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 function of 3 way manifold valve in a closed loop system?

1 Answers   Emerson,

---

What is the difference between EPROM & EEPROM.

1 Answers   Sabic,

---

what is difference between fork type and capacitance type level switch. where it is using

0 Answers  

---

what is sequence table in DCS . make a logic in sequence table for tripping of ID fan in Boiler(in YOKOGAWA CS 3000 DCS).

1 Answers   Yokogawa,

---

What are the different type of instrument used in cement industry with uses

2 Answers   Lafarge,

---

What is 3 selection available when configure the burnout protection for controller

0 Answers   EI Electrotechnical Institute,

---

what is the exact job for automation enggineer?

0 Answers  

---

How does electro magnetic pump works ?

1 Answers   IGCAR,

---

Draw block diagram BOILER COMBUSTION loop & Explain

1 Answers   Bajaj Hindusthan, Exxaro,

---

Which wiring connection is preferred in motor for industrial use?

2 Answers  

---

what is the meaning of potential free contact. difference between dry and wet contact?

6 Answers   GAIL,

---

what is the difference between auto tuning and manual tuning of controllers(eg:PID,PI,PD CONTROLLERS )

2 Answers   GATE,

---