Why HC900 cannot be called as DCS and is it equal to Foxboro T2550 series. and what are main points to be considered before classifying to DCS and PLC.

Please let me know the above details.
regards,
chit.

 

Invensys calls the Foxboro T2550 a PAC (process automation controller) in the title of its manual, T2550 Foxboro PAC Handbook HA028898. That tells you it's not a DCS, its a PAC and probably makes it a direct competitor to Honeywell's HC-900. However, the Invensys download site requires page long detailed registration, so I did not go through the effort to look at it.

I'll compare the HC-900, which I've used, to what little I know about Honeywell's Experion DCS, because most DCS details are not well publicized.

Honeywell calls its HC900 a hybrid controller, but it could also be termed a PAC (process automation controller). These two are marketing terms, used to designate categories of capabilities.

DCS's view themselves as a plant-wide control management, using terms like 'cockpit' to represent a unified, integrated means of supervision and control. Whereas a PAC or hybrid is local and its tools are for local controller configuration. There's a soup manufacturing plant down the road, it has 4 cookers in about a 4,000 sq ft plant (single loading dock and a 10 car parking lot). An HC-900 could easily be a plant-wide system for that little plant, but that's not where DCS's are ever considered.

The HC 900 is controller centric, a DCS is server based. With a server database, a variable tag can
be accessed across control logic, asset mgmt, an historian, and the HMI graphics, and this is an
aspect of the high level integration of a DCS. There is no common on-line database for a PAC like the HC-900, or amongst multiple HC's.

Experion has an asset manager (don't know the name of it), but HC-900 does not.

An historian, while an 'option', is always available for a DCS as an integrated function. The HC-900's HMI panel will show some graphs and saves data files on flash, but it really isn't an "historian".

There is no simulation/tor for the HC900, many DCS's have simulation capability.

The integration of all these high level software functions comes at a cost. Development software for the HC-900 is a one time cost of a little over $1,000 for the controller and CS900 HMI panel.

Updates are publicly available. I do not know Experion's development software costs, but I'll bet it is an order of magnitude (if not 2) and a multiplier factor greater and that updates are a not free downloads, but whatever a service/subscription costs. Each category of software is in a different league.

The set of function blocks for the HC900's C30/50/70 controllers is a subset of those for the Experion C200/C300 controllers. There is no provision for custom-programmed function blocks in the HC900 controller. But we use HC without needing custom programmed function blocks.

The scalability of an HC900 maxes out at about 1,900 I/O points (5 racks of I/O modules). The DCS is an order of magnitude or 2 greater.

HC-900 has no fieldbus capability, Experion does.
One soft difference is the availability of documentation.

One way to identify a DCS product is to look for documentation in a public venue, like the web. The absence of documentation beyond marketing brochures is a key indicator of a DCS. There is no publicly available documentation for Honeywell's Experion DCS, but all the HC900's documentation is publicly available on Honeywell's HPS web site.

Our plant, its processes and process reporting do not warrant either the cost or the complexities that come with a DCS. It is very well served with HC900s and some paperless recorders for process recording.

We don't need an asset manager because the bulk of our analog I/O is thermocouple direct, so we don't have to manage hundreds, if not thousands of field instruments. In fact, we use the thermocouple drift detection on the HC900 that thermocouple transmitters do not even have.

We've had to 'cold start' the HC-900 on occasion when adding a rack or adding I/O modules, but
again, we can plan for that and handle it, our processes are not continuous processes where control interruptions are very serious matters.

Foundation Fieldbus does not make sense for our style operation, so we don't miss it, everyone
understands T/C and 4-20mA.

We looked at redundancy, but determined that it isn't warranted. Our experience is that the HC
hardware is very robust and some (now dust covered) spare modules on the shelf cover our needs.

I am impressed at the ease of updating the HC by downloading the updates from the web. Vastly
different than the service agreements for PLCs on some other equipment in the plant.

Our ISA local group has people who run DCS's for all the reasons DCS's exist, but the PAC or
hybrids have their place as well.

Given that Invensys classes the T2550's as a PAC and its documentation is on the web, the T2550 and HC900 are probably competitive devices.