How to judge the quality of temperature sensor with multimeter
Nowadays, electric water heaters have entered ordinary people's families and become one of the main household appliances. The temperature sensor of the water heater is the main measuring sensor to obtain the heated medium water. If the temperature sensor is damaged, the temperature of the measured medium water cannot be obtained accurately and timely, which makes the electric water heater unable to control the temperature accurately.
The temperature sensors used in electric water heaters mainly include thermistor temperature sensors and platinum thermal resistance temperature sensors, and their outputs to the secondary instrument thermostat are all resistance signals. Among them, the thermistor commonly used in electric water heaters is a thermistor temperature sensor with negative temperature coefficient, and its output resistance decreases with the increase of temperature. However, the output resistance of platinum thermal resistance increases with the increase of temperature.
Measuring NTC thermistor with multimeter
Place the temperature sensor of the water heater at room temperature. Connect the two probes of the digital multimeter to the two pins of the thermistor respectively, and measure its actual stop. Then compare the measured actual resistance with the nominal resistance. If the actual resistance differs from the nominal resistance by 2 ohms, it is considered normal. On the contrary, the performance of thermistor temperature sensor becomes worse or even damaged. You can also test the thermistor and heat it with a lighter. The resistance of the multimeter decreases with the increase of temperature, indicating that the thermistor temperature sensor is normal and the resistance has not changed, indicating that the thermistor temperature sensor is damaged.
Measuring the quality of platinum thermal resistance temperature sensor with multimeter
Since there are three lead wires of platinum thermal resistance temperature sensor, find out which one is of different colors and connect it with one of the probes of multimeter. The other stylus is respectively connected with two additional leads. The resistance values measured separately, if it is found that the resistance value is infinite or lower than 100 ohms after pairwise measurement, it means that the platinum thermal resistance is damaged. If the resistance values are different after two measurements, it indicates that there is a problem with the compensation line or its lead-out line of platinum thermal resistance. At the same time, the platinum thermal resistor can be heated manually. If the resistance value does not change, it means that the platinum thermal resistor is damaged. If there is a big difference between the measured actual resistance and the nominal resistance, it shows that the performance of platinum thermal resistance is getting worse.
Therefore, the temperature sensor of electric heater is very important if it wants to control the temperature normally. When the temperature sensor fails, the thermostat of the electric water heater cannot receive the resistance signal transmitted by the temperature sensor, so the temperature control system fails. No matter how the temperature set point is set, it cannot play a controlling role. Because there are four links in the closed-door control system, the damage of temperature sensor is the detection and transmission link, so there is something wrong with the detection instrument in this link, and the thermostat can not play a control role.
A temperature sensor is a variable resistance controlled by temperature, which can be measured with a resistance of 100K. If it is a sensor with negative temperature coefficient, the resistance will decrease when the sensor is heated up. If it is completely open, it is unnecessary to measure it, and it must be broken. If the temperature of the temperature sensing part of the sensor changes, but the resistance of the sensor does not change, it is also a problem!
Use a multimeter to measure the resistance value of both feet (be careful not to touch the resistance tube), and then hold the resistance body by hand to see if the resistance value increases slowly. If it increases slowly, it is good. If it is short-circuited, open-circuited, or the resistance value remains unchanged, it is bad. The specific resistance value is not the same, because the thermistor value selected by the brand is not necessarily the same, it should be based on the actual measurement.
Use the ohm gear of multimeter to measure the temperature sensor, and then heat it by hand. If the resistance changes, it is good. If the resistance is constant or there is no resistance, it is bad.
