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Yokogawa NFAI841-S50 Analog Input Module

Configured for acquisition of 4 to 20 mA DC field loop signals in FOUNDATION Fieldbus based control architectures, the Yokogawa NFAI841-S50 (NFAI841 Analog Input Module) provides direct electrical conversion of analog current inputs into system-level process data for FIO backplane integration within Yokogawa distributed control systems.

Suffix Breakdown & Model Matrix

• NFAI841: Base module type, analog input processing unit
• S50: Configuration/assembly variant (terminal and mounting specification dependent on system integration)

No additional functional decomposition is defined for suffix S50 based on provided manufacturing data.

Hardware Specifications

Parameter	Specification
Model	NFAI841-S50
Brand	Yokogawa
Origin	Japan
Module Type	Analog Input Module
Series	FOUNDATION Fieldbus (FF)
Channels	8 (AI, 4 to 20 mA DC)
Input Signal	4-20 mA DC
Input Accuracy	+/-0.1% of full scale
Input Impedance	250 ohm (power on), 500 kohm or more (power off)
Output Current	25 mA
Power Supply	24 VDC
Power Consumption	3 W
Operating Temperature	-40 degC to +85 degC
Ingress Protection	IP66
Dimensions	35 mm (W) x 110 mm (H) x 58 mm (D)
Weight	Approx. 200 g

FOUNDATION Fieldbus Analog Signal Interface Behavior

The NFAI841-S50 executes 4 to 20 mA DC signal acquisition with mapping into FOUNDATION Fieldbus function block structures. Field device integration is performed through FF communication layers, allowing cyclic process variable updates from each of the 8 input channels into the control system scan cycle.

The module input stage is designed without galvanic isolation between signal paths, requiring common grounding reference integrity across field wiring segments. Signal conditioning is performed at the A/D conversion stage prior to FF protocol encapsulation.

Frequently Asked Questions

Q: Can the NFAI841-S50 channels be hot-swapped during operation?
A: Hot-swap capability depends on system rack configuration. The module itself supports field-side signal presence detection, but removal under load requires system-level FIO rack support.

Q: Does each channel support individual electrical isolation?
A: No. The module is specified as a non-isolated input design; all channels share a common electrical reference structure.

Q: What happens if input current exceeds 20 mA range?
A: Inputs above full-scale 20 mA may result in saturation at the A/D conversion stage without protective isolation limiting at channel level.

Field Installation Guidelines

• Maintain shield grounding at a single-point earth reference to prevent loop current distortion
• Use twisted-pair cabling for all 4 to 20 mA loops to reduce electromagnetic coupling
• Ensure terminal torque and mechanical seating are consistent with Yokogawa FIO rack specifications
• Avoid mixed grounding potentials across field instruments connected to the same module
• Verify power supply stability at 24 VDC with minimal ripple before energizing module backplane

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