Method for detecting flatness of heating wire in miniature thermal protector

Abstract

The invention relates to a method for detecting flatness of a heating wire in a miniature thermal protector. The method comprises detection of heating wire shaping flatness and heating wire shaping height, wherein the heating wire flatness detection is characterized by measuring height of left and right two measurement points on two middle steps of a nonmetal base; if the difference value of the height values is smaller than a preset value, judging that the flatness of the nonmetal base is qualified, or otherwise, judging that the flatness of the nonmetal base is unqualified; and then, measuring height of two measurement points on the heating wire, and if the difference value of the height values is smaller than a preset value, judging that the flatness of the heating wire is qualified, or otherwise, judging that the flatness of the heating wire is unqualified; and the heating wire height detection is characterized by calculating mean height difference of the heating wire and two middle steps in the nonmetal base. The heating wire does not have thermal deformation due to power-on expansion when meeting instantaneous large current, and meanwhile, the heating wire shaping flatness and the heating wire shaping height can reach regulated requirements.

Description

technical field [0001] The invention relates to a detection method for the flatness of a heating wire in a miniature thermal protector, which is mainly used for simultaneous protection of over-temperature rise and over-current of a micro-motor or other control circuit boards. Background technique [0002] Chinese Patent No. ZL200410098345.1 discloses an invention patent named "Low Current Motor Protector". The two ends of the spiral heating wire are connected to two separate metal shells, which are connected by spot welding, and the metal bottom plate and the two separate metal shells are separated by high-temperature insulating parts. The above-mentioned parts are connected After that, the power circuit of the thermal protector is formed; specifically, the patent features include: the metal shell and the flange on it, the first cover part and the second cover part separated on the metal cover, the first cover part and the second cover part At least one of the cover parts f...

AI Technical Summary

Problems solved by technology

[0003] The above-mentioned patents have the following disadvantages in actual use: 1. Since the electrical insulation gap between the two separated metal first cover parts and the second cover part and the spiral heating wire is small, generally only 0.5-1mm, the heating wire is sealed in the heating wire after welding. Inside the metal cover, its position is guaranteed by the welding process, and the electrical insulation gap is small, so it is difficult to measure accurately. If an instantaneous large current is encountered, the heating wire will expand when it is energized, and the spiral heating wire will be deformed under the thermal effect, such as on the heating wire. The arch may be short-circuited with two separate metal covers, resulting in the failure of the current protection feature. In severe cases, the spiral heating wire will be blown and the thermal protector will be defective, resulting in the motor not working normally; 2. The circular arch structure of the metal cover, Not only is it easy to cause a partial short circuit of the heater and cause the product to fail, but sometimes a secondary abnormal conduction is formed after the short circuit, causing a greater safety risk

Since the semi-arc-shaped heating wire is fixed in the semi-arc-shaped heating wire loading cavity, and then energized and shaped, if an instantaneous large current is encountered, the heating wire will expand when energized, and the spiral heating wire will be deformed under the thermal effect, which is extremely It may be upturned. At this time, the heating wire will short-circuit with the bimetal sheet, resulting in the failure of the current protection feature.

[0006] In the above-mentioned patents, the detection of the flatness of the heating wire and the height of the heating wire is carried out by visual inspection, and the visual inspection method usually produces deviations. If the deviation is large, it will bring the following problems: 1. If the flatness of the heating wire There is a large deviation. Once the instantaneous large current is encountered, the heating wire will expand when it is energized, and the heating wire will be deformed under the thermal effect. Burning out the heating wire causes the thermal protector to be defective, causing the motor to fail to work normally; 2. If the height of the heating wire has a large deviation, it will directly affect the protector’s cold-state operating time and thermal overload characteristics. When the problem is serious, it will cause the motor to fail. unable to work properly

Images