Interfacing PLC and SCADA


Thread Starter


1. I would like to have SCADA system such that it will connect all 5 Compressors with their individual PLC system. also I want to on/off these compressors from SCADA. share me the basic required details for the same.

2. does SCADA reads all parameters of field instruments which connected to PLC?

3. does SCADA can able to change the set points mentioned in PLC for field parameters such as analog inputs?

requests all to guide me for the above queries.
SCADA is generic term for a class of software packages for data collection and supervisory operations, like changing an alarm setpoint.

There is development software that provides the tools to:

- configure and make a communications connection to the field device

- select which data is collected, configure the associated properties like engineering units, scale, max/min limits, tag name.

- some form of HMI application to view which is being collected and what the data is.

Then there is run-time software which runs the program/configuration as established by the development software. Low end SCADA software runs as a Windows application, higher end software typically runs as a Windows service. I'm sure that there are Linux implementations as well.

Nowadays, SCADA packages are OPC clients that talk to an OPC server whose job it is to talk to the field device, for which one buys a license for a driver that is specific to the end device's communication capability.

Some SCADA is oriented towards specific industry segments, like power distribution, where the logging of alarms and events on a millisecond basis to a common synchronized clock is essential.

Sometimes the historian that is used to analyze collected data is sold separately. Sometimes packages are sold by point count.

There are various databases that are used for holding the collected data and debates about the usefulness of each.

HMI packages are similar to SCADA with some form of data collection, a database and an historian. If your PLCs are from the same vendor, then you should take a look at whatever HMI software the PLC vendor offers.
SCADA stands for Supervisory Control And Data Acquisition

Ans1-Yes SCADA is able to do that for you

Ans2-Yes,SCADA can read/write directly to any PLC models,it really depends on the communication protocol you will use.

Ans3-Yes,SCADA is capable of changing Analog or Digital setpoints

As I mentioned,the preferred driver is OPC communication via TCP/IP (Ethernet)

I am not sales rep of Schneider-ELectric but I suggest you check this web:
Yes, the SCADA system can do that. If you have multiple PLC system, you can connect each PLC via Ethernet or serial RS-485. In the case of serial communication, define a different node address for each one of them. If you choose Ethernet, define a different IP address for each one of them. The SCADA can read all published parameters from the devices connected to the PLC. PLC analog variables can be changed by the SCADA system, like setpoints.

An example of an SCADA system that is able to do this is LAquis SCADA
I would use a Pro-face touchpanel and program it with GP Pro EX.

It is easy to use and you can set up communication very quick and easily.
It also has functionality for ladder logic on board.
I make many projects with this nice small one: the GP4116 with a RS-485 bus (for i.e. Modbus RTU RS-485). There is also the GP4114 with ethernet (for Modbus TCP).
It's a nice and bright screen. Looks great.

Important question: what communication is on your compressor? Modbus RTU RS-485 (3 wire) or Modbus TCP? Or something else.
Or do you interface with digital IO for start/stop and analog IO (i.e. 4-20mA) for giving setpoint and reading actual values.

If you specify what you exactly want in the application, I can also make it for you.
I do it for lots of my customers.
But I can also assist you with the programming, also did that lots of times.

gr. Patrick