Answer / mahesh

Nodes are I/O communication protocols.
Eg: DCS is the master controller, then Nodes slaves.
Nodes are normally receives data from field instruments and processes in DCS.

Answer / ranjith

In Mahesh's answer, it says 'Nodes are I/O communication protocols' this part is wrong.

In a typical DCS architecture from top you have got,
0. MES/SAP/
1. Operator station
2. Runtime/Database/Historian/Batch/Gateway & Engineering Servers
3. Controller
4. IO nodes
5. Marshalling Panel
6. ...(I'll stop here)

The IOs are generally not clustered with the Controllers, IOs will be in a different panel communicating with the controller in various communication protocols(exceptions are there).
There will be a slave module communicating to the master(Controller) and also communicating to the IOs connected to its Backplane/Bus of the slave. This slave module and the IOs are collectively called as 'Node'.
There will be multiple nodes due to segregation of IOs(Plant/unit/Process part) or to distribute the slave module's load (different manufacturer has different IO density specified or may be limitation of protocol).

Now imagine wiring the whole bunch of field signal cables to your control room...!
An alternative is to take a communication cable from 'Main control Room/Center' to 'Remote/Sub station' may be kilometers apart and enjoy limited wiring.

Total number of nodes are limited by the communication protocols itself. (Payload, Noise, Cycle Time ...)

Further reading:
Industrial Communication Protocols /Fieldbus

What is the Difference between CNC and PLC

1 Answers  

---

key phaser where is use and work

0 Answers   BAP,

---

i have used level transmitter in starch cooking preparation tank. tank total height 2mtr.sometime LT display shows some error value when tank is fully empty and diaphragm side i already checked okay no problem in diaphragm area. field cable checked 24volt and mA shows correct value while tank empty mA is 4mA. 4mA i needed that 0% but display showing 10% or 15% percentage values are varying continously please give any good solution for me.....

0 Answers  

---

Close loop and open loop diagram for instrumentation

1 Answers   Petron ltd,

---

what is controlling card in dcs? how u measure dcs memory?what is bus in dcs?how u know dcs speed n ehternet speed?

0 Answers  

---

What is the meaning of Feedback? How many types it is? Explain it?

2 Answers   Bharathi Cement,

---

what r all the closed loop used in boiler? for this related tell some web address..

3 Answers  

---

Difference HAZOP and HIRA

1 Answers  

---

give eg of how I/P is used in control loops

0 Answers   CEPC,

---

WHY WE WILL USE 0-24VdC IN ELECTRONIC CIRCUITS AND INSTRUMENTATION TRANSMITTERS?

3 Answers   Aban Power, Jindal, JSW, Sugar Factory,

---

which type of signal used in instrument?

3 Answers   Emco, Makson, Sail, TATA,

---

what is hall effect?where it is use in power plant?

2 Answers  

---