Model meaning and parameters of NTC thermistor

　　As we all know, an NTC thermistor is a thermal element with a negative temperature coefficient that can pass a strong current of 1 to 10A. The typical characteristic of thermistor is that it is sensitive to temperature, showing different resistance values at different temperatures. Let's take a look at the model naming rules of thermistors and the technical parameters of thermistors.

　　Naming rules for thermistor models:

　　According to the standard SJ1152-82 "Sensitive Component Model Nomenclature", the product model of a sensitive resistor consists of the following four parts. The first part: main name (represented by letters); the second part: category (represented by letters); the third part: use or characteristics (represented by letters or numbers); the fourth part: serial number (represented by numbers). ①The symbols and meanings of the main name and category part are shown in Table 1. ② When the purpose or characteristic part is represented by numbers, it shall comply with the regulations in Table 2; when it is represented by letters, it shall comply with the regulations in Table 1-7. ③The part of the serial number is represented by numbers.

　　The diameter of the NTC thermistor is between 5 and 20mm. Its main technical parameters are as follows:

　　Zero power resistance value RT (Ω)

　　RT refers to the resistance value measured with a measurement power that causes the resistance value change to be negligible relative to the total measurement error at a specified temperature T

　　Rated zero-power resistance value R25 (Ω)

　　According to the national standard, the rated zero-power resistance value is the resistance value R25 measured by the NTC thermistor at the reference temperature of 25 ℃, and this resistance value is the nominal resistance value of the NTC thermistor. The resistance value of the NTC thermistor is usually referred to as this value.

　　Thermal time constant (τ)

　　Refers to the thermal inertia of the thermistor. That is, in the reactive power state, when the ambient temperature changes abruptly, the time required for the temperature of the resistor body to change from the initial value to 63.2% of the difference between the final temperature.

　　Dissipation coefficient (δ)

　　At a specified ambient temperature, the NTC thermistor dissipation factor is the ratio of the change in power dissipated in the resistor to the corresponding temperature change in the resistor body.

　　Material constant (thermal index) B value (K)

　　It is a parameter describing the physical properties of the thermistor material, and it is also an index of thermal sensitivity. The larger the B value, the higher the sensitivity of the thermistor. It should be noted that in actual operation, the B value is not a constant, but increases slightly with the increase of temperature.

　　Zero power temperature coefficient of resistance (αT)

　　At a specified temperature, the ratio of the relative change of the zero-moving power resistance value of the NTC thermistor to the temperature change value that causes the change.

　　Rated power Pn

　　Under the specified technical conditions, the allowable power consumption of the thermistor for long-term continuous operation. At this power, the temperature of the resistor body itself does not exceed its maximum operating temperature.

　　Maximum working temperature Tmax

　　Under the specified technical conditions, the maximum temperature allowed for the thermistor to work continuously for a long time.

　　Measured power Pm

　　When the thermistor is at a specified ambient temperature, the resistance change caused by the heating of the resistance body by the measurement current can be ignored relative to the total measurement error.

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