Allen-Bradley SLC 500 ™ 1746 series I/O modules

Allen-Bradley SLC 500 ™  1746 series I/O modules

Overall architecture of 1746 I/O system

（1） System composition

The 1746 I/O system is a modular expansion unit of the SLC 500 programmable logic controller, with core components including:

I/O module: Various functional modules of the 1746 series (such as digital IB/OB series, analog NI/NO series, special function modules) provide signal acquisition and control output functions for the system.

I/O rack (Chassis): includes models such as 1746-A1 (1 slot), 1746-A2 (2 slots), 1746-A7 (7 slots), 1746-A10 (10 slots), etc., used for installing modules and providing backplane buses (data and power transmission). Slot 0 is default for processor modules (such as 1747-L511), and the rest are I/O module slots.

Power modules, such as 1746-P2 (24V DC 2.0A) and 1746-P4 (24V DC 4.0A), provide stable DC power to the rack and modules. The appropriate model should be selected based on the total power consumption of the module.

Communication link: Supports industrial buses such as DH-485, ControlNet, DeviceNet, etc., to achieve data exchange between I/O modules, processors, and upper computers.

（2） System characteristics

Modular design: Modules can be combined as needed, supporting mixed installation of digital, analog, and special functional modules, and flexibly adapting to different industrial scenarios (such as manufacturing production lines and process control).

Backplane bus technology: The rack is equipped with a 16 bit data bus with a transmission rate of 1Mbps, ensuring real-time data exchange between modules. Class 1/3 interface modules can flexibly allocate memory addresses.

Environmental adaptability: The entire series of modules comply with industrial standards, with a working temperature range of 0-60 ℃ (some modules can withstand high temperatures of 60 ℃ in the rightmost slot), humidity of 5% -95% (no condensation), and adaptability to complex environments such as workshops and outdoor control cabinets.

Redundancy and Expansion: Supports multi rack expansion (connected through communication modules), and some key modules (such as power and control modules) can be configured redundantly to improve system reliability.

Module Classification and Core Features

The 1746 series I/O modules are divided into four categories according to their functions, and the core models and characteristics of each category are as follows:

（1） Digital input module

Model Channel Number Input Type Core Characteristics Typical Applications

1746-IB16 16 16 channel 24V DC sinking 4 groups isolated (4 points/group), response time ≤ 3ms, with fuse protection (Series A/B/C) button, limit switch signal acquisition

1746-IB32 32 channel 24V DC sinking 4 groups isolated (8 points/group), low-power design, suitable for high-density signal acquisition pipeline workstation status monitoring

1746-IV16 16 16 channel 24V DC sourcing has the same structure as IB16, with opposite input polarity, and is compatible with PNP type sensor photoelectric sensor signal acquisition

1746-IV32 32 channel 24V DC sourcing 32 channel high-density design, inter group isolation, supports long-term operation in harsh environments, multi state monitoring of large equipment

（2） Digital output module

Model Channel Number Output Type Core Characteristics Typical Applications

1746-OB16 16 24V DC sourcing 2 groups isolated (8 points/group), single channel maximum current 0.5A, with fuse protection small relay and indicator light control

1746-OB32 32 channel 24V DC sourcing 32 channel high-density, 2 groups isolated (16 points/group), total continuous current 8A multi actuator synchronous control

1746-OB32E 32 channel 24V DC sourcing with built-in electronic protection (short circuit, overload thermal cut-off), automatic reset of fault channels, key equipment control (requiring fault self recovery)

1746-OV16 16 channel 24V DC sinking output polarity opposite to OB16, compatible with NPN type actuators, inter group isolation solenoid valves, and small motor control

（3） Analog input module

Model Channel Number Input Signal Core Characteristics Typical Applications

1746-NI4 4-channel voltage (± 10V/0-10V, etc.), current (4-20mA, etc.) successive approximation A/D conversion, accuracy ± 0.1%, automatic temperature compensation pressure, temperature transmitter signal acquisition

1746-NI8 8-channel voltage and current, 8-channel high-density, supports single ended/differential wiring, programmable filtering (8 frequencies), multi parameter process monitoring (such as liquid level, flow rate)

1746-NR4 4-channel RTD (Pt100, Cu100, etc.) dedicated RTD signal conditioning, strong anti-interference ability, accurate ± 0.05% temperature monitoring (such as chemical reaction kettle)

1746-NT4 4-channel thermocouple (J, K, T, etc.) with built-in cold end compensation, supports open circuit detection, and is suitable for temperature acquisition in high-temperature environments such as kilns and heating furnaces

（4） Analog output module

Model Channel Number Output Signal Core Characteristics Typical Applications

1746-NO4I 4-channel current (4-20mA) D/A conversion accuracy ± 0.1%, output short-circuit protection, inter group isolation valve positioner, frequency converter control