The QJ72LP25-25 is Mitsubishi Electric’s MELSECNET/H optical ring remote I/O station module for the MELSEC-Q programmable controller series, enabling MELSEC-Q base units to participate in a MELSECNET/H optical ring network as a remote I/O station — allowing the I/O modules installed in a MELSEC-Q base unit equipped with the QJ72LP25-25 to be controlled by a MELSEC-Q master CPU in a different location over MELSECNET/H optical fibre, without a local CPU at the remote station. As the remote station counterpart to the QJ71LP21-25 master/local module, the QJ72LP25-25 forms the remote end of distributed I/O architectures where MELSEC-Q I/O modules must be placed close to field devices in areas remote from the main control panel. The QJ72LP25-25 is available through Atlantech Drives — quote within 24-48 hours, worldwide express shipping, 12-month warranty.
What Is the QJ72LP25-25?
The QJ72LP25-25 is a MELSEC-Q series remote I/O station module for MELSECNET/H optical ring networks. Unlike the QJ71LP21-25 which operates as a master or local station with a CPU, the QJ72LP25-25 operates as a pure remote I/O station — it has no CPU and cannot execute a PLC program. Instead, it acts as a transparent extension of the master CPU’s I/O space: the I/O modules installed in the same base unit as the QJ72LP25-25 appear to the master CPU as if they were installed locally in the master’s own base unit, with their I/O addresses allocated via GX Works2 network parameter settings. The QJ72LP25-25 connects to the MELSECNET/H optical ring using two optical fibre connectors (IN and OUT ports) for the ring topology, and communicates at 10 Mbps with the master station. Up to 64 remote I/O stations can be connected to a single MELSECNET/H optical ring managed by a QJ71LP21-25 master, enabling very large distributed I/O systems with optical isolation and long-distance fibre connectivity.
Key Technical Specifications
- Model: QJ72LP25-25
- Function: MELSECNET/H remote I/O station (no CPU)
- Network: MELSECNET/H optical ring
- Transmission Speed: 10 Mbps
- Transmission Medium: Plastic optical fibre (POF), ST connector
- Maximum Station-to-Station Distance: 25 m (plastic optical fibre)
- Maximum Remote I/O Stations per Network: 64
- I/O Points per Station: Up to 256 I/O points (16 modules × 16 points)
- Network Redundancy: Automatic loop-back on single cable fault (ring topology)
- Current Consumption (5 VDC internal bus): 0.50 A
- Operating Temperature: 0°C to 55°C
- Compatible Base Units: All MELSEC-Q main and extension base units
- Weight: Approx. 0.22 kg
Series Comparison & Selection Guide
The MELSECNET/H remote station module range includes two physical medium variants: the QJ72LP25-25 (plastic optical fibre, POF, 25 m maximum distance, ST connector) and the QJ72LP25B (glass optical fibre, GOF, longer distances). The QJ72LP25-25 is the standard choice for remote I/O stations within the same building where the 25 m station-to-station distance is sufficient — plastic optical fibre is lower cost, easier to terminate with simple snap connectors, and more tolerant of bending than glass fibre, making it practical for panel-to-panel connections within a factory floor section. For remote stations located more than 25 m from the previous ring station, the glass fibre QJ72LP25B or the coaxial remote station QJ72BR15 (for bus topology systems) should be specified. When comparing the QJ72LP25-25 remote I/O architecture to CC-Link remote I/O (using QJ61BT11N master with distributed I/O), MELSECNET/H remote I/O provides a larger I/O capacity per station (256 points versus 128 points for CC-Link) and supports MELSEC-Q intelligent function modules at remote stations (analogue, temperature control, and communication modules can be installed in the QJ72LP25-25 base), while CC-Link primarily supports simple I/O modules at remote stations.
Replacement & Upgrade Notes
The QJ72LP25-25 is the MELSEC-Q replacement for the legacy MELSEC-A series AJ72LP25 and MELSEC-AnS series A1SJ72LP25 remote I/O station modules in MELSECNET/H networks being migrated to MELSEC-Q hardware. When replacing an AJ72LP25 with a QJ72LP25-25 in an existing network, the plastic optical fibre cable and ST connectors are compatible between the A-series and Q-series remote station modules — existing fibre infrastructure can typically be reused without replacement, provided the cables and connectors are in good condition. The I/O module slots in the QJ72LP25-25 base unit must be populated with MELSEC-Q I/O modules (QX/QY series) to replace legacy MELSEC-A I/O modules — the A-series modules are not compatible with Q-series base units. For long-term planning, facilities operating MELSECNET/H remote I/O systems should evaluate migration to CC-Link IE Field Network remote I/O (using RJ71GF11-T2 master with RX/RY remote I/O modules) as part of their MELSEC iQ-R upgrade roadmap, as MELSECNET/H is a mature technology without further development investment from Mitsubishi.
Frequently Asked Questions
Q: Can intelligent function modules (analogue, temperature control) be installed in a QJ72LP25-25 remote station base unit?
A: Yes. Unlike CC-Link remote I/O which primarily supports simple digital I/O modules at remote stations, the QJ72LP25-25 remote station fully supports MELSEC-Q intelligent function modules — including analogue input (Q64AD), analogue output (Q62DA), temperature control (Q64TCRTN), and communication modules (QJ71E71-100) — installed in the remote station base unit alongside digital I/O modules. The intelligent module data is exchanged via the MELSECNET/H link device area between the remote station and the master CPU, with the master CPU executing FROM/TO instructions to access the intelligent module’s buffer memory as if the module were locally installed.
Q: How is the station number assigned to a QJ72LP25-25 module?
A: The QJ72LP25-25 station number is assigned via rotary switches on the front of the module. Set the tens digit on the upper rotary switch and the units digit on the lower rotary switch before powering up the system — for example, station 12 requires the upper switch at 1 and the lower switch at 2. Station numbers must be unique across all stations on the MELSECNET/H ring, including the master station. Changes to the station number take effect only after power cycling the module.
Q: What is the maximum I/O response time between the master CPU and a QJ72LP25-25 remote station?
A: The I/O response time for a QJ72LP25-25 remote station depends on the MELSECNET/H link scan time and the master CPU scan time. With a typical link scan time of 3–5 ms (for a network with 8 remote stations) and a master CPU scan time of 5 ms, the total I/O response time from input change at the remote station to output change at the remote station via the master program is approximately 13–20 ms. For time-critical I/O that requires faster response than MELSECNET/H remote I/O can provide, local I/O in the master base unit or interrupt-driven input modules should be specified instead.
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