Multimeter - how to measure thermistor
Thermistors are a type of sensitive data information system components, which can be divided into positive temperature and correlation coefficient thermistors (PTC) and negative temperature coefficient thermistors ( NTC). The main characteristic of the typical structure of the thermistor is that it is sensitive to changes in the temperature environment, and different temperatures can have different resistance values. Positive temperature coefficient thermistors (PTC) increase the resistance value of negative temperature coefficient thermistors (NTC) at higher temperatures when the temperature is higher, and the resistance value decreases, which belongs to semiconductor devices.
However, we need to pay attention to this: the thermal resistance of the material is not subject to import and export trade links as part of the tariff 85.41 semiconductor electronic devices.
Test its resistance in the indoor environment, and then pinch the handle product test to see if the resistance becomes smaller, if the change indicates that it is normal, abnormal, and vice versa.
Note: To accurately control the measurement during the test, we must use a special instrument.
Thermal methods can be used to test thermistors. Use a multimeter resistance file to connect the two leads to the two leads, and then a hot soldering iron (20W can be a) to heat the thermistor (near the thermistor) connected to the thermistor. The material used for the resistance of the PTC thermistor, such as when the temperature rises, the resistance should increase; for the NTC type thermistor, when the temperature gradually increases, the resistance should decrease. If the resistance does not change when the thermistor is heated, the thermistor is damaged.
Detecting whether the thermistor is good or bad by heating method
Measuring resistance with a multimeter is a method with a very important theoretical basis for management engineers, and it is also something new engineers need to master through solid student learning. In today's multimeter resistance measurement knowledge sharing, we will share the basic knowledge of multimeter resistance measurement technology for new engineers, that is, how to use a multimeter to test the quality of thermistor components. Let's take a look at it.
The effect of detecting a positive temperature coefficient thermistor (PTC) is
Detection, with a multimeter R & times; 1 block, the specific operation in two steps:
1. Analysis and detection of normal temperature environment (indoor space design working temperature data can be close to 25°C); touch the two test leads to the two pins of the PTC thermistor to measure the actual development affecting resistance value, and compare it with the nominal resistance value , the difference between the two is within ±2Ω, which means it can be normal. If the difference between the nominal and actual resistance of the resistor is too large, then the performance is poor or damaged.
2. Warm detection; test at room temperature periodically to test the second step - heating is measured, a heat source (for example, soldering iron) close to the PTC thermistor to heat, while monitoring the resistance value, use a multimeter to see if the temperature increases, And if so, as described by the normal thermistor, if there is no change in resistance, it indicates that the performance is degraded and cannot continue to be used. Be careful not to get too close to the PTC thermistor material or to prevent direct contact with the thermistor from scorching the heat source.
Detection of the Negative Temperature Coefficient of Thermal Material Resistance (NTC)
1. Measuring the nominal resistance value Rt of the control system: The method of measuring the NTC thermistor with a multimeter is the same as the method of measuring a resistance, that is, we can freely choose according to the nominal resistance of the NTC thermistor. The electrical barrier can directly affect the actual value of Rt measured. Since the NTC thermistor is sensitive to temperature, the following points should be noted during the test: ARt is measured by the manufacturer when the ambient temperature is 25°C, so when measuring Rt with a multimeter, it should also be carried out when the ambient temperature is close to 25°C , to ensure the reliability of the test. B The measurement power must not exceed a predetermined value in order not to cause heating effects of measurement error currents. C Pay attention to the correct operation. When testing, do not hold the main body of the thermistor with your hands to avoid a significant impact on the test results.
2. Estimate the temperature coefficient of αt: at room temperature t1 to Rt1, then use the electric soldering iron as the heat source, close to the room temperature of the thermistor to measure the resistance value, RT2 to measure the first resistance value, and measure the temperature with the thermistor RT The surface case average temperature t2 is then calculated.
