Estimating Required Automation System Cabinets

I’ve mentioned in a recent post about the power of on-line communities to connect folks on a peer-to-peer basis to quickly find answers. Here’s a recent example from the DeltaV Digital Automation System LinkedIn group.

A new thread, Cabinets Number estimation., was started a few days ago. The engineer who began the thread asked:

I have an estimate of 500 I/Os count for my DCS. How do I estimate the number of marshalling/system cabinets required for this? This is being implemented by Delta V standard Cabinet size of 800mm width x 800mm depth x 2100mm height with front and rear entries.

A consultant responded within a day that it’s a function of the mix of traditional and bussed I/O and how you engineer your AC and DC voltage distribution. Next, an Emerson project manager, Luuk Somers weighed in noting that the use of WirelessHART devices can lessen the cabinet footprint needed. He also noted the CHARM I/O in the imminent DeltaV release could also have an impact.

Emerson’s Andre Dicaire, a DeltaV product manager responsible for the DeltaV hardware, succinctly stated how electronic marshalling could simplify the cabinet estimation process:

Actually, the answer is now easy. Select the Cabinet type and divide into the total I/O to determine the number of standard Electronic Marshalling cabinets needed.

Siraj indicates he plans to use DeltaV standard cabinets, front/back entry. These cabinets are based on Electronic Marshalling with CHARM IO. This cabinet supports 576 I/O channels, of any mix. There are 6 CHARM IO cards in the cabinet, each card supporting 96 channels. The channels are individually characterized with the needed signal types by the installed CHARM. In addition, each channel can be assigned to any one of up to 4 controllers. This means you can start with one controller, and if needed add up to three additional controllers to handle your control logic. You can reassign any signal without touching the wiring.

Also, you can re-task any channel if the project changes a signal type, such as upgrading a limit switch to an anlog sensor. Install the sensor and change the CHARM. The wiring need not change.

Early on, you only need the I/O count. Once the I/O types are known, you can order the CHARMs. In the meantime, you can start the installation of field wiring knowing that any signal can land on any channel.

OK, You should separate any high voltage type signals from low voltage instrumentation, since most plants require AC level signals to be segrated. So, divide the signals into these two voltage levels, calculate the number of cabinets by dividing by 576 (or 288 for front only access).

Yes, you can still design the system with traditional I/O cards, and wait until the engineering is more advanced so you know how many controllers you need, where the I/O must be landed and then plan the field wiring. Or you can look at Electronic marshalling to decouple the field wiring from the control strategy/controller designs.

Within the span of a couple of days project engineers, consultants, project managers, and product managers shared their expertise on a peer-to-peer basis to address a question that faces most project engineers. This is especially important in this rapidly advancing world of technology in which we live.

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