Description
Product Introduction
The Allen-Bradley 1746-NI8 is a high-density, 8-channel analog input module designed for the SLC 500 programmable logic controller platform. Installed into any standard slot of a 1746 chassis (such as a 1746-A7, 1746-A10, or 1746-A13 rack), the module processes continuous process signals with high precision across industrial automation systems.
Unlike basic 4-channel analog cards (such as the 1746-NI4), the 1746-NI8 offers up to 16-bit conversion resolution, faster update times, and programmable filtering per channel. Featuring individual channel configuration for either voltage or current inputs, it serves as the backbone for precision process monitoring in water treatment, chemical processing, and HVAC systems.
Key Technical Specifications
| Parameter | Specification |
| Manufacturer Part Number | 1746-NI8 |
| Number of Inputs | 8 Individually Configurable Analog Channels |
| Input Signal Ranges (Voltage) | ±10V DC, 0 to 10V DC, 0 to 5V DC, 1 to 5V DC |
| Input Signal Ranges (Current) | 4 to 20 mA, ±20 mA, 0 to 20 mA |
| Converter Resolution | Up to 16-bit (depends on signal range selected) |
| Backplane Current Draw | 200 mA at 5V DC / 100 mA at 24V DC |
| Channel Bandwidth & Filter | Programmable low-pass digital filter (10 Hz to 250 Hz) |
| Isolation | 500V DC channel-to-backplane isolation |
| Terminal Block | Removable 18-pin Terminal Block (Included) |
| Operating Temperature | 0°C to 60°C (32°F to 140°F) |
Application Scenarios & The “Trench” Experience
It is 3:15 AM at a wastewater treatment facility. A critical tank level loop drops offline on Channel 4, preventing the automatic effluent discharge sequence from initiating. The technician suspects a blown input converter on an aging 1746-NI4 card. Upgrading the rack to a 1746-NI8 not only provides additional spare channels for future instrumentation expansion but also delivers 16-bit signal resolution, allowing operators to detect subtle level oscillations before high-level alarms trigger. Thanks to the removable terminal block assembly, swap-out and recalibration take less than 15 minutes.
- Municipal Water & Wastewater – Level, Flow, & Pressure Monitoring – Reads 4–20 mA signals from submersible level transmitters and magnetic flowmeters.
- Chemical Batching & Processing – Tank Temperature & Dosing Loops – Interfaces with 0–10V or 4–20 mA transmitter outputs for precise dosing control.
- HVAC & Building Automation – Duct Static Pressure & Airflow Rates – Processes low-voltage differential signals across large multi-zone duct networks.
- 1746-NI8
- 1746-NI8
Transparency SOP: Quality Assurance & Testing
We don’t just ship boxes; every 1746-NI8 module undergoes comprehensive analog bench calibration and testing prior to dispatch.
- Inbound Physical & Terminal Audit: Inspected housing plastic, backplane edge connector pins, internal DIP switches, and terminal block screw threads for damage or oxidation.
- Backplane Logic Verification: Placed in a live 1746 rack; verified 5V DC and 24V DC backplane power consumption and CPU handshake without backplane communication faults.
- 8-Channel Calibration & Precision Check: Utilized a Fluke 754 Precision Calibrator to sweep 0–10V DC and 4–20 mA inputs across all 8 channels; verified 16-bit digital word accuracy in RSLogix 500 data tables (
I:e.0throughI:e.7). - DIP Switch & Filter Configuration Test: Tested internal current/voltage selection switches and verified software-configurable digital filter response times.
- ESD Protection & Packaging: Cleaned, sealed in static-shielding wrap, and packed inside padded protective shipping containers.
The Veteran’s Tech Trap Guide (Crucial Value-Add)
- ⚠️ DIP Switches MUST Match Software Configuration!
Each channel on the 1746-NI8 has corresponding hardware DIP switches located on the internal circuit board to select Voltage or Current mode. If the physical DIP switch is set to Voltage while RSLogix 500 is programmed for 4–20 mA (or vice-versa), reading errors, out-of-range faults, or signal clipping will occur!
- ❗ Mind the 24V DC Backplane Power Requirement!
Unlike basic digital I/O cards that only draw 5V DC from the backplane, the 1746-NI8 requires 100 mA at 24V DC directly from the 1746 power supply (e.g., 1746-P1 or 1746-P2). Ensure your rack power supply has sufficient 24V DC capacity available before adding this card to a crowded chassis.
- ⚠️ Ground Cable Shields at ONE End Only
Analog signals are highly susceptible to ground loop noise. Always use individual shielded twisted-pair cables for each transmitter, landing the cable shield at the 1746-NI8 shield terminal or ground bar—never ground both ends of the shield wire.
- ❗ Never Hot-Swap Modules in a 1746 Chassis!
Like all SLC 500 modules, inserting or removing the 1746-NI8 while rack power is applied will cause electrical arcing across sensitive analog backplane pins, potential CPU memory corruption, or permanent board damage. Always isolate main rack power prior to swapping modules.
Frequently Asked Questions (FAQ for Conversion)
Q: What is the primary difference between 1746-NI4 and 1746-NI8?
A: The 1746-NI4 provides 4 analog channels with 12-bit resolution. The 1746-NI8 provides 8 analog channels with higher 16-bit resolution, faster update rates, and enhanced software-configurable filtering per channel.
Q: Can I mix 4–20 mA current and 0–10V voltage inputs on the same 1746-NI8 card?
A: Yes! Each of the 8 channels is individually configurable via internal DIP switches and software settings, allowing you to run 4–20 mA transmitters on some channels while reading 0–10V sensors on others simultaneously.
Q: Does the 1746-NI8 require external loop power for 2-wire transmitters?
A: Yes. The 1746-NI8 measures current but does not provide loop power. You must supply an external 24V DC power supply in series with 2-wire 4–20 mA transmitters.
Q: Are 1746-NI8 modules still manufactured by Allen-Bradley?
A: The SLC 500 platform has matured into legacy/discontinued status by Rockwell Automation. We maintain extensive stock of certified New Surplus and fully bench-tested, refurbished original 1746-NI8 modules.
Q: What warranty is provided with this module?
A: Every Allen-Bradley 1746-NI8 analog module includes a full 12-month replacement warranty. If any analog channel or backplane interface fails under standard operating conditions within one year, we send an immediate replacement from stock.
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