A few less screws here and a few less wires there might not seem like that big an improvement, but every process control engineer and technician knows they can mean a lot less labor and expense—or a lot more if efficient materials and methods aren't used.
Such is the potential of DeltaV Characterization Module (Charms) I/O cards (CIOCs) for electronic marshalling unveiled this week at the Emerson Global Users Exchange in Orlando, Fla. The company began taking orders for Charms I/O cards in September and will begin shipping in mid-2010.
"Traditionally, wires and signals coming in from the field are screwed to a terminal strip in a marshalling cabinet and then cross-wired on the back side from the strip to I/O points on the controller card," said Andre Dicaire, DeltaV's product manager. "This meant three sets of screws—one to land on the strip, another to wire to the I/O card and a third to hook the I/O card to the controller terminal. This was convenient for controls manufacturers, but it's very hard on the users. So we recently asked ourselves, ‘What if we landed the field wiring on the strip and did the analog-to-digital converting right there with a single-channel I/O card, and then come out with a digital signal that could go right from the I/O card to a cloud of controllers. That would eliminate two-thirds of the physical connections that users usually have to do."
This was the initial idea for Charms I/O cards. However, it was only recently that analog-to-digital (A/D) technologies became small and affordable enough to make one-channel I/O cards practical. "Traditional I/O cards do signal interface and communication bus functions together, but we split them," explained Dicaire. "This means a Charms I/O card can sit on the strip, collect individual signals and immediately distribute them to the controllers. Besides functioning as a signal converter or interface, Charms I/O cards also allow I/O signals to be sent to up to four different controllers. So if you need to change to another controller, you can just specify it without having to rewire to a different controller or add more cards."
The real difficulty is 10% to 20% of a project's cost can come from late wiring changes, and this can delay a project by one or two months at the end, said Dicaire. "Also, the typical I/O card has eight or 16 channels that are grouped together for the same type of signal, but the field wiring on the marshalling strip has a mix of analog and digital signals, and so it can be very hard to get the right signals to the right cards," he added. "As a result, the risk is overloaded or under-loaded controllers, so users always have to buy extra to make sure they have enough. The also have to cope with late changes from their customers, such as changing wiring from altered tanks or limit switches to transmitters, or finding they need to make other changes when they test the controllers."
Unfortunately, the risk of over- or under-loaded controllers meant that users didn't just have to buy too many controllers, but they also had to find added space for them and their associated I/O devices.
"Users can just land their multi-core cables in order, each signal tells what it is, and so the users can simply insert a Charm I/O card for that signal type, whether it's analog, digital, input or output," said Dicaire. "It doesn't matter what a device is because there's an appropriate Charms module that can take its signal, convert it and put in on the bus. For example, if a user already has a mix of signals, but wants to add their first RTD, then they can just wire it in, plug in the right Charm module, and they're done."
In general, Charms I/O cards mean users don't have to rewire their I/O nearly as much, don't have to buy as many I/O cards, and don't need to manually reassign I/O to different controllers. "Now, it can be just a quick point and click. Users can reassign up to 50 signals in a matter of seconds. This used to be a three- or four-day job," said Dicaire.
Another key feature of Charms I/O cards is they also have a HART channel and model that comply with the new HART 7 protocol. "This means users can pull and update their HART data in about 0.5 seconds, instead of the 5-6 seconds that it used to require," added Dicaire.
Charms I/O cards also comply with DeltaV Version 11 and will comply with its future versions. "Charms I/O cards change the game because of the huge amounts time they can save for users," said Dicaire. "For example, some users could cut their wiring time in half. The need for many wiring changes, especially late wiring changes, will effectively go away. This could enable some users to commission their applications one or two months earlier.