Description
The 1756-IF8I is a high-performance, 8-channel, individually isolated analog input module designed for the ControlLogix Control System. By providing channel-to-channel isolation, this module eliminates ground loop errors and protects sensitive control architecture from high common-mode voltages common in harsh industrial processing environments. It supports voltage, current, and differential signaling inputs without requiring external isolation barriers.
Technical Specifications
| Parameter | Specification / Value |
| Brand / Manufacturer | Rockwell Automation / Allen-Bradley |
| Model Series | ControlLogix (1756) |
| Catalog Number | 1756-IF8I |
| Inputs | 8 isolated voltage or current channels |
| Input Ranges | ±10 V, 0–10 V, 0–5 V, 1–5 V, 0–20 mA, 4–20 mA |
| Resolution | 24-bit effective resolution |
| Channel-to-Channel Isolation | 250 V continuous (basic insulation type), inputs-to-backplane |
| Backplane Current Draw | 150 mA @ 5.1 V DC, 120 mA @ 24 V DC |
| Power Dissipation | 3.5 W (maximum) |
| Module Keying | Electronic (Software Configurable) or Mechanical |
| Removable Terminal Block (RTB) | 1756-TBCH or 1756-TBS6H (not included) |
| Operating Temperature | 0 to +60 °C (+32 to +140 °F) |
| Vibration / Shock Resistance | 2 g @ 10–500 Hz / 30 g operational |
Commercial Supply Profile
- Condition: New Original (New Surplus) in factory-sealed Allen-Bradley packaging with unbroken security seals.
- Warranty: 12-Month Comprehensive Technical Warranty covering functional performance and hardware calibration integrity under specified operating limits.
- Availability & Lead Time: Standard stocking item. Dispatched from inventory within 24 to 48 hours via expedited international couriers (DHL, FedEx, UPS).
- Pricing Notice: Price is subject to market conditions; contact us for a firm quote. Standard trade discounts apply for system integrators and volume procurement.
Field Implementation & Wiring Architecture
When installing the 1756-IF8I in a ControlLogix chassis, proper field-side wiring is critical to maximize the 24-bit analog resolution and maintain channel-to-channel isolation.
Grounding and Shielding
For current loops (4–20 mA), use twisted-pair shielded cable (e.g., Belden 8760). Ground the cable shields at one end only—ideally at the marshalling panel or the chassis ground bar. Grounding both ends introduces parallel ground paths, defeating the purpose of the module’s channel-to-channel isolation.
2-Wire vs. 4-Wire Transmitter Configuration
The 1756-IF8I does not supply loop power directly to field transmitters.
- 4-Wire Transmitters: Have an independent power supply. Connect the active signal output directly to the designated channel (IN\_x+) and return (IN\_x-) terminals.
- 2-Wire Transmitters: Require an external 24 V DC power supply wired in series with the loop. The external power source must be integrated carefully into the loop to avoid bypassing the channel’s isolation barrier.
Software Configuration Note (Studio 5000)
In the Logix Designer I/O tree, the module allows you to configure notch filter settings (e.g., 50 Hz, 60 Hz) per channel. Selecting the correct notch filter drastically reduces AC line noise. Keep in mind that lower notch frequencies increase the module’s internal analog-to-digital converter (ADC) scan time; choose the frequency that matches your local utility power grid to optimize the noise-rejection-to-speed ratio.
Frequently Asked Questions
What is the advantage of the 1756-IF8I over the non-isolated 1756-IF8?
The standard 1756-IF8 uses a single common return for all channels (differential/non-isolated). If a voltage differential exists between the grounds of two separate field instruments connected to a standard module, it causes a ground loop, skewing data readings or damaging the module. The 1756-IF8I isolates every channel optically and electronically, allowing you to connect inputs from disparate power regimes safely.
Which Removable Terminal Block (RTB) should I order with this module?
The 1756-IF8I requires a 36-pin RTB. You can use either the 1756-TBCH (Cage clamp style) or the 1756-TBS6H (Spring clamp style). RTBs are shipped separately from the module and must be specified during procurement.
Can I mix voltage and current signals on the same 1756-IF8I module?
Yes. Because each channel is fully isolated and independently configured within Studio 5000 Logix Designer, you can set Channel 0 for 4–20 mA current loops, Channel 1 for a ±10 V DC voltage source, and so forth. No physical jumpers are required on the module board; all scaling and signal selection are handled via software firmware properties. Verify with OEM datasheet parameters if configuring high-speed cyclic tasks.
