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.

1746-NI8 New Sealed 1746NI8 SER A SLC 500 Analog Input Module