Omron PLC Overview

There are a variety of manufacturers of Programmable Logic Controllers (PLCs), with Omron Corporation being one of the leading makers of compact micro-range PLCs that are used in the automation industry. The company offers a flexible product line of scalable and high-performing industrial PLCs for use in stand-alone machines or as part of larger machine control systems.

A PLC is a ruggedized, compact digital computer designed to control specific industrial processes, machine systems, or an entire production line in a manufacturing setup. It controls these machines, equipment, and processes based on a programmed sequence of instructions and conditions. The PLC controller not only provides control functionalities such as control of positions, continuous quantities, and speeds, but it also enables data exchange among devices. Essentially, PLCs are like the brains of almost all industrial automation systems/equipment that require high-reliability control, process fault diagnosis, and ease of programming.

For example, instead of having several operators or machines managing different industrial automation equipment/systems, you can use a PLC controller with integral I/O modules to complete different control tasks concurrently. A common example of a PLC application is the traffic light system. Where rather than having an operator reading data and pushing the light buttons, a PLC system is used to monitor and control the traffic light signals. Other recognizable applications of PLCs include automatic doors, elevators, amusement rides, and automatic car washes.

Omron PLC Architecture

The most important hardware and software components of any Omron PLC system include:

A) CPU Module

The Central Processing Unit (CPU) can be said to be the brain of the Omron PLC system, as it performs all the arithmetic and logical functions of this PLC controller. It also executes the sequence of instructions stored in a user-defined program. The CPU module consists of three components, namely:

• Processor: It performs all the necessary computations like monitoring the status of inputs, managing the controller’s memory, and activating appropriate outputs as per the logical instructions stored in the PLC program by the user. The processor also regulates the timing of all PLC operations.  
• Memory: The Omron PLC uses two types of memory, Random-Access Memory (RAM) and Read Only Memory (ROM), to store the logic involved in the execution of the PLC program. The ROM location stores fixed data sets and programs used by the processor such as the PLC operating programs. While the RAM location stores timer and mathematical values, counters, and information about the status of the connected field I/O devices (i.e. scaling of analog inputs). 
• Power Supply: Most Omron PLC systems use a 24V DC input voltage, which is provided by a power supply module. This power supply module provides the right input voltage to each module of the PLC system including the CPU module. It actually receives either 240 or 120 VAC from AC mains and then converts it mainly to 24 VDC. The converted 24 VDC voltage is then transmitted from the power supply module to the PLC circuitry to power the other PLC components. 

B) Input/Output Modules

I/O modules connect field input and output devices to the CPU module of an Omron PLC system. The connected field devices are either PLC Inputs or Outputs. Input field devices supply data or signals to the PLC CPU. Examples of PLC inputs include toggle switches, Start/Stop pushbuttons, measurement devices (i.e. RTD or Thermocouple sensors, strain gauges, liquid-level detectors, pressure sensors), safety switches, etc. On the other hand, field output devices receive data or signals from the PLC CPU. Motors, solenoid valves, lights, relays, pumps, and electric heaters are common examples of PLC outputs.

PLC inputs and outputs are classified as either Digital or Analog. Digital Inputs/Outputs only have two states–ON or OFF, HIGH or LOW, OPEN or CLOSED, etc. As a result, they only send or receive binary signals (1s or 0s) to/from the CPU of an Omron PLC system. Relay contacts, Toggle switches, Pushbuttons, and Safety switches are common examples of digital PLC inputs. Examples of digital PLC outputs include Hooters, Motors, Solenoid Valves, Lights, etc.

Conversely, Analog PLC Inputs and Outputs have more than two states. They send or receive complex signals to/from the PLC CPU that are in the form of current or voltage signals. For example, an RTD sensor can provide many temperature values like 20℃, 40℃, 32℃, 51℃, etc, since temperature is not only cold or hot. Examples of analog PLC inputs include temperature sensors, weight scales, level sensors, pressure sensors, etc. The most common example of an analog PLC output is a control valve, which may be 0%, 10%, 15%, 30%, 50%, 75%, or 90% open. Another popular analog PLC output is the Variable Frequency Drive (VFD).

C) Communication Protocols

A communication protocol is used to exchange data between the PLC system and the connected analog/digital field I/O devices and other peripheral devices. 

Some of the communication protocols supported by Omron PLCs include: 

• EtherNet/IP: This is an industrial communication protocol that adapts the Common Industrial Protocol (CIP) to standard Ethernet protocol for network connectivity. It allows structured, tag-based network communications, and is widely used by various manufacturers of automation PLCs like Omron and Rockwell Automation (Allen-Bradley PLCs). There are specific Omron PLC models which include one or more Ethernet communication interfaces with an EtherNet/IP data link function. 
• Serial Protocols: Most Omron PLC models support RS-232, RS-485, and RS-422 serial communication options through additional option boards. Thus, additional devices like motion controllers can be interfaced directly to an Omron PLC system via those serial protocols. 
• CompoBus/S: This is a high-speed, long-distance Field Network protocol used for remote I/O connections with the aim of reducing component wiring. Some Omron PLC models like CP1E, CS1, and CP1H support the proprietary CompoBus/S Input/Output subsystem. 
• PROFIBUS-DP and DeviceNet: Various Omron PLC models such as CS1, CPM1A, CPM2A, CP1L, and CP1H support PROFIBUS-DP and DeviceNet communication protocols, which enable the connection of additional field devices like motor drives and weigh scales to the Omron PLC network. 

D) Programming Terminal

Omron PLC users require a programming terminal to develop and download a PLC program onto the CPU memory. All Omron PLC Series use the CX-Programmer terminal that’s fully integrated into the CX-ONE software package for programming purposes. CX-ONE software is a programming software suite that enables users to build, program, and configure Omron PLCs using only one software package with just one installation and license number. This significantly reduces the complexity of programming and configuring Omron PLCs.

The CX-ONE software can be installed on programming devices (i.e. personal computers (PCs) or desktop consoles) using Windows 10, Windows 8.1, or Windows 7 Service Pack Operating System (OS). Select the CX-ONE software model that’s compatible with your Omron PLC, as there are many models available with a different number of user licenses.

The CX-Programmer includes standard function blocks in IEC 61131-3 conventional ladder logic or structured text PLC programming languages. Thus, with the CX-Programmer, you can develop a PLC program for any Omron PLC using either Ladder Diagram or Structured Text (ST) programming languages.

How Do Omron PLCs Operate? 

An Omron PLC begins operating once the user downloads a program onto its memory, determines the inputs and outputs, and selects appropriate I/O modules. The CPU receives and processes signals from the connected field input devices, executes the logical instructions from the stored PLC program, and updates the appropriate outputs based on the programmed logic and provided information (input data).

Omron PLC’s operation can be summarized into three main steps, namely: 

• Input Monitoring: The CPU constantly checks the state of the field input devices connected to the PLC system, and processes the received input data as pre-programmed data for use in the next steps. 
• Logic Execution: The CPU executes the logical instructions in the control program created by the user, and stores the program execution results to be used in the following step. 
• Output Control: The PLC processor activates the appropriate outputs to control the corresponding field output devices based on the detected input variables(pre-programmed data in step 1) and execution results of the programmed logic(in step 2). 

Another crucial step in Omron PLC’s operation is housekeeping. In this step, the CPU processor communicates with the programming terminal to avoid any programming and configuration errors. It also runs memory routines continuously to ensure that the PLC memory is functioning properly. Moreover, it constantly performs internal diagnostics of the entire PLC system by checking the other hardware and software PLC components for faults.   

Since the Omron PLC is a dedicated controller it operates in a repeating loop, which brings about the concept of Scan Cycle and Scan Time. Scan Cycle is the cycle in which the PLC processor detects the input variables, executes the stored control programs, and then activates the appropriate outputs. This takes a short period of time referred to as the Scan Time or Cycle Time, usually in milliseconds (ms).

Thus, scan time is the amount of time the processor takes to perform one complete scan cycle. Cycle time includes time for self-diagnosis (overhead processing), execution of user-defined control programs, I/O status updating, and peripheral servicing. The cycle time determines the processing speed of a given Omron PLC–I/O response time and the command execution cycle.

Types of Omron PLCs 

Omron PLC models are classified into three categories, as follows:    

A) Compact PLC Series

Compact PLCs, also known as unitary or integrated PLCs, are the simplest type–as all the modules(CPU, communication cards, power supply, etc) are housed within a single case. This type of PLC series has a fixed number of I/O modules, an integral CPU with connection ports, and is appropriate for simple processes. Usually, compact PLCs can be connected directly to the equipment or system being controlled    

The table below lists the available Omron PLC models classified as Compact types: 

B) Modular PLC Series

Modular PLCs contain several different modules that can be connected together to build a customized PLC system. But a base module with a CPU, power supply, and inputs is still needed for core PLC functions such as data processing and program execution, electrical power regulation, and input connections. This PLC series gives users more flexibility, as you can customize your PLC system by adding extra I/O modules and peripheral devices like Analog to Digital (A/D) signal converters. You can actually add as many additional modules as your PLC system allows.

Omron PLC Models Classified as Modular PLCs Include: 

• CJ2M-CPU1 [] Simple Type PLC Model: It features up to Program Memory capacity of 60K Steps, Data Memory capacity of up to 160K Words, and 2,560 I/O Bits. It includes a USB port, an RS-232C serial port, and Serial PLC Links. This model supports up to two Pulse I/O modules, whereas for CJ2M-CPU1 Version 2.0 or Later at least one Pulse I/O module should be mounted. 
• CJ2M-CPU3[] Standard Type PLC Model: It features up to 60K Steps Program Memory capacity, up to 160K Words Data Memory capacity, and 2,560 I/O Bits. It includes a USB port, an EtherNet/IP port, an RS-232C or RS-485/RS-422A serial communication port, and one (1) serial option board is required for Serial PLC Links. It supports up to two Pulse I/O modules, where at least one Pulse I/O module should be mounted for CJ2M-CPU3 Version 2.0 or Later  
• CJ2H-CPU6 [] High-End PLC Model: It features up to 400K Steps of Program memory, up to 832K Words of Data memory, and 2,560 I/O Bits. It includes a USB port, an RS-232C serial communication port, and a High-Speed Interrupt function. It supports Synchronous Unit operation in combination with a Position Control Unit, model CJ1W-NC[][]4.  
• CJ2H-CPU6[]-EIP Flagship Type PLC Model: This Omron PLC features up to 400K Steps of Program Memory, up to 832K Words of Data Memory, and 2,560 I/O Bits. It includes a USB port, an RS-232C serial communication port, an EtherNet/IP port, and a High-Speed Interrupt function. It supports Synchronous Unit operation in combination with a Position Control Unit, model CJ1W-NC [][]4.  
• CJ1M Model: This Omron PLC model consists of several built-in I/O including Sixteen(16) Digital I/O, Four(4) Interrupt Inputs, Two(2) 100 kHz Counter Inputs, and two(2) 100 kHz Pulse Outputs. It features an Ethernet CPU (available in 3 models), and a choice of CPU models without and with built-in I/O. It includes 5-20K Steps of Program Memory, 32K Words of Data Memory, and up to 64 MBs of CompactFlash Memory. It has an Execution Time (Bit Instruction) of 0.1 µs (microseconds). It supports 160-640 Digital I/O points, and up to 20 x 8 Analog I/O points of 12-bit resolution or 15-bit resolution. 
• CJ1G/CJ1H Model: This Omron PLC series does not include built-in I/O. It features a Loop control CPU, which is available in 4 models. It includes 10 -250K Steps of Program Memory, 64 – 448K Words of Data Memory, and up to 64 MBs of CompactFlash Memory. It has an Execution Time (Bit Instruction) of 0.04/0.02 µs (microseconds). It supports 960-2560 Digital I/O points, and up to 36 x 8 Analog I/O points of 13-bit resolution or 15-bit resolution. 

Note: All Omron PLC models in the SYSMAC CJ1 PLC Series support several special function units including SSI encoder input, High-Speed counters (500 kHz), Temperature Control, Position Control, RFID sensor unit, Process Control, Protocol Macro, and Motion Control units. Also, they offer a variety of  communication options including Serial, Controller Link and Ethernet (100 Base-TX) industrial networks, Fieldbus Master Communications with DeviceNet, PROFIBUS-DP, and CompoBus/S protocols, as well as Fieldbus I/O Links for PROFIBUS-DP and DeviceNet. 

C) Rack PLC Series

Racking mounting PLC types are similar to modular PLCs, but the concept is implemented differently. While each module in a modular PLC is connected directly to the base unit, each module in a rack mounting PLC is kept separate–the modules are held separately in organized racks and can be removed and re-inserted as required. Additional modules are connected via a network. This approach makes it possible to build larger PLC systems without them being overly complicated or cluttered.

OMRON PLC Models Classified as Rack PLCs Include:

CS1H/CS1G Model: This PLC model has no built-in inputs and outputs. It features a Program Memory of 10-250K Steps, a Data Memory of 64-448K words, and a CompactFlash Memory of up to 64 MBs. Its CPU features two (2) serial ports and it has a Loop Control option board. It has an Execution Time (Bit Instruction) of 0.02/0.04 µs (microseconds).

It supports 960-5120 Digital I/O points, up to 80 x 8 Analog I/O points with 13-bit resolution or 80 x 4 Analog I/O points with 16-bit resolution, and various special function units such as SSI encoder input, High-Speed counters (500 kHz), Temperature Control, Position Control, RFID sensor unit, Process Control, Protocol Macro, and Motion Control units.

In addition, the CS1H/CS1G Omron PLC model supports various communication protocols including Serial, Controller Link, and Ethernet (100 Base-TX) industrial networks, Fieldbus Master protocols (DeviceNet, PROFIBUS-DP, and CompoBus/S), and Fieldbus I/O Link (PROFIBUS-DP and DeviceNet).

CS1D Model: This Omron PLC model does not include integral inputs and outputs. It features a Program Memory of 60-250K Steps, a Data Memory of 128-448K Words, and a CompactFlash memory of up to 64 MBs. Its CPU module features a Duplex CPU, communications, and a power supply unit. Its processor has an Execution Time (Bit Instruction) of 0.02 µs (microseconds). It also includes a Loop Control option board.

It supports a maximum of 5120 Digital I/O points, up to 75 x 8 Analog I/O points with 13-bit resolution or 75 x 4 Analog I/O points with 16-bit resolution, and various special function units such as SSI encoder input, High-Speed counters (500 kHz), Temperature Control, Position Control, RFID sensor unit, Process Control, Protocol Macro, and Motion Control units.

Moreover, the CS1D Omron PLC model supports a variety of communication protocols including Serial, Controller Link, and Ethernet (100 Base-TX) industrial networks, Fieldbus Master protocols (DeviceNet, PROFIBUS-DP, and CompoBus/S), and Fieldbus I/O Link (PROFIBUS-DP and DeviceNet).

This entry was posted on August 3rd, 2022 and is filed under Automation, Hardware Comparison, PLC, Technology, Uncategorized. Both comments and pings are currently closed.