Component Snapshot At-a-Glance

• Model: A2H124-24FX, Foxboro OEM part marking P0973BJ
• Alt. P/N: Cross replace: A2H124-24TX (copper variant), P0973BL alternate Foxboro OEM part number
• Product Series: Enterasys SecureStack A2, factory preconfigured for Foxboro I/A Series DCS control networks
• Hardware Type: 1U rack mount Layer2 stackable managed fast ethernet fiber switch
• Key Feature: 24×MT-RJ multimode 100BASE-FX fixed fiber ports + dual SFP gigabit uplink slots, factory DCS QoS preloaded
• Primary Field Use: Edge aggregation for remote Foxboro FBM/FCP field controllers via multimode fiber across refinery unit rack rooms and boiler DCS cabinets

A2H124-24FX

Hard-Numbers: Technical Specifications

• Protocol Support: 802.1Q VLAN, 802.1p QoS, MSTP, SNMPv2, RMON, stacking protocol, port security
• Port Count: 24×Fixed MT-RJ 100BASE-FX multimode fiber; 2×SFP Mini-GBIC gigabit uplink slots; 1×RJ45 out-of-band management port + Console RS232 port
• Baud/Data Rate: Fixed 100Mbps fiber on base ports; SFP slots auto 10/100/1000Mbps copper/fiber uplink
• Operating Temperature: 0°C ~ +50°C continuous cabinet operation; -40°C ~ +70°C non-operational storage
• Isolation Rating: 1500V surge isolation between fiber port transceiver bank and main CPU PCB for industrial cabinet surge suppression
• Power Draw: Max 38W full load; universal AC input 100–240VAC 50/60Hz, optional auxiliary DC 24V redundant feed
• Switch Fabric: 48Gbps backplane capacity, 35.7Mpps wire-speed forwarding rate
• MAC Table Depth: 8,192 MAC address entries fixed onboard flash memory
• Stack Limit: Up to 8 identical A2-series switches chained into single logical stack via dedicated stacking SFP links
• Form Factor: Standard 19-inch 1U EIA rack chassis, dimensions 442×44×230mm

The Real-World Problem It Solves

Long copper CAT5 runs from field controllers suffer EMI interference near pump motors and high-current MCC panels, spawning random CRC errors and intermittent Foxboro controller dropouts. Discrete small standalone fiber media converters clutter rack space and inflate spare part inventories at process plants.

Where you’ll typically find it:

• Refinery FCC/CDU remote I/O rack room connecting field-mounted FBM modules via multimode fiber trunk runs
• Coal power plant boiler feedwater DCS cabinet edge rack aggregating dozens of field controller fiber drops
• Chemical plant outdoor auxiliary control shelters with long-distance fiber runs exceeding 100m copper cabling limits

Integrated fixed MT-RJ fiber ports eliminate field-side media converters and block motor-driven electrical noise from corrupting critical DCS interlock traffic.

Hardware Architecture & Under-the-Hood Logic

This unit uses a split PCB layout; fiber transceiver bank sits electrically isolated from main switch ASIC to stop field-side cabinet surges frying core management circuitry. It functions as edge tier between remote I/A field hardware and central core aggregation switches on plant DCS network topology.

1. Inbound 100Mbps fiber signals from field Foxboro controllers land on dedicated MT-RJ optical transceivers mounted on front port PCB.
2. Transceivers convert optical pulses to electrical Ethernet frames before passing packets to main switching ASIC.
3. Preloaded factory QoS rules tag all Modbus TCP and DCS proprietary control frames for highest priority forwarding.
4. ASIC either routes local traffic between base fiber ports or forwards uplink bound frames out SFP gigabit slots toward core backbone switches.
5. Stack protocol syncs running-config and firmware across all chained A2 switches to operate as unified single switching domain.
6. Onboard flash stores startup-config and DCS custom VLAN definitions, retains data after full power cycle.

A2H124-24FX

Field Service Pitfalls: What Rookies Get Wrong

Mixing single-mode SFPs into multimode fixed port switch uplink slotsNew technicians install single-mode LX SFPs into SFP uplink bays intended for multimode SX; light mismatch creates unstable uplink flapping and random stack split faults mid-production run.

• Quick Fix: Only deploy SX multimode Mini-GBIC transceivers rated for 850nm wavelength per Foxboro OEM specification.

Unmatched firmware versions across stacked switch groupField crew adds spare replacement unit into active stack without matching firmware revision; version mismatch locks new switch offline, all port LEDs stay dark and fails stack election.

• Field Rule: Pull replacement switch offline, upgrade/downgrade firmware to match existing stack master build before stacking cable installation.

Improper MT-RJ fiber crimp termination leading intermittent link dropsInstallers crimp MT-RJ fiber with oversized stripping, leaving exposed core prone to cabinet vibration-induced intermittent light loss and sporadic DCS PV communication loss.

• Quick Fix: Recrimp all faulty MT-RJ ends per spec, test optical power with handheld fiber meter before returning to live DCS service.

Commercial Availability & Pricing Note

Please note: The listed price is for reference only and is not binding. Final pricing and terms are subject to negotiation based on current market conditions and availability.