Resistance of glaze: The difference between special resistors and thermistors
2025-11-22
What is resistance?
The full name of resistor is resistor. As the name suggests, the resistive coating is an element that blocks current. Resistance is measured in ohms, and the size of the resistance is the measure of the degree of obstruction. The unit is ohm (Ω). Due to writing issues, engineers usually use the capital letter R to represent the unit. Classification of resistors: According to various practical application requirements, resistors are divided into special resistors and thermistors. Next, the editor of Fourchu will briefly introduce them for us. Let's take a look!
Special resistor
1) Definition: Special resistors are a type of limiting element that responds rapidly to voltage changes. They can be regarded as a kind of nonlinear coated resistors. This voltage is called the rotation voltage. When the voltage applied across the coated resistor is less than the rotation voltage, it can be considered that the coated resistor is infinitely large. When the voltage applied across the two ends exceeds the rotation voltage, the value of the coated resistor will be very small within a short period of time, resulting in a short circuit at the two ends, and are generally used in the power protection circuits of electrical appliances, that is, to short-circuit the neutral and live wires, thereby protecting the subsequent circuits. In daily life, this is manifested as tripping or tripping the circuit breaker, and the solution is to replace the coated resistor or directly remove the voltage-sensitive tank.
2) How to Select the Model
The commonly used resistive circuits with glaze coating are all applied in power levels. If the selection is improper, a phenomenon of voltage-sensitive explosion will occur in the circuit. When selecting, the limit of the turning voltage should be considered. For example, for the 471 type, its turning point voltage is around 470V, while the average voltage of our power grid is around 220V, with a peak-to-peak voltage of 220/√2, which is around 390V. Generally, 80V is considered as the limit. If the blank voltage is too small, the glaze resistor will heat up during continuous operation, affecting its service life.
Thermistor
Code: RT. Thermistors are divided into two types: positive temperature coefficient thermistors and negative temperature coefficient thermistors. Unlike thermocouples, positive temperature coefficient thermistors (commonly known as PTC) have a resistance of only a few ohms to a few ohms at room temperature. Negative temperature coefficient thermistors (NTC) have a resistance of several thousand ohms at room temperature. Even a resistance of a few ohms can change with specific environmental conditions. Generally, within a certain interval, they have an approximately linear volt-ampere characteristic curve, meeting our design requirements. The selection of thermocouples is the same accordingly.
Practical application
Engineers often use PTC as a protection mechanism to safeguard the input or output. When the circuit gets extremely hot, the resistance of the PTC thermistor becomes very high, effectively acting like an open circuit to protect the circuit. NTC thermistors are commonly used in AD sampling circuits. For more information on the resistance-related details, please visit Fourchu Electric.
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