How to use a multimeter to determine the temperature sensor good or bad
Nowadays, the electric water heater enters the ordinary people's family, has become one of the main household appliances. The temperature sensor of the water heater is the main measurement sensor to obtain the heated medium water, the temperature sensor is damaged, it is unable to accurately and timely access to the temperature of the measured medium water heating, so that the electric water heater can not accurately control the temperature.
In the electric water heater with the temperature sensor mainly thermistor temperature sensor and platinum RTD temperature sensor, their output to the secondary instrumentation thermostat are resistance signals. One of the electric water heater is generally used thermistor negative temperature coefficient of the thermistor temperature sensor, as the temperature rises its output resistance becomes smaller. And platinum thermistor as the temperature rises its output resistance becomes larger.
Multimeter measurement of NTC thermistor good or bad
Place the temperature sensor of the water heater at room temperature. Connect the two pens of the digital multimeter to the two pins of the thermistor, and measure its actual blocking. Then the measured actual block and the nominal resistance value comparison, if the actual resistance value and the nominal resistance value difference ± 2 ohms is considered normal. On the contrary, thermistor temperature sensor performance deterioration or even damage. Can also be thermistor temperature detection, heating with a lighter, the resistance of the multimeter is with the temperature increases and becomes smaller, indicating that the thermistor temperature sensor is normal, the resistance did not change, indicating that the thermistor temperature sensor damage.
As the platinum thermistor temperature sensor has three lead wires, find out which one of the different colors, one of the pens with a multimeter connected to the immobility. Another pen were hit to connect the additional two leads. Resistance value measured separately, if the two two measurements found after the resistance value of infinity or less than 100 ohms, indicating that the platinum RTD damage. If the two measurements after the resistance value is not the same, that the platinum RTD compensation line or its lead line there are problems. At the same time you can give the platinum RTD manual heating, if the resistance value does not change that the platinum RTD is damaged. If the measured actual resistance value and the nominal resistance value of the difference is large, indicating that the performance of platinum RTD in the deterioration.
Therefore, electric heaters want to control the temperature normally, the temperature sensor is critical. Temperature sensor failure, electric water heater thermostat will not be able to accept the resistance signal transmitted from the temperature sensor, so the temperature control system failure. Temperature setting value, no matter how to set, can not play a role in controlling. Because there are four links in the closed control system, the temperature sensor damage is detected in the transmission link, so this link of the detection instrumentation problems, the thermostat can not play a control role.
Temperature sensor is controlled by the temperature of the variable resistance, can be measured with 100K resistance grade, if the negative temperature coefficient of the sensor, in the heating to the sensor warming time, the resistance value was down, if completely open circuit, do not have to measure, is definitely bad. If the sensor temperature sensing parts of the temperature change, and the sensor resistance does not change, it is also a problem!
With a multimeter resistance 1KΩ file, measure the resistance value of the two feet (note that the hand does not touch the resistor tube), and then, pinch the resistor body itself, to see if the resistance value is slowly increasing, if it slowly increases, it is good, if short-circuit, open-circuit, or the resistance value of the unchanged is bad, the size of the specific resistance value because the brand of the thermistor selected value is not necessarily the same, it should be based on the actual measurement.
Use the multimeter ohm gear to measure the temperature sensor, and then give it a warming by hand if the resistance value changes is good. If the resistance value is unchanged or no resistance value is bad.
