How to judge the temperature sensor with a multimeter
Nowadays, electric water heater into the ordinary people's families, 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, temperature sensor damage, 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 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 and become smaller, indicating that the thermistor temperature sensor is normal, the resistance did not change, indicating that the thermistor temperature sensor is damaged.
Measure the platinum thermistor temperature sensor with a multimeter.
As the platinum RTD temperature sensor has three lead wires, to find out which one of the different colours, 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 is normal, 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 to detect 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 gear, if the negative temperature coefficient of the sensor, in the sensor heated to warm up, the resistance 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 resistance tube), and then, with the hand pinch the resistor body itself, to see if the resistance value is slowly increasing, if it slowly increases, it is good, if the 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 according to the actual measurement shall prevail.
