Construction Hoist Safety Device
Safety is one of the most important for Construction Hoist, thus the Construction Hoist Safety Device is required. SAJ safety device is a product of BQ. When a cage over-speeds the device should act cut off the power stop the cage on mast gradually. The safety device is adjusted and sealed. Do not disassemble it. The using time limit of safety device are signed on it`s nameplate. Safety device must be delivered to the factory and inspected after it reached to time limit.
Safety device board is the connected part between safety device and other structures, it can take the impact of stopping the cage. There are installed lower speed switch, upper travel limit switch and final limit switch, once the switchs touch the relevant cam the cage will act.
We also supply other spare parts for construction hoist, such as construction hoist Mast Section, Construction Hoist Anchorage Frame, Passenger Hoist Cage, Construction Hoist Overload Protector, Sliding Contact Line, Construction Hoist Motor, Construction Hoist Reducer and so on.
SAJ Safety Device,Passenger Hoist Safety Device,Construction Hoist Overload Protector,Overload Limiter,Anti-fall Device SHEN YANG BAOQUAN BUSINESS CO., LTD , https://www.sysuspendedplatform.com
LEDs must be cooled to ensure their light output is stable and long-lived?
The LED must be cooled to achieve optimum efficiency and to ensure the stability and longevity of its light output. LEDs are complex devices. LEDs not only have common problems associated with semiconductor design and operation, but LEDs are primarily used for illumination. Therefore, optical coatings, beam management devices such as reflectors and lenses, wavelength converting phosphors, and the like, have further systemic complexity. Still, thermal management is critical to reliable solid-state lighting (SSL) products. In addition, you need to know how to cool the LEDs in both static and transient backgrounds. For LEDs, two thermal management parameters need to be observed. One is the required operating temperature and the other is the highest operating temperature. Usually, the required operating temperature needs to be as low as possible. Achieving this ensures high electro-optic efficiency, good spectral quality and long device life. Operating at high temperatures not only reduces the amount of light produced by the LED, but also reduces the quality and quantity, which ultimately triggers many failure mechanisms. LED manufacturers are well versed in these defects and are able to design products with junction temperatures up to 130C. Due to the thermal resistance of the LED package, the temperature of the printed circuit board (PCB) is approximately 10C. If it is higher than the rated junction temperature, the LED lifetime will be reduced by about half for every 10C rise. Converting electrons into phonons, LED efficiency is relatively low. High-brightness white LEDs can achieve 40% efficiency, while UVC LEDs can have only 5% efficiency. In both cases, the remaining heat must be removed by conduction to prevent overheating. This is the responsibility of the LED light source or lighting designer. Static Cooling LEDs The usual way to keep the LEDs cool is to mount the LED devices on the heat sink. Heat from the LEDs is conducted into the heat sink and then dissipated into the air. If heat is removed by water or other fluids, the heat sink is sometimes referred to as a cold plate because the associated heat sink system often has to design the working fluid to be at a fixed temperature below the indoor environment. The ability to efficiently transport heat from LEDs to heat sinks depends on materials with high thermal conductivity. For example, it can be seen from the graph of Figure 1 that copper is superior to aluminum and brass and superior to stainless steel. Figure 1. Materials have varying degrees of thermal conductivity. Although copper is the best thermal conductor among these metals, the thermal conductivity is independent of the thickness of the material. The ability to transfer heat through material conduction is primarily related to thermal resistance. The thicker the thickness, the greater the thermal resistance. Dielectrics and Gas Flows For example, medium to high power LED arrays are typically built on thermally conductive PCBs. On the top side, there is a copper plate that is electrically connected to the LED, and a piece of aluminum underneath to conduct heat. There is a dielectric layer between copper and aluminum to prevent electrical shorting of the copper to aluminum. Manufacturers have adopted different approaches in the selection of dielectric materials, from organic materials to inorganic compounds, covering the entire spectrum. As shown in Figure 2, the dielectric material with the lowest thermal resistance is almost an order of magnitude, and the thinnest dielectric material can be applied while still providing the required insulation isolation. Figure 2. The thickness of the dielectric material affects heat resistance. However, Figure 2 does not describe all of them. Assuming the device is air cooled, there will be many interfaces in the thermal path between the LED and the heat sink. Some are bridged by solder, some are bridged by adhesive, and others will be pressed together (for example using screws). These joints present additional obstacles to heat transfer, which can be large, unpredictable, and change over time. The series/parallel addition of all thermal resistance and interface resistance in the system is called thermal impedance and the conduction path is designed to keep the LEDs cool. The calculation is similar to a resistor network. In Figure 3, the voltage is essentially the temperature, the current is the heat flux, and the resulting resistance is the thermal resistance. Figure 3. In development work, you can rely on the equivalent resistance of the heat conduction path. In order to obtain a complete thermal impedance system model, thermal interface resistance must be added at each transition between materials. Transient Cooling LEDs The previous discussion was based on the assumption that the LED is permanently energized and the heat sink continuously dissipates thermal energy into the surrounding air. This thermal model can fail in both cases. One is when the LED is turned on, more typically in pulsed operation. Surprisingly, a thermal path can be designed to keep the LEDs cool while working continuously, but overheating when switched on. When so operated, the associated thermal offset may cause the LED to suddenly fail, similar to a sudden break when the tungsten filament is turned on. Therefore, LED thermal solution design needs to consider transient operation and includes time and space variables. Time-Dependent The time component of transient cooling is due to the specific heat capacity of the material in the thermal path. This can be added as a capacitor to the electrical model of the RTD (Figure 4). Heat capacity refers to the property of the material to absorb (or release) heat when heated (or cooled). The size of the heat capacity is expressed by the specific heat capacity (abbreviated as specific heat). Figure 4. The time dependence of heat conduction is due to the thermal capacity of the material in the system. The electrical equivalent model is the RC low-pass filter. The electrical model analogy means that thermal impedance is sometimes used to describe the time-dependent thermal properties of a material. Please note that it is important to distinguish between them because thermal impedance can also be used to describe the static thermal resistance of the entire system. Space Dependence The spatial component of transient cooling stems from the direction in which heat is diffused more. For example, an LED mounted on a large thin metal plate. Initially, the entire board is at ambient temperature. The LED acts as a point heat source. When turned on, the LED generates heat that is transferred to the board by conduction. The heat quickly passes through the metal plate, increasing the temperature in the area under the LED. Therefore, at the first time, a small part of the metal plate was used to cool the LEDs. The conductivity of the metal plate means that some of the heat of the LED will expand laterally within the panel and eventually appear on the surface (shown in Figure 5). Therefore, the volume of the metal plate participating in cooling the LED increases with time, resulting in a significant change in thermal resistance and heat capacity. Figure 5. A hot body on a thin metal plate. This simple finite element thermal model represents spatial dependence by the volume change of the plates involved in cooling. The calculation of these models is performed in increments from the top left to the bottom right. Spatial dependence is especially important when there are high thermal resistance interfaces or layers in the path. By taking measures, the heat is spread over the largest possible area before the barrier, so that in steady state and pulsed operation, the LED can achieve better cooling. Convection and radiation Any material above ambient temperature loses heat through convection and radiation. Although these are the main mechanisms for tungsten filament cooling, they play a minor role in the thermal management of LEDs. However, convection and radiation should be included in any model to ensure that they are closest to reality. In summary, the LED must be cooled to achieve optimum efficiency and ensure the stability and longevity of its light output. A simple heat conduction steady state model can be constructed using an electrical component based model. However, in order to properly understand the thermal path, especially in transient conditions, it is best to use tools that can accommodate changes in time, space, and temperature. The temporal and spatial dependence of heat transfer explains why there is a hierarchy in material selection. The high specific heat capacity or thermal conductivity will vary with the location of the material in the thermal path and the desired mode of operation of the LED.