How to judge the quality of a temperature sensor using a multimeter
Nowadays, electric water heaters have entered ordinary households and become one of the main household appliances. The temperature sensor of the water heater is the main measurement sensor for obtaining the heated medium water. If the temperature sensor is damaged, it cannot accurately and timely obtain the temperature of the heated medium water, making it difficult for the electric water heater to accurately control the temperature.
The temperature sensors used in electric water heaters mainly include thermistor temperature sensors and platinum thermistor temperature sensors, which output resistance signals to the secondary instrument temperature controller. The thermistor commonly used in electric water heaters is a thermistor temperature sensor with a negative temperature coefficient, and its output resistance decreases as the temperature increases. As the temperature increases, the output resistance of platinum thermistors increases.
The quality of measuring NTC thermistors with a 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 and measure its actual resistance. Then compare the measured actual resistance with the nominal resistance. If the actual resistance differs by ± 2 ohms from the nominal resistance, it is considered normal. On the contrary, the performance of thermistor temperature sensors deteriorates or even damages. It is also possible to perform heating detection on the thermistor and use a lighter for heating. The resistance value of the multimeter decreases as the temperature increases, indicating that the thermistor temperature sensor is normal and the resistance value has not changed, indicating that the thermistor temperature sensor is damaged.
Use a multimeter to measure the quality of a platinum thermistor temperature sensor
Due to the platinum thermistor temperature sensor having three lead wires, find out which one is of different colors and use a multimeter to connect one of the probes without moving. The other probe is connected to two additional leads. If the resistance values measured separately are found to be infinite or below 100 ohms after pairwise measurement, it indicates that the platinum thermistor is damaged. If the resistance values are different after two measurements, it indicates that there is a problem with the compensation wire or its lead wire of the platinum thermistor. At the same time, the platinum thermistor can be manually heated. If the resistance value does not change, it indicates that the platinum thermistor is damaged. If the actual resistance value measured differs significantly from the nominal resistance value, it indicates that the performance of platinum thermistors is deteriorating.
Therefore, if an electric heater wants to control temperature normally, its temperature sensor is crucial. If the temperature sensor malfunctions, the temperature controller of the electric water heater cannot receive the resistance signal transmitted by the temperature sensor, resulting in a malfunction of the temperature control system. No matter how the temperature setting value is set, it cannot have a control effect. Because there are four stages in the closed control system, and a damaged temperature sensor is the detection transmission stage, the detection instrument in this stage has problems, and the temperature controller cannot play a control role.
A temperature sensor is a variable resistor controlled by temperature, which can be measured using a 100K resistance range. If it is a negative temperature coefficient sensor, the resistance value decreases when heating the sensor. If it is completely open circuit, there is no need to measure it, it is definitely broken. If the temperature of the temperature sensing part of the sensor changes, but the resistance value of the sensor does not change, then there is also a problem!
Using a multimeter with a resistance of 1K Ω, measure the resistance value of both pins (note that do not touch the resistance tube with your hands). Then, pinch the resistance body with your hands and see if the resistance value slowly increases. If it increases slowly, it is good. If there is a short circuit, an open circuit, or a constant resistance value, it is bad. The specific resistance value is different because the thermistor value selected by the brand may not be the same, and should be based on actual measurement.
