Technical Specifications
| Parameter Name | Parameter Value |
|---|---|
| Product Model | 1756-IF8H |
| Manufacturer | Allen-Bradley (Rockwell Automation) |
| Product Type | ControlLogix HART Analog Differential Input Module |
| Number of Inputs | 8 differential voltage or current channels |
| Input Ranges (Voltage) | ±10V, 0–5V, 1–5V, 0–10V DC |
| Input Ranges (Current) | 0–20 mA, 4–20 mA |
| Resolution | 16 to 21 bits (signed) |
| HART Protocol Support | HART 5.x, 6.x, 7.x; FSK superimposed on 4–20 mA |
| HART Modem Architecture | Series A: 1 modem per module; Series B/C: 1 modem per channel |
| Backplane Current (Series A) | 5.1V DC @ 300 mA; 24V DC @ 135 mA (4.77 W total) |
| Backplane Current (Series B/C) | 5.1V DC @ 230 mA; 24V DC @ 80 mA (3.1 W total) |
| Power Dissipation (Series A) | 3.21 W (voltage mode); 4.01 W (current mode) |
| Isolation Rating | 250V AC continuous channel-to-backplane |
| Connection Type | 36-pin Removable Terminal Block (RTB), e.g., 1756-TBCH |
| Open Circuit Detection Time | Positive full-scale reading within 5 seconds |
| Operating Temperature | 0 to 60 °C (32 to 140 °F) |
| Storage Temperature | –40 to 85 °C (–40 to 185 °F) |
| Relative Humidity | 5 to 95% noncondensing |
| Vibration | 2 m/s² at 5–500 Hz |
| Certifications | CE, cULus Listed, ATEX, C-Tick, KC (KCC), Marine (ABS) |
| Country of Origin | United States |
Main Features and Advantages
Dual-signal acquisition capability is the core differentiator of the Allen-Bradley 1756-IF8H. Each of the eight differential channels independently accepts conventional analog process signals while a HART modem superimposes bidirectional digital communication on the same conductor pair — meaning a single wiring run delivers both the primary 4–20 mA measurement and the full suite of secondary process variables, device diagnostics, and status flags from any HART-compatible smart transmitter. This architecture dramatically reduces panel wiring, marshalling hardware, and engineering effort in multi-variable measurement applications such as Coriolis flowmeters, multivariable pressure transmitters, and smart temperature assemblies.
Measurement precision and configuration flexibility further reinforce the module’s value. The 1756-IF8H provides 16 to 21-bit signed resolution across all six supported voltage and current ranges, with on-board data alarming, engineering-unit scaling, and real-time channel sampling performed at the module level rather than in the controller — offloading the processor and enabling deterministic scan behavior. Differential input architecture rejects common-mode noise, ensuring signal integrity in electrically hostile plant environments, while per-channel configuration in Studio 5000 Logix Designer allows a single module to serve mixed-loop applications spanning voltage-driven analyzers and current-driven transmitters simultaneously.
HART integration depth distinguishes the 1756-IF8H from non-HART analog siblings. Acquired HART data — including PV, SV, TV, QV dynamic variables and device status — is exposed directly through module-defined CIP data types, allowing controller logic and supervisory systems to access transmitter diagnostics without custom messaging. For advanced use cases such as MicroMotion totalizer access or device-specific HART command 48 reads, the module supports Generic HART messaging (type 0x0E) through MSG instructions in RSLogix 5000, providing full command-level access to the connected device. Compatibility with HART 5.x, 6.x, and 7.x ensures the module supports both legacy field instruments and the latest generation of smart transmitters with enhanced diagnostics. The Series B and C hardware revisions — identifiable by catalog number suffix — provide one dedicated HART modem per channel, allowing all eight transmitters to be polled concurrently rather than sequentially through a shared modem, reducing effective HART data refresh latency proportionally.
Environmental robustness and integration breadth complete the value proposition. Channel-to-backplane isolation of 250V AC continuous protects the ControlLogix chassis from ground-loop faults and transient surges originating in field wiring, while ATEX, cULus, CE, C-Tick, KC, and Marine (ABS) certifications permit deployment in European hazardous locations, North American industrial facilities, and shipboard applications without regional hardware substitutions. The 1756-IF8H installs into any standard 1756 ControlLogix chassis — from 4-slot to 17-slot configurations — and operates alongside digital, thermocouple, RTD, and specialty I/O modules, allowing unified system architecture across discrete and process control zones within a single chassis.
