Product Overview

The Allen-Bradley 1746-IH16 SLC 500 Digital DC Input Module is a 16-point discrete input module designed for industrial automation systems using the Allen-Bradley SLC 500 programmable logic controller platform. It receives DC signals from field devices and transfers their ON/OFF status to the PLC processor for monitoring, logic execution, and machine control.

Digital input modules provide the connection between field-level equipment and a programmable controller. They allow a PLC to detect operating conditions such as switch positions, equipment status, process interlocks, and machine limit conditions. The controller can then use this information to make decisions and coordinate other automation devices.

The 1746-IH16 is specifically designed for 125 V DC signal input and uses a sinking input configuration. Its operating voltage range is 90–146 V DC, making it different from standard 24 V DC input modules in the SLC 500 family. Engineers must verify the field signal voltage and input wiring arrangement before installation.

The module provides 16 input points, with all 16 points assigned to one common. It communicates with the SLC 500 processor through the system backplane and has a maximum ON and OFF signal delay of 9 ms. Its removable terminal block supports field wiring and maintenance access.

The 1746-IH16 is suitable for industrial control applications where higher-voltage DC signals need to be monitored by an SLC 500 controller. Correct voltage matching, wiring, and configuration are essential for dependable operation.

Technical Specifications

Note: Maximum simultaneous ON-point capacity depends on operating voltage and ambient temperature. Follow the manufacturer’s derating specifications when designing the I/O system.

Function and Working Principle

The 1746-IH16 receives discrete DC signals from field devices and converts their electrical states into input information that can be processed by an SLC 500 controller.

1. Digital Signal Acquisition

Industrial field devices generate electrical signals representing different operating conditions. These may include the status of limit switches, control contacts, position switches, and other compatible DC signal sources.

When a suitable signal is applied to an input channel, the module detects its electrical state and reports the corresponding input status to the PLC processor.

2. 125 V DC Sinking Input Operation

The 1746-IH16 is designed for 125 V DC sinking input applications. Its operating voltage range is 90–146 V DC.

The input circuit must be wired according to the module’s sinking configuration and the field device’s electrical characteristics. The input voltage should not be confused with the 24 V DC signal level used by many other SLC 500 input modules.

Using an incompatible signal voltage or wiring arrangement may prevent reliable input detection or damage the equipment.

3. Sixteen-Point Input Monitoring

The module provides 16 independent input points. Each point can monitor a compatible discrete signal from a field device.

All 16 points share one common connection. This arrangement should be considered when planning field wiring and selecting the connected devices.

4. Signal Processing and Response

The module detects changes in input conditions and transfers the corresponding information through the SLC 500 backplane.

Its specified maximum signal delay is 9 ms for both ON and OFF transitions. This response characteristic is suitable for many conventional industrial monitoring and sequencing applications, although faster applications should be evaluated against the complete system response requirements.

5. Backplane Communication

The module receives its required backplane power from the SLC 500 chassis. Its documented backplane current consumption is 85 mA at 5 V DC and 0 mA at 24 V DC.

The processor accesses input status through the controller’s I/O system, allowing the PLC program to use field conditions in control logic.

Role in Industrial Control Systems

The 1746-IH16 acts as an interface between higher-voltage DC field signals and the SLC 500 programmable controller.

PLC Input Monitoring

The module supplies the processor with information about connected field devices. PLC logic can use these input states to determine whether a machine is ready, a process condition has been reached, or an interlock is active.

Machine Sequencing

In automated machinery, multiple input signals are often used to coordinate sequential operations. The 1746-IH16 can monitor compatible DC signals from switches and other discrete devices, allowing the PLC to determine when the next operation should begin.

Equipment Status Detection

The module can be used to monitor operating conditions from compatible industrial equipment. These signals may include auxiliary contacts, position indications, and machine status outputs.

Process Interlocking

Input information can be incorporated into PLC interlock logic to prevent certain operations from proceeding when required conditions are not satisfied. Safety-related functions, however, must use appropriately designed and certified safety systems rather than relying on an ordinary standard input module alone.

Industrial Applications

The Allen-Bradley 1746-IH16 is suitable for industrial installations that use compatible 125 V DC field signals and SLC 500 control hardware.

1. Manufacturing Equipment

Production machinery often relies on discrete signals to indicate machine position, operating status, and sequence completion. The module can collect these signals and make them available to the PLC program.

2. Material Handling Systems

Conveyors, transfer equipment, and material-handling machinery use switches and auxiliary contacts to monitor equipment conditions. The 1746-IH16 can receive compatible DC signals for machine coordination and status monitoring.

3. Industrial Power Equipment

Some industrial electrical systems provide higher-voltage DC status signals from auxiliary contacts and monitoring devices. The module can interface with compatible 125 V DC signals, provided the electrical characteristics and wiring arrangement meet its specifications.

4. Process Automation

In process plants, discrete input signals can indicate valve positions, equipment states, and operating conditions. The module allows the SLC 500 controller to incorporate these signals into its control logic.

5. Machine Interlock Monitoring

Industrial machines often use interlocks to coordinate equipment operation. The 1746-IH16 can monitor compatible status contacts and provide their states to the PLC. The overall interlock design must be appropriate to the machine’s risk and safety requirements.

Installation and System Integration

Correct installation ensures that the 1746-IH16 operates reliably and communicates properly with the SLC 500 controller.

1. Verify Input Voltage

Before wiring, confirm that the field devices provide signals within the module’s 90–146 V DC operating range.

Do not connect ordinary 24 V DC signals unless the complete electrical design specifically supports the required input conditions. The 1746-IH16 is a 125 V DC input module, not a general-purpose 24 V DC input card.

2. Confirm the Sinking Input Arrangement

The module uses a sinking input configuration. Verify the field device output type, common wiring, and DC supply polarity before connecting the input circuits.

Incorrect wiring can cause false input states or prevent the module from detecting the intended signal.

3. Install the Module in the SLC 500 Chassis

Ensure that the selected chassis and slot are suitable for the module. Install the card securely and verify that it is properly seated in the backplane connector.

The module should be installed in accordance with the SLC 500 hardware installation instructions.

4. Connect the Removable Terminal Block

The 1746-IH16 uses a removable terminal block for field wiring. Label conductors clearly and verify terminal assignments before applying power.

Keep wiring organized and use appropriate conductor ratings, insulation, and protection for the system voltage.

5. Configure the PLC

When configuring the system through programming software or a handheld terminal, use the documented module identification code 0507.

Confirm that the controller recognizes the module and that the input status corresponds to the actual field-device conditions.

6. Test Input Operation

After installation, verify each input channel individually. Apply the appropriate field signal and confirm that the PLC reports the correct ON/OFF state.

Check signal polarity, common connections, voltage levels, and field-device operation if an input does not respond correctly.

Compatible System Components

The 1746-IH16 operates as part of an SLC 500 control system. The following components may be involved in a typical installation.

The components listed above are examples of equipment used in an SLC 500 installation. They are not necessarily included with the 1746-IH16 module.

Alternative Models and Replacement Considerations

The SLC 500 family includes several digital input modules with different voltage categories and input configurations. They should not be treated as direct substitutes without checking the electrical specifications.

Before replacing a 1746-IH16, check the following:

• Confirm that the replacement supports 125 V DC input signals.
• Verify the 90–146 V DC operating range.
• Check the sinking input configuration.
• Confirm the 16-point arrangement and common connection.
• Verify chassis and processor compatibility.
• Check the removable terminal block and wiring assignments.
• Confirm the module identification code and PLC configuration.
• Review the maximum simultaneous ON-point limitations.

A 24 V DC input module cannot automatically replace the 1746-IH16 simply because it has the same number of channels. The field voltage and input circuit design must match.

Key Advantages

Sixteen Discrete Input Channels

The module provides 16 input points for monitoring multiple compatible field signals through a single SLC 500 I/O slot.

High-Voltage DC Signal Compatibility

Its 125 V DC input category supports industrial control installations that use higher-voltage DC signals rather than standard 24 V DC inputs.

SLC 500 Backplane Integration

The module communicates with the SLC 500 processor through the chassis backplane, allowing input information to be incorporated into the controller program.

Defined Signal Response

The specified maximum ON and OFF signal delay of 9 ms provides a documented response characteristic for system design.

Removable Terminal Block

The removable terminal block supports convenient wiring access during installation and maintenance.

Industrial Control Applications

The module can support equipment monitoring, machine sequencing, status detection, and process interlocking when used within its electrical specifications.

Technical FAQs

1. What is the Allen-Bradley 1746-IH16?

The 1746-IH16 is a 16-point digital DC input module designed for Allen-Bradley SLC 500 programmable controllers. It receives compatible 125 V DC field signals and transfers their status to the PLC processor.

2. What is the input voltage range?

Its documented operating voltage range is 90–146 V DC. The module belongs to the 125 V DC signal input category.

3. Is the 1746-IH16 a 24 V DC input module?

No. It is designed for 125 V DC sinking inputs. A standard 24 V DC input module, such as the 1746-IB16, has a different electrical specification and should not be used as a direct replacement without redesigning the field interface.

4. How many input channels does it provide?

The module provides 16 digital input channels, with 16 points per common.

5. What is the maximum signal delay?

The documented maximum signal delay is 9 ms for both ON and OFF transitions.

6. What is the backplane current consumption?

The module draws 85 mA from the 5 V DC backplane supply and 0 mA from the 24 V DC backplane supply.

7. Does it use a removable terminal block?

Yes. The module uses a removable terminal block for field wiring connections.

8. What identification code is used for configuration?

The documented module identification code is 0507 when configuring the system with programming software or a handheld terminal.

9. How many inputs can be ON simultaneously?

The maximum number depends on input voltage and ambient temperature. The manufacturer’s specifications include different limits for operation at 146 V DC, 132 V DC, and 125 V DC. Consult the applicable installation documentation when determining the allowable channel loading.

10. What should be checked before purchasing a replacement?

Verify the complete model number, input voltage category, sinking configuration, channel count, terminal block condition, module condition, and compatibility with the existing SLC 500 chassis and controller.

Procurement and Maintenance Recommendations

When purchasing an Allen-Bradley 1746-IH16, verify the complete catalog number and inspect the module’s physical condition. Check the front label, terminal block, connector contacts, housing, and any visible signs of overheating or damage.

For used or refurbished units, request clear product photographs and available functional test information. Confirm whether the removable terminal block is included and whether the module has been tested in an appropriate SLC 500 system.

During installation, verify the field voltage before connecting the wiring. Pay particular attention to the sinking input configuration and common connections. Incorrect voltage or polarity can lead to unreliable input operation or hardware damage.

For maintenance, inspect terminal connections and wiring condition periodically. Review the PLC input status during troubleshooting and compare the reported state with the actual field signal. If an input fails to respond, check the field device, DC supply, wiring, common connection, terminal block, and module condition.

Keep the PLC program and hardware configuration records updated. Documenting module positions and input assignments can make future replacement and troubleshooting more efficient.

Conclusion

The Allen-Bradley 1746-IH16 SLC 500 Digital DC Input Module provides 16 discrete input channels for monitoring 125 V DC field signals in industrial automation systems. With a 90–146 V DC operating range, sinking input configuration, 9 ms maximum signal delay, and removable terminal block, it serves as an interface between compatible field devices and the SLC 500 controller.

For maintenance and replacement applications, the most important consideration is its 125 V DC input specification. Confirming the field voltage, wiring arrangement, module identification code, and chassis compatibility helps ensure dependable integration into an existing control system.