The QJ72BR15 is Mitsubishi Electric’s MELSECNET/H coaxial bus remote I/O station module for the MELSEC-Q programmable controller series, enabling MELSEC-Q base units to participate in a MELSECNET/H coaxial bus network as a remote I/O station — the coaxial bus counterpart to the plastic optical fibre QJ72LP25-25, providing distributed I/O capability for MELSEC-Q systems connected via coaxial cable infrastructure where the longer 500 m segment distance of coaxial medium is required or where existing coaxial MELSECNET/H cable infrastructure is already in place. In stock at Atlantech Drives. Request your quote within 24-48 hours with worldwide shipping and 12-month warranty.
What Is the QJ72BR15?
The QJ72BR15 is a MELSEC-Q series remote I/O station module for MELSECNET/H coaxial bus networks, operating under the control of a QJ71BR11 master station CPU without a local CPU at the remote station. The I/O modules installed in the same base unit as the QJ72BR15 are controlled by the master CPU over the MELSECNET/H network, with their I/O addresses allocated in the master’s device space via GX Works2 network parameter settings. The QJ72BR15 connects to the MELSECNET/H coaxial bus using a BNC T-connector, joining the linear bus topology at a tap point alongside other stations. Unlike the ring topology of the QJ72LP25-25 optical station, the coaxial bus topology means that a cable break between any two stations isolates all stations beyond the break from the master — a single cable fault can partition the network, which is the primary reliability disadvantage of coaxial bus versus optical ring topology. Up to 32 remote I/O stations can be connected on a single QJ71BR11 coaxial bus network, with each QJ72BR15 station supporting up to 256 I/O points across its installed modules.
Key Technical Specifications
- Model: QJ72BR15
- Function: MELSECNET/H remote I/O station (coaxial bus, no CPU)
- Network: MELSECNET/H coaxial bus
- Transmission Speed: 10 Mbps
- Transmission Medium: 75 Ω coaxial cable, BNC connector
- Maximum Station-to-Station Distance: 500 m per segment
- Maximum Remote I/O Stations per Network: 32
- I/O Points per Station: Up to 256 I/O points
- Topology: Bus (linear, BNC T-connector tap)
- Current Consumption (5 VDC internal bus): 0.45 A
- Operating Temperature: 0°C to 55°C
- Compatible Base Units: All MELSEC-Q main and extension base units
- Weight: Approx. 0.20 kg
Compatibility & System Integration
The QJ72BR15 is compatible with all MELSEC-Q base units and I/O modules and operates exclusively on MELSECNET/H coaxial bus networks managed by a QJ71BR11 master station. Like the optical QJ72LP25-25, the QJ72BR15 supports MELSEC-Q intelligent function modules installed in the remote station base — analogue modules (Q64AD, Q62DA), temperature control modules (Q64TCRTN), and communication modules can all be installed alongside digital I/O modules in a QJ72BR15 station, with intelligent module buffer memory accessible from the master CPU via FROM/TO instructions referencing the remote station’s network link device area. In mixed MELSECNET/H installations where some remote stations use coaxial connection (QJ72BR15) and others use optical fibre (QJ72LP25-25), the two media types require separate network segments managed by separate master modules — coaxial and optical remote stations cannot share the same MELSECNET/H network. For facilities planning migration from MELSECNET/H to CC-Link IE Field Network, the QJ72BR15 remote I/O stations can be replaced with RX/RY series CC-Link IE Field remote I/O units managed by an RJ71GF11-T2 master in a MELSEC iQ-R controller, as part of a phased network modernisation programme.
Installation Advice
Coaxial bus installation for the QJ72BR15 requires careful attention to bus termination and cable routing to ensure reliable communication across all stations. Install 75 Ω BNC termination resistors at both physical ends of the coaxial trunk cable — one at the first station and one at the last station on the bus. Do not install termination at intermediate stations. Unterminated or incorrectly terminated coaxial bus ends cause signal reflections that degrade communication reliability at 10 Mbps, particularly on longer cable runs. For the BNC T-connector at each QJ72BR15 station, use a quality BNC T-connector with gold-plated contacts — corrosion of the BNC connector’s center pin contact is the most common cause of intermittent coaxial MELSECNET/H failures in systems more than five years old, and connector quality directly affects long-term reliability. Route the coaxial cable away from high-voltage power cables and variable frequency drive output cables, maintaining a minimum separation of 200 mm — coaxial cable’s lower noise immunity compared to optical fibre makes it more susceptible to electromagnetic interference from adjacent power conductors. When cutting and terminating coaxial cable in the field, use a proper coaxial cable stripper and crimping tool to ensure the shield braid is not bridged to the center conductor — even partial shorts between the shield and center conductor caused by poor termination will prevent the affected station from communicating on the bus.
Frequently Asked Questions
Q: Can the QJ72BR15 and QJ72LP25-25 be mixed on the same MELSECNET/H master network?
A: No. The QJ72BR15 coaxial bus remote station and the QJ72LP25-25 optical ring remote station use incompatible physical media and network topologies — coaxial bus stations require a QJ71BR11 coaxial master, while optical ring stations require a QJ71LP21-25 optical ring master. Each master manages only its own medium type, so coaxial and optical remote stations must be on separate networks managed by separate master modules.
Q: What happens to the QJ72BR15’s I/O outputs if the coaxial bus communication is interrupted?
A: When communication between the QJ71BR11 master and the QJ72BR15 remote station is interrupted (due to cable fault, station power loss, or master CPU fault), the QJ72BR15 holds its last output states by default. The output hold or clear behaviour on communication error can be configured via the master station’s GX Works2 network parameters — setting outputs to clear (0) on communication error is recommended for most machine safety applications to ensure actuators return to a safe state when communication is lost.
Q: Is the QJ72BR15 station number set by hardware switches or software configuration?
A: The QJ72BR15 station number is set via rotary hex switches on the front panel of the module, identical to the QJ72LP25-25. Set the tens digit on the upper rotary switch and the units digit on the lower switch — for example, station 5 requires upper switch at 0 and lower switch at 5. The station number is read at power-up only; changes take effect after power cycling the module.
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