Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 642 of 707

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 com- puter 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 com- puter 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 typ- ically 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. Input Devices In most cases a keyboard is used to enter information into the computer. It allows an operator to change process data, load parameter profiles, or commence or ter- minate plating cycles, along with other functions determined by the user. Most host PCs will include a floppy disk drive. Floppy disks may contain data such as profile information, system software updates, and security codes. The flop- py disk can be programmed by a supervisor on a PC in his/her office, and the disk 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 exam- ples 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 nec- essary 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 infor- mation 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. 641

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