Metal Finishing Guide Book


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computer's ability to repeat a particular operation or procedure time after time. Computers can perform a variety of different functions when integrated with rectifiers. The computer can simultaneously monitor a number of output currents and voltages, detailing them on a video-display terminal. It can also maintain those voltages and currents within designated parameters, thereby compensating for varying input voltage or load changes. The computer can easily regulate pulsing and reversing power supplies. The computer replaces the switches, meters, and potentiometers typically required for manual operation; yet a manual override is included in case of malfunction. The advantages of a simple computer package are easily seen. The first major improvement is in the consistency of a finished product. Due to the precise application of power, the coating is exact from piece to piece, and this can significantly reduce rework and reject rates. Furthermore, a computer's precision control of cycle times and rectifier operation can reduce power consumption, resulting in lower electricity bills. Finally, the computer can calculate and transfer exact amounts of chemicals to finishing tanks, minimizing associated material costs and reducing waste and sludge-disposal expenditures. A computerized system should be custom designed for the specific application, regardless of the size of the finishing operation or the degree of automation desired. Customization is the key to successful systems integration. The system should, however, be designed and constructed using standard components. This procedure provides a system that exactly matches the needs of the user while minimizing the initial cost. A computer control system typically consists of a number of basic component groups. The illustration in Fig. 4 shows the structure of a multiple rectifier computer control system. A review of each of the basic groups provides a better understanding of how the system works as a whole. The Rectifier For a rectifier to be controlled by a computer, there must be a means for the computer to communicate with the rectifier. The rectifier must then be capable of modifying its operation to satisfy the requests of the computer. Typical commands sent from the computer to the rectifier include output voltage, output current, ramp timer, ramp rate, power on/off, and cycle start/stop. Additionally, information might be sent from the rectifier to the computer, for example, power status, output voltage, output current, interlock status, and cooling system operation. In some instances these signals will be transferred directly between the computer and the rectifier. In other cases there may be an intermediary computer that processes some or all of the information. A third situation may arise in which there is a single board computer located in the rectifier itself that has the singular role of operating the rectifier based on data from the control computer. Virtually any rectifier utilizing solid-state electronics to control the output can be adapted to computer automation. The Host Personal Computer The host personal computer (PC) is the center of the automated system. It is typically configured around a PC compatible and can be enhanced by a wide variety of peripherals. The host computer is the "brains" of the system, providing the input/ output, storage, and communications capabilities needed for optimum operation. 744

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