NTC Thermistor Detection Method

1. Measure the nominal resistance value Rt

The method for measuring an NTC thermistor with a multimeter is the same as that for measuring a regular fixed resistor, i.e., select the appropriate ohm range based on the nominal resistance of the NTC thermistor to directly measure the actual value of Rt. However, since NTC thermistors are highly sensitive to temperature, the following precautions should be taken during testing: diode

1. As defined by the nominal resistance value Rt, this value is measured by the manufacturer at an ambient temperature of 25°C. Therefore, when measuring Rt with a multimeter, the ambient temperature should also be close to 25°C to ensure the reliability of the test.  diode

2. The measured power must not exceed the specified value to avoid measurement errors caused by the thermal effect of current. For example, for the MF12-1 NTC thermistor with a rated power of 1W, the measurement power P1 is 0.2mW. Assuming the nominal resistance value Rt is 1kΩ, the test current is:

It is clearly more appropriate to use the R×lk range, where the full-scale current Im typically ranges from several tens to a hundred or so microamps. For example, the commonly used 500-type multimeter's R×1k range has an Im of 150uA, which is very close to 141uA.  3. Pay attention to proper operation. During testing, avoid holding the thermistor body with your fingers to prevent the influence of body temperature on the test results.

II. Estimating the Temperature Coefficient αt

First, measure the resistance value Rt1 at room temperature t1; then use a soldering iron as a heat source, bring it close to the thermistor Rt1, and measure the resistance value Rt2. Simultaneously, use a thermometer to determine the average temperature t2 on the surface of the thermistor RT at this point. Input the measured results into the following formula: diode

αt≈(Rt2-Rt1)/[Rt1(t2-t1)]

The αt of NTC thermistors is less than 0.

Notes:

When heating a thermistor, use a small-power soldering iron of about 20W, and avoid direct contact or proximity of the iron tip to the thermistor to prevent damage.

2. If the measured αt > 0, it indicates that the thermistor is not NTC but FTC. diode