Allen-Bradley 1746-NO4I SLC 500 1746-NO4I

SKU: 1746-NO4I Category: PLC Brand: Allen-Bradley

Description
Additional information

The Allen-Bradley 1746-NO4I is an analog output module belonging to the SLC 500 series of modular programmable logic controllers manufactured by Rockwell Automation (Allen-Bradley). It is designed to provide four isolated current output channels for use within the SLC 500 chassis, enabling precise analog signal generation for process control applications. The module integrates seamlessly into the SLC 500 backplane and is configured and monitored through RSLogix 500 or RSLogix Micro software.

The 1746-NO4I provides four independently isolated 4–20 mA current output channels, with each channel electrically isolated from the others and from the backplane, significantly reducing noise and ground loop interference in sensitive process environments. The module offers 12-bit resolution across its output range, delivering fine control granularity suitable for demanding process applications. It supports a data format compatible with the SLC 500 output image table and provides diagnostics including open-circuit detection per channel. The module draws power from the SLC 500 backplane and requires an external 24 V DC user power supply for the output circuits.

The 1746-NO4I is widely used in industries such as oil and gas, water and wastewater treatment, chemical processing, food and beverage, and manufacturing automation. It is particularly suited for applications requiring isolated analog outputs to drive control valves, variable-speed drives, positioners, and other field devices that accept 4–20 mA signals. The channel isolation makes it the preferred choice over non-isolated alternatives in installations where multiple field devices share different ground references or where electrical noise is a concern.

Technical Specifications

Number of Output Channels	4
Output Signal Type	Current (4–20 mA)
Channel Isolation	Isolated (channel-to-channel and channel-to-backplane)
Resolution	12-bit
Output Range	4–20 mA
External User Power Supply	24 V DC
Backplane Current Draw (5 V)	75 mA
Backplane Current Draw (24 V)	0 mA
Maximum Load Resistance	600 Ω
Operating Temperature	0 °C to 60 °C
Storage Temperature	-40 °C to 85 °C
Relative Humidity	5–95% (non-condensing)
Series/Product Family	SLC 500
Certifications	UL, CE, CSA
Mounting	SLC 500 modular chassis (1746 series)

Common Fault Codes

Fault Code 01: Output channel open circuit detected on one or more channels. The module has detected that the current loop is open, typically due to a disconnected or broken field wiring connection.
Check field wiring continuity on the affected channel. Verify that the load device is connected and within the specified resistance range (maximum 600 Ω). Inspect terminal connections for loose or broken wires.
Fault Code 02: Module configuration error. The configuration data written to the module does not match the expected format or contains out-of-range values.
Verify the output data file configuration in RSLogix 500. Ensure output values are within the valid 12-bit range and that the module type matches the I/O configuration in the project.
Fault Code 03: User power supply fault. The external 24 V DC user power supply required for the output circuits is absent or below the acceptable voltage threshold.
Measure the external 24 V DC supply voltage at the module terminals. Verify the power supply is energized and within specification. Check fusing and wiring to the user power supply input.
Fault Code 04: Module hardware fault. An internal hardware error has been detected within the analog output module.
Cycle power to the SLC 500 chassis. If the fault persists, reseat the module in the chassis slot. If the fault continues, the module likely requires replacement or professional repair.
Fault Code 05: Backplane communication error. The module is not communicating correctly with the SLC 500 processor over the backplane.
Reseat the module firmly in the chassis slot. Verify the chassis backplane is not damaged. Check that the slot assignment in the RSLogix 500 I/O configuration matches the physical slot location of the module.
Fault Code 06: Output value out of range. The processor has written an output value to the module that exceeds the valid 12-bit output range.
Review the ladder logic program in RSLogix 500 to ensure output values written to the module's output image table are within the valid range (0–4095 counts for 4–20 mA). Add range-limiting logic if necessary.

Frequently Asked Questions

What output signal type does the 1746-NO4I provide?

The 1746-NO4I provides four current output channels with a 4–20 mA signal range. Each channel is independently isolated from the others and from the SLC 500 backplane.

Does the 1746-NO4I require an external power supply?

Yes, the output circuits require an external 24 V DC user power supply in addition to the backplane power provided by the SLC 500 chassis. The backplane supplies logic power while the external supply drives the current output loops.

What is the resolution of the 1746-NO4I analog outputs?

The module provides 12-bit resolution across the 4–20 mA output range, giving 4096 discrete steps for precise analog signal control.

What is the maximum load resistance supported by each output channel?

Each current output channel supports a maximum load resistance of 600 Ω, which must be considered when selecting field devices and calculating cable resistance.

Is the 1746-NO4I compatible with RSLogix 500 software?

Yes, the 1746-NO4I is fully compatible with RSLogix 500 and RSLogix Micro programming software, which are used for configuration, programming, and diagnostics of SLC 500 systems.

Troubleshooting

One or more analog output channels produce no current output

Verify that the external 24 V DC user power supply is present and within specification at the module terminals. Check field wiring continuity and confirm the load resistance does not exceed 600 Ω. Inspect the output image table in RSLogix 500 to confirm valid output values are being written.

Restore the external 24 V DC supply if absent. Repair any open-circuit field wiring. Correct out-of-range output values in the ladder logic program. If wiring and power are confirmed good, the module may have a failed output channel and require repair or replacement.

Output current is inaccurate or drifts from the commanded value

Measure the actual output current with a calibrated milliammeter in series with the load. Compare the measured value against the expected value based on the output image table count. Check for excessive load resistance or noise on the output wiring.

Verify load resistance is within the 600 Ω maximum. Shield and separate analog output wiring from power cables to reduce noise pickup. If inaccuracy persists after wiring corrections, the module may require recalibration or replacement.

Module fault LED is illuminated and the processor reports a module fault

Read the fault code from the SLC 500 processor using RSLogix 500. Check the I/O configuration to confirm the module type and slot assignment match the physical installation. Inspect the module seating in the chassis.

Reseat the module firmly in the chassis slot. Correct any I/O configuration mismatches in RSLogix 500. Cycle power to the chassis. If the fault LED remains on after these steps, the module likely has an internal hardware fault and should be replaced or sent for repair.

Backplane communication errors reported by the SLC 500 processor

Check that the module is fully seated in the chassis slot and that the backplane connector is not damaged. Verify no other modules in the chassis are reporting faults that could indicate a backplane issue.

Remove and reseat the 1746-NO4I module. Try moving the module to a different chassis slot and update the I/O configuration accordingly. If the error follows the module to a different slot, the module backplane interface may be faulty. If the error remains in the original slot, the chassis backplane may be damaged.

Open-circuit fault detected on a channel despite field device being connected

Measure the loop current with a milliammeter and verify the field device is powered and operational. Check all terminal connections for tightness and inspect wiring for breaks or high-resistance joints. Confirm the load resistance is within specification.

Re-terminate any loose or corroded wiring connections. Replace damaged cable sections. Verify the field device input impedance is within the 600 Ω maximum. If the fault persists with a known-good load connected directly at the module terminals, the output channel may be internally faulty and the module should be repaired or replaced.

Condition	Repair, Used, Refurbished, New in box (sealed)