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A programmable logic controller (PLC) is a type of device used to control an automated machine, such as an industrial robot or factory assembly line. Many different varieties of logic controllers are available, each with different features and benefits. To choose the best PLC, you should consider if an existing unit will be replaced, or if a completely new installation is needed. It is also important to estimate how many inputs and outputs will be needed on the device, and analyze any special environmental or communication requirements in the usage location.
In situations where an existing programmable logic controller is being replaced, the best option is usually to choose a PLC that is produced by the same manufacturer as the old unit. Generally, it is much simpler to transfer a logic program to a replacement controller if both the old and new devices are the same brand. This also helps ensure that connected accessories and sensors will continue to be compatible. Substituting an old PLC with a similar unit should be the first choice, unless other requirements make this option impractical.
Regardless of whether an existing PLC is being replaced or a completely new device is being installed, the number of inputs and outputs must be carefully checked. Create a diagram of each automated process, and map out exactly how many devices and sensors need to be controlled. Choose a programmable logic controller that has enough digital and analog ports to cover the intended installation. It is usually a good idea to select a controller with several more inputs and outputs than are minimally required, in case the facility is expanded in the future.
The operational environment is another consideration when selecting a programmable logic controller. Make a note of any potentially hazardous conditions in the installation location, such as extreme temperatures or high humidity. Choose a PLC that is specifically designed to withstand the environment. Again, it is usually a good idea to err on the side of caution and select a device that is built to be rugged. This will help mitigate future repair or replacement costs if an inadequate PLC becomes damaged.
Select a PLC with communication and programming features that match the project limitations. If existing sensors need to be interfaced, be sure to choose a controller that uses the same communication protocol. Plan where the logic controller will be physically located at the final installation, and be sure that the chosen unit can be easily monitored and updated. Locations that are difficult to reach may necessitate a controller with wireless or remote interface capabilities.