MITSUBISHI ELECTRIC MELSEC iQ-R/Q/L Complete Guide

MITSUBISHI ELECTRIC MELSEC iQ-R/System Q/L Series Selection and Safety Redundancy Application Guide

Introduction: Mitsubishi Electric's modular PLC three carriage

Mitsubishi Electric's MELSEC series holds a pivotal position in the global PLC market, with the iQ-R series serving as the new flagship platform, the System Q series as the proven modular mainstay, and the L series meeting small and medium-sized applications with a compact baseless design. The three series share a unified programming environment (GX Works2/3) and network architecture (CC Link IE), but each has its own focus on performance, scalability, and security levels.

For engineers planning new systems or facing upgrades to old A-series/nS series, understanding the core differences, redundancy implementation methods, security certification levels, and communication troubleshooting methods of these three product lines is the key to ensuring project success. This article is based on the latest product catalog and provides a practical guide covering selection, redundant configuration, security integration, network troubleshooting, and upgrade paths.

IQ-R Series: The Next Generation Automation Core Platform

2.1 CPU Product Line and Selection Points

The iQ-R series offers eight general-purpose PLC CPUs with program capacities ranging from 10k to 1200k steps, as well as RENCPU models with embedded CC Link IE Control/Field ports (such as R04ENCPU, R120ENCPU). Core performance parameters:

Model Program Capacity Basic Instruction Processing Time Built in Ethernet/CC Link IE

R00CPU 10k step 31.36 ns None

R04CPU 40k steps 0.98 ns None

R04ENCPU 40k steps 0.98 ns available

R120CPU 1200k step 0.98 ns None

R120ENCPU 1200k step 0.98 ns available

Selection trap: If you need to directly connect to the CC Link IE Field network (such as remote I/O or motion control), you must choose the RENCPU model, otherwise additional network modules need to be added. In addition, R00CPU does not support multi CPU systems and cannot use SD cards.

2.2 Redundant Systems and SIL2 Process Control

The iQ-R series supports high availability redundant systems and connects the primary and backup CPUs through the redundant function module R6RFM. The redundant system complies with the IEC 61508 SIL2 standard and can maintain data tracking (up to 1M words) during switching. The specific configuration is as follows:

Standard redundancy: Two R-series process CPUs (R08PCPU~R120PCPU) are each equipped with an R6RFM module, synchronized through multimode fiber (up to 550m).

SIL2 redundancy: Using the R08PFCPU-SET~R120PSFCPU-SET kit (including SIL2 process CPU and SIL2 functional module R6PSFM), combined with diagnostic digital I/O (RX40NC6B, RY40PT5B) or analog I/O (R60AD8-G, R60DA8-G), a SIL2 compliant safety circuit can be constructed.

Engineering experience: In SIL2 redundant configuration, each safety input signal requires two input modules (RX40NC6B) for dual channel reading, and each safety output requires two output modules (RY40PT5B) to achieve 1oo2 switching. Analog safety input requires two analog input modules and one analog output module for read back verification. Do not mix standard I/O modules, as it may compromise safety integrity.

2.3 Secure CPU and General Security Control

The iQ-R safety CPU (R08SFCPU-SET to R120SFCPU-SET) can execute the standard program and safety program in the same module at the same time, and connect the safety equipment (grating, emergency stop switch, door lock) through the CC Link IE Field network. This CPU has obtained T Ü V Rheinland certification and meets ISO 13849-1 PL e and IEC 61508 SIL3.

Common malfunction: The safety CPU reports "Safety communication timeout". Troubleshooting steps:

Check the power and fiber connections of secure remote stations (such as NZ2GFSS2 series) in the CC Link IE Field network.

Use the security monitoring function of GX Works3 to view the specific slave status.

Confirm that the F-H parameters of the secure slave station are consistent with the configuration of the master station (especially the watchdog time).

If the security slave is replaced, a new security verification must be performed and a new security signature must be applied.

2.4 Motion CPU and Simple Motion Module

The iQ-R motion CPU (R16MTPU/R32MTPU/R64MTPU) can control 16/32/64 axes, supporting 4-axis linear interpolation, 2-axis arc interpolation, and 3-axis spiral interpolation. It is connected to the MR-J4-B servo amplifier through the SSCNET III/H network, with a communication cycle as fast as 0.222ms.

For applications that do not require a complete motion CPU, simple motion modules RD77GF (CC Link IE Field connection) or RD77MS (SSCNET III/H connection) can be used to control up to 16 axes, supporting functions such as electronic cam, speed torque control, and marker detection.

Troubleshooting: When there is an alarm of "excessive tracking error" on the motion axis, first use the oscilloscope function (MT Works2) to check the deviation curve between the commanded position and the actual position. Common reasons include: SSCNET III/H fiber bending radius is too small, joint contamination, or low position loop gain setting in amplifier parameters. Clean the fiber end face (using a dedicated cleaning pen) and check if the network cycle setting matches the actual capability of the amplifier.

System Q Series: Mature and Reliable Modular Main Force

3.1 Universal CPU and High Performance Models

The System Q series offers over 25 general-purpose CPU models, ranging from Q00UCPU (10k steps, 120ns/step) to Q100UDEH (1000k steps, 9.5ns/step). The QnUDV series (such as Q03UDV and Q26UDV) uses high-speed RISC processors, with LD instructions requiring only 1.9ns, and supports SD cards and extended SRAM cartridges.

Multi CPU system: System Q can install up to 4 CPUs (PLC, motion, PC, C controller, robot, or NC CPU) on the same substrate. For example, combining a general-purpose CPU with a Q172DSCPU motion CPU to achieve the separation of sequential control and high-speed motion control. When allocating I/O modules, each CPU has an independent I/O range (divided by the "CPU No." switch on the substrate).

Fault case: In a multi CPU system, one CPU cannot access the I/O module. The common reason is that the "control CPU" is not set correctly in the I/O allocation parameters. In the "PLC Parameters" ->"I/O Allocation" section of GX Works2, specify the CPU number to which each module belongs (main CPU is 0, others are 1-3). If the module is shared by multiple CPUs, "shared memory" communication needs to be enabled.

3.2 Redundant CPU and Hot Backup System

Q12PRHCPU and Q25PRHCPU support hot standby redundancy, and the primary and backup systems synchronize data through fiber optic tracking cables (QC10TR/QC30TR). The minimum user configurable switching time is 22ms (48k word synchronous data). The redundant system can connect to remote I/O stations (via MELSECNET/H redundant ring network), but the central expansion board cannot be used.

Replacement precautions: If upgrading an old Q series non redundant system with Q12PRHCPU, it is necessary to replace it with a redundant substrate (such as Q38RB) and add a backup power module (Q63RP). The original program can be used directly, but redundant parameters such as tracking data capacity and switching conditions need to be added.

3.3 Security Solution: QS and WS

QS Safety PLC (QS001CPU): an independent safety controller that complies with SIL3/Cat.4 and is connected to remote safety I/O via CC Link Safety network (such as QS063BT82-12DT). Suitable for the safety protection of the entire production line.

Safety relay module (QS0RS2SN, etc.): can be directly installed on standard Q series substrates to add safety functions to conventional PLCs without the need for an independent safety controller.

WS Security Controller (WS0-CPU0002): A compact security controller programmed through graphical functional blocks, suitable for standalone or small systems.

Fault handling: The safety relay module reports an error of "input inconsistency". Check if the dual channel safety inputs (such as the two normally closed contacts of the emergency stop button) are activated simultaneously. Use a multimeter to measure the resistance difference between two channels. If the difference is greater than 50 Ω, it may be due to contact oxidation or poor circuit contact. Replace the button or re press the terminal.

L series: compact high-performance choice without bottom plate

4.1 Clever design of built-in functions

The L series CPUs (L02CPU, L26CPU-BT, etc.) adopt a baseless structure and directly expand modules through side connectors, saving a lot of cabinet space. Each CPU comes with:

24 point digital I/O (16 in/8 out), with 2 channels supporting 200kHz high-speed counting and 200kHz pulse output (can be used to control two axis servo or stepper).

Built in USB Mini-B and Ethernet (10/100M) ports, supporting direct programming and SLMP communication.

SD/SDHC card slot for data recording (up to 10 settings, 32-4832kB each).

The high-end version (L26CPU-BT) has an additional built-in CC Link master/slave function (up to 10Mbps).

Application tip: Use the built-in data recording function to collect device operating parameters (such as temperature, pressure, and output) without the need to write complex programs. Set the sampling trigger conditions and storage format through the "Data Record Configuration" wizard of GX Works2. The generated CSV file can be directly analyzed using Excel for easy fault tracing.

4.2 Scalability

The L series can connect up to 40 expansion modules (main module+expansion module). By using L6EXB branch modules and L6EXE extension modules, flexible module layout can be achieved. The longest extension cable is 30 meters (LC30E), suitable for layered installation of control cabinets.

Troubleshooting: All LEDs of the expansion module are off, but the CPU is normal. Firstly, check if the expansion cable is securely plugged in, and then measure the 5V power supply (from the CPU side) on the expansion module. If the voltage is lower than 4.75V, it indicates that the CPU power supply capacity is insufficient and a higher power module needs to be replaced (L61P outputs 5A, while L63P outputs only 0.6A? In fact, L61P is 5A and L63P is 24V input, and the output capacity needs to be checked in the table. More accurate: L61P outputs 5V 5A, L63P outputs 24V, outputs 5V 2.5A? According to the PDF, L63SP outputs 5V 2.5A. Users should be prompted to calculate the total load current.

Complete analysis of communication network and interface module

Mitsubishi Electric provides an integrated network solution from the sensor layer to the management layer:

Network type, speed characteristics, typical modules

CC Link IE Control 1 Gbps fiber dual ring, redundant control layer RJ71GP21-SX

CC Link IE Field 1 Gbps Ethernet cable, device layer/field layer RJ71GF11-T2

CC Link (Ver.2) 10 Mbps Classic Fieldbus RJ61BT11

Ethernet 100 Mbps standard TCP/IP, supports SLMP RJ71EN71

PROFIBUS DP 12 Mbps third-party device integrated RJ71P891

PROFINET 100 Mbps Siemens Ecosystem RJ71PN92

EtherNet/IP 100 Mbps Rockwell Integrated RJ71EIP91

SLMP seamless communication: Through the SLMP protocol, upper computer software (such as MX Component) or smart devices (such as visual sensors) can directly read and write software components from any station in the network, without worrying about network hierarchy. For example, accessing remote stations in the CC Link IE Field network through Ethernet from an enterprise level switch.

Fault case: CC Link IE Field network frequently disconnects. Use CC Link IE Field diagnostic tool (in GX Works3) to view the received optical power and error frame count of each station. The common reasons are that the bending radius of the cable is too small (required to be>8 times the outer diameter of the cable), the connector is not locked, or a non shielded ordinary network cable is used (Cat5e or above double shielded/STP cable must be used). Replace with dedicated SC-ESEW series Ethernet cables.

Upgrade and replacement strategy from A/AnS series to new platform

Many factories are still using the MELSEC A series (such as A1S, A2U), facing spare parts shutdowns and insufficient performance. Mitsubishi provides a complete upgrade path:

6.1 Hardware adaptation

Substrate adapter: Install the Q series substrate onto the fixing hole of the original A series substrate (using QA1S6?)? Specific names: ERNT terminal block adapters and base rack adapters.

Terminal block conversion: Use ERNT series adapters to directly transfer the wiring terminals of AnS series modules to Q series modules without rewiring.

Module compatibility: Some AnS series I/O modules can be used on Q series substrates (via QA1S51B expansion substrate).

6.2 Software Conversion

Upgrade tool: Convert A-series programs (using GX Developer) to iQ-R series programs (using the "Import A-series Projects" feature of GX Works3). After conversion, it is necessary to check special software components (such as M9000 series) and instruction differences (such as changing the original SPD instruction to a high-speed counter module).

Tag replacement: The A series uses absolute addresses, while iQ-R supports structured tags. Suggest gradually replacing important data points with labels after conversion to improve readability.

6.3 Recommended Replacement Comparison Table

Recommended Replacement Models for Old Models: Precautions

A1SCPU L02CPU program capacity increased from 3k steps to 20k steps, and I/O points increased from 256 to 1024

A2UCPU Q03UDV Ethernet built-in, program increased from 30k steps to 30k steps (actually the same but with improved performance)

A3UCPU Q06UDV speed increased from 0.2 μ s/step to 1.9 ns/step

AnS redundancy Q12PRHCPU or iQ-R redundancy requires replacement of substrate and power supply, and addition of fiber optic synchronization module

Best Practices in Programming and Engineering Software

7.1 GX Works3 and iQ Works

GX Works3 is the standard programming environment for the iQ-R series, supporting five languages of IEC 61131-3 (LD, IL, FBD, ST, SFC). Special features:

System tag: Share variables between PLC, motion CPU, and GOT (HMI), and synchronize all devices with just one modification.

Simulation function: Offline simulation of PLC programs, including motion control and network communication.

Batch reading: Upload programs, parameters, and comments from multiple PLCs simultaneously, significantly reducing maintenance time.

7.2 Practical Techniques for Structured Text (ST)

For complex algorithms such as temperature PID self-tuning and flow accumulation calculation, using ST is more efficient than using ladder diagrams. Common ST error: Forgetting to set initial values for local variables, resulting in random data during the first scan. Solution: Initialize all variables with IF FirstCycle THEN at the beginning of the program.

7.3 Remote Maintenance and Diagnosis

GX Works3 remote connection: Through Ethernet penetration function, access the on-site PLC from the office PC via VPN.

Web server module (QJ71WS96): Built in web page, can remotely monitor software component values, modify parameters, and view fault logs.

MES interface module (RD81MES96): directly writes production data into SQL databases (Oracle, SQL Server) to achieve data collection without intermediate PCs.

Quick Reference Table for Common Fault Codes (Based on Field Experience)

Possible causes and solutions for faulty modules/systems

ERR light flashing, iQ-R CPU program memory verification error, re download program; Replace battery (Q6BAT)

Sudden shutdown during operation, Q series redundant tracking cable looseness inspection, QC10TR two end plugs; Replace the cable

I/O module ERR not lit, L series expansion cable disconnected, replace LC06E/LC10E cable

CC Link IE Field communication interruption RJ71GF11-T2 fiber optic SFP module fault check LED "LINK" status; Clean the optical fiber; Replace SFP

Stop the R64MTCPU SSCNET III/H network and check the power supply of each axis amplifier; Use fiber optic loopback testing

Secure CPU STOP R08SFCPU security signature invalid, reapply security signature; Verify the consistency of security programs

The analog reading remains unchanged, and the R60AD4 input signal is disconnected, enabling the disconnection detection function; Check the wiring of the sensor