What is needed for automation are not protocols that transmit messages intended for human eyes to interpret, but rather protocols that transmit information structured for automation devices to interpret. An example of a control automation problem can be used to illustrate this need.

An engineer who plans to automate a candy packaging machine must consider not only the sequential functions that fill the open bag with candy, close the bag, and drop the sealed bag into a box, but also the critical temperature control of the sealing bar that insures the candy stays safe, secure, and fresh in the sealed package. The engineer must also consider the reliability of the process and its ease-of-use.

This SERIES PD controller features embedded Ethernet technology, providing a means for setting and viewing key variables such as process pressure and humidity.

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Performing temperature control in a PLC presents numerous challenges. Programming can be difficult, requiring expertise that may not be available. Control algorithms can interfere with other program functions by consuming processing bandwidth, or require the use of a more expensive PLC than would otherwise be required. Control may be sub-optimal due to the sum of a simple on-off control algorithm, which is the easiest to program in a PLC.

The alternative, using a standalone temperature controller, resolves these issues. Commercially available temperature controllers include advanced control algorithms and automatic tuning, so little expertise is required. The calculations and I/O updates associated with temperature control are performed by the PID (Proportional Integral Derivative) controllerís processor, freeing the PLCís processing bandwidth for other tasks. But in the past due to differences in the supported protocols, getting standalone temperature controllers and PLCs to communicate has been time consuming, costly and difficult as well. If the PLC and temperature controller do not communicate, the machine depends on the operator to integrate these functions.

For example, if the candy packaging machine uses a PLC to move the product and a separate temperature controller to heat-seal the package, when the demand for candy increases and the production line speeds up, the sealing operation must happen faster. That may require a higher temperature set point. If the PLC and temperature controller are not coordinated by the automation system, if they do not communicate, someone has to manually change the temperature setting on the controller. Without the communications link, the chances are greater that the temperature setting will not be correct and the candy will not be properly sealed in the package.