1. What are you manufacturing and how? This may seem like a very basic question, but it is fundamental to determining the requirements of the application and, therefore, the best fit automation system. The way a product is manufactured, the performance needed, along with any physical limitations of the process, all influence the system selection. Typical factory automation applications, for which the PLC was originally designed, involve the manufacturing and/or assembly of specific items – things. These applications may employ one or more machines and a fair amount of material movement from machine to machine. A typical characteristic of this type of process is that the operator can usually monitor the things visually as they progress through the manufacturing line. The process is, by nature, very logic control intensive, often with high-speed requirements (throughput = profits). This type of process is often controlled by a PLC and Human Machine interface (HMI) combination. Process automation applications typically involve the transformation of raw materials through the reaction of component chemicals or the introduction of physical changes to produce a new, different product – stuff. These applications may be composed of one or more process unit operations piped together. One key characteristic is that the operator cant see the product. It is usually held within a vessel and may be hazardous in nature. There is usually a large amount of simple to complex analog control (i.e., PID or loop control), although the response time is not that fast (100ms or greater). This type of process is often controlled by a DCS, although the analog control capability of a PLC may be more than adequate. A determining factor in the selection process is often how large in scope the control application is (i.e., plant wide versus single unit and number of I/O points). There may also be sequential (or batch) control needs. A PLC can be used effectively for simple batch applications, while a DCS is typically better suited for complex batch manufacturing facilities that require a high level of flexibility and recipe management. Again, the requirements of the batch application determine whether it is simple or complex: Number of products manufactured: Single product or multiple products Recipe parameters: Constant or Variable Procedures: Single procedure or multiple (different) procedures Equipment utilization and arbitration: Fixed/none or Flexible/often Frequency of changes to formulas and recipes: Never or Often [email protected] 079 6616 8867 / 8875
Posted on: Mon, 29 Sep 2014 08:40:04 +0000
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