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Brand: Allen-Bradley
Allen-Bradley 1756-OB16D Diagnostic DC Output Module
Description
A 24 V DC output card that reports load and wiring faults
The Allen-Bradley 1756-OB16D is a diagnostic 24 V DC sourcing output module with sixteen points. Beyond switching, it checks the circuits it drives: the technical data lists no-load detection in the off state, output verification in the on state, a short-trip response and a configurable pulse test, with diagnostic time stamps of plus or minus 1 ms.
It targets solenoid and trip circuits where an undetected broken wire or burnt-out coil would only be discovered when the valve fails to move. Eight points share each group and every point is electronically fused.
Technical specifications
| Parameter | Specification |
|---|---|
| Catalog number | 1756-OB16D (1756-OB16DK conformal coated listed separately) |
| Outputs | 16 diagnostic, 8 points per group, electronically fused per point |
| Voltage category | 24 V DC source |
| Operating voltage range | 19.2 to 30 V DC |
| Current per point, max | 2 A at 30 C; 1 A at 60 C (linear derating) |
| Current per module, max | 8 A at 30 C; 4 A at 60 C (linear derating) |
| Surge current per point | 4 A for 10 ms, repeatable every 1 s |
| On-state voltage drop, max | 1.2 V DC at 2 A |
| Off-state leakage, max | 1 mA per point; load current min 3 mA |
| Output delay, off to on / on to off | 60 us nominal, 1 ms max / 630 us nominal, 5 ms max |
| Short trip | 8 A for 180 ms, min; 10 A for 120 ms, min |
| Diagnostics | No load (off-state detection), output verification (on-state detection), configurable pulse test |
| Backplane current | 250 mA at 5.1 V DC; 140 mA at 24 V DC (4.64 W) |
| Power dissipation, max | 3.3 W at 60 C (11.25 BTU/hr) |
| Isolation | 250 V continuous basic, output to backplane and group to group |
| Terminal block | 1756-TBCH (ordered separately) |
| Operating temperature | 0 to +60 C |
| Non-operating temperature | -40 to +85 C |
| Vibration / shock | 2 g at 10-500 Hz / 30 g operating, 50 g non-operating |
| Slot width / keying | 1 slot; electronic keying, software configurable |
| Enclosure / wire category | Open-style; wire category 1 |
Diagnostics in practice
No-load detection works only in the off state and output verification only in the on state, as the data sheet states, so a complete picture of a circuit needs both modes over time. The pulse test lets the module briefly switch an output to check the load without disturbing the process, with a user-set maximum pulse width. Together with the time-stamped fault records, this supports sequence analysis after a trip.
Selection and derating
Note the derating: 2 A per point is available only at 30 C, falling to 1 A at 60 C, and the module total falls from 8 A to 4 A. The module also draws 140 mA from the 24 V rail, so check the chassis supply. If diagnostics are not needed, the plain 1756-OB16E is cheaper and has a wider voltage range. Check the series, K suffix and terminal block with the manufacturer data before ordering.
Documents and quotation
The linked Rockwell Automation technical data covers the full 1756 I/O range (file size about 15 MB, hosted by Rockwell Automation). Related PLC hardware sits in the PLC & I/O Cards category. Request pricing by sending the catalog number and quantity to Seven Star LLC, an independent supplier in Muscat.
Datasheets & Documents
- Technical data Rockwell Automation 1756 ControlLogix I/O Specifications, publication 1756-TD002U (September 2026) Download
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About brand
Allen-Bradley is the brand of Rockwell Automation for industrial control: ControlLogix and CompactLogix controllers, I/O systems, PanelView operator terminals, PowerFlex drives, motor control and industrial network equipment. The company began in Milwaukee in 1903, when Lynde Bradley and Dr. Stanton Allen formed the Compression Rheostat Company to make the motor speed controller Bradley had invented in 1901. It took the name Allen-Bradley in 1909 and was bought by Rockwell International in 1985. Since 2001 its owner has been Rockwell Automation, which is still headquartered in Milwaukee, Wisconsin.
Allen-Bradley company profile
| Founded | 1903, Milwaukee, Wisconsin, USA, as the Compression Rheostat Company |
|---|---|
| Founders | Lynde Bradley (inventor of the compression rheostat, 1901) and Dr. Stanton Allen (investor); Harry Bradley joined in 1904 |
| Name | Allen-Bradley Company from 1909 |
| Ownership | Acquired by Rockwell International in 1985 for about USD 1.65 billion; a brand of Rockwell Automation (NYSE: ROK) since 2001 |
| Headquarters | Milwaukee, Wisconsin, USA |
| Product families | Logix programmable automation controllers (ControlLogix, CompactLogix), legacy SLC 500 and MicroLogix PLCs, Micro800 controllers, POINT, FLEX and Compact I/O, PanelView HMIs, PowerFlex AC drives, contactors, motor starters and soft starters, safety components, Stratix Ethernet switches |
Milestones
- 1901: Lynde Bradley invents the compression rheostat to control the speed of electric motors.
- 1903: The Compression Rheostat Company is formed in Milwaukee with an initial investment of USD 1,000.
- 1904: Harry Bradley joins; a crane controller is shown at the St. Louis World's Fair.
- 1909: The company is renamed Allen-Bradley.
- 1985: Rockwell International acquires Allen-Bradley.
- 2001: Rockwell Automation becomes the company's name; the Allen-Bradley brand marks 100 years in 2003.
Reading Allen-Bradley catalogue numbers
The first digits of an Allen-Bradley catalogue number identify the platform, which tells you what is compatible with what. 1756 is ControlLogix (chassis-based, used for large process and plant control), 1769 is CompactLogix 5370 with Compact I/O, 5069 is CompactLogix 5380 with Compact 5000 I/O, 1734 is POINT I/O, 1794 and 5094 are FLEX and FLEX 5000 distributed I/O, 1746 and 1747 belong to the older SLC 500 family, 1766 is MicroLogix 1400 and 2080 is Micro800. For drives, 25B is PowerFlex 525 and 22B is PowerFlex 40; in a code such as 25B-D010N114, "D" means 380–480 V, "010" is the output current rating, and N114 instead of N104 means the drive has an integrated EMC filter. Many plants in the region still run SLC 500 and older MicroLogix systems, which Rockwell has discontinued, so exact spares and migration to CompactLogix are both common requests.
Where Allen-Bradley products are used
In Oman and the GCC, Allen-Bradley controllers and drives run on oil and gas facilities, water treatment and pumping stations, cement, food and beverage and packaging plants, and on machines supplied by American OEMs. ControlLogix is often the platform for plant control systems, while PowerFlex drives are used on pumps, fans and conveyors.
Allen-Bradley products we list
| Family | Examples |
|---|---|
| ControlLogix | 1756-L85E, 1756-EN2T, 1756-EN2TR, 1756-IF16, 1756-IB32, 1756-PA75, 1756-A10 |
| CompactLogix and Micro controllers | 5069-L320ER, 5069-L340ERM, 1769-L33ER, 1769-L16ER, MicroLogix 1400, Micro820, SLC 500 (1746) |
| Distributed I/O | 1734-AENTR, 1734-IB8, 1734-IE2C, 1734-IB8S safety, 1794-AENTR, 5094-AENTR, 5069-IF8 |
| Operator terminals | PanelView Plus 7 10-inch, PanelView Plus 7 15-inch, PanelView 800, PanelView 5310 |
| Drives, motor control and networking | PowerFlex 525, PowerFlex 755, PowerFlex 4, 150-A180NBD SMC, Stratix 2000, 1783-NATR |
Ordering Allen-Bradley products: what we need
Send the full catalogue number and the series letter from the label (for example 1756-EN2T Series D), because firmware and compatibility can change between series. For drives, add the motor power, voltage and filter option. For a discontinued SLC 500 or MicroLogix part, tell us whether you need the exact spare or a migration proposal.
Facts checked against Rockwell Automation's published company history, October 2026.
Browse Allen-Bradley products by category: PLC & I/O Cards, AC Drives.
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Frequently Asked Questions
What diagnostics does the 1756-OB16D offer?
No-load detection, output verification, short trip detection and a configurable pulse test.
What is the voltage range?
19.2 to 30 V DC, 24 V DC sourcing.
What are the current limits?
2 A per point at 30 C falling to 1 A at 60 C, and 8 A falling to 4 A per module.
Which terminal block does it use?
The 1756-TBCH, ordered separately.
How are the points protected?
Electronically fused per point.
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