Month: October 2026

Application Scenarios

A regional food-and-beverage plant in the U.S. Southeast operated an SLC 5/04-controlled clean-in-place (CIP) skid whose output complement mixed three valve-actuator solenoids on 24 VDC, two CIP pump contactors on 208 VAC, one tank-agitator contactor on 480 VAC via an interposing relay, and two status lamps on 120 VAC. The original panel had been built from separate solid-state AC and DC output cards, each with its own supply and each vulnerable to a different failure mode — solid-state triacs failed short on surge-prone contactor coils, and the DC transistor outputs were lost when a valve-actuator harness shorted. When the integrator rebuilt the panel around the 1746-OX8/A, all eight outputs consolidated onto one relay card with full point-to-point isolation, and the mixed-voltage load scheme was served from a single slot with no interposing hardware between the card and the field.

The 1746-OX8/A addresses three recurring pain points in SLC 500 output design: the slot-count penalty of splitting AC and DC loads across separate solid-state output cards, the failure-mode mismatch where solid-state outputs are either ill-suited to high-inrush contactor coils or unprotected against field-side shorts, and the wiring complexity of interposing-relay panels that add labour, panel space, and a second layer of hardware to maintain. Wherever an SLC 500 processor must switch a mixed AC and DC load complement — pump contactors, valve solenoids, indicating lamps, damper actuators, small heaters, horn annunciators — the 1746-OX8/A provides the universal relay-output backbone.iqelectro.com+1

Parameter

Application Scenarios

In a beverage bottling plant’s control system, engineers needed to control solenoid valves for caustic soda, hot water, and process water demand across multiple production lines. The valves operated on 24V DC, while indicator lamps and alarm horns in the same cabinet used 120V AC. Using a single output module type for both voltage categories would have required separate modules or interposing relays.

The 1746-OW16 solved this problem directly. Its 16 relay outputs are divided into two isolated groups of 8 points per common, allowing one group to switch DC loads while the other group handles AC loads . Each output channel is a dry contact, so the module itself imposes no voltage on the field wiring—the load circuit defines whether the channel switches AC or DC. Wiring diagrams from the bottling plant show the 1746-OW16 in Slot-01 controlling valve demand signals on channels 0 through 15, with physical addresses ranging from POINT_2:1:O:0 to POINT_2:1:O:15 .

Parameters

Description

The 1746-OV8​ is an Allen-Bradley 8-channel DC output module for the SLC 500 programmable controller system. Manufactured by Rockwell Automation, it converts discrete output data from the SLC 500 processor into switched 24V DC control signals.The 1746-OV8​ is a current-sinking output module, which means each channel switches the load-return or negative side of the output circuit. It is commonly used to operate solenoid valves, motor-starter coils, relays, indicators and other 24V DC field devices in compatible SLC 500 control panels.

Application Scenarios

A metal-stamping plant used an SLC 500 controller to operate clamping solenoids, lubricant pumps and safety-interlock relays. The control logic was still stable, but one output module produced erratic results after years of vibration and cabinet heat exposure. Replacing the entire control platform would have required requalification of the safety logic and a prolonged production stoppage.The maintenance team installed a tested Allen-Bradley 1746-OV8​ in an available chassis slot. They verified the sinking-output wiring, checked load current, reassigned the output image addresses and performed a point-by-point functional test. Each channel was then observed through the SLC 500 program and at the module terminals.The replacement restored reliable control without rewriting the application or replacing compatible field devices. For plants that still depend on proven SLC 500 logic, the 1746-OV8​ can be the difference between a short, predictable repair and a costly platform-wide migration.

Parameter

Application Scenarios

A stamping shop in an automotive parts plant controlled pneumatic valves and auxiliary contactors across multiple press lines using an SLC 500 system. The original standard output modules could not deliver enough current per channel, forcing engineers to install over 40 interposing relays in a single cabinet. Wiring became a rat’s nest, and relay contact oxidation caused three unplanned shutdowns per month. After switching to the 1746-OBP16, the relays were removed entirely. The 1746-OBP16 drives those loads directly with 1.5A per channel at 30°C and 6.4A total per module. Cabinet space expanded by nearly one-third, and relay-related downtime dropped to zero.

Parameter

Description

The 1746-OBP8​ is an eight-output high-current DC output module manufactured by Allen-Bradley, a brand of Rockwell Automation, for the SLC 500 family of programmable controllers. It switches up to 2 A per point at voltages from 10 to 60 V DC — with a 72 V DC absolute maximum — and is the module to reach for when the load is too heavy for a standard 24 V DC output card but still within the SLC 500’s single-slot form factor.What defines the 1746-OBP8​ is the current rating rather than the voltage. At 2 A per point and 8 A per module, it drives contactor coils, solenoid valves, small motors, and indicator banks directly, without an interposing relay. The eight outputs are arranged in two fused groups of four, each protected by a 4 A slow-blow fuse, so a shorted load takes out four points rather than all eight — and the status LEDs show immediately which group dropped. The module is sinking (current-sourcing), switches in 2.5 ms OFF→ON and 1.5 ms ON→OFF, and carries 500 V DC of isolation between the output group and the backplane (but not between outputs). It is not socketed, has no conformal coating, and carries no hazardous-location approval, so it belongs in a clean, dry cabinet. Discontinued on 31 August 2016, the 1746-OBP8​ now circulates as new-surplus and tested spare stock — which makes a verified unit and a migration plan the sensible purchase.

Application Scenario

A grain terminal in the Canadian prairies runs a 1990s-vintage SLC 500 on its conveyor and loader skids, switching a mix of 48 V DC solenoid valves and 24 V DC contactor coils. The original output cards were standard 0.5 A modules, and every heavy load needed an interposing relay — a cabinet full of relays, a parts list nobody could keep straight, and a failure rate that rose with every relay contact that pitted or welded. During a harvest-season breakdown, the terminal lost a loader to a failed interposing relay and discovered it had no spare for the output card either.The panel was rebuilt around the 1746-OBP8. The eight high-current outputs drove the solenoids and coils directly, and the interposing relays were removed — fewer parts, fewer contacts, fewer things to stock. The two fused groups of four meant a shorted solenoid disabled its own group but not the whole skid, and the status LEDs turned fault-finding into a glance at the rack. The terminal now carries a tested 1746-OBP8​ on the critical-spare list and reports fewer after-hours callouts — the kind of gain that barely shows up in a spec sheet but dominates the maintenance budget during harvest.

Parameter

Product Overview

The Allen-Bradley 1746-OB16 is a 16-point current sourcing digital DC output module engineered by Rockwell Automation for the widely deployed SLC 500 modular PLC platform, serving as one of the most frequently specified discrete output cards across the entire Bulletin 1746 I/O catalogue. Categorised as a 24V DC sourcing module, the 1746-OB16 provides sixteen solid-state transistor outputs referenced to a single common, delivering the deterministic on/off actuation required for contactors, motor starters, solenoid valves, indicator stacks, relay coils, and low-voltage control circuits throughout general machine and process applications.

With an operating window of 10 to 50V DC, the Allen-Bradley 1746-OB16 tolerates realistic supply variation in field cabinets while remaining fully compatible with standard 24V DC control supplies. Each point is rated for 0.5 A continuous at 30°C (derating to 0.25 A at 60°C), with a module-level capacity of 8 A across the full ambient range and a surge tolerance of 2 A per point for 10 ms to absorb contactor coil inrush and indicator lamp cold-filament current without module damage. Signal switching delays are exceptionally short — 0.1 ms on and 1.0 ms off into resistive loads — providing the responsiveness needed for high-speed sequencing, interlock logic, and time-critical discrete control.

As a proven member of the SLC 500 ecosystem, the 1746-OB16 installs into any available 1746 chassis slot and is equipped with a colour-coded removable terminal block that accepts two 14 AWG conductors per point, allowing rapid module exchange without disturbing adjacent field wiring. Sixteen front-panel status LEDs give operators point-level visual feedback during commissioning and troubleshooting, and the module’s wiring can optionally be terminated through a Bulletin 1492 interface module with pre-wired cable for accelerated panel build and simplified field replacement. Because Rockwell Automation has transitioned the SLC 500 family to its mature lifecycle status, the 1746-OB16 is now predominantly supplied through specialist automation distributors as a lifecycle replacement part, with tested stock available to support the extensive installed base of SLC 500 systems still operating reliably across manufacturing, water treatment, automotive, and general process industries worldwide.

Technical Specifications

Product Overview

The Allen-Bradley 1746-OAP12 is a 12-point high-current AC output module from the SLC 500 series, engineered for applications requiring robust switching of 120/240VAC loads. The 1746-OAP12 provides twelve discrete AC output channels organized into two groups of six points per common, each group protected by an internal fuse designed to safeguard the module from short-circuit conditions . This high-current module is suitable for directly driving contactors, solenoids, motor starters, and other inductive or resistive AC loads common in industrial control panels.

The 1746-OAP12 operates across a wide voltage range of 85 to 265VAC at 47–63Hz, accommodating both nominal 120VAC and 240VAC control circuits without requiring configuration changes . Each output point is rated for 2.0A continuous at 30°C, derating to 1.0A at 60°C, while the module supports a maximum total continuous current of 9.0A at 30°C . With an OFF-to-ON signal delay of 11ms and ON-to-OFF delay of 1ms, the 1746-OAP12 responds quickly to control commands while providing predictable timing for sequencing logic.

The 1746-OAP12 includes a removable terminal block (RTB) color-coded red for AC I/O modules, enabling module replacement without disturbing field wiring . A configurable jumper (JP1) allows the user to determine whether a blown fuse triggers a processor fault or permits continued operation, with the factory setting disabling fuse monitoring . The 1746-OAP12 is compatible with all SLC 500 processors and mounts in any slot of the 1746 chassis .

Technical Specifications

Product Overview

The Allen-Bradley 1746-NT8​ is an 8-channel thermocouple and millivolt input module from Rockwell Automation’s SLC 500 (1746) family. Its purpose is to take the low-level signals produced by thermocouples and mV transmitters and convert them into usable temperature or voltage data for the SLC 500 processor. In a legacy SLC 500 rack, the 1746-NT8​ is the temperature interface: up to eight thermocouples can be landed on one module, each channel converted at 15-bit resolution, with the cold-junction compensation and linearization handled on the module rather than in the ladder logic.The module accepts eight differential inputs and supports a wide range of thermocouple types — B, E, J, K, L, N, R, S, T, U and W — together with a direct millivolt mode. This range is what makes the 1746-NT8​ usable across applications rather than tied to one sensor family: a furnace application can mix type K on the hot zones with type J on the auxiliary circuits, while a test rig can use the mV mode to read a non-thermocouple transducer. The cold-junction compensation is built in, so the terminal-block temperature is measured and used to correct the thermocouple reading — a necessary step, because a thermocouple measures a temperature difference, not an absolute temperature, and an uncompensated reading drifts with the cabinet temperature.For plants still operating SLC 500 systems, the value of the 1746-NT8​ is continuity. These are mature installations in heat treatment, plastics, furnaces, ovens, process skids, and machine-tool thermal monitoring, where replacing the controller would cost more than the value of the upgrade. A verified spare with the correct channel configuration is what keeps such a system running; the module’s straightforward mapping means a replacement can be dropped in without re-engineering the rack. Because the module is obsolete and has no direct replacement, procurement should be treated as verified spare stock rather than new-system design.

Technical Specifications

Product Overview

The Allen-Bradley 1746-NT4 is a four-channel thermocouple and millivolt analog input module designed for the SLC 500 programmable controller platform. As a dedicated temperature input module, the 1746-NT4 accepts direct signals from thermocouple sensors and low-level millivolt devices, converting them to digital temperature data for use by SLC 500 processors without requiring external transmitters or signal conditioners. The module supports eight thermocouple types—J, K, T, E, S, R, B, and N—as well as direct ±50 mV and ±100 mV analog inputs, making it a versatile solution for temperature monitoring and low-level signal acquisition in industrial control systems .

Within the SLC 500 architecture, the 1746-NT4 occupies a standard chassis slot (any slot except slot 0, which is reserved for the processor) and draws power directly from the backplane, consuming 60 mA at 5V DC and 55 mA at 24V DC . The module features four backplane-isolated input channels with differential inputs, providing protection against ground loops and common-mode noise in electrically noisy industrial environments. Two integrated cold-junction compensation (CJC) thermistors on the removable terminal block ensure accurate temperature readings by measuring the terminal junction temperature and compensating for the thermocouple’s cold junction .

The Allen-Bradley 1746-NT4 distinguishes itself through its sigma-delta analog-to-digital conversion architecture, delivering 16-bit input resolution with update periods ranging from 26 milliseconds to 1.2 seconds depending on channel configuration and filter settings . The module provides open-circuit detection with selectable zero, upscale, or downscale response, and five green LED indicators—one for module status and one per channel—enable rapid visual diagnostics without programming software. The 1746-NT4 is compatible with both fixed and modular SLC 500 styles and supports remote I/O configurations with block transfers .

Technical Specifications

Product Overview

The 1746-NR4​ is a four-channel RTD and resistance input module manufactured by Allen-Bradley, a brand of Rockwell Automation, for the long-established SLC 500 family of programmable controllers. Purpose-built for direct temperature and resistance measurement, the 1746-NR4​ eliminates the need for external transmitters, signal conditioners, and analog input cards by accepting RTD sensor elements and variable-resistance devices straight into the controller backplane. Seated in any available I/O slot of a 1746 modular or fixed-style SLC 500 chassis, the module communicates with the processor through an image table of eight input words and eight output words, delivering temperature data in degrees Celsius or Fahrenheit, or resistance values in ohms, already scaled and ready for use in ladder logic.At the heart of the 1746-NR4​ is a sigma-delta analog-to-digital converter that provides 16-bit input resolution and strong inherent noise rejection. Each of the four channels is independently configurable for RTD type, wiring configuration, filter frequency, excitation current, open-circuit response, and data format, meaning a single module can simultaneously read a Pt100 probe on channel 0, a Ni120 sensor on channel 1, a Cu10 element on channel 2, and a potentiometer on channel 3. The module supports platinum sensors with alpha coefficients of 0.00385 and 0.003916, copper RTDs at 10 and 427 ohms, nickel RTDs at 120, 618, and 672 ohms, and nickel-iron sensors at 518 and 604 ohms, covering a temperature span from -200 °C to +850 °C depending on sensor selection.What makes the 1746-NR4​ technically distinctive is its three-wire Kelvin lead-resistance compensation. Because an RTD changes resistance with temperature while the copper extension leads add their own resistance, a long cable run can introduce a significant temperature offset if uncompensated. The 1746-NR4​ excites one pair of leads and senses only through the third, mathematically subtracting the lead drop and reporting the element’s true resistance. The module also performs automatic self-calibration whenever a channel is enabled or a configuration parameter changes, requires no external power supply, and carries UL, CSA, CE, C-Tick, and Class I Division 2 certifications. Rockwell Automation has since classified the 1746-NR4​ as a mature, end-of-life product, but it remains in daily service in thousands of legacy SLC 500 installations and is widely available through aftermarket channels.

Technical Specifications