Common installation and repair precautions for temperature measurement of thermistor and platinum resistor

Possible causes of thermal resistance temperature measurement faults include instrument display values lower than actual values or unstable readings. There may be metal shavings, dust, dirt between terminal posts, and thermal resistance short circuits (such as water droplets) inside the protective tube. Remove the metal shavings, clean up dust, water droplets, etc., find the short circuit point, strengthen insulation, etc. The display value is infinite. Replace the resistor body, or weld and tighten the wiring screws. The relationship between resistance and temperature changes. Platinum resistance wire material is corroded and deteriorated. Replace the thermal resistance wire. The instrument display value is zero or has negative values. The instrument and thermal resistance wire are connected incorrectly. Correct the wiring of the thermal resistance short circuit, or find the short circuit and strengthen insulation.

The insertion depth of the thermal resistor should generally not be less than 8-10 times the outer diameter of the sleeve, and should generally not be less than 300mm. If the insertion depth is not sufficient and the exposed part is well ventilated, the measured temperature will be 3-4 degrees lower than the actual temperature.

When installing on pipelines, the temperature sensing element of the thermal resistor should form a reverse flow with the measured medium, at least at a 90 ° angle to the direction of the measured medium flow; At the same time, half of the total length of the temperature sensing element should be placed at the position of the highest flow velocity, and the end of the protective sleeve of the platinum resistor should cross the centerline of the current beam by 50-70mm.

To prevent liquids and dust from seeping into the junction box of the resistor, the junction box cover should be facing upwards and the outlet bolt should be facing downwards, especially in places where rainwater splashes, special attention should be paid.

Repair of Platinum Resistors and Several Issues to Consider

1. Platinum resistors that have been repaired and restored must pass inspection before they can be used again.

2. If you want to change the length of the resistor, you are only allowed to change the length of the lead wire, and it is not allowed to change the length of any part of the resistor.

3. After opening the cable tie, first check if the mica sheet is damaged, and then check if the connection between the platinum wire lead and the lead wire is good. If the platinum wire is broken, it can be welded with an arc of voltage 6-8 V. If the connection between the platinum wire and the silver lead wire is broken, it can be welded with an arc of voltage 10-14 V. After welding, check whether it meets the standards and cut off excess parts to avoid measurement accuracy caused by changes in resistance.

4. Resistance short circuit faults are rare and easy to handle. As long as the short circuit point is identified, heat-resistant insulation material (mica sheet) is used to cushion the insulation, and a small amount of paint is used to fix it, it can be repaired.

5. The platinum wire is very fine (Φ 0.03~0.07mm), and repair requires patience and attention to detail. When repairing, gently pull the platinum wire out of the protective sleeve (do not forcefully pull it out when the platinum wire collides with the inner wall of the pottery jar).