1746-NI8 New Sealed 1746NI8 SER A SLC 500 Analog Input Module
PRODUCT DETAILS
1746-NI8 — SLC 500 8-Channel Analog Input Module
The 1746-NI8 is an 8-channel analog input module for the SLC 500 control system. Each of the eight channels reads a voltage or current signal from a field instrument — pressure transmitter, flow meter, temperature transmitter, position sensor — and converts it to a 12-bit digital value that the SLC processor reads on each scan cycle. Channel configuration is flexible: voltage modes (0–10V, ±10V, ±5V, ±5V extended, ±10V extended) and current mode (4–20 mA) can be mixed across the eight channels in software.
In installed SLC 500 systems, the 1746-NI8 is one of the most common analog modules in service. It covers the majority of process measurement applications — most industrial transmitters output either 4–20 mA or 0–10V, both of which this module reads directly. For facilities maintaining legacy SLC 500 systems, keeping a spare 1746-NI8 available is standard practice given how frequently analog input modules appear in process control panels.
Specifications
| Parameter | Value |
|---|---|
| Part Number | 1746-NI8 |
| Platform | SLC 500 (1746 series) |
| Input Channels | 8 |
| Input Modes (Voltage) | 0–10V, ±10V, ±5V, ±5V extended, ±10V extended |
| Input Mode (Current) | 4–20 mA |
| Resolution | 12-bit (4095 counts across the input range) |
| Accuracy | ±0.25% of full scale @ 25°C |
| Input Impedance (voltage) | ≥ 100 kΩ |
| Max Loop Resistance (current) | 250 Ω |
| Update Rate | ~6 ms per channel (all 8 channels: ~50 ms) |
| Isolation | Not isolated (channels share a common reference) |
| Backplane Current (5V) | 170 mA |
| Field Power | 24V DC external (for 4–20 mA loop supply) |
| Operating Temperature | 0°C to 60°C |
| Standards | UL 508, CE |
Where It Gets Used
Eight channels covers most small-to-medium process measurement installations without requiring a second analog input module. A few typical configurations:
- Four 4–20 mA pressure transmitters plus two 4–20 mA temperature transmitters plus two 0–10V level sensors — a complete instrumentation complement for a small process vessel system in one module slot.
- A batch process unit where 6–8 flow or temperature measurements feed a PID ladder routine in the SLC processor, with each channel's engineering unit value displayed on an operator station HMI.
- Legacy HVAC control panels where temperature and pressure measurements from multiple zones connect through the 1746-NI8 for building automation sequence control.
FAQ
Q: Can thermocouple or RTD sensors connect directly to the 1746-NI8?
No. The 1746-NI8 reads standard voltage and current signals — it doesn't have the millivolt-level input sensitivity or cold-junction compensation for thermocouples, or the resistance measurement circuitry for RTDs. Use the 1746-NR4 (RTD) or 1746-NT4 (thermocouple) for direct temperature sensor connections.
Q: What is the 12-bit count value for a 4–20 mA input at 12 mA?
The 4–20 mA range spans 4095 counts across 16 mA. At 12 mA (midpoint), the count value is approximately 2047 — the midscale count. The exact mapping is linear: (input mA − 4) / 16 × 4095.
Q: How is the module configured if RSLogix 500 software isn't available?
The channel configuration (mode, averaging settings) must be done in RSLogix 500 — there's no physical hardware jumper or DIP switch on the module for channel configuration. Without RSLogix 500, the module uses whatever configuration was last stored. For a new installation, RSLogix 500 is required for initial channel setup.
Q: Can I replace a failed 1746-NI8 with a different 8-channel analog input module?
Other analog input modules in the 1746 series may have different I/O image structures, data file formats, or channel configurations. A direct drop-in replacement requires the same catalog number. Substituting a different module type requires verifying I/O image compatibility and potentially updating the RSLogix 500 program.