Applications of PTC thermistors:
1. Delayed Start PTC Thermistor: From the It characteristic curve of the PTC thermistor, it can be seen that after an external voltage is applied, the PTC thermistor needs to go through a certain period of time to reach the high resistance state. This delay characteristic is used for delayed start applications.
Application Principle: When a motor starts, it must overcome its own inertia and the reaction force of the load (such as the reaction force of the refrigerant when a refrigerator compressor starts). Therefore, a large current and torque are required when starting a motor. Once it is running normally, the required torque needs to be significantly reduced to save energy. Adding an auxiliary coil to the motor, which only operates during startup and disconnects after normal operation, achieves this effect. Connecting a PTC thermistor in series with the starting auxiliary coil, so that the PTC thermistor enters a high-resistance state after startup and disconnects the auxiliary coil, perfectly achieves this effect.
2. Overload Protection PTC Thermistor: A PTC thermistor is a protective element that automatically protects against and recovers from abnormal temperatures and currents, commonly known as a "self-resetting fuse" or "recovery fuse." It replaces traditional fuses and can be widely used for overcurrent and overheat protection in motors, transformers, switching power supplies, electronic circuits, etc. The PTC thermistor reduces residual current by limiting the energy dissipation throughout the circuit through its resistance fluctuations.
Traditional fuses cannot reset themselves after a circuit blows, while PTC thermistors for overload protection can return to their pre-protection state after the fault is cleared. When a fault recurs, they can resume their overcurrent and overheat protection functions. When selecting a PTC thermistor for overload protection, first determine the maximum normal operating current of the circuit (the non-operating current of the PTC thermistor) and the highest ambient temperature at the installation location (during normal operation). Second, consider the protection current (the operating current of the PTC thermistor), the maximum operating voltage, and the rated zero-power resistance. The component's dimensions should also be considered. Application principle: When the circuit is in normal operation, the current through the PTC thermistor is less than the rated current. The PTC thermistor is in its normal operating state with very low resistance, which does not affect the normal operation of the protected circuit.
When a circuit fault occurs and the current greatly exceeds the rated current, the PTC thermistor used for overload protection heats up suddenly, becoming high-resistance, thus putting the circuit in a relatively "open" state and protecting it from damage. Once the fault is cleared, the PTC thermistor automatically returns to a low-resistance state, and the circuit resumes normal operation.
3. Overheat Protection PTC Thermistors: PTC thermistor sensors have a Curie temperature range of 40-300℃. The section on the RT characteristic curve of a PTC thermistor sensor where the resistance value rises sharply after entering the transition region can be used for temperature, level, and flow sensing applications. Based on the temperature-sensitive characteristics of PTC thermistors, they are designed for overheat protection and temperature sensing applications, including switching power supplies, electrical equipment (motors, transformers), and power devices (transistors). Their advantages include small size, fast response time, and easy installation.
The difference between PTC and KTY: Siemens uses KTY.
First of all, they are all types of motor temperature protection devices;
PTC is a resistor with a positive temperature coefficient, meaning that its resistance increases as the temperature rises.
Another type is the NTC (Negative Temperature Coefficient) variable resistor, where the resistance decreases as temperature rises; it is generally not used for motor protection. The KTY (Knowledge-Temperature Coefficient) resistor boasts high accuracy, high reliability, and strong stability. It is primarily used in temperature measurement. The KTY is covered with a layer of silicon dioxide insulation material, with a 20mm diameter metal hole in the insulation layer; the entire bottom layer is metallized. The current distribution is conical from top to bottom through crystal arrangement, hence the name "diffusion resistor." The KTY exhibits a practically linear temperature coefficient throughout the entire temperature measurement range, ensuring high accuracy in temperature measurement.
PT100 platinum resistance thermometers are designed and manufactured based on the fundamental principle that the resistance of platinum wire changes with temperature. They are available in 10-ohm (Pt10) and 100-ohm (Pt100) models, based on their resistance value R (°C) at 0°C, with a temperature range of -200 to 850°C for both. The 10-ohm platinum resistance thermometer uses a thicker platinum wire as its sensing element, resulting in significantly better temperature resistance than the 100-ohm model, suitable for temperatures above 650°C. The 100-ohm platinum resistance thermometer is primarily used for temperatures below 650°C, although it can also be used above 650°C, where a Class A error is not permitted. The resolution of the 100-ohm platinum resistance thermometer is 10 times greater than that of the 10-ohm model, placing a correspondingly higher demand on the secondary instrument. Therefore, for temperature measurements below 650°C, the 100-ohm platinum resistance thermometer should be used whenever possible.
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