Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 643 of 707

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 num- ber of different ways, from statistical process control to process tracking. 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 met- al-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 Data Storage 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 reprogram- ming 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 rec- tifier. 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. This eliminates the many wires that are commonly found connecting remotely located control panels to rectifiers. The Software The software should consist of standard control packages modified to meet the user's specific requirements. A language such as Quick Basic, used on the host computer, will provide the necessary operating speed for the host, along with the ability to modify or upgrade the program easily at any point. Faster languages, such as assembly code, may be required for a microcomputer located on the rec- tifier to control output waveforms adequately. A Main Frame A link between a main frame and the host computer is always a possibility, increasing the overall capability of the system. Such a link might be the first step toward complete factory automation. Use of a main frame provides a means for data from all parts of the finishing operation to be accumulated, correlated, and disseminated to various departments. 642

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