What are the features where we can differ between a hybrid controller and a DCS system?

 

Hybrid controllers are the combination of a DCS and PLC function. In can control discrete application, process application and different bus devices in factory floor setup.

While DCS are more of a process automation controller.

 

A DCS system such as Yokogawa CS3000 is structured as follows:
1. Controller houses CPUs and runs independently from the HMI. If PC crashes, control continues. Trends and reports are generated in the HMI.
2. Single database - Create a PID controller once and it is available for control AND to view immediately.
3. Fixed scan period for maximum amount of tags, guaranteed. (100 000 tags, max 1 sec)
4. Faster scan times are possible.
5. Can control discrete and continuous processes with ease.
6. Large process plant such as Petrochem, etc. would only select DCS, not hybrids.

The hybrid systems rely on communications from the controller to a server type HMI, and require two databases. Too many disadvantages to describe.

 

Dear Sirs,

I need but differences between these. In special which this defined each one from some book of control or standard.

 

The problem is that they are rather broadly applied terms. It's not inconceivable the same system might be tagged either way.

Regards

cww

 

DCS was developed as a replacement for large amounts of single loop PID controllers. PLC was developed as a replacement for large amounts of relays.

These days the difference between these two architectures is not very big - and this is what is called a hybrid system. Both have a CPU card (controller module) and an I/O subsystem with I/O modules. In the past a PLC was purely logic while the DCS was purely continuous controller. The PLC was programmed in ladder and the DCS in function blocks. Today both handle all kinds of I/O and can be programmed in multiple languages - the hybrid. In the past a DCS included servers and workstations software whereas for the PLC the HMI software was purchased separately. I.e. with a DCS you got an integrated system whereas with PLC you did system integration. In the past a DCS used only proprietary networking whereas a PLC used open networking making it possible to connect third party hardware. In the past only the DCS applications were proprietary whereas the PLC was an open system. I.e. with
the DCS all applications were tailored for the native hardware minimizing configuration work but making impossible or unfeasible to add hardware and software from third parties. The PLC can freely use third party hardware and software, required lots of configuration work, but at least it was possible. Today PLC use OPC to make data available to software as a single integrated database with little of no duplicate work. At the same time, DCS also
implement OPC as a gateway that makes access to some data possible although it is still impossible to choose the workstation software and you still cannot connect third party devices to the DCS networking. These days most PLC manufactures have either bought or aligned themselves with HMI software companies supplying a total solution. Other differences in that past included far better diagnostics and redundancy in the DCS, but this gap has been closed. Today, many PLCs are sold as and used in applications where in the past only DCS could be used - hybrid. Historically a DCS was also far more expensive, but the competition from PLC and new architectures have driven the initial price of DCS down although the long term cost may be higher since with a DCS you are pretty much locked to a single supplier.

With the standardization of the FOUNDATIONT Fieldbus HSE control-level network based on IP over Ethernet media, a new control system architecture has emerged, an architecture based on standard networking rather than a
backplane. This new architecture is poised to become the successor of DCS and PLC architectures. In the networked architecture FOUNDATIONT Fieldbus HSE is used as a backbone. Linking devices then connect to underlying
device-level and remote-I/O networks to which instruments and devices such as variable speed drives are connected. The Ethernet backbone also connects controllers, I/O-subsystems, servers, and workstations. All the devices on the control-network exchange data peer-to-peer. Control-level network interoperability makes it possible to select these devices from different suppliers for this purpose. Functionality such as control, conventional I/O,
interface to different device-level buses, and other specialized functions may be distributed into different devices connected through the control-level Ethernet rather than devices in a backplane. The total combined capability of these devices provides all the functionality required of a system. This is the first step towards a more pervasive use of Ethernet in process control. Using industrial Ethernet such as FOUNDATIONT Fieldbus HSE the controller is just another device. When main control system and package units use the same control-level network, integration becomes easy and tight without gateways.

Jonas Berge
SMAR
===========
[email protected]
www.smar.com
Learn fieldbus and Ethernet at your own pace: www.isa.org/fieldbuses
Learn OPC and automation software at your own pace: www.isa.org/autosoftware