More Than Just Cost
More Than Just Cost
There are, however, conditions where this approach is ill-suited for industrial applications, so the choice should always be a well considered one. There are still cases where single-function machines are built, installed, and rarely tinkered with. The up-front cost advantages of "When the machine is to be built on site and located where it will be used, the need for quick connectors might not be necessary," believes Gilliford. "If the plant has a skilled in-house service department, they can quickly diagnose a problem and fix it."
Assembly and re-assembly of machine modules is
simplified with rugged quick connectors, junction boxes,
and cordsets. (Source: Lumberg)
But if companies look only at the cost difference between IP-20 and IP-67 I/O, they probably won't go forward--the acquisition cost is higher for machine-mountable components. "Our IP-67 products are about 15-20% more expensive than IP-20," says Harris. "What they need to look at is the enclosure space needed to mount the I/O." Certainly, if the user has a large cabinet with available space, then the space could be considered free.
"However, if they can reduce their cabinet size by replacing the in-cabinet I/O with on-machine IP-67 I/O, then they need to add that savings to the cost equation," argues Harris. "This can account for a 5-10% savings depending upon the amount of change that is possible."
Osbelt agrees, and is convinced that the huge labor savings and reduced wiring costs make a compelling argument for machine-mountable I/O. "We don't have to push our customers to see the advantages," he says. "Besides, machine footprints in general are getting smaller, so being able to reduce the control cabinet size by making better use of distributed I/O makes sense to everyone."
Another cost that needs to be considered is the miscellaneous material needed to mount in-cabinet I/O such as DIN rails, mounting hardware, ground connections, terminal blocks, and cabinet-wall penetrations. This may add another 5-10% to the IP-20 I/O cost.
Design flexibility also means that changes are easier to make as custom designs often are modified during the build cycle. "Products such as our Fieldbus Box allow I/O expansions or changes to be easily made without adding more I/O nodes, because the master module has an expansion bus built-in," reminds Harris.
Osbelt sees the most activity in Profibus and DeviceNet for bus-style discrete I/O, much the same as preferences for standard IP-20 I/O. "At lot depends on the customer's PLC of choice," he says. "If they favor Siemens PLCs, then the I/O will probably be Profibus-based. We use a lot of Beckhoff hardware, too, since they offer PC-based solutions, as well as the major bus I/O configurations."
The uptime of the machine. "If an assembly line in the automotive industry has a problem, many dollars are being lost because the system is not working." Other processes and machines, if broken down, can be more forgiving and the consequences are much less critical." Machines that are more easily assembled and easier to change out parts because of the level of expertise of the installer. "This eliminates a service person having to fly across the country, or world, to fix a problem," says Gilliford. "Now, with a disconnect/reconnect approach, the solution is to quickly install a new part and fix the problem." Worldwide manufacturing that requires consistent machines and parts production around the world;
Ideal for Rugged Environments
Another prime reason to consider quick disconnects and junction boxes becomes evident in rugged environments. "One of our customers in oil and gas exploration and production was using enclosures and terminal blocks for the electrical wiring of various motors, pumps and other process monitoring equipment on their offshore oil drilling platforms," says Mark Sweeney, vice president, sales and marketing at Remke Industries (www.remke.com). "All the equipment wiring was terminated inside the enclosure with terminal strips. However, the company was experiencing chronic problems with the traditional hardwiring of equipment particularly where enclosures were subjected to extreme conditions of seawater, rain, and wind. In these environments the air space within the enclosure can build-up condensation, which causes terminal strip corrosion and electrical shorting."
Dealing with these problems meant increased downtime spent on troubleshooting, repair of corroded terminal strips, replacing gaskets on enclosures, and rewiring equipment.
"This company had a unique set of physical and environmental conditions to overcome, so our design team decided a custom solution was needed," says Sweeney. "First, we redesigned the internal footprint of an eight-outlet mini-port distribution box to accommodate various pre-wired circuits and then tested it thoroughly to eliminate any circuit mis-wiring. Material of construction was changed to a polyester resin for enhanced corrosion-resistance and durability. The design of the distribution box was also changed to include stainless steel legend plates for easier circuit identification, and then completely sealed internally to eliminate air gaps and moisture/water ingress.
"The custom design all but eliminated downtime, as was the time and cost associated with troubleshooting and repair," says Sweeney. "In addition, it provided foolproof circuit identification, an enclosure completely sealed against corrosives and moisture, and, as a bonus, a smaller footprint: the company was pleased to have a smaller distribution box as available space is at a premium on an oil rig."