Words of Wisdom: How plastics processors can benefit from the DeviceNet protocolWords of Wisdom: How plastics processors can benefit from the DeviceNet protocol

The DeviceNet digital communication protocol has been around since 1994 and has been used extensively, for example, in the automotive industry. The protocol has been proven to dramatically reduce wiring costs, including labor and downtime, for control components and devices. It also allows users to view data and perform diagnostics remotely through digital communication, readouts, and functions.

Anyone who has taken a look at the control panel of an injection molding machine or extruder has seen the vast network of wires and control cards used to power, measure, and control the machine. These machines would seem a natural for the benefits provided by the DeviceNet protocol. So why hasn?t it been embraced yet by the plastics industry?

Dynisco, for one, is betting that DeviceNet will not only be embraced by the industry, but will become the industry standard in the not-too-distant future. It?s a matter of time before OEMs and processors take advantage of the benefits of DeviceNet?it?s a proven protocol that saves money by reducing installation and maintenance costs.

Dynisco is the first (and still the only) company in the plastics industry to introduce a DeviceNet melt pressure transmitter. As part of the process of developing the technology, the company has also produced a DeviceNet transmitter for general industrial applications. Currently a number of end users and a few OEMs are implementing DeviceNet. With the continued pressures on manufacturers to find ways to cut costs while increasing or at least maintaining profits, this number is expected to increase rapidly.

DeviceNet: A Technical Overview

?DeviceNet is a simple networking solution that reduces the cost and time to wire and install industrial automation devices, while providing interchangeability of like components from multiple vendors.? This is the description of DeviceNet used by the Open DeviceNet Vendor Assn. (ODVA; www.odva.org), the professional organization that supports network technologies built on the Common Industrial Protocol (CIP), which includes DeviceNet.

ODVA?s more detailed definition of DeviceNet is as follows: ?DeviceNet is a proven, stable network technology designed to meet the performance and reliability requirements of the industrial environment. DeviceNet uses CAN (controller area network) for its data link layer, and CIP (common industrial protocol) for the upper-layers of the network. DeviceNet is an open standard managed by ODVA and accepted by international standards bodies around the world. In addition, users will appreciate the seamless bridging and routing provided by DeviceNet to other CIP-based networks that currently include EtherNet/IP and ControlNet.?

ODVA continues, ?DeviceNet is supported by vendors around the world. Over 700 Vendor IDs have been issued by ODVA. The fact that so many vendors have chosen to implement DeviceNet in their products allows users to employ best-in-class products from vendors around the world who are best suited to support them based on application expertise and geographic coverage.?

?DeviceNet is a digital, multidrop network that connects and serves as a communication network between industrial controllers and I/O devices. Each device and/or control is a node on the network . . . DeviceNet systems offer a single point of connection for configuration and control by supporting both I/O and explicit messaging. DeviceNet also has the unique feature of having power on the network. This allows devices with limited power requirements to be powered directly from the network, reducing connection points and physical size.?

?DeviceNet follows the Open Systems Interconnection (OSI) model, an ISO standard for network communications that is hierarchical in nature. Networks that follow this model define all necessary functions from the physical implementation up to the protocol and methodology to communicate control and information data within and across networks.?

Fewer Wires, Less MaintenanceThe primary benefit of DeviceNet is the fact that it greatly reduces the number of wires necessary to the control system of the machine for which it is used. This also translates to less cabinet space required; an all-digital network, meaning there are no analog channels to calibrate; and a software configuration that equates to faster setup and more flexibility. In plastics, let?s take a look at a typical extruder control system setup.Figure 1 shows an extruder control system with discrete control. Note that all pressure transducers, transmitters, and thermocouples are connected to the central control system individually. Figure 2 shows an extruder with DeviceNet. Instead of each transducer, transmitter, and thermocouple requiring its own wires to the control system, note that only one cable is required. In fact, DeviceNet can accept up to 64 different items on one control loop.

In the DeviceNet network, each device (transducer, transmitter, thermocouple, and so on) is referred to as a ?node.? During operation, the central control system asks each node to provide readings and data. In the case of the smart transmitter, each one has diagnostic capabilities; the user can set high/low alarms on each transducer, and in addition they can be monitored remotely. This translates into reduced downtime.

The bottom line? Save cabling, save costs. Save wiring, save maintenance.

Coming Soon?

So, back to the original question: Why has the plastics industry been slow to adopt DeviceNet? One factor is that the plastics processing industry, like many others, is slow to embrace change. If an OEM builds its machines relatively cost-efficiently, and they operate well, it?s easier to accept the current norm than to try a completely new way of wiring your system. However, an impressive list of industry leaders is currently testing DeviceNet setups using Dynisco?s transmitters, and that list is growing.