Methods to determine the good or bad status of a temperature sensor

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I. Classification and applications of temperature sensors 1. Thermocouples: Based on the thermoelectric effect, they are suitable for high temperatures (around -200°C to 2000°C), but cold-junction compensation is required. Common types include K type, E type, J type, etc. Used in metallurgical furnaces (Type S) and aero-engine turbines (Type K). 2. Thermal resistors (such as platinum resistors PT100): high precision of 0.1°C, good stability, suitable for temperatures ranging from -200°C to 850°C. Used in aerospace and precision instruments. 3. Thermistors (NTC/PTC): They have high sensitivity, fast response times, and low costs, but their temperature measurement range is narrow (-50°C–150°C). It is commonly used in home appliances and automotive electronics. Second, how to determine whether a temperature sensor is damaged. Air conditioners primarily use thermistor temperature sensors (mainly of the NTC type). For NTC thermistors, the resistance value decreases as the temperature rises; for PTC thermistors, the resistance value increases as the temperature rises. In fixed-frequency air conditioners, one tube temperature sensor is usually installed in the indoor unit, while in inverter air conditioners, tube temperature sensors are required in both the indoor and outdoor units. Method 1: Measurement of basic parameters (thermistors). Disconnect the power supply of the device and unplug the probe wires, then set the multimeter to the resistance measurement mode. At around 25°C, measure the resistance at both ends of the probe in the given environment; if the resistance is less than 1k or greater than 10ok, it is generally damaged. The basic performance is also evaluated by comparing it with the nominal values indicated on the probe (commonly 5K, 10K, 20K, etc.); if the error exceeds 10%, the probe needs to be replaced. Method 2: Dynamic temperature testing – Ice water test: Immerse the probe in an ice-water mixture at a certain temperature (in °C); the measured resistance value should match the nominal value for that temperature (for example, a PT100 probe should have a resistance of 100). Hot water test: Place the probe in water at around 50°C; the resistance value should be significantly lower than that measured at room temperature (for example, the resistance of a 10K probe drops to around 3-4K at 50°C). Rapid change detection: Heat the probe with a hair dryer and observe whether the resistance value displayed on the multimeter changes steadily over time; if there are any fluctuations or stalls, the performance is abnormal.