Purchase now: Allen Bradley 1746-IO8 Combination Module
Purchase now: Atlantechdrives provides you the 1746-IO8, a highly versatile combination digital I/O module engineered for the legacy Allen Bradley SLC 500 programmable logic controller system. This space-saving module is designed to maximize chassis efficiency by integrating two distinct functions into a single slot: it provides 4 input points rated for 120V AC and 4 output points utilizing normally open, hard-contact relays. It is the perfect solution for small-scale automation nodes, remote panels, or machine upgrades where rack space is limited and adding a separate input and output card is not feasible. By handling both high-voltage AC sensing and universal relay switching, the 1746-IO8 simplifies field wiring and reduces overall hardware costs.
Technical Specifications of the 1746-IO8
The 1746-IO8 is built to industrial standards, featuring robust optical and electrical isolation between the field devices and the sensitive 5V DC backplane of the SLC 500 processor. The relay outputs offer excellent flexibility, allowing you to switch AC or DC loads independently.
- Part Number: 1746-IO8
- Module Type: Combination Digital I/O
- Platform: SLC 500 (1746 Series)
- Inputs: 4 Points (120V AC, 85…132V AC operating range)
- Outputs: 4 Points (Relay, N.O. Contacts)
- Relay Switching Capacity: 24…125V DC / 120…240V AC
- Maximum Continuous Current per Output: 2.5 A (Load dependent)
- Backplane Current Draw: 60 mA at 5V DC, 45 mA at 24V DC
- Isolation: 1500V AC withstand (field to backplane)
Expert Tips: Protecting Relay Outputs
While the internal relays of the 1746-IO8 are robust, they are susceptible to damage from inductive loads. Expert Tip: When switching inductive devices such as motor starters, solenoids, or large contactor coils, you must install surge suppressors across the load. For AC inductive loads, install an RC network (snubber) or an MOV in parallel with the load. For DC inductive loads, use a freewheeling diode. Failure to use suppression will result in severe electrical arcing across the relay contacts when they open, drastically reducing the mechanical life of the module and potentially causing the relay to weld shut.
Maintenance and Troubleshooting
To ensure longevity, periodically inspect the Removable Terminal Block (RTB) for loose connections caused by machine vibration. If an output fails to energize a load despite the LED indicator being illuminated, use a multimeter to check for continuity across the relay contacts; a welded or carbonized contact means the internal relay has failed. If the inputs fail to register, verify that the incoming AC voltage is consistently above the 85V AC threshold required for a logical «ON» state.
Frequently Asked Questions (FAQs)
Q: Can I mix AC and DC voltages on the output relays?
A: Yes. Because the outputs are dry relay contacts, they act as simple mechanical switches. You can wire 24V DC through one relay and 120V AC through another, provided you respect the voltage and current limits of the module.
Q: Does this module require an external power supply?
A: The module draws its logic and relay coil power from the chassis backplane. However, you must provide external power for your field inputs (120V AC) and external power for whatever loads the relays are switching.
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This combination module is a space-saving choice for small racks like the 1746-A4 4-slot chassis.
