Skip to main content

ControlLogix Architecture – Rockwell Automation

 In the last article, we discussed the most common type of PLC used in large-scale industries i.e. AB PLC (1756 ControlLogix).

ControlLogix Architecture

Today we will discuss about its architecture.


As seen in the picture, the control system consists of power supply modules, communication module, controller (1756-L55xx), redundancy module, ControlNet communication modules (1756-CNBR), remote IO modules & some other modules like flex IO & AC drive module.

As we are aware that a system has 2 controllers and the system we are talking about here also has 2 controllers installed in 2 different chassis. In the above picture, you can find the primary and secondary ControlLogix chassis.

The controller (CPU) can be identified by a key slot given on it. The CPU has 3 different modes like RUN, REMOTE RUN & PROGRAM.

Redundancy can be established through redundancy modules installed in both chassis connected through Fiber Optic cable. It is shown in the red color line in the above picture.
Once the redundancy modules in the redundant chassis pair are connected and powered, they determine which chassis is the primary chassis and which is the secondary chassis.

There are two PLC systems, we can simply call them PLC A and PLC B, or, chassis A and chassis B. We can also call them the primary controller (PLC A) and secondary controller (PLC B).

Either primary controller or secondary controller will be active and online for monitoring and controlling the plant. The other controller will be in standby mode. The other controller will be active if there is a problem with the primary controller.

If a switchover occurs, the new primary controller continues to execute programs, which begin with the highest-priority task that had been executed on the previous primary controller. The PLC’s switchovers occur as fast as 20 ms.

As we have seen controllers in redundancy, we can place the same IO modules in both chassis to make them redundant too.

Now the system we have taken has IO installed in the remote chassis. So here a 1756-CNBR card is installed in the main chassis and remote IO chassis so that they can communicate.

A redundant type connection or single connection can be used as per requirement (Here redundant is used). Remote IO chassis has separate power modules.

Similarly, different modules like flex IO & AC drive modules can be connected using ControlNet.

We can use Ethernet to communicate with server/HMI, although ControlNet can also be used. The advantage of Ethernet is high bandwidth i.e. 100 Mbps of 1 Gbps depending on the module used whereas ControlNet only gives 5 Mbps bandwidth.

Also, Ethernet is more preferred while having communication with other networks/systems. Other communication modes available are DeviceNet, DH+, DH485, Modbus & SynchLink.

The architecture we discussed is for a single controller used in a very small plant. But if the plant is big and has more areas then more controllers are required.

Also, a network of all controllers is also necessary to access them.


Now if the plant is large with many units in different physical areas and each having its own dedicated PLC, then the above-shown network can be made with the use of switches and Ethernet connection.

This was all about the architecture of AB PLC ControlLogix.

-END-


Labels:

Comments

Post a Comment

Popular posts from this blog

PLC Program for Mixing Tank

 Create a ladder diagram for controlling a batch mixing process. Implement a PLC program for mixing tank or Mixing Process using PLC Ladder Logic. PLC Program for Mixing Tank Fig : Mixing tank A tank is used to mix two liquids. The required control circuit operates as follows: A. When the START button is pressed, solenoids A and B energize. This permits the two liquids to begin filling the tank. B. When the tank is filled, the float switch trips. This de-energizes solenoids A and B and starts the motor used to mix the liquids together. C. The motor is permitted to run for 1 minute. After 1 minute has elapsed, the motor turns off and solenoid C energizes to drain the tank. D. When the tank is empty, the float switch de- energizes solenoid C. E. A STOP button can be used to stop the process at any point. F. If the motor becomes overloaded, the action of the entire circuit will stop. G. Once the circuit has been energized, it will continue to operate until it is manually stopped. Solution : A
1 comment
Read more

What is Relay? How it Works? Types, Applications, Testing

 We use relays for a wide range of applications such as home automation, cars and bikes (automobiles), industrial applications, DIY Projects, test and measurement equipment, and many more. But what is Relay? How a Relay Works? What are the Applications of Relays? Let us explore more about relays in this guide. What is a Relay? A Relay is a simple electromechanical switch. While we use normal switches to close or open a circuit manually, a Relay is also a switch that connects or disconnects two circuits. But instead of a manual operation, a relay uses an electrical signal to control an electromagnet, which in turn connects or disconnects another circuit. Relays can be of different types like electromechanical, solid state. Electromechanical relays are frequently used. Let us see the internal parts of this relay before knowing about it working. Although many different types of relay were present, their working is same. Every electromechanical relay consists of an consists of an Electroma
1 comment
Read more

Chlorine dioxide Analyzer Principle

 Chlorine dioxide measurement Chlorine dioxide (ClO2) is an instable, non-storable, toxic gas with a characteristic scent. The molecule consists of one chlorine atom and two oxygen atoms – represented in the chemical formula ClO2. It is very reactive. To avoid the risk of spontaneous explosions of gaseous chlorine dioxide or concentrated solutions, it is generally handled in dilution with low concentrations. ClO2 is soluble in water, but tends to evaporate quickly. Typically it is prepared on site, for example from hydrochloric acid and sodium chlorite. The procedure provides solutions with approx. 2 g/l ClO2 that can be safely handled and stored for several days. Image Credits : krohne Sensor Parts : Reference electrode Applied chlorine dioxide specific potential Current needed to maintain the constant potential Counter electrode Measuring electrode The disinfection effect of ClO2 is due to the transfer of oxygen instead of chlorine, so that no chlorinated byproducts are formed. ClO2
5 comments
Read more