When a Legacy SLC 500 Line Needs Precise Current Control
A food processing plant in the Midwest faced a familiar problem. Its SLC 500-controlled batching line needed to drive four modulating valves with precise current signals. The existing output cards drifted, causing inconsistent batch weights and costly product waste. The maintenance team needed a reliable analog output module that could fit directly into their existing 1746 chassis without a full control system overhaul. The Allen-Bradley 1746-NO4I solved that problem.
What Is the Allen-Bradley 1746-NO4I?
The 1746-NO4I is an SLC 500 analog output module manufactured by Rockwell Automation under the Allen-Bradley brand. It provides four current output channels with a range of 0 to +20 mA. The module works with both fixed and modular SLC 500 hardware styles. Its 14-bit resolution and 512-microsecond update time make it suitable for closed-loop control applications where signal accuracy matters.
Key Technical Specifications
Output Channels and Range
The module delivers four independent current outputs. Each channel produces 0 to +20 mA with a full-scale output of 21 mA. The overrange capability reaches 5% (0 to +21 mA minus 1 LSB). This range covers most industrial modulating devices and proportional valves.
Resolution and Update Speed
With 14-bit resolution using the R-2R ladder conversion method, the 1746-NO4I resolves output changes in fine increments. The update time of 512 microseconds applies to all channels in parallel. The step response reaches 95% in 2.5 milliseconds. These figures support responsive control loops without noticeable lag.
Power Requirements
The module draws 55 milliamps at 5 Volts DC and 195 milliamps at 24 Volts DC from the backplane. An embedded selector switch lets you choose between internal backplane power and an external 24 VDC supply rated at 195 mA maximum. Backplane isolation is rated at 500 Volts DC.
Environmental Tolerance
The 1746-NO4I operates in ambient temperatures from 0 to 60 degrees Celsius. Storage temperature ranges from -40 to 85 degrees Celsius. Non-condensing relative humidity tolerance spans 5 to 95%.
Where the 1746-NO4I Fits in Real Applications
PID Loop Control
In a PID control loop, the analog output represents the Control Output (CO). The 1746-NO4I sends that signal to modulating instruments such as control valves or variable frequency drives. Its 14-bit resolution helps maintain tight process control.
Manual Loading Stations
Operators at manual loading stations enter commands directly. The module converts those commands into current signals for field devices. This setup suits batch processes where operators adjust setpoints on the fly.
Signal Re-Transmission
You can use the 1746-NO4I to re-transmit an important signal to one or more devices. This supports indication, data logging, and signal conversion tasks. The four channels handle multiple destinations from a single module.
Installation and Wiring Guidance
Mount the 1746-NO4I in a compatible 1746 chassis. The module has an open enclosure style. Use shielded communication cable such as Belden 8761 or equivalent. Keep cable lengths as short as possible to reduce noise pickup. The module includes a removable terminal block for simplified wiring and easier replacement. An LED status indicator helps confirm module operation during commissioning.
Maintenance and Reliability Considerations
Periodic Inspection
Inspect the module and terminal connections periodically. Check for loose wiring, corrosion, or signs of overheating. Follow the manufacturer’s safety manual for all maintenance activities.
Environmental Management
Keep the enclosure within the specified 0 to 60 degrees Celsius operating range. Maintain non-condensing humidity between 5 and 95%. Excessive heat or moisture accelerates component aging.
Accuracy Drift Awareness
The maximum overall accuracy drift is +/- 70 ppm per degree Celsius of full-scale accuracy. In precision applications, periodic calibration checks help maintain performance. This factory-calibrated module may need recalibration after extended service.
Compatibility and Integration
The 1746-NO4I works exclusively with the 1746 chassis. It supports both fixed and modular SLC 500 hardware configurations. The module communicates through the SLC 500 backplane. It integrates with SLC 500 processors and related I/O modules in the same chassis.
What to Verify Before Buying
Confirm your chassis accepts 1746-series modules. Check that your power supply provides adequate backplane current at both 5 VDC and 24 VDC. Verify that your application requires current outputs in the 0 to +20 mA range. If you need voltage outputs or different channel counts, consider other SLC 500 analog modules. SpareTechPLC stocks the 1746-NO4I and can help confirm compatibility with your existing system. Please verify current lifecycle status and availability with SpareTechPLC before ordering.
Frequently Asked Questions
What is the output range of the 1746-NO4I?
The module provides four current outputs with a range of 0 to +20 mA. Full-scale output is 21 mA.
How many output channels does this module have?
The 1746-NO4I has four current output channels.
What resolution does the 1746-NO4I offer?
It offers 14-bit resolution using the R-2R ladder conversion method.
Can I use the 1746-NO4I with any PLC chassis?
No. It is only compatible with the 1746 chassis used in SLC 500 systems.
What is the update time for all channels?
The update time is 512 microseconds for all channels in parallel.
