Today's integrated drive products are designed to provide a wealth of
information about their configuration and status. Communication networks
enable companies to gather this information and use it to optimise
production and control costs. Mark Daniels explains how the DeviceNet
protocol achieves these aims, as well as making the maintenance
engineer's job a lot easier
DeviceNet provides many benefits including simplified assembly, reduced
wiring, and powerful and flexible diagnostics. As an open network, a wide
range of devices is available from multiple vendors allowing users to
design and configure systems to suit their exact requirements. Control
systems using a DeviceNet network are quick to install and simple to
configure, requiring a single network cable to daisy-chain devices
together, reducing installation time and costs. Integrated cabling
systems can reduce costs by up to 50% by eliminating the cutting and
stripping of cable. The system used by DeviceNet comprises a flat,
four-wire cable and clamp-on insulation displacement connectors, allowing
nodes to be added quickly and easily without severing the network.
Automatic Device Replacement
DeviceNet's communications and diagnostics capabilities enable drives to
be configured and parameters set from a remote location. Changes can be
made using the software and network, and in applications with multiple
motors and drives, a common configuration can be quickly downloaded. A
feature that is exclusive to PLCs and ac drives manufactured by the
author's company is Automatic Device Replacement (ADR) When connected
over a DeviceNet network, ADR enables a faulty device to be replaced with
a new unit straight out of the box. Pre-programming is unnecessary as the
parameters are uploaded automatically from the DeviceNet scanner,
reducing downtime and de-skilling the work. At a time when many
maintenance departments are being reduced both in size and technical
competence, ADR can have a big impact on the mean time to repair.
How does it work?
When a problem is experienced with a networked drive, ADR quickly
identifies which drive has failed (say node #50), as well as its type and
manufacture, using DeviceNet's standard diagnostic capabilities. This
information can then be communicated quickly and easily to a maintenance
engineer who can go to the stores and take a new, replacement drive off
the shelf. The DeviceNet scanner in the control system knows it has lost
communication with node #50 and will periodically check for it. Also,
with auto-address recovery enabled, the scanner will periodically look
for a device at node #63.
When the maintenance engineer connects the replacement drive to the
network, it will have the default DeviceNet node #63 straight out of the
box. The scanner will see that a device with node address #63 has been
installed and will try to match its electronic key with the device
configuration it had stored for the lost node #50. If it matches, the
scanner will automatically change the replacement drive's node address to
#50, then automatically download the correct configuration parameters.
The drive immediately works as before.
In addition to ADR, the integrated architecture provided by DeviceNet,
enables remote access to data at the device level, allowing preventative
maintenance to be planned. The network can also be used for condition
monitoring by tracking critical parameters in a device and using the
information to plan maintenance schedules.
One international manufacturer of soft drinks with factories throughout
Europe, uses DeviceNet to access data from variable speed drives on the
network via Ethernet/IP. In this way ad hoc diagnostic data can be
analysed by any authorised person with access to the network. This can
speed the correction of faults by allowing engineers and managers to
share information about the performance of devices acros