The acronyms themselves give some hints. Each is a kind of automation / control system and each has different functions. At first sight they may seem similar and use the same terminology to sometimes mean slightly different concepts.

A PLC is a device that (typically) has inputs and outputs and a logic engine. It is programmed to read the inputs (to collect field data), perform some calculation and operate the outputs to affect the equipment that it controls. It usually performs a automation function locally and can operate automatically without supervision or operator intervention. The configuration and programming of the logic is closely tied to the physical process that is being monitored or controled. Typically the process depends on the PLC operating correctly and the process might need to be shut down if the PLC fails. Critical systems usually include separate safety or shutdown systems to perform this function if needed and these operate independently of the PLC.

A physical process might have multiple PLCs, each of which automates a different part of he process. PLCs may have communication interfaces and share data with other devices: Sometimes other PLCs or a SCADA system, etc.

A SCADA system includes communication to allow monitoring of a control system (which might contain PLC or RTUs or might be a DCS) and permits an operator to modify the operational parameters by issuing commands (such as turning on a pump, opening a valve, closing a switch or changing a tuning control setting). The operator may be monitoring locally (e.g. from a room inside the factory that is being monitored) or remotely (e.g. from a control room in a different country). Typically the system being monitored does not depend on the SCADA system in order to operate: If the SCADA system fails (e.g. the communication network has a fault), the process continues to operate as it was before the fault. SCADA always includes communication between the monitored equipment and the operator's workstation. The communication network is always subject to failure and (good) SCADA systems are designed to allow for graceful behavior during failures and while recovering from a failure.

Larger or more complex control systems might have separate data collection and logic processing at the process site and these larger systems are typically called DCS. The crossover from PLC to DCS is sometimes blurry. One common distinction is that PLCs are programed to operate independently while a DCS typically only operates as a collection of devices that share information between each other. If these systems experience a communications network failure they typically need to shut down the process.

IoT is a catch-all term that seems to be applied to anything that can be cobbled together. While PLCs, DCSs and SCADA systems need to be configured to operate closely with the process and are part of the process, IoT systems are typically set up as a number of separate devices which each provide some data or control function but are generally not designed into the process in the same way and are often not a critical part of the process.

Some systems have combinations of these features and are not easily categorized as just a PLC system or just a DCS or just a SCADA system. Sometimes they are combined DCS and SCADA, etc.

Rather than worrying about the names of the system or trying to define exactly what each kind of system must or must not have, pay more attention to the functional requirements. Typically the most cost-effective way to meet the functional requirements ends up looking a lot like one of these kinds of systems, but the requirements could be met by several different kinds of systems. Over time you may gather experience which will help you assess how to meet different requirements quickly and effectively.

in simple wording i will introduce my answer from industrial point of view:

PLC : is the controller mainly deal with logic programming and can be extended to handle integer or floating point signals. PLC can have a PI controllers and other simple structure controllers but cannot handle real-time control with fixed sampling time (some PLC can have special functions driven by fixed sampling time). PLC has limited database (data blocks). Those DataBlocks are used only to store the present status of control signals but not used as a historical storage. PLC is not used to analyze data and hence cannot be used for historical or statistical analysis.

DCS: It can perform all function of PLC and also can have its large database for historical and statistical analysis. DCS can host complex programs that can perform complex tasks and can be programmed with hi-level languages. DSC is wider than PLC function-wise. DCS has its own visualization graphic user interface (HMI).

SCADA: is considered a system that can visualize signals. when term SCADA is mentioned, we always think about power system visualization (power system monitor).

There are more and more to explain each term. i am open for any further clarifications.

Thank you Dears, Andrew West and Hany A. Hamed , We have written an article on intelligent water control

( An experimental setup of multi-intelligent control system of water management using Internet of Things), designed with the Internet of Things and mobile network(GSM/GPRS), and one of the Reviewers has asked for the difference in our approach. We have designed a table to answer this question from a different point of view. I am very pleased to compare your opinions with this table.

Abstract :

This paper focuses on an innovative technique of multi-intelligent control system (MICS) of a water pump and a pump station, which is practically designed, set up and used in an agricultural sector. The main components of MICS consist of three control systems, including the electro-pump controller, water level in reservoir and alarm control system. The entire system can be governed by the Internet of Things technology and operated via SMS or Ringtone, which is manageable from anywhere at any time. A soft starter mechanism was designed and considered for running an electro-pump to eliminate the electrical shocks and mechanical stresses. In the proposed control system, a 4-state switch was designed and employed, which facilitates running and controlling the system manually, automatically, using IoT state, and finally in off mode state. Description of the control and power circuits of the system are explained and discussed in detail. MICS has a very reliable operation and provides a convenient solution for water management with high accuracy. This intelligent system can be widely employed in different applications such as the agricultural and industrial sectors due to the robust and flexible construction. A smart flowchart and multiple security layers were designed and explained for the management, protection, and supervision of MICS.

Keywords: Intelligent water management; agriculture and industry, Internet of Things; control and automation system, wireless sensor.

Please find the table in the attachment and apply your comments.

I will be happy to hear your feedback

Thanks a lot

Market Introduction:

Replacement of . . .:

Products Manufactured . . .:

Classic Application:

Type of Control:

Redundancy:

Engineering Mindset:

Operator Interaction:

Operator Interface:

Size/Footprint:

Up-front cost:

System:

Repair and maintenance:

Reliability:

safety and Security :

Programming, wiring and ...:

Implement and run:

user:

Creativity in devising new ways;

Application in small farming farms:

I checked the doc attached and i guess that it will not satisfy the reviewer. Reviwer from the way he wrote the question understsnd very well the difference between all what he pointed out and not expect to answer him this way. The best reply to that comment is to list in points the advantages of your proposal which one/many of what he mentioned does not have for example

* The proposed scheme is able to do xxxxxx which yyyy cannot achieve zzzz

* The xxxx cannot be controlled by xyz while with simple configuration we can do xxxxx.

* the below table summerize the advantages of our proposal