thermal resistance should be as close as possible to the surface temperature of the protection sleeve and the measured medium, and the black coefficient of the thermal resistance protection sleeve should be reduced.
When measuring the temperature with a secondary instrument that matches the thermal resistance, the thermal resistance is placed on the site where the temperature is measured and the secondary instrument is placed in the operating room. If measured with an unbalanced bridge, the wires connecting the thermistors are distributed on one arm of the bridge. Since the RTD and the meter generally have a long distance between them, the resistance of the two connecting wires changes with the temperature and will be added to the one arm of the unbalanced bridge together with the change of the resistance value of the thermal resistance, so that the measurement Produce large errors. In order to reduce this error, the three-wire connection method (Fig. 1) is generally adopted when the temperature-measurement thermal resistance is connected with the meter. That is, three leads are drawn from the thermal resistance, and the two wires connecting the thermal resistance are respectively adjacent to each other. Two bridge arms (Figure 2). When the ambient temperature changes so that the resistance value of the wire changes, the generated effects just cancel each other out so that the unbalanced voltage at the output of the bridge will not change. The change in the resistance of the other conductor R1 has only a slight effect on the supply voltage, but within the accuracy range.
1. Platinum thermal resistance: widely used to measure the temperature in the range of (-200 ~ 850) °C. In a few cases, the low temperature can be measured to 1K, and the high temperature can be measured to 1000°C. Its physical and chemical properties are stable and its reproducibility is good, but it is expensive. Platinum thermal resistance is approximately linear with temperature. Its index number is mainly Pt10 and Pt100.
2. Copper thermal resistance: widely used to measure the temperature in the range of (-50 ~ 150) °C. The advantage is that the high purity copper wire is easy to obtain, the price is cheap, the interchangeability is good, but it is easy to oxidize. Copper thermal resistance is linear with temperature. The index number is mainly Cu50 and Cu100.
Armored thermal resistors are developed on the basis of armored thermocouples and are manufactured from a combination of thermal resistors, insulating materials, and metal sleeves. They are characterized by a small form factor (up to a diameter of 20 Millimeters), so the reaction speed, has good mechanical properties, resistance to shock and vibration, has good flexibility, and is not susceptible to the erosion of harmful media.
Before using a thermal resistor, it must be checked for good loops. A simple check method is to pull the thermal resistor out of the protective tube and measure its resistance with a multimeter. If the multimeter reads “0†or the multimeter reading is less than the R0 value, the thermal resistor is short-circuited and a short circuit must be found to repair it; if the multimeter reads “∞â€, the thermal resistor has been disconnected and cannot be used; if the multimeter reads The resistance value is higher than R0, indicating that the thermal resistance is normal.
When the resistance value of the thermal resistance is incorrect, the resistance wire should be increased or decreased from the intersection of the lower end points and should not be adjusted from other places. After completely adjusting, the resistance wire should be arranged neatly and cannot be touched, and it is still wrapped as it is.
The repaired thermal resistance must be qualified before being used.
When the thermal resistance is installed, the insertion depth is not less than 8 to 10 times the outer diameter of the thermal resistance protection tube, and the thermal resistance of the thermal resistance is increased as much as possible. The thermal resistance is mounted as vertically as possible to prevent bending at high temperatures. In order to reduce the error caused by radiant heat and heat conduction during use, the thermal resistance should be as close as possible to the surface temperature of the protection sleeve and the measured medium, and the black coefficient of the thermal resistance protection sleeve should be reduced.
When measuring the temperature with a secondary instrument that matches the thermal resistance, the thermal resistance is placed on the site where the temperature is measured and the secondary instrument is placed in the operating room. If measured with an unbalanced bridge, the wires connecting the thermistors are distributed on one arm of the bridge. Since the RTD and the meter generally have a long distance between them, the resistance of the two connecting wires changes with the temperature and will be added to the one arm of the unbalanced bridge together with the change of the resistance value of the thermal resistance, so that the measurement Produce large errors. In order to reduce this error, the three-wire connection method (Fig. 1) is generally adopted when the temperature-measurement thermal resistance is connected with the meter. That is, three leads are drawn from the thermal resistance, and the two wires connecting the thermal resistance are respectively adjacent to each other. Two bridge arms (Figure 2). When the ambient temperature changes so that the resistance value of the wire changes, the generated effects just cancel each other out so that the unbalanced voltage at the output of the bridge will not change. The change in the resistance of the other conductor R1 has only a slight effect on the supply voltage, but within the accuracy range.
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