How field networking unlocks automated setup and diagnostics

Editor's note: For long conveyance systems and other large machinery, machine-mounted devices, such as variable-frequency drives (VFDs), can shorten the amount of cable or decrease the amount of power needed. Read about the shift to field-mounted controls automation as an introduction to this article.

Field-mounted devices change the way controls engineers approach industrial networking. The shift toward on-machine connectivity can simplify design, streamline wiring and enable strategies like conveyor zone management.

For conveying, field-mounted devices can be networked together so that additional functionality can be gained. Consider a length of conveyor with field-mounted zone controllers that have both inputs, such as package sensors on the conveyor, and outputs like pneumatic zone brakes used to control each zone, or two, if so configured.

If all of the zone controllers communicate with each other over a field network, the status of the photo-eyes on each zone can be passed on to the central processor for further decision-making. One popular network for zone controllers is actuator-sensor interface (ASi). This network protocol relies on a two-conductor flat wire for network cable.

The application uses insulation displacement to make connections so the zone controllers can be located wherever they are needed along a conveyor, and the unit just clamps through the flat cable passing through it. It works on a master-slave principle, where there is a master located in the main processor rack, and each field device is a slave to that master.

This example is a rather simple application for simple I/O—binary OFF/ON—devices but machine-mounted devices can be much more elaborate.

Traditional position indicators are used on machines to assist the operator or setup technician with changing over a machine for producing different products. These can be analog in nature, such as a dial on a device that advances or retires a count as the device is cranked in and out, or can be digital.

More recent advances in this technology involve networking the various position counters on the machine and bringing the information back to the central processor via an interface module. With this approach, information is two-way, in that the current readings come back to the processor, and the target position is sent to each position indicator. A live example of that might show a target value in blue with the current value being red if it is out of position and green if it is in the correct position.

From a setup standpoint, the setpoints for each product can be stored in a recipe in the processor. The operator screen can call up the recipe and display it on the screen, along with the current value of that setting. As the operator moves around the machine to move devices into the appropriate position for the product selection, the values on the position indicator will direct the person on where the device needs to be located and gives them a real-time, local indication of that correct position. Back at the operator terminal, the setpoint and actual numbers are displayed on the screen for verification purposes. Since desired setpoint and actual are available to the programmable logic controller (PLC), the code can be written to stop the machine cycle if critical setpoints get out of specification.

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Not all values need to be changed for each different product to be run on a machine, so both the operator terminal and the machine-mounted position indicators create a visual clue to what needs to be changed. Conceivably, a machine can be changed over without a physical guide or checklist with the operator following a particular path around the machine, looking for indicators that have an actual value that is red, indicating that it is out of position, and green when it is moved to the correct position. If the indicators are labelled in sequence, the operator will know if they miss a step because they will arrive at the next indicator with a non-sequential number/letter label. Further, when the operator gets back around to the operator screen, they will see indicators in red if the value hasn’t yet to be changed.

Glossed over during the original description of machine-mounted devices, most pneumatic vendors have machine-mounted manifolds that communicate via some sort of fieldbus technology. Since the connection back to the processor has already been made, these vendors offer non-pneumatic modules that simply add to the manifold blocks.

Digital and analog I/O modules can be mounted right there on the machine, instead of making individual connections back to the main control panel and without locating a separate field distribution block on the machine to pick up these points.

On-machine connectivity continues to evolve and this creates great opportunities for savings when it comes to design and implementation of controls. On-machine means not in the main or sub- control panels. Smaller enclosure size means more visibility to the machine itself, and that means better vantage points for the operator and maintenance personnel.

On machines that have a larger footprint, on-machine devices mean that some setup and diagnostics can happen right at the field-mounted device, instead of having to go back and forth to the operator station for confirmation of actions. On-machine mounting of drives, both variable-frequency and servo, means changes in operation can happen right at the point of control, instead of having to make a change at the operator station and moving around the machine to observe the result. This can be a significant advantage with conveying and material-handling systems where the distances can be substantial.

On-machine technology will continue to evolve and the benefits to both designer and operator will simply tasks further.