How to use a multimeter to determine whether the temperature sensor is good or bad
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 negative temperature coefficient thermistor temperature sensor, and its output resistance decreases as the temperature increases. As the temperature increases, the output resistance of platinum thermistors increases.
Measuring the Quality of 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. Alternatively, the thermistor can be subjected to heating detection using a lighter. If the resistance value of the multimeter decreases with increasing temperature, it indicates that the thermistor temperature sensor is functioning properly. If the resistance value remains unchanged, it suggests that the thermistor temperature sensor is damaged.
Measure the quality of platinum resistance temperature sensor with a multimeter
Due to the fact that the platinum resistance temperature sensor has three lead wires, it is difficult to find which wire of different colors to connect with one of the multimeter probes. Connect the other probe to two additional leads. If the resistance values measured separately are found to be infinite or lower than 100 ohms after pairwise measurements, 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 measured actual resistance value differs significantly from the nominal resistance value, it indicates that the performance of the platinum thermistor is deteriorating.
Therefore, in order for an electric heater to maintain normal temperature control, its temperature sensor is crucial. The temperature sensor has malfunctioned, and the temperature controller of the electric water heater cannot receive the resistance signal transmitted by the temperature sensor, causing the temperature control system to malfunction. No matter how the temperature setting is set, it cannot have a controlling effect. Because there are four links in the closed door control system, and the temperature sensor is damaged in the detection and transmission link, the detection instrument in this link has a problem, and the temperature controller cannot control it.
A temperature sensor is a variable resistor controlled by temperature, which can be measured in the 100K resistance range. If it is a sensor with a negative temperature coefficient, the resistance value will decrease 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 of the sensor does not change, then there is also a problem!
Use a multimeter with a resistance of 1K Ω to measure the resistance value of both feet (note not to touch the resistance tube with your hands). Then, hold the resistance body with your hand and see if the resistance value gradually increases. If it increases slowly, it is good. If there is a short circuit, open circuit, or the resistance value remains unchanged, it is bad. The specific resistance value should be based on the actual measurement, as the thermistor value selected by the brand may not be the same.
