For Selecting Modular Processors the following Criteria examined include:
I/O points .
Each PLC processor will only be capable of working with a limited number of each type of I/O modules.
Memory size and Performance .
The size of program is dependent upon the complexity of the control problem and the skill and style of the programmer.
The required operating speed for all the I/O must be determined, with a PLC selected to match. This requires the estimation of the program size and the proportion of slow instructions. The scan speed is normally expressed in terms of
ms/K for a stated mix of simple and complex instructions. A PLC with an appropriate memory capacity and speed can be selected.
For any particular application it is essential to ensure that the
PLC selected can handle the required operations.
When a communications facility is required we need to determine whether the built-in port is adequate for the application, or whether a separate module will be required.