Remote I/O can save money by reducing panel cost and cost of electrical installation.įinally you should know your communication requirements. ![]() The location of I/O needs to be taken into account to determine if local or remote I/O can be used. A small system may easily turn into a larger system and require more memory. Always consider expandability when planning your control system. If the system you are programming for is small obviously less memory is required. It is also important to try to determine how large your program will be to determine the amount of memory is required. Planning ahead will help you select the correct processor and I/O for your specific application. Another important factor in determining the type of CPU and I/O is whether the system requires any special capabilities such as high-speed counting or servo control. On many systems it is a good idea to add about 20% to your I/O count for spares to cover I/O you may have missed during planning or future expandability. You will need to choose a PLC model that supports the amount and type of I/O. You should always research the product to be sure the equipment satisfies the environmental constraints or you must design the installation to meet those requirements (i.e., panel enclosures, purging, etc.).īefore ordering any equipment you should determine how much discrete and analog I/O the system will have and what voltages the field devices will have. Next you must determine how environmental issues may affect your application. For instance, if you are upgrading a CPU of an existing system it may be beneficial to select a processor that is compatible with existing I/O to save money. You should also consider if the system is new or existing. Often times you get what you pay for but there are also excellent components out there priced reasonably. ![]() The downside to the bigger brand PLCs are the programming software and hardware can be more expensive. But with cheaper PLCs you may find support is limited and the hardware may not be as robust. If not, your first instinct may be to select the cheapest PLC you can find. Often times your facility, if it applies, will request a certain brand of PLC. When selecting the brand of PLC components (Allen-Bradley, Siemens, Modicon) you must consider factors such as standards, support, cost and capability.
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