A technique for forming an application particular list of necessary properties for picking programmable controller was built up. There are some criterions selection is made by comparing results table with technical data of controller. Below is short description of each criteria.
Nature of solution decides conditions it is developing of old system or entirely new development. In initial case the system architecture and requirements of hardware are limited by already presented solution. With hardware from same company builds servicing easier and keeps away from combination problems that would happen when utilizing products form different manufacturers. For instance a lot of hardware producers incorporate their own particular communication interfaces straight into module of processor and for each universal protocol a special module is required. It is also potential to decrease spare part stock amounts when using similar type hardware all above the system.
Allowed maximum number of electrical inputs-outputs is traditional criteria to decide processor class. If complex algorithms of control and non standard functions are required, it is not the most vital parameter any more. Usually it is money saving to utilize one bigger module of processor for signals of input-output that create from close to locations than some smaller ones. In this case there will be no require for network of communication and programming will be simpler too.
Special modules and signals are generally presented for large and medium controller families only. A lot of microcontrollers are not having opportunity to put in analogue output. By means of particular modules is just method, it is just a chance to save the money.
Sensors and actuators layouts can be extremely different; sometimes the sensors are placed some kilometers away from the actuator. Special network communication such as AS-interface, Profibus, might be the only answer. If not, it can as a minimum save costs by decreasing cabling works. Not all of the PLCs contain interfaces for protocols of communication. Processor Properties have vital role in complicated applications. Most general problem is require of memory programming, occasionally also memory of data. The requirements of memory can be expected by input and output signals number.
Specialties of Program comprise special program functions required. Different applications areas have some characteristically utilized functions, for instance building automation temperature control. Programming is much easier if these functions are already created into processor system software. In automation process two digital output closed loop regulation of PID is quite frequently used.