Electrical equipment and electronic equipment, and even motor, transformer electromagnetic conversion equipment, they are at the beginning of the impending failure often will appear the phenomenon of temperature anomaly.
Such as electric motors, transformers in the overload or short circuit fault occurs, the winding temperature will rise sharply; Electronic circuit of resistance, class ii/triode components will also be in front of the breakdown of elevated temperature anomalies occur; As for due to overpressure or interturn short circuit or used in a closed environment for a long time and the contactor/burnt relay coil, I'm afraid you are exposed to. Therefore, in view of the above equipment temperature protection become very necessary preventive protection means, so today we're going to talk about some knowledge on the subject.
First, let's look at an irreversible temperature protection device -- the temperature fuse. Different from using high temperature melting point of lead alloy pan/silver copper alloy, mainly in view of the current fuse circuit current value protection, temperature insurance is sensitive to temperature of the alloy material. Temperature insurance will not only in the current value rises to a certain value, more will be protected object after fusing temperature rise to a certain value, thereby the preventive protection function.Temperature insurance at the present stage in the hair dryer, rice cooker and other home appliances: T, handheld electric devices often seen in medium and small capacity transformer.
Now the temperature of the common insurance are: cylindrical porcelain tube (see more at rice cooker, electric pressure cooker, cooker etc.), laminate sheet temperature insurance (embedded within the transformer primary winding, small power motor winding) two types. Insurance at the present stage temperature using more two action temperature is 920 c and 980 c, respectively. Need emphatically pointed out that, in light of preventive protection insurance focuses on the temperature level, so that the temperature in practical work safety fuse, electric quality should be carefully checked to be protected, in 80-90% of cases were usually protection appliances will be in good condition, this situation is very different with current insurance after the fuse!
Again, given the temperature insurance belongs to the disposable protection device, after the damage had to replace the disadvantage factors, in order to maintenance and easy to use and gave birth to a reusable temperature protection device - temperature switches. Temperature switch is using the bimetallic strip as a temperature sensing element protection device, when the normal work of the load, bimetallic strip to maintain the original state in the conduction on/off state; And when the temperature of the protected object rose to bimetallic strip after action value, bimetallic strip is heated to produce internal stress and fast action, to protect the object's temperature back to normal after the bimetallic strip. In terms of its protection action mechanism of temperature switch with a traditional - almost the same thermal relay overload protection device.
Temperature switch of the rated current value (through the current value between bimetallic strip), generally speaking, there are 1 a, 2 a, 5 a grade three. Temperature switch common forms of encapsulation has a rectangular laminate sheet, metal shell, etc., in electric frying pans, electric, electric oven, electric cooker is widely used in; In the soft starter, inverter, the inverter type welding machine and other industrial control equipment, temperature switches are fixed in high-power components (thyristor, IGBT) behind an aluminum heat sink; In addition the temperature switch will be implanted in transformer winding motor, large capacity, early warning, act as overtemperature protection components.
Finally introduced the thermistor, thermocouple both temperature detecting element, with the corresponding electronic circuit, after they all need to have the corresponding temperature measurement, overtemperature protection, etc. Thermocouple for voltage output type temperature sensor output level (mV), its output has the branch of polarity, its wide temperature measurement accuracy, general multi-purpose temperature detection in industrial heating equipment. Thermistor for resistance value output type temperature sensor (see more than 10 k2 and k2 two resistance level of 100), its temperature range is narrow, but the precision is higher, more are used for general temperature measurement, the induction cooker, light wave stove, often use electronic thermometer, etc.
In terms of the four kinds of temperature protection, measuring devices, insurance and temperature switches in the electric equipment is the most common, because has certain current-carrying capacity, therefore, can be directly involved in the circuit of control; Thermistor, thermocouple, see more at temperature measurement/protection of electronic devices, they used only as a temperature sensing element, not directly connected with the main road or control circuit is used.
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