Allen BradleyTwo-Slot 1771 I/O Chassis with Integral Remote I/O Adapter and 3 A Module Power Supply

Product Description

What this part is

A two-slot Allen-Bradley 1771 I/O chassis with an integral Remote I/O (RIO) adapter and its own 3 A power supply built into the assembly. That combination is the whole point of the part: it is a complete small remote drop in a single box. An ordinary 1771 chassis needs a separate 1771-ASB adapter module, a separate power supply and slots to put them in; the 1771-AM2 has the adapter and the supply integrated, so both of its slots stay available for actual I/O modules.

Correcting the source data

Earlier copy described this simply as a 2-slot I/O chassis for adding modules. That undersells it in a way that changes what a buyer needs to order. This chassis already contains the Remote I/O adapter and the module power supply — you do not need to buy a 1771-ASB, a 1771-P4S or equivalent to use it. If you were sizing a job around a plain chassis plus adapter plus supply, this replaces all three.

Decoding the catalogue number

1771 — the classic Allen-Bradley 1771 I/O platform, used with PLC-5, PLC-3, PLC-2 family and (via RIO) ControlLogix scanners.A — chassis / rack assembly.M — the integrated-adapter-and-supply variant, as against the plain 1771-A1B/A2B/A3B/A4B chassis, which are 4, 8, 12 and 16 slot racks with no electronics fitted.2 — two I/O slots.

Published specifications

I/O slots: 2, both usable for I/O modulesIntegral Remote I/O (RIO) adapter — the drop connects directly to a scanner such as a PLC-5 RIO port, a 1771-SN, a 1747-SN or a 1756-DHRIOIntegral 3 A power supply for the I/O modules in the chassisAddressing: supports 2-slot, 1-slot and 1/2-slot (half-slot) addressing, so it accepts I/O modules of 8, 16 and 32 point densitiesRIO data rate: up to 57.6 kbit/s, with a maximum trunk length in the order of 10,000 cable feet at that rate using 1771-CD or Belden 9463 twinaxial “blue hose”Dimensions: approximately 298 x 130 x 187 mm (11.7 x 5.1 x 7.3 in)Weight: approximately 2.3 kg (5 lb)Manufacturer status: legacy platform, long superseded; supported through surplus and repair

What these specs mean in practice

Two slots plus a 3 A supply is a genuine constraint, and it is the number to check first. The 3 A figure is the backplane current available to whatever you fit; a pair of high-density digital modules is comfortable, but analogue and intelligent modules draw far more, and two of those can exceed 3 A between them. Add up the backplane current of both intended modules before ordering.

The addressing mode is the other decision. In 2-slot addressing the chassis presents a single rack word pair across both slots and you are limited in how many points you can use; 1-slot and 1/2-slot addressing free up density at the cost of rack-number consumption on the RIO link. Set this on the chassis and make the scanner’s rack configuration match — a mismatch here is the classic reason a new drop shows up in the scan list but the I/O data lands in the wrong words.

Where this chassis earns its keep is a small remote cluster: two modules out at a machine, one twinax run back to the scanner, no local cabinet full of adapter and supply modules. That is exactly the job it was built for.

Quantity and configuration

One chassis assembly, tested.

What is not included

I/O modules, field wiring arms and terminal blocks (1771-WA / WB / WG and similar), slot filler or blanking modules, RIO twinaxial cable and connectors, terminating resistors for the RIO link, mounting hardware or panel, keying bands for the backplane, and documentation. No scanner, PLC processor or program is included, and no I/O configuration is preset.

Installation and setup notes

Set the addressing mode and the RIO rack number, starting group and data rate on the chassis before you connect it to a live link; the switches are inside and are far easier to reach on the bench. Insert the backplane keying bands to match the modules you intend to fit, so a module cannot be plugged into the wrong slot later. Terminate the RIO trunk at both physical ends with the correct resistor value for the data rate — an unterminated or double-terminated blue hose produces intermittent drop faults that look like a failing chassis. Land a proper protective earth, and confirm the scanner sees the drop before wiring field devices.

Interchange guidance

Direct interchange with other 1771-AM2 chassis. Related but different parts, not equivalents: 1771-AM1 (the one-slot member of the same integrated family), and the plain 1771-A1B, 1771-A2B, 1771-A3B and 1771-A4B chassis, which have no adapter and no supply and therefore need a 1771-ASB plus a rack power supply and the slots to hold them. Do not treat those as substitutes on a job costed around this part. There is no current-production replacement: modern equivalents are a 1734 POINT I/O or 1794 FLEX I/O remote drop on EtherNet/IP, which is a design change rather than a swap.