Application of PTC Thermistor
1. Delay start PTC thermistor
From the It characteristic curve of the PTC thermistor, it is known that the PTC thermistor takes a period of time to reach the high resistance state after the voltage is applied, and this delay characteristic is used for delayed start-up purposes.
When the motor starts, it needs to overcome its own inertia and the reaction force of the load (for example, the reaction force of the refrigerant must be overcome when the refrigerator compressor is started), so the motor needs a large current and torque to start. When the rotation is normal, in order to save energy, the required torque will be greatly reduced. Add a set of auxiliary coils to the motor, it only works when it starts, and it disconnects when it is normal. Connect the PTC thermistor in series with the starting auxiliary coil. After starting, the PTC thermistor enters the high resistance state to cut off the auxiliary coil, which can achieve this effect.
2. Overload protection PTC thermistor
PTC thermistor for overload protection is a protection element that automatically protects and recovers from abnormal temperature and abnormal current, commonly known as “resettable fuse” and “ten thousand-time fuse”. It replaces traditional fuses and can be widely used for overcurrent and overheating protection of motors, transformers, switching power supplies, electronic circuits, etc. PTC thermistors for overload protection limit the consumption in the entire line through the sudden change of resistance value to reduce the residual current value.
The traditional fuse cannot recover by itself after the line is blown, and the PTC thermistor for overload protection can be restored to the pre-protection state after the fault is removed, and its overcurrent and thermal protection function can be realized when the fault occurs again. Select the PTC thermistor for overload protection as the overcurrent thermal protection element. First, confirm the maximum normal working current of the line (that is, the non-operating current of the PTC thermistor for overload protection) and the installation position of the PTC thermistor for overload protection (during normal operation). ) The highest ambient temperature, followed by the protection current (that is, the operating current of the PTC thermistor for overload protection), the maximum working voltage, the rated zero-power resistance, and factors such as the dimensions of the components should also be considered.
When the circuit is in a normal state, the current passing through the PTC thermistor for overload protection is less than the rated current, and the PTC thermistor for overload protection is in a normal state, with a small resistance value, which will not affect the normal operation of the protected circuit.
When the circuit fails and the current greatly exceeds the rated current, the PTC thermistor for overload protection suddenly heats up and is in a high resistance state, making the circuit in a relatively “off” state, thereby protecting the circuit from damage. When the fault is eliminated, the PTC thermistor for overload protection also automatically returns to a low resistance state, and the circuit resumes normal operation.
3. Overheat protection PTC thermistor
The Curie temperature of the PTC thermistor sensor is from 40 to 300°C. On the RT characteristic curve of the PTC thermistor sensor, the steep rise of the resistance value after entering the transition zone can be used as a temperature, liquid level, and flow sensing. application. According to the temperature-sensitive characteristics of PTC thermistors, it is designed to be used in overheat protection and temperature sensing occasions, and is used in switching power supplies, electrical equipment (motors, transformers), power devices (transistors). It is characterized by small size and fast response time. , Easy to install.
The difference between PTC and KTY: Siemens uses KTY
First of all, they are a kind of motor temperature protection device;
PTC is a resistance with a positive temperature coefficient, that is, the resistance value increases as the temperature rises;
Another is that NTC is a variable resistor with a negative temperature coefficient, and the resistance value decreases as the temperature rises, and is not used for general motor protection. KTY has high precision, high reliability and strong stability. Mainly used in the field of temperature measurement. KTY is covered with a layer of silicon dioxide insulating material, a metal hole with a diameter of 20mm is opened on the insulating layer, and the entire bottom layer is completely metalized. The current distribution that is tapered from top to bottom is obtained by the arrangement of the crystals, so it is named diffusion resistance. KTY has a practical in-line linear temperature coefficient over the entire temperature measurement range, thus ensuring high temperature measurement accuracy.
PT100 platinum thermal resistance is designed and manufactured by using the basic principle that the resistance value of platinum wire changes with the change of temperature. ) and 100 ohms (graduation number is Pt100), etc., the temperature measurement range is -200~850 ℃. The temperature sensing element of the 10 ohm platinum thermal resistance is made of thicker platinum wire, and the temperature resistance performance is obviously excellent. 100 ohm platinum thermal resistance, as long as it is used in the temperature zone above 650 ℃: 100 ohm platinum thermal resistance is mainly used in the temperature zone below 650 ℃, although it can also be used in the temperature zone above 650 ℃, but in the temperature zone above 650 ℃ Class A errors are not allowed. The resolution of 100 ohm platinum thermal resistance is 10 times larger than that of 10 ohm platinum thermal resistance, and the requirements for secondary instruments are correspondingly an order of magnitude. Therefore, 100 ohm platinum thermal resistance should be used as far as possible for temperature measurement in the temperature zone below 650 °C .
Post time:
Aug-20-2022
