How to use a multimeter to assess the temperature sensor's quality
Nowadays, electric water heaters have entered the families of ordinary people and have 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, the temperature heated by the measured medium water cannot be obtained accurately and in time, so that the electric water heater cannot accurately control the temperature.
The temperature sensors used in electric water heaters mainly include thermistor temperature sensors and platinum thermal resistance temperature sensors, which output resistance signals to the secondary instrument thermostat. Among them, the thermistor commonly used in electric water heaters is a thermistor temperature sensor with a negative temperature coefficient, and its output resistance becomes smaller as the temperature increases. The platinum thermal resistance increases its output resistance as the temperature rises.
Multimeter to measure the quality of NTC thermistor
Set the temperature sensor of the water heater to normal temperature. Connect the two test leads of the digital multimeter to the two pins of the thermistor to measure its actual resistance. Then compare the measured actual resistance with the nominal resistance, if the difference between the actual resistance and the nominal resistance is ±2 ohms, it is considered normal. On the contrary, the performance of the thermistor temperature sensor becomes worse or even damaged. It is also possible to heat the thermistor and heat it with a lighter. The resistance of the multimeter decreases as the temperature rises, indicating that the thermistor temperature sensor is normal, and the resistance value does not change, indicating that the thermistor temperature sensor damage.
Since the platinum thermal resistance temperature sensor has three lead wires, find out which one is of a different color, and connect it with one of the test leads of the multimeter. The other test lead is connected to the additional two lead wires respectively. The resistance values measured separately, if the resistance value is found to be infinite or lower than 100 ohms after two measurements, it means that the platinum thermal resistance is damaged. If the resistance values are not the same after two measurements, it means that there is a problem with the compensation line of the platinum thermal resistance or its lead-out line. At the same time, you can manually heat the platinum thermal resistance. If the resistance value does not change, it means that the platinum thermal resistance is damaged. If the measured actual resistance value differs greatly from the nominal resistance value, it means that the performance of the platinum thermal resistance is deteriorating.
Therefore, if the electric heater wants to control the temperature normally, its temperature sensor is very important. If 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-off control system, the damage of the temperature sensor is the detection and transmission link, so there is a problem with the detection instrument in this link, and the temperature controller cannot play a controlling role.
The temperature sensor is a variable resistor controlled by temperature. It can be measured with a 100K resistance range. If it is a sensor with a negative temperature coefficient, the resistance will decrease when the sensor is heated up. If it is completely open, there is no need to measure it. is broken. If the temperature of the temperature-sensing part of the sensor changes, but the resistance of the sensor does not change, there is a problem!
Use a multimeter with a resistance of 1KΩ to measure the resistance value of the two feet (note that the hands do not touch the resistance tube), and then pinch the resistance body itself with your hand to see if the resistance value increases slowly. If it increases slowly, it is good. If A short circuit, an open circuit, or a constant resistance value is bad. The specific resistance value is because the thermistor value selected by the brand is not necessarily the same, and the actual measurement should prevail.
Use the ohm position of the multimeter to measure the temperature sensor, and then warm it up by hand. If the resistance changes, it is good. If the resistance value does not change or there is no resistance value, it is bad.
