Application Scenarios
In a water treatment plant’s chemical dosing control system, engineers needed to monitor raw water turbidity and pH while controlling the stroke frequency of two metering pumps. The turbidity transmitter output a 4-20mA signal, the pH meter provided a ±10V voltage signal, and both metering pumps accepted 4-20mA current commands. Engineers selected the 1746-NIO4I as the signal interface: two input channels configured for current and voltage modes respectively, directly connected to the turbidity meter and pH meter; two output channels driving the metering pump controllers.
The 1746-NIO4I‘s channel-level input configuration is accomplished via toggle switches on the module side—channels 0 and 1 each have independent switches, with the ON position selecting current input and OFF selecting voltage input. This hardware-level configuration method eliminates software jumpers, simplifying field commissioning. After commissioning, the 1746-NIO4I‘s 16-bit sigma-delta converter provided a stable signal foundation for the dosing control loop, reducing turbidity fluctuation amplitude by approximately 40% compared to the original system.
Parameters
| Parameter | Value/Description |
|---|---|
| Product Model | 1746-NIO4I |
| Manufacturer | Allen-Bradley (Rockwell Automation) |
| Product Category | SLC 500 Analog Combination I/O Module |
| Channels | 2 Inputs + 2 Outputs |
| Input Signal Range | ±20 mA (current mode) / ±10V DC (voltage mode) |
| Input Configuration | Per-channel toggle switch selection |
| Output Signal Range | 0–20 mA (current output, sourcing) |
| Backplane Current (5V) | 55 mA |
| Backplane Current (24V) | 145 mA |
| Backplane Isolation | 500V AC / 710V DC withstand for 1 minute |
| Conversion Method | Sigma-delta modulation |
| Converter Resolution | 16-bit input, 14-bit output |
| Step Response | Input 60ms / Output 2.5ms |
| Module Throughput Delay | 512 µs nominal |
| Bandwidth | 10 Hz |
| Operating Temperature | 0°C to +60°C |
| Mounting | SLC 500 chassis single-slot insertion |
| Terminal Block | Removable (1746-RT28) |
| Recommended Cable | Belden #8761 shielded twisted pair |
| Certifications | UL 508, CSA |
| Lifecycle Status | Discontinued (April 29, 2021) |
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