CD Automation s.r.l. CD Automation sales Manual CD Automation s.r.l. 1. What is an SCR? SCR is used in place of conventional AC power controllers made with Variable Voltage controllers, or variable transformer and electromagnetic contactor. SCR are typically used in electrothermal control applications of various industries including temperature control for electric furnaces and heat treatment processing. 2. The Principle behind SCR. • There are two types of control systems used in SCR. These are: (1) Phase angle control (2) Cycle control • Phase angle control As shown in Figure 1, under phase angle control, power is supplied to the load only during part of the AC voltage waveform. Output voltage can be controlled by increasing or decreasing the portion that is cut out. CD Automation s.r.l. • Cycle control As shown in Figure 2, the power is supplied to the load for an ON time and OFF Time during the cycle time. Adjusting the ON time is possible to control the load power. Other more sophisticated firing are available and will be treated after. CD Automation s.r.l. 3. Reason to use SCR? 1) SCR improve control precision. The degree of precision offered by SCR as compared with a magnetic switch system is shown in Figure 3. 2) As solid-state devices, SCR provide increased reliability and longer life. 3) Maintenace is not necessary since there are no moving parts. 4) SCR produce no noise. CD Automation s.r.l. 4. Applications Tempering furnaces Annealing furnaces and heat treatment equipment Molding equipment Melting furnaces Evacuated furnaces Drying equipment Heater Preheaters Control Baking ovens Food-related equipment Packaging and wrapping equipment Road heaters Defrosters • Air conditioners Agriculture and livestock industries • Petrochemicals Crystal growing equipment Environmental test equipment Vacuum tubes CD Automation s.r.l. 5. Applications Leading marks Photo studios Illumination and Lighting Hotels and theaters Planetariums Fish gathering lights Rectifiers Power Induction lamps Supply Crack detection equipment Active charcoal manufacturing equipment Test and inspection equipment Particle accelerators Magnetizing equipment Motors Dc Motors Torque motors Vibrators Miscellaneus Clutches CD Automation s.r.l. 6. Specific Examples of Applications Plastic Molding Equipment Since injection machine used to make plastic products require the temperature of all parts to be precisely controlled,many control zones are used. Therefore several SCR to be used in a injection machine. CD Automation s.r.l. 6. Specific Examples of Applications Extruder • Extruders are one of the best applications for thyristors units. • In Italy we sell 24,000 units in this application. • Coextrusion systems are everyday more and more used, we have done systems with 120 zones. • An important feature on CD Automation Thyristor units is the Heater Break alarm. • H.B. inside thyristor unit can be An important feature to overcome the non availability of H.B. inside C460 MLC9000 module. CD Automation s.r.l. Chillers • This application is tipical for plastic machinary. • Actually in Italy is an important application for SCR units, CD3000S and CD3000-2PH. • In each chillers can be used from 1 to 4 heating zones. CD Automation s.r.l. Paint Drying Equipment Paint drying equipment usually produces heat through infrared lamps. Usually drying takes place in a tunnel containing a succession of drying lamps such that it is necessary to independently control electric power at the tunnel entrance, exit and points in between. Since temperature can be tightly controlled with SCR product quality after drying treatment IS greatly improved. This type of drying equipment is widely used for plant manufactured products including cars and household applications. CD Automation s.r.l. Food Processing There are many types of electric ovens used to bake such items as bread and confectioneries, depending on the exact type of food involved and the level of production necessary. There are ovens which have upper and lower heating elements and “tunnel-type” ovens configured for mass production levels which utilize a conveyor belt. Figure 12 shows a tunnel-type oven. Each item can be consistently and evenly baked through the use of SCR. CD Automation s.r.l. Melting Furnaces Melting furnaces are electric furnaces meant for the melting and heat maintenance of both metallic and non-metallic substances. One typical example of a melting furnace for metals is the aluminium melting furnace used as one stage in die casting and pressing equipment. Figure 13 shows aluminum die casting equipment capable of melting aluminum ingots while maintaining a constant internal temperature. A heater is used to melt metals such as aluminum and certain alloys which have a relatively low melting point. Substances which become conductive when melted, such as glass, will themselves heat up if voltage is applied directly. A system requiring heaters is said to use “indirect heating”, while a system depending on the electrical resistivity of the substance being heated is said to use “direct heatig” CD Automation s.r.l. Ceramic Furnaces The growing applications found for ceramics can be seen in everyday life. From semiconductors to cars and ceramics products. Since the temperatures required to bake such ceramics are extremely high from 1,500 to l,600°C, the heaters used in such furnaces are made with special materials such as molybdenum. Special firing and special feed back must be used. Application with special loads will be treated during this training. CD Automation s.r.l. DC Power Sources Figure 15 illustrates an example of a DC motor driven by an SCR combined with a rectifier. This cheap solution is used in amusement parks have built-in DC motors which take DC voltage supply by the rail. The voltage required varies depending on the number of cars running at the same time on rails. By using a feedback control system are therefore commonly used for DC constant voltage control. By using SCR in this way, it can be assured that all cars will run at a constant speed.
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