Metal Finishing Guide Book


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can then be taken to the host PC and the data transferred. Another type of input device is a bar-code reader. A bar code consists of a series of alternating black and white vertical bars that contain information defined by the user. A bar-code scanner is passed across the bar code to read it. The spacing and width of the bars determine the data contained therein. Information such as part number, process identification, vendor, and customer are typical examples of data that can be contained in a bar-code format. Output Devices A monitor to verify data being entered from one of the input devices is necessary with any computerized system. Once a process is running, the monitor can display a number of different screens. These screens can include process status, alarm conditions, rectifier operation, and virtually any other information desired by the user. It is quite possible for the computer to monitor, display, and control nonrectifier operations, such as bath heaters/coolers, bath agitators, and chemical feeders. A printer may be desired to obtain a hard copy of any of the data recorded or operations performed by the computer. This information can be used in a number of different ways, from statistical process control to process tracking. Data Storage A means to store the operating system, control programming, process profiles, and operating data must be provided. The most economical data storage device is a hard disk, which should be located in the host computer. By using a hard disk a process profile can be retrieved almost instantaneously simply by calling up a code number or name. By using profiles from the computer to control the metal-finishing operation, as opposed to setting parameters manually by turning knobs and pushing buttons, consistency is maintained. Some method of backing up the data on the hard disk is mandatory. If, for example, there is a power disruption or a failure of the computer, information will most likely be lost. If a regular backup is performed many hours of reprogramming may be avoided by simply restoring the data from the backup device to the computer. Although floppy disks are commonly used for backup, a streaming tape system, which utilizes a removable tape cassette, is a much better alternative, as all the data from a hard disk can usually be stored on one tape. The Interface Controller The interface controller acts as the translator between the computer and the rectifier. It receives commands from the computer and converts those commands to a language the rectifier can understand. The rectifier transmits information to the interface controller, which sends it to the computer. Both inputs to, and outputs from, the interface controller come in digital signals over interface cables. The interface controller may be situated in the computer itself, or it may be a separate system located adjacent to the computer. The Interface To keep the equipment as standard as possible, the popular choices for interfaces are the RS-232 and RS-422. Each requires only a pair of shielded, twisted wires to transmit information. This significantly reduces the number of wires needed for a multiple-rectifier system, as the twisted pair simply connects from the interface controller to each rectifier in a sequential fashion. In other words, the same pair of wires goes to the first rectifier to the second to the third, and so on. 777

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