Troubleshooting Logic

Figure 4-10a. Troubleshooting Logic for Spikes and Rapid Changes...

Stand-alone computer systems, usually based on a personal computer (PC) or programmable logic controller (PLC), provide a separate computer system for each pilot plant. This allows for economical expansion for new units, separates pilot plants completely for maintenance and troubleshooting, and often has the lowest initial cost. Standardization can be a problem and software control, data gathering, and storage packages can be limited in size, scope, and capabiUty these are usually acceptable trade-offs. 

The control system is based on an industrial programmable logic controller (PTC). It includes all software required for the completely automatic operation, maintenance, and troubleshooting of the accelerator. ... 

The support and maintenance of the software is simplified when consistent formats and techniques are utilized. Troubleshooting programming logic not implemented in a structured format is frustrating and tedious. 

Effective troubleshooting will require some experience just for the background required to analyze the problem at hand, but there are also some other logical steps that need to be remembered. Ask yourself the question, Is there a problem. Perhaps it is as simple as a customer expecting too much from the computer. If there is a problem, is it just one problem. ... 

As described in Chapters 2, 3, and 10, there is a logical approach to setting up a troubleshooting guide. Details reviewed in those chapters concerning the approach to be used are applicable to BM and other processes. Table 4-14 lists some of the common BM problems with information on causes and solutions (192). 

Incomplete instrumentation can severely hamper quick and accurate troubleshooting in fact, it can turn troubleshooting from a logical step-by-step process into a guessing game. Without good instrumentation it can be days, weeks, or even months before a problem is located and solved. When an extrusion problem results in off-quality product or downtime, it is very important to find the cause of the problem quickly because such problems can be very costly. In some instances, a downtime of just one day is more expensive than an entire new extruder In most cases, trying to save money on instrumentation is penny-wise and pound-foolish. 

Logic probe functions. Signal high/low and pulse detection circuitry built into a DMM probe permits the instrument to function as both a conventional multimeter and a logic probe. This eliminates the necessity to change instruments in the middle of a troubleshooting sequence. 

Troubleshooting a digital system requires a wide range of test instruments, from simple to complex. Some of the more common conventional test instruments include frequency counters and logic instruments of various types. 

The close spacing of pins and conductors on a crowded PWB invites short circuits. On a large board, locating a short can be a difficult and time-consuming task. The logic current tracer can be a valuable tool in troubleshooting such failures. 

The presence of bubbles could be due to air alone or moisture, plastic surface agents or volatiles, degradation, or the use of contaminated regrind. With molds such as those used for injection, compression, casting, or reaction injection, air or moisture in the mold cavity will be the culprit. So the first step to resolving a bubble or air problem is to be sure what problem exists. A logical troubleshooting approach can be used. 

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