1756-IF16H — ControlLogix 16-Channel HART Analog Input Module

The 1756-IF16H is a 16-channel analog input module for the ControlLogix 1756 platform that reads standard 4–20 mA signals while simultaneously passing HART digital data from connected field instruments. Each channel handles both the conventional 4–20 mA process variable and the HART communication layer, giving the controller access to the instrument's secondary variables, device health status, and configuration parameters without any additional wiring or hardware.

Sixteen channels in a single slot is a high-density configuration for a HART input module. In process plants where transmitters — pressure, temperature, level, flow — run into the dozens per unit, consolidating them into 16-channel HART modules reduces chassis slot count, backplane cabling, and the number of module catalog numbers to manage. The process variable is available on the same scan cycle as other analog I/O; HART data updates at a slower rate but is accessible to the controller program as additional tag data for diagnostics and monitoring.

Specifications

Parameter	Value
Part Number	1756-IF16H
Platform	ControlLogix 1756
Input Channels	16
Signal Range	4–20 mA (primary), 0–20 mA supported
Resolution	16-bit
Accuracy	±0.1% of full scale @ 25°C
HART Protocol	HART 5, 6, 7 (simultaneous with analog)
HART Update Rate	~1 second per channel (background polling)
Channel Configuration	Independent per channel
Isolation	Channel-to-backplane isolated; channels share common
Loop Supply	External 24V DC (user-supplied)
Backplane Current (5V)	375 mA
RTB	1756-TBNH or 1756-TBS6H (36-pin)
Operating Temperature	0°C to 60°C
Standards	UL 508, CE, HART Communication Foundation certified

HART in a ControlLogix Context

HART (Highway Addressable Remote Transducer) is a protocol that superimposes a digital signal on the standard 4–20 mA analog loop. The digital signal carries secondary process variables, device identification, calibration data, and diagnostic information — all over the same two-wire loop that already carries the 4–20 mA primary signal. No additional wiring is needed; the HART modem in the field device and the HART modem in the 1756-IF16H communicate while the analog measurement runs simultaneously.

The ControlLogix controller accesses HART data through the module's input data tags. HART variables appear as separate tags alongside the 4–20 mA process variable. A pressure transmitter's primary variable (differential pressure in engineering units) is in one tag; its secondary variable (sensor temperature) is in another; its device status byte (indicating calibration needed, communication failure, or sensor degradation) is in a third. All read from the same module, the same wiring, the same channel.

When 16 HART Channels in One Slot Makes Sense

The practical cases where the 1756-IF16H earns its place over a standard 16-channel analog input module:

Process plants with HART transmitters already installed — if the field is populated with HART-capable transmitters, the instrument intelligence is already there. Replacing a standard analog input module with a HART module unlocks diagnostics and secondary variables from the entire instrument population without any additional field wiring.
Predictive maintenance programs — HART device status bits flag incipient failures: plugged impulse lines, drifting calibration, sensor degradation. Reading these in the controller program enables condition-based maintenance alerts without additional sensor hardware.
Multivariable transmitters — some flow and pressure transmitters output multiple independent measurements as HART variables (static pressure, differential pressure, and temperature from one device). The 1756-IF16H makes those additional variables available in the controller as extra tags from the same physical loop.

FAQ

Q: Can a standard 4–20 mA transmitter (non-HART) be used on this module?

Yes. The 1756-IF16H reads any 4–20 mA signal regardless of whether the device supports HART. Non-HART devices work exactly as they would on a standard analog input module — the HART functionality simply doesn't activate for that channel.

Q: How often does HART data update compared to the analog process variable?

The 4–20 mA process variable updates at the module's analog scan rate — every few milliseconds. HART data updates approximately once per second per channel, which is the typical HART polling rate. HART data is suitable for diagnostics and status monitoring, not for fast closed-loop control.

Q: Is the external loop supply provided by the module?

No. The 24V DC loop supply must be provided externally via the terminal base. The module reads the signal current but does not source loop power. Size the loop supply for the total current draw of all 16 transmitters on that module.

Q: Does the pass-through function disrupt the process measurement while in use?

HART pass-through communication shares the loop with the 4–20 mA measurement but does not interrupt it. The 4–20 mA signal and the HART digital signal coexist on the same loop. The process measurement continues normally during pass-through sessions.

Q: Can HART status bits be used to trigger alarms in the controller program?

Yes. HART device status data — including malfunction flags, calibration alerts, and communication errors — appears as tag data in the controller's I/O image. Standard alarm instructions in the program can monitor these bits and trigger process alarms or maintenance notifications when a device reports a fault condition.

1756-IF16H New ControlLogix 16-Channel HART Analog Input Module 1756IF16H