Parameter
| Main Parameters | Value/Description |
|---|---|
| Product Model | 1746-NIO4I (Series A, “/A”) |
| Manufacturer | Allen-Bradley / Rockwell Automation |
| Product Category | SLC 500 Analog Combination I/O Module (2-in / 2-out) |
| Input Channels | 2 differential, voltage or current selectable per channel via onboard DIP switch (not individually isolated) |
| Input Ranges | ±20 mA, 0–20 mA, 4–20 mA (current); ±10V, 0–10V, 0–5V, 1–5V (voltage) |
| Input Converter Resolution | 16-bit (Delta-Sigma modulation); ±1 LSB repeatability; 0.01% non-linearity |
| Input Accuracy | ±0.365% of full scale @ 25 °C (current); ±0.284% @ 25 °C (voltage); ±0.642% over 0–60 °C (current) |
| Input Impedance (current) | 250 Ω; impedance to ANL COM 500 KΩ on Series A (380 KΩ on Series B+) |
| Input Absolute Maximum | ±30 mA; overvoltage protection 7.5V AC RMS (current mode); 220V AC RMS continuous (voltage mode) |
| Common-Mode Rejection | 105 dB min @ 60 Hz; 50 dB min @ 0–10 Hz; normal-mode rejection 55 dB min @ 60 Hz |
| Output Channels | 2 analog current outputs (not individually isolated), R-2R ladder conversion |
| Output Range / Resolution | 0 to 20 mA (overrange to 21 mA); 14-bit, 2.56348 µA/LSB; step response 2.5 ms @ 95% |
| Output Load Range | 0 to 500 Ω (100 µH max reactance) |
| Output Accuracy | ±0.298% of full scale @ 25 °C; ±0.541% over 0–60 °C |
| Backplane Current Draw | 55 mA @ 5V DC; 145 mA @ 24V DC |
| Isolation (Field ↔ Backplane) | 500V DC continuous; type-tested at 500V AC / 710V DC for 1 second |
| Update Time | 512 µs for all channels in parallel |
| Data Format | 16-bit two’s-complement binary |
| Terminal Block | Removable, max wire size #14 AWG, torque 0.57 N·m (5 lb·in) |
| Recommended Cable | Shielded Belden #8761 (drain + foil grounded at one end only) |
| Loop Power | Not provided — external transmitter power supply required |
| Dimensions / Weight | Single-slot SLC 500 module, approx. 0.4 kg (14 oz) installed |
| Operating Temperature | 0 °C to +60 °C; storage −40 °C to +85 °C; 5–95% RH non-condensing |
| Agency Certifications | c-UL Listed Industrial Control Equipment; Class I Div 2 Groups A,B,C,D; CE marked; NEMA ICS 2-230 noise immunity |
| Lifecycle Status | Discontinued by manufacturer; supplied as verified surplus or professionally rebuilt |
*Key annotation:* the two onboard DIP switches (SW1 and SW2) independently configure Channel 0 and Channel 1 for current or voltage input — ON selects current, OFF selects voltage — and applying a direct voltage source to a channel configured for current input can damage the module, making DIP verification a mandatory pre-installation check.
Technical Principles and Innovative Values
- Innovation Point 1 — Delta-Sigma 16-bit A/D conversion on the input side. The 1746-NIO4I uses delta-sigma modulation to convert incoming analog signals into 16-bit two’s-complement binary values, delivering a nominal resolution of 305.176 µV/LSB on the ±10V range and 1.2207 µA/LSB on the ±20 mA range. Compared with the 12-bit fast-analog 1746-FIO4I sibling, the delta-sigma architecture trades conversion speed for dramatically better noise rejection and linearity — exactly the right trade for slow-moving process variables like level, pressure, and flow.
- Innovation Point 2 — 105 dB common-mode rejection at 60 Hz. Because SLC 500 panels routinely share enclosures with contactors, VFDs, and 120V AC wiring, the analog front end must reject common-mode noise aggressively to keep a 4–20 mA signal honest. The 1746-NIO4I achieves a minimum 105 dB CMR at 60 Hz and 55 dB normal-mode rejection — the specification difference that separates a stable reading in a noisy panel from one that drifts every time a motor starter pulls in.
- Innovation Point 3 — Per-channel V/I selection via onboard DIP switch. Each input channel can be independently configured for voltage or current via its own DIP switch, letting one module serve a 4–20 mA flow transmitter on Channel 0 and a 1–5V level signal on Channel 1 simultaneously. This per-channel flexibility eliminates the need to stock separate V-input and I-input modules for mixed-signal panels.
- Innovation Point 4 — 14-bit R-2R current output with 5% overrange. The two output channels use an R-2R ladder DAC at 14-bit resolution (2.56348 µA/LSB), support load resistances from 0 to 500 Ω, and provide a 5% overrange capability (0 to 21 mA) beyond the nominal 20 mA span — useful for driving smart positioners that use the >20 mA region for HART signalling or fault indication.
- Innovation Point 5 — 512 µs parallel update across all channels. Unlike multiplexed analog cards that sample channels sequentially, the 1746-NIO4I updates all four channels in parallel every 512 µs, so the input and output channels maintain a consistent temporal relationship — important in closed-loop control applications where the output command must reflect the most recent input reading without channel-skew artifacts.
