Honeywell XNX-AMAV-FHIC1 vs. XNX-AMAV-FNCB1: Hardware Differences, Sensor Technology, and Gas Detector Selection Guide

Selecting the correct gas detector configuration is essential for industrial safety and reliable process monitoring. Honeywell XNX Universal Transmitters offer a flexible platform for different gas sensing technologies and communication requirements.

However, two XNX models can share a similar enclosure while performing completely different measurement functions. This distinction becomes particularly important when comparing the XNX-AMAV-FHIC1 and XNX-AMAV-FNCB1 configurations.

The FHIC1 configuration supports infrared carbon dioxide detection through an MPD sensor. The FNCB1 configuration supports catalytic bead combustible gas detection. Their sensor principles, measurement ranges, and local communication options differ significantly.

Both configurations use the XNX mV personality platform and share the FOUNDATION Fieldbus option. They also differ in their factory-selected local HART hardware configuration.

This engineering guide examines their hardware architecture, sensing principles, communication interfaces, installation requirements, calibration considerations, and replacement compatibility. It helps instrumentation engineers, maintenance teams, and procurement specialists select the correct equipment.

1. Core Value: Why XNX-AMAV-FHIC1 and XNX-AMAV-FNCB1 Are Different

The Honeywell XNX Universal Transmitter supports multiple gas detection technologies through a common transmitter platform. Its modular architecture allows different sensor configurations and communication options to serve various industrial applications.

However, a common transmitter platform does not make every configuration interchangeable. The installed sensor technology determines the gas measurement function and its associated operating requirements.

The XNX-AMAV-FHIC1 targets carbon dioxide monitoring. It uses an MPD infrared sensor configuration with a nominal measuring range of 0–5% volume.

The XNX-AMAV-FNCB1 targets combustible gas monitoring. It uses an MPD catalytic bead configuration with a nominal measuring range of 0–100% LEL.

The local HART configuration also differs. FHIC1 includes the local HART option, while FNCB1 does not include that dedicated local interface.

Importantly, the absence of local HART does not mean that FNCB1 automatically loses the standard HART capability associated with the XNX 4–20 mA current loop. Engineers must distinguish the local connection from the main communication arrangement.

For industrial safety applications, this distinction affects purchasing, installation, maintenance, calibration, and control-system integration. A replacement must match the original measurement purpose and approved system configuration.

2. Quick Hardware Comparison: FHIC1 vs. FNCB1

The following table summarizes the principal differences between these two Honeywell XNX configurations.

The comparison highlights two important purchasing decisions. First, confirm the required gas detection principle. Second, verify whether the installation requires the optional local HART connection.

Other specifications, including electrical approvals, thread arrangements, operating limits, and environmental ratings, require confirmation against the complete product identification and applicable Honeywell documentation.

3. Understanding the XNX-AMAV-FHIC1 Model Configuration

Understanding the ordering structure helps engineers identify the hardware configuration before purchasing replacement equipment.

The XNX ordering system combines transmitter construction, sensor personality, communication options, and sensor selection. Each section describes a different configuration feature.

For the supplied FHIC1 reference, the important configuration elements include:

• XNX: Identifies the Universal Transmitter product family.
• AM: Identifies the applicable approval and M25 port configuration in this ordering arrangement.
• A: Identifies the aluminium enclosure selection.
• V: Identifies the mV sensor personality.
• F: Identifies the FOUNDATION Fieldbus communication option.
• H: Identifies the optional local HART interface.
• IC1: Identifies the infrared CO2 sensor configuration.

The IC1 selection is particularly important because it identifies the measurement application. Honeywell’s product configuration guide identifies IC1 as infrared CO2 detection with a 0–5% volume range.

Therefore, the FHIC1 configuration supports carbon dioxide monitoring rather than general combustible gas detection. Engineers should preserve this measurement function when selecting replacement equipment.

For procurement, always compare the complete order reference with the original nameplate. A shortened model description may omit important approval or interface information.

4. Understanding the XNX-AMAV-FNCB1 Model Configuration

The FNCB1 configuration uses the same general XNX-AMAV transmitter platform. However, its final sensor selection identifies a catalytic bead combustible gas application.

Its important ordering elements include:

• XNX: Honeywell XNX Universal Transmitter family.
• AM: Applicable approval and M25 port configuration.
• A: Aluminium enclosure selection.
• V: mV sensor personality.
• F: FOUNDATION Fieldbus communication option.
• N: No dedicated local HART option.
• CB1: Catalytic bead combustible gas sensor configuration.

The CB1 designation identifies a catalytic bead sensor operating in %LEL measurement applications. The nominal range reaches 100% LEL under the applicable configuration.

This arrangement suits combustible gas monitoring in locations where flammable gas releases could create fire or explosion hazards.

However, the catalytic sensor requires sufficient oxygen for its measurement reaction. Engineers must consider this limitation when selecting equipment for inerted or oxygen-deficient process environments.

The FNCB1 therefore serves a different safety function from FHIC1. Its selection must follow the site’s combustible gas detection requirements and approved detector design.

5. Sensor Technology Difference: Infrared Detection vs. Catalytic Bead Detection

The most important engineering difference involves the physical principles behind gas measurement. Infrared and catalytic sensors respond to gases through different mechanisms.

These technologies also have different environmental limitations, calibration requirements, and application characteristics. Understanding their behavior helps engineers avoid incorrect substitutions.

5.1 Infrared sensing principle in FHIC1

The MPD-IC1 sensor uses non-dispersive infrared technology to measure carbon dioxide. Its optical system detects changes in infrared absorption associated with the target gas.

Carbon dioxide absorbs infrared energy at characteristic wavelengths. The sensor evaluates the resulting optical response and converts it into a concentration measurement.

Unlike catalytic bead detection, infrared measurement does not depend on combustible gas oxidation. It also does not require oxygen to support a catalytic combustion reaction.

This characteristic makes infrared technology useful in applications where oxygen concentration may vary. It also avoids catalytic poisoning mechanisms associated with certain contaminants.

However, infrared sensing has its own limitations. Optical contamination, condensation, environmental conditions, and incorrect calibration can affect measurement performance.

Engineers should therefore maintain the sensor inlet and follow Honeywell’s maintenance instructions. They should also confirm the selected measurement range against the actual process hazard.

5.2 Catalytic bead sensing principle in FNCB1

The MPD-CB1 sensor uses catalytic oxidation to detect combustible gases. Its sensing element operates at an elevated temperature through a controlled electrical heating arrangement.

When combustible gas reaches the active element, catalytic oxidation produces additional heat. The resulting temperature change affects the element’s electrical resistance.

The transmitter processes this response and calculates the corresponding combustible gas concentration. The instrument then reports the result within its configured %LEL measurement range.

A reference element helps compensate for environmental changes. This arrangement supports measurement stability under the sensor’s specified operating conditions.

However, catalytic detection requires adequate oxygen. It also requires attention to catalyst contamination and sensor poisoning.

Silicone compounds, certain sulfur compounds, and other contaminants can reduce catalytic sensitivity. Therefore, maintenance teams should control contaminant exposure around the detector.

5.3 Why these sensing technologies cannot replace each other

Both technologies belong to the same MPD product family, but they measure different gas properties. Their measurement ranges and calibration procedures also differ.

An infrared CO2 detector cannot automatically replace a catalytic combustible gas detector. Likewise, a catalytic bead detector cannot provide the original infrared CO2 measurement function.

Even if both devices fit a similar mechanical arrangement, their sensing elements require different configurations. The transmitter must also recognize the correct sensor type and associated measurement parameters.

For safety-critical applications, never treat a different sensor technology as a direct replacement. Confirm the complete approved configuration before returning the detector to service.

6. Measuring Range Difference: 0–5% Volume vs. 0–100% LEL

The two models use different concentration units because they address different gas hazards.

FHIC1 measures carbon dioxide as a percentage of gas volume. FNCB1 measures combustible gas concentration relative to the lower explosive limit.

One percent volume equals 10,000 parts per million by volume. Therefore, a 5% volume CO2 range corresponds to 50,000 ppm.

However, engineers must not compare % volume and %LEL as equivalent units. They describe different measurement relationships and serve different hazard assessments.

The LEL represents the minimum concentration of a combustible gas that can ignite under specified conditions. A 100% LEL indication represents the defined lower explosive limit for the configured gas.

For mixed combustible gases, the detector’s response depends on the sensor characteristics and calibration gas. Engineers must follow the manufacturer’s gas selection and correction guidance.

Do not assume that a catalytic detector produces identical readings for every combustible gas. Gas sensitivity varies, and the calibration method must match the application.

7. Local HART Interface: The Important Difference Between FHIC1 and FNCB1

Communication hardware represents the second major difference between these configurations. FHIC1 includes the optional local HART interface, while FNCB1 omits this dedicated connection.

Honeywell distinguishes the local HART interface from the standard HART communication associated with the transmitter’s current loop. This distinction matters during maintenance and procurement.

7.1 What the local HART interface provides

The local HART option allows technicians to connect a compatible handheld communicator directly to the transmitter. This connection supports configuration, diagnostic access, and maintenance activities.

It provides a convenient field access point when technicians need to inspect device information. It can also simplify commissioning where control-room access is limited.

The local interface uses dedicated hardware and associated installation requirements. For hazardous-area installations, technicians must verify the correct intrinsically safe barrier and communicator compatibility.

FHIC1 includes this option according to its H ordering code. Therefore, it provides the dedicated local connection required by installations using that configuration.

7.2 Why FNCB1 does not include the same local connection

The N code indicates that the dedicated local HART option is absent. Technicians should not expect the same external local connection hardware as FHIC1.

However, the standard XNX HART-over-current-loop capability remains an important distinction. The absence of the local interface does not automatically eliminate all HART communication.

Depending on the installed wiring and selected communication arrangement, engineers can use the supported current-loop communication path. They must verify the actual field wiring and system configuration before connecting a communicator.

7.3 Maintenance implications

The local HART option can reduce the effort required for certain field configuration tasks. It also gives maintenance teams a convenient diagnostic connection.

Without this option, technicians must use the supported alternative communication path. They may need access to the current loop or the relevant host system.

For procurement, this difference should appear in the technical comparison. A replacement that omits a required local HART interface may increase maintenance complexity.

8. FOUNDATION Fieldbus and 4–20 mA Communication Architecture

Both supplied model references include the F communication option. This identifies the FOUNDATION Fieldbus interface within the XNX configuration.

FOUNDATION Fieldbus supports digital communication between field instruments and compatible control-system infrastructure. It allows multiple field devices to exchange information through a shared network architecture.

For the XNX transmitter, the Fieldbus option uses the applicable H1 communication arrangement. Engineers must verify segment wiring, power requirements, termination, device configuration, and host compatibility.

Importantly, the XNX technical manual also describes the standard 4–20 mA current loop and HART functionality. However, engineers should not assume that every ordered communication configuration uses every interface in the same way.

The actual interface arrangement depends on the selected option board and installation design. Confirm the transmitter wiring diagram and terminal configuration before commissioning.

Key checks include:

• Fieldbus interface: Confirm that the FOUNDATION Fieldbus option board matches the order configuration.
• Segment wiring: Verify polarity, cable type, shielding, and grounding arrangements.
• Segment termination: Check that the network uses the required termination arrangement.
• Device identification: Confirm that the host recognizes the correct device identity and configuration.
• Separate power: Honeywell specifies that FOUNDATION Fieldbus XNX transmitters require a separate power source.
• Analog communication: Verify the actual current-loop availability and wiring for the installed configuration.

Do not assume that the Fieldbus cable powers the transmitter. Honeywell explicitly requires a separate transmitter power supply for its FOUNDATION Fieldbus configuration.

For replacement projects, compare the original communication option with the replacement nameplate. A mismatch can affect control-system integration even when the sensing technology matches.

9. Shared Transmitter Hardware and Construction Features

Despite their different sensor configurations, FHIC1 and FNCB1 share important parts of the XNX transmitter architecture.

Both references identify an aluminium transmitter arrangement and an mV sensor personality. Both also specify the FOUNDATION Fieldbus communication option.

The mV personality provides the interface for supported MPD sensor arrangements. However, the personality board alone does not define the gas measurement function.

The installed sensor type determines whether the instrument measures CO2 through infrared absorption or combustible gases through catalytic oxidation.

Engineers should also distinguish shared transmitter construction from sensor approval requirements. The transmitter and sensor cartridge must carry the appropriate approvals for the intended hazardous-area installation.

Before procurement, verify the following information:

• Complete XNX transmitter part number.
• Enclosure material and mechanical arrangement.
• Applicable port thread and cable-entry configuration.
• Sensor personality and installed MPD cartridge type.
• FOUNDATION Fieldbus and local HART options.
• Power supply and wiring requirements.
• Applicable ATEX, IECEx, or other regional approvals.
• Environmental and operating temperature limits.

Do not transfer specifications from a similar XNX order code without verification. Honeywell offers numerous configurations with different communication and approval combinations.

10. Installation Considerations for FHIC1 Infrared CO2 Detection

Infrared CO2 detection requires careful consideration of the monitored area and gas release characteristics. Carbon dioxide can displace oxygen and create an asphyxiation hazard.

Facilities commonly use CO2 in beverage production, fermentation, food processing, industrial refrigeration, and gas storage. A leak can create dangerous concentrations in enclosed or poorly ventilated locations.

Although CO2 is denser than air under comparable conditions, detector placement should not rely on density alone. Air movement, temperature, ventilation, release pressure, and enclosure geometry also affect gas distribution.

Engineers should assess the following installation factors:

• Potential release points: Identify valves, pipe joints, storage vessels, and transfer connections.
• Ventilation: Evaluate air movement and possible stagnant areas.
• Low-level accumulation: Assess pits, trenches, enclosed spaces, and other potential collection points.
• Environmental exposure: Consider condensation, dust, water ingress, and contamination.
• Maintenance access: Ensure technicians can safely inspect and calibrate the sensor.
• Alarm response: Confirm that the detector supports the required ventilation and evacuation strategy.

Keep the MPD sensing inlet free from contamination. Follow Honeywell’s recommendations for accessories, weather protection, calibration, and inspection.

The 0–5% volume range must also match the intended hazard assessment. If the application requires a different range or measurement technology, select an appropriate detector configuration.

11. Installation Considerations for FNCB1 Catalytic Combustible Gas Detection

Catalytic bead detectors serve combustible gas applications where ignition hazards require continuous monitoring. Typical locations include compressor areas, fuel handling facilities, pump rooms, and chemical processing plants.

Unlike infrared detection, catalytic measurement depends on the oxidation of combustible gas at the sensing element. Therefore, environmental conditions can directly affect sensor performance.

11.1 Oxygen availability

The catalytic reaction requires sufficient oxygen to oxidize the target combustible gas. An oxygen-deficient environment can cause inaccurate or unreliable measurements.

Honeywell’s MPD operating guidance identifies approximately 15% oxygen as sufficient for most combustible gases. However, engineers must follow the actual sensor documentation and application requirements.

Do not install a catalytic detector where the process routinely operates under insufficient oxygen conditions without a suitable alternative measurement strategy.

11.2 Catalyst poisoning and contamination

Some contaminants can reduce the sensitivity of catalytic sensing elements. Silicone compounds present a particular concern during installation and maintenance.

Other potential contaminants include certain sulfur compounds, halogenated hydrocarbons, and heavy-metal compounds. Their effects depend on exposure concentration and duration.

Maintenance teams should therefore control the use of silicone-based sealants, lubricants, and cleaning products near the detector. They should also prevent oil and dirt from blocking the sensing element’s sintered disc.

11.3 Gas selection and calibration

Choose calibration gas according to the target combustible gas and Honeywell’s specified procedure. Different combustible gases can produce different catalytic responses.

Do not assume that calibration with methane guarantees accurate propane or hydrogen measurements. Confirm the required gas selection, correction factors, and calibration equipment.

12. Calibration and Maintenance: Different Requirements for Different Sensors

Calibration verifies that the detector produces an appropriate response to a known gas concentration. It also helps maintenance teams identify sensitivity changes and abnormal sensor behavior.

However, FHIC1 and FNCB1 require different calibration gases and procedures. Their sensing technologies cannot share an assumed calibration routine.

12.1 FHIC1 calibration considerations

Use a suitable CO2 reference gas within the manufacturer’s specified calibration range. Confirm the correct gas concentration, flow arrangement, and calibration accessories.

Before calibration, inspect the sensing inlet and surrounding installation. Check for moisture, dirt, mechanical damage, and environmental conditions that may affect the measurement.

Allow the detector to stabilize according to the applicable instructions. Then perform zero and span checks using the approved procedure.

Record the calibration results, gas concentration, equipment identification, and any adjustments. Compare the results with previous maintenance records to identify changes in sensor performance.

12.2 FNCB1 calibration considerations

Use the specified combustible calibration gas and verify the detector’s configured gas selection. Follow the manufacturer’s recommended calibration range and gas application method.

Inspect the catalytic sensor for contamination or physical damage. Review the detector’s operating environment for possible catalyst poisoning.

Perform zero and span calibration according to the approved instructions. If the sensor cannot achieve an acceptable response, investigate poisoning or sensor deterioration.

Do not increase calibration adjustments repeatedly to compensate for a potentially poisoned sensing element. Such actions may conceal a genuine sensor problem.

12.3 Functional testing and maintenance records

Calibration alone does not replace periodic functional testing. A bump test can confirm that the sensor responds to the target gas under the prescribed test conditions.

Honeywell recommends regular bump testing and maintenance according to the applicable detector manual. The site safety program should define suitable test intervals and documentation requirements.

Maintenance records should include:

• Detector model and complete part number.
• Sensor cartridge identification.
• Calibration gas type and concentration.
• Zero and span results.
• Functional test results.
• Fault messages and maintenance actions.
• Sensor replacement date and reason.
• Relevant changes to the process environment.

Consistent records help engineers identify deteriorating performance before the detector becomes unavailable during a critical event.

13. Can FHIC1 and FNCB1 Directly Replace Each Other?

No. These configurations do not provide equivalent gas detection functions.

FHIC1 measures carbon dioxide through an infrared sensor. FNCB1 measures combustible gases through a catalytic bead sensor.

Changing between these models changes the target gas, sensing technology, measuring range, and calibration requirements. It may also change the local maintenance connection.

For example, replacing FHIC1 with FNCB1 would remove the original CO2 measurement function. The replacement would not provide the same process safety information.

Replacing FNCB1 with FHIC1 would create the opposite problem. The new instrument would not provide the original catalytic combustible gas detection function.

Even when the transmitter platform and communication option appear similar, the replacement must preserve the original safety function. Engineers should verify the detector’s approved sensor configuration before installation.

For safety-related gas detection systems, an undocumented field conversion is not an acceptable substitute for an approved engineering review.

14. Can FNCB1 Be Converted into FHIC1 by Changing the Sensor Cartridge?

Engineers should not assume that changing the MPD cartridge alone creates an approved FHIC1 configuration.

The two configurations differ in their factory-selected sensor type and local HART option. The complete transmitter arrangement must match the intended application.

A proposed conversion would require a technical review of several items:

• Compatibility of the mV personality board.
• Correct MPD sensor cartridge and electrical interface.
• Required local HART hardware configuration.
• Transmitter firmware and sensor recognition settings.
• Measurement units, range, and alarm configuration.
• Electrical installation and communication wiring.
• Hazardous-area certification and approval conditions.
• Calibration and commissioning requirements.

Honeywell’s MPD documentation requires replacement cartridges to match the original factory-configured sensor type. Substituting a different sensor type can invalidate the applicable agency certification.

Therefore, purchasing the correct factory-configured transmitter is generally the more reliable replacement strategy. Any proposed conversion requires explicit manufacturer approval and a documented assessment of the complete installation.

15. Industrial Application Scenarios: Selecting the Correct XNX Configuration

The correct model depends on the gas hazard rather than the transmitter enclosure. Engineers should begin with the process hazard assessment and required measurement function.

Scenario A: Beverage production and CO2 storage

A beverage facility stores and distributes carbon dioxide for carbonation and production processes. A leak can create an oxygen displacement hazard in enclosed areas.

The FHIC1 configuration supports CO2 monitoring within its specified measurement range. Engineers should assess detector placement around storage vessels, transfer lines, filling areas, and potential accumulation points.

Alarm settings should follow the facility’s hazard assessment and applicable occupational safety requirements. The detector should also connect to the appropriate ventilation or safety response system.

Scenario B: Natural gas compressor station

A compressor station handles combustible gas under pressure. Leaks around seals, flanges, valves, and pipe connections can create an explosive atmosphere.

The FNCB1 configuration supports catalytic combustible gas detection. Engineers must verify oxygen availability, target gas compatibility, calibration requirements, and potential catalyst contaminants.

Detector placement should consider ventilation, release locations, gas dispersion, and the station’s hazardous-area classification.

Scenario C: Chemical processing facility

A chemical facility may require both CO2 monitoring and combustible gas detection. These functions address different hazards and should use suitable sensor technologies.

Engineers should evaluate each detection point independently. They should not substitute one sensor configuration merely because the same transmitter family supports both technologies.

The control system should also distinguish the measurement units and alarm thresholds for each gas. This prevents incorrect interpretation of process data and safety alarms.

Scenario D: Existing gas detection system replacement

A maintenance team may need to replace a failed XNX transmitter during a planned shutdown. The original equipment may have been installed many years earlier.

The team should photograph the nameplate and record the complete order number. It should also identify the sensor cartridge, communication options, and current control-system connections.

After selecting the replacement, engineers should verify the approved configuration and complete the required calibration and functional tests. They should confirm alarm transmission and control-system response before restoring normal operation.

16. Industry Safety Context: Why Correct Gas Detection Selection Matters

Industrial gas detection forms part of a wider occupational safety strategy. Accurate measurement helps facilities identify hazardous atmospheres and initiate appropriate protective actions.

The International Labour Organization estimated approximately 2.93 million work-related deaths annually. Its estimates also identified around 395 million non-fatal work injuries worldwide.

These figures cover occupational accidents and diseases across industries. They do not represent gas detector failures or incidents caused specifically by combustible gas releases.

Nevertheless, they demonstrate the wider importance of effective workplace safety management. Reliable detection equipment supports that objective when engineers select, install, test, and maintain it correctly.

For industrial gas detection projects, equipment selection should follow a documented hazard assessment. Engineers should also consider relevant standards and local regulations.

IEC 60079-14 provides requirements for electrical installations in explosive atmospheres. The applicable IEC 60079-29 series addresses combustible gas detection equipment and performance requirements.

Always check the specific detector approval and applicable standard edition. A transmitter’s general certification does not automatically establish suitability for every gas, installation, or safety function.

17. Practical Replacement Checklist for Procurement and Maintenance Teams

Before ordering an XNX replacement, collect the information needed to identify the complete original configuration. This step reduces the risk of receiving equipment with an unsuitable sensing or communication arrangement.

Use the following checklist during purchasing and maintenance planning.

• Model identification: Record the complete XNX transmitter part number.
• Sensor technology: Confirm infrared CO2 or catalytic combustible gas detection.
• MPD cartridge: Verify IC1 or CB1 and the applicable cartridge reference.
• Measurement range: Confirm 0–5% vol CO2 or 0–100% LEL combustible gas.
• Personality: Verify the mV configuration.
• Local HART: Confirm whether the installation requires the H option.
• Fieldbus: Verify the FOUNDATION Fieldbus configuration and host compatibility.
• Power supply: Check the actual electrical requirements and terminal arrangement.
• Mechanical details: Verify enclosure, threads, entries, mounting, and accessories.
• Certifications: Confirm approvals for the specific sensor and transmitter combination.
• Calibration: Identify the correct reference gas and approved calibration method.
• Commissioning: Plan alarm testing, signal verification, and control-system checks.

For critical installations, procurement should involve both instrumentation engineering and process safety personnel. Their review helps ensure that the replacement preserves the original detection function.

18. Frequently Asked Questions

FAQ 1: If the transmitter powers up normally after a sensor replacement, does that confirm correct compatibility?

No. A successful startup does not prove that the replacement sensor provides the correct measurement function or certification.

Engineers should verify the sensor identification, configured gas type, measuring range, and applicable approvals. They should also complete calibration and functional testing using the specified reference gas.

For example, an infrared CO2 cartridge and a catalytic combustible gas cartridge may use the same broad transmitter platform. However, they cannot provide equivalent process measurements.

FAQ 2: What should technicians do when a combustible gas detector gives unstable readings after calibration?

First, verify the calibration gas, regulator, flow rate, and gas application method. Then inspect the sensor inlet for contamination and review possible exposure to silicone or sulfur-containing compounds.

Also check oxygen availability and environmental conditions. Catalytic sensors require sufficient oxygen for the oxidation reaction, and contamination can reduce sensitivity.

If the detector cannot achieve a stable response, follow the manufacturer’s troubleshooting procedure. Replace the sensor only after confirming the cause and selecting the correct approved cartridge.

FAQ 3: How should an engineering team manage a replacement when the original local HART interface is unavailable?

First, confirm whether the original maintenance procedure actually requires direct local access. Some installations use HART communication through the main current loop or another supported system connection.

Compare the ordered communication options and wiring diagrams before selecting a replacement. If local HART is essential, specify the correct H option and verify its associated hardware.

Do not treat standard HART-over-4–20 mA communication as an automatic substitute for a dedicated local connection. Confirm communicator access, hazardous-area requirements, and commissioning procedures before installation.

19. Final Engineering Recommendation: Choose by Gas Hazard, Sensor Technology, and Communication Requirements

The Honeywell XNX-AMAV-FHIC1 and XNX-AMAV-FNCB1 share the XNX Universal Transmitter platform. However, they serve different industrial gas detection applications.

FHIC1 uses an MPD infrared CO2 configuration with a nominal range of 0–5% volume. It also includes the optional local HART interface.

FNCB1 uses an MPD catalytic bead configuration with a nominal range of 0–100% LEL. Its ordering code does not include the dedicated local HART option.

Both references include the FOUNDATION Fieldbus option and use the mV sensor personality. Nevertheless, their sensing elements and calibration requirements remain different.

For replacement projects, engineers should prioritize the original gas detection function and approved sensor configuration. They should then verify communication hardware, mechanical compatibility, electrical requirements, and certification details.

Our engineering recommendation is straightforward: select FHIC1 for the specified infrared CO2 application and FNCB1 for the specified catalytic combustible gas application. Never choose between them based only on transmitter appearance or a shared model prefix.

Correct identification and documented commissioning help maintain reliable industrial gas detection. They also reduce the risk of introducing an unsuitable measurement configuration into an existing safety system.