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1785-LT/B

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Allen-Bradley 1785-LT/B is a Series B Classic PLC-5/15 processor with DH+ and remote I/O for legacy control systems.
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Technical specifications for 1785-LT/B

  • Manufacturer:
    Allen-Bradley
  • Part Number:
    1785-LT/B
  • Product Family:
    PLC-5
  • Product Type:
    PLC-5/15 Processor
  • Stock:
    1
  • Maximum total I/O:
    512 any mix; or 512 input + 512 output in complementary mode
  • Maximum analog I/O:
    512 points
  • Base user memory:
    6K words
  • Expansion options:
    10K or 14K words
  • DH+ channels:
    1
  • Remote I/O channels:
    1
  • Program scan time per K word:
    2 ms discrete logic; 8 ms typical
  • Maximum I/O racks:
    4
  • Maximum total I/O chassis:
    13 total; up to 12 remote
  • EEPROM backup memory:
    8K words (1785-MJ module)
  • RS-232/422/423 ports:
    0
  • Remote I/O transmission rate:
    57.6 kbps
  • Remote I/O scan time per rack:
    10 ms at 57.6 kbps
  • Maximum multiple control programs:
    No; one processor
  • Backplane current load:
    2.5 A
  • Operating temperature:
    0 to 60 °C (32 to 140 °F)
  • Storage temperature:
    -40 to 85 °C (-40 to 185 °F)
  • Relative humidity:
    5 to 95%, non-condensing
  • Vibration, operating and non-operating:
    1 g at 10 to 500 Hz; 0.012 in peak-to-peak displacement
  • Operating shock:
    30 g peak acceleration for 11 ± 1 ms
  • Weight:
    2.95 lbs (1.339 kg)
  • Tariff Code:
    8537101190
  • Country of origin:
    USA
  • Place of shipment:
    Xiamen, Fujian, China
By purchasing this item, you agree to the Terms & Conditions, ApterPower is not an authorized distributor for listed manufacturers or tradenames and therefore the manufacturer's warranty does not apply. All our products come with ApterPower's 1-year warranty.

More Information

Overview Manuals Applications Communication Installation & Integration Diagnostics

Features:

  • Classic PLC-5/15 processor with Series B identification.
  • 6K-word user memory supports expansion to 10K or 14K words.
  • Provides one DH+ channel and one remote I/O channel.
The 1785-LT/B is the Series B form of the PLC-5/15 processor for a Classic PLC-5 control system.

It coordinates PLC-5 program execution with DH+ communications and remote I/O scanning or adapter operation, depending on system configuration.

Before replacement, verify the full processor label, memory arrangement, program backup, I/O rack map, and remote I/O role; do not assume another PLC-5 catalog number is interchangeable.

Availability is subject to Apter Power inventory and sourcing confirmation.
Verified resources for Allen-Bradley 1785-LT/B: Important Notice: Other accessories, manuals, cables, calibration data, software, etc. are not included with this equipment unless listed in the above stock item description. All prices are shown in USD.
  • Maintenance spare for an installed Classic PLC-5/15 Series B controller.
  • Support for legacy DH+ and remote I/O installations tied to a 1785-LT/B program.
  • Exact-model inventory during a phased PLC-5 migration.
  • The Classic PLC-5/15 processor communicates through the Data Highway Plus and Remote I/O paths documented for the 1785-LT platform.
  • Channel settings, station addresses, and network rates must agree with the existing PLC-5 project and connected adapters.
  • Confirm cable topology and program-transfer access before exchanging a Series B processor in an operating chassis.
  • Archive the current 1785-LT/B program and controller settings under the plant change procedure.
  • Capture the chassis, communication cabling and associated memory module before removal.
  • Use the documented Classic PLC-5/15 Series B installation procedure for the actual rack.
  • Compare processor indicators and the recorded fault history before assuming that the 1785-LT/B itself has failed.
  • If DH+ or remote I/O traffic changes, review network and adapter records alongside the processor.
  • Keep the original module and its program backup available for a controlled rollback review.
Description
Allen-Bradley 1785-LT/B is a Series B Classic PLC-5/15 processor for legacy 1771-based control systems. The processor combines user-program execution with one Data Highway Plus channel and one Remote I/O channel in the established PLC-5 architecture.

Its base memory supports discrete, analog, sequencing, and supervisory logic for machines and process units that remain dependent on PLC-5 hardware. The processor can coordinate local and remote chassis while communicating with programming and operator devices over the configured DH+ network.

A replacement must preserve the saved program, memory option, chassis addressing, remote I/O rack configuration, DH+ node settings, and installed Series B requirements. Other PLC-5 processors can differ in channel count, memory, and I/O capacity, so migration must be engineered rather than treated as a direct card swap.
Revisions

Revision Part #

Also known as

1785-LT Ser B
1785-LT/B, Series B, Rev B
Alternative Names
1785LTB 1785 LT/B 1785-LT/B Series B 1785-LT-B Allen-Bradley 1785-LT/B Allen Bradley 1785 LT/B Allen-Bradley PLC-5/15 1785-LT Series B PLC-5/15 Series B 1785-LT
Technical notes
1785-LT/B commissioning depends on a verified backup, Series B hardware match, memory arrangement, DH+ node, and remote-I/O rack map; do not power a substitute with an unverified program.
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FAQS

The following is a list of questions commonly asked by our customers. Please contact us if you have a question about our process that is not answered below.
Is 1785-LT/B the same processor as 1785-LT2?
No. The official Classic PLC-5 manual lists 1785-LT as PLC-5/15 and 1785-LT2 as PLC-5/25. Match the Series B label and the saved project before choosing a replacement.
What should be archived before replacing 1785-LT/B?
Save the controller program and document the installed memory, chassis position, DH+ address and remote I/O configuration. Keep the removed unit available until the restored system has been validated.
Why does a spare 1785-LT/B need a memory check?
The PLC-5/15 has a base 6K-word user memory arrangement with 10K or 14K expansion options. Compare the memory used by the installed program with the spare hardware before any transfer.
If a 1785-LT/B is healthy but remote I/O is missing, what should be reviewed?
Compare the processor and adapter status with the network fault log, cabling record and configured rack addresses. A remote I/O issue is not by itself proof of a failed processor.
Which official manual should I consult for 1785-LT/B setup and memory details?
Consult Rockwell publication 1785-UM001, Classic 1785 PLC-5 Programmable Controllers User Manual, for PLC-5/15 selection and configuration guidance; verify the Series B label and installed memory arrangement against the manual.
What should I send Apter Power to request a 1785-LT/B quote?
Include the exact Series B label, required quantity, destination, and available program, memory, chassis, and network details. Apter Power can provide a quotation and help review the documented system match.

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