1. Product Overview
The Allen-Bradley SLC 500 1747-L20A is a compact, modular programmable controller designed for industrial control applications. This processor unit features 20 I/O points, providing robust control capabilities for various automated systems. It is part of the SLC 500 series, known for its reliability and versatility in industrial environments.
Figure 1: Front view of the Allen-Bradley 1747-L20A Processor Unit, showing the main housing, input/output terminals, and indicator lights.
2. Setup and Installation
2.1. Mounting
The 1747-L20A processor unit is designed for panel mounting. Ensure the mounting surface is stable and provides adequate ventilation to prevent overheating. Use appropriate fasteners for secure installation.
Figure 2: Bottom view of the processor unit, highlighting the mounting brackets for secure installation.
2.2. Wiring Connections
Proper wiring is crucial for safe and reliable operation. Refer to the unit's label for specific voltage and current ratings. Ensure all power is disconnected before making any connections.
- Power Input: Connect the appropriate AC power supply (100 V-AC or 240 V-AC) to the designated power terminals.
- Input Wiring: Connect field devices to the input terminals. The unit supports 20 I/O points.
- Output Wiring: Connect control devices to the output relay terminals.
- Grounding: Ensure the unit is properly grounded to prevent electrical hazards and ensure stable operation.
Figure 3: Detailed view of the input terminal block, showing screw terminals for wiring connections.
Figure 4: Top view of the processor unit, illustrating the output relay terminals.
3. Operation
3.1. Indicator Lights
The 1747-L20A processor unit features several indicator lights on its front panel to provide status information:
Figure 5: Close-up of the front panel, detailing the status indicator lights and input numbering.
- POWER: Illuminates when the unit is receiving power.
- PC RUN: Indicates the processor is in Run mode and executing the user program.
- CPU FAULT: Illuminates if a processor fault occurs. Refer to the troubleshooting section for details.
- FORCED I/O: Indicates that I/O points are being forced (overridden) by programming software.
- BATTERY LOW: Warns that the internal battery, which backs up the program and data, is low and requires replacement.
3.2. Programming and Configuration
The SLC 500 processor is configured and programmed using Rockwell Software's RSLogix 500 programming software. This software allows users to create, download, and monitor ladder logic programs, configure I/O, and manage processor settings. Consult the RSLogix 500 documentation for detailed programming instructions.
4. Maintenance
4.1. General Cleaning
Keep the processor unit clean and free from dust and debris. Use a soft, dry cloth for cleaning. Avoid using solvents or abrasive cleaners that could damage the unit's surface or internal components.
4.2. Battery Replacement
The 1747-L20A contains an internal battery to retain the user program and data in the event of a power loss. When the "BATTERY LOW" indicator illuminates, the battery needs to be replaced promptly to prevent loss of program data. Refer to the specific battery replacement procedure in the detailed SLC 500 documentation for your safety and to ensure data integrity.
4.3. Inspection
Periodically inspect the unit for any signs of physical damage, loose connections, or excessive heat. Ensure all wiring is secure and free from corrosion.
5. Troubleshooting
This section provides guidance on common issues you might encounter with the 1747-L20A processor unit.
| Symptom | Possible Cause | Action |
|---|---|---|
| CPU FAULT indicator is ON | Program error, hardware fault, or memory issue. | Connect with RSLogix 500 software to view the fault code and clear the fault. Check for wiring errors or damaged components. |
| BATTERY LOW indicator is ON | Internal battery is nearing end of life. | Replace the battery immediately to prevent loss of program and data. Refer to maintenance section. |
| No indicator lights ON | No power supply to the unit. | Verify power connections and ensure the power source is active and within specified voltage range. |
| I/O not responding | Incorrect wiring, faulty I/O device, or program logic error. | Check I/O wiring, verify I/O device functionality, and review program logic in RSLogix 500. |
6. Technical Specifications
The following table outlines the key technical specifications for the Allen-Bradley 1747-L20A Processor Unit:
- Model Number: 1747-L20A
- Series: SER B
- I/O Points: 20
- Input Voltage: 100 V-AC, 240 V-AC
- Output Current Rating: 1 A AMP
- Product Dimensions: 9 x 9 x 8 inches
- Weight: 2 Pounds
- Manufacturer: ALLEN BRADLEY
Figure 6: Product label with detailed electrical specifications and certifications.
6.1. Electrical Ratings (from Product Label)
| Parameter | Value |
|---|---|
| Line Voltage (Nominal) | 100/200 VAC, 120/240 VAC, 50/60 Hz |
| Input Voltage | 85-132 VAC, 50/60 Hz |
| Output Voltage | 10-250 VAC, 50/60 Hz; 10-125 VDC |
| Output Contact Ratings (AC) | 240VAC: 7.5A Make, 7.5A Break, 2.5A Cont. (180VA) |
| Output Contact Ratings (AC) | 120VAC: 15A Make, 15A Break, 2.5A Cont. (180VA) |
| Output Contact Ratings (DC) | 125VDC: 22A Make, 1.0A Break, 1.0A Cont. (28VA) |
| V.A. Rating (Maximum per Chassis) | 1440VA |
7. Warranty and Support
For information regarding product warranty, technical support, or service, please contact your authorized Allen-Bradley distributor or visit the official Rockwell Automation website. Ensure you have your product model number (1747-L20A) and serial number available when seeking support.
Important: This unit is an industrial control component. Installation, operation, and maintenance should only be performed by qualified personnel in accordance with all applicable electrical codes and safety standards.
