Tag: Honeywell XNX Spare Parts

XNX-AMAV-RHIC1: Can the Relay Board and FOUNDATION Fieldbus Module Be Installed Together?

The Honeywell XNX Universal Transmitter supports several optional communication interfaces. However, these options have specific hardware compatibility restrictions.

A common question concerns the XNX-AMAV-RHIC1 configuration. Can engineers install a Relay Board and a FOUNDATION Fieldbus Module simultaneously?

Engineering conclusion: No. Honeywell does not support simultaneous installation of these two optional interface modules.

According to the Honeywell XNX Universal Transmitter Technical Manual Rev.19, the Relay, Modbus, and FOUNDATION Fieldbus interfaces are mutually exclusive.

This restriction applies to the optional communication interface architecture. An available internal space or connector does not automatically support additional functionality.

Before upgrading an XNX transmitter, engineers should verify its POD configuration, Personality Board, hardware revision, and approved option combination.

1. Core Functionality: Understanding XNX Communication Compatibility

1.1 Why Are the Relay and FOUNDATION Fieldbus Modules Mutually Exclusive?

The XNX Universal Transmitter provides three optional interface configurations:

• Relay Module: Provides hardwired alarm and fault contacts.
• Modbus Module: Supports Modbus RTU communication through an RS-485 interface.
• FOUNDATION Fieldbus Module: Provides digital communication through an H1 network.

Honeywell specifies that users can install only one of these three optional interfaces.

Therefore, installing a FOUNDATION Fieldbus Module alongside an existing Relay Board is not a supported configuration.

The restriction concerns the transmitter’s internal interface architecture. It is not simply a limitation of physical installation space.

Engineers should distinguish between mechanical installation and functional compatibility. A board that physically fits may still lack supported electrical connections or software recognition.

1.2 How Do These Options Affect Industrial Control Systems?

Each interface serves a different purpose in industrial automation.

For example, a chemical plant may require independent hardwired alarm signals.

In this situation, the Relay Module provides direct contact outputs to the PLC or alarm system.

However, a facility using FOUNDATION Fieldbus instrumentation may prefer digital communication.

The FF interface allows the control system to receive measurement values and supported device information.

Engineering recommendation: Select the interface according to the plant’s control architecture. Do not choose a communication module based only on available internal space.

2. Technical Insights: Relay and FOUNDATION Fieldbus Specifications

2.1 XNX Relay Board: Three Independent SPDT Outputs

The XNX Relay Module provides three Form C relay contacts.

These contacts support two alarm levels and one fault indication.

The three relays serve different operational purposes:

• Alarm 1: Indicates the first configured gas alarm condition.
• Alarm 2: Indicates the second configured gas alarm condition.
• Fault: Reports transmitter faults and designated abnormal conditions.

The contact ratings must be interpreted according to the specified load conditions.

Engineers should not assume that inductive loads can use the same ratings as resistive loads.

Production significance

The Relay Board provides a direct interface to external control circuits.

This arrangement supports local alarm annunciation and hardwired PLC input monitoring.

It also allows certain alarm functions to operate without depending on continuous digital network communication.

However, relay contacts do not replace a certified SIS logic solver or safety-rated final element.

2.2 FOUNDATION Fieldbus Module: H1 Digital Communication

The XNX FOUNDATION Fieldbus option uses the H1 physical layer.

It supports a communication speed of 31.25 kbit/s using Manchester encoding.

Key technical characteristics include:

• Communication protocol: FOUNDATION Fieldbus H1.
• Physical layer: H1.
• Communication speed: 31.25 kbit/s.
• Signal connections: Signal positive, signal negative, and screen.
• Typical application: Digital field instrumentation networks.

The module allows compatible control systems to receive measurement and device information.

This information can support centralized monitoring, equipment diagnostics, and maintenance activities.

Production significance

FOUNDATION Fieldbus provides more diagnostic information than a basic hardwired alarm contact.

Maintenance engineers can access supported device information through the control system.

This can improve fault investigation and reduce unnecessary field inspections.

However, communication availability does not guarantee that every diagnostic parameter is accessible.

The DCS configuration and device description files must also support the installed transmitter.

Engineers should follow the dedicated Honeywell FOUNDATION Fieldbus installation documentation for power supply, wiring, grounding, and network configuration.

2.3 XNX POD Architecture and Option Board Compatibility

The XNX transmitter uses a modular internal assembly called the POD.

POD refers to the Personality, Options, and Display assembly.

However, its internal architecture does not function like a universal expansion rack.

Different circuit boards perform specific functions.

The Personality Board provides the sensor interface and determines the supported sensor configuration.

The optional communication circuit board provides the selected external interface.

These boards connect through designated internal connectors.

Therefore, engineers must check more than the board dimensions and pin arrangement before purchasing replacement parts.

The following information is particularly important:

1. Existing POD hardware revision.
2. Installed sensor Personality Board.
3. Current communication option.
4. Replacement board part number.
5. Applicable hardware and software configuration.
6. Product certification and approved installation requirements.

Honeywell’s Rev.19 manual identifies the three communication options as mutually exclusive.

This is the primary technical reason why a Relay Board and FOUNDATION Fieldbus Module cannot operate together.

3. Installation and Maintenance: Practical Engineering Considerations

3.1 Do Not Attempt to Stack Two Optional Interface Boards

A common mistake during field upgrades is assuming that an unused internal position can accommodate another communication board.

For example, an existing XNX transmitter may use a Relay Module.

A project engineer may later request FOUNDATION Fieldbus connectivity.

Adding another board without checking the supported configuration can create installation and commissioning problems.

A safer replacement procedure includes the following steps:

1. Record the complete transmitter model and serial number.
2. Identify the existing POD and Personality Board.
3. Confirm the currently installed communication option.
4. Check whether the plant can remove the hardwired relay function.
5. Verify the replacement FF module against Honeywell documentation.
6. Complete installation according to the approved procedure.
7. Perform communication and alarm function tests.

Do not force an additional board into an unsupported position.

For equipment installed in hazardous areas, follow the applicable isolation and permit procedures.

Only qualified personnel should perform internal maintenance.

3.2 Verify DCS Communication After Installing the FF Module

Replacing a Relay Board with a FOUNDATION Fieldbus Module changes the transmitter’s interface architecture.

Therefore, checking the local LCD display is not sufficient.

Commissioning engineers should verify the following items:

• Correct H1 signal wiring and polarity.
• Proper fieldbus network connection.
• Correct device identification and addressing.
• Successful device recognition by the DCS.
• Stable gas measurement updates.
• Correct alarm and fault status transmission.
• Proper device diagnostics.
• Compliance with the specified power supply requirements.

The DCS must also use compatible device descriptions and configuration settings.

A successful network connection does not automatically confirm that every process variable and alarm parameter works correctly.

3.3 Review Alarm and Interlock Logic Before Replacing the Board

This is one of the most important considerations during an industrial retrofit.

Suppose an existing XNX transmitter sends Alarm 1 and Alarm 2 signals directly to PLC digital inputs.

The plant then replaces the Relay Module with an FF interface.

The original hardwired alarm paths are no longer available through those relay contacts.

Therefore, engineers must review the entire alarm transmission architecture.

Consider these questions:

• Does the DCS receive the required alarm information?
• Does the existing PLC logic depend on hardwired contacts?
• Does the safety system require independent fault indication?
• Are communication failures handled correctly?
• Does the revised design meet the plant’s safety requirements?

Do not transfer an existing safety function to a communication network without an approved engineering assessment.

3.4 Recommended Maintenance Procedure

Before replacing any internal option board, complete these checks:

• Isolate the equipment according to site procedures.
• Confirm hazardous-area maintenance requirements.
• Record the original configuration and parameter settings.
• Photograph the existing board and terminal connections.
• Verify the replacement part number.
• Inspect wiring, grounding, seals, and enclosure condition.
• Restore power according to the approved procedure.
• Perform functional testing and document the results.

A transmitter that powers up successfully is not necessarily fully commissioned.

Always verify the actual measurement, alarm, fault, and communication functions.

4. Practical Application: Choosing the Right XNX Interface

The following examples illustrate how interface selection affects industrial control system design.

Scenario A: Chemical Plant Using Hardwired PLC Alarms

The existing PLC receives gas alarm signals through digital inputs.

The plant requires independent Alarm 1, Alarm 2, and fault contacts.

In this case, the Relay Module is the appropriate interface choice.

Replacing it with FF requires a review of the existing alarm architecture.

Scenario B: Oil and Gas Facility Using FOUNDATION Fieldbus

The facility uses an H1 fieldbus network for compatible field instruments.

The DCS requires gas measurement values and supported transmitter diagnostics.

In this case, the FOUNDATION Fieldbus option may be more suitable.

However, the project must confirm network compatibility and the required independent power arrangements.

Scenario C: Existing Installation Requiring Both Digital Monitoring and Independent Alarms

The plant wants digital instrument monitoring while retaining independent hardwired alarm signals.

The XNX transmitter cannot provide both functions through simultaneous Relay and FF option boards.

The engineering team should consider an alternative system architecture.

Possible approaches include:

• Using a separate compatible hardwired alarm interface.
• Providing an independent gas detection channel where the design requires it.
• Reviewing the PLC/DCS input architecture.
• Selecting another approved transmitter configuration.

Any alternative must satisfy the plant’s functional safety and certification requirements.

5. Frequently Asked Questions

Q1: Can I Replace the XNX Relay Board with a FOUNDATION Fieldbus Module Without Changing the Sensor?

Not necessarily. The communication option and sensor interface perform different functions.

However, that does not guarantee compatibility with every Personality Board revision.

Before ordering, compare the existing POD configuration with the replacement module requirements.

Also confirm the sensor type, transmitter revision, and applicable product certification.

A board replacement should not proceed based only on similar connectors or dimensions.

Q2: Will the Standard 4–20 mA Output Remain Available After Installing the FOUNDATION Fieldbus Option?

Do not assume that every XNX configuration provides identical analog and digital outputs.

The transmitter’s analog output architecture depends on its selected Personality Board and hardware configuration.

The optional communication interface also affects available diagnostic behavior.

In particular, Honeywell documents differences in open-loop fault detection for certain communication configurations.

Before purchasing an FF module, confirm the required 4–20 mA functionality against the exact transmitter configuration.

This is especially important when the DCS expects both analog gas measurement and digital diagnostics.

Q3: What Should I Check If the New FF Module Is Installed but the DCS Cannot Identify the Transmitter?

Start with the fieldbus installation rather than immediately replacing the communication board.

Check the following items:

1. Verify the H1 signal connections.
2. Check the network power supply and segment condition.
3. Confirm the device address and network configuration.
4. Check the device description and DCS compatibility.
5. Inspect the module connections inside the POD.
6. Review the transmitter’s configuration and diagnostic status.

If the DCS still cannot recognize the device, compare the installed module revision with the approved XNX configuration.

Do not assume that an unidentified device indicates a defective communication board.

6. Engineering Conclusion: XNX Relay and FOUNDATION Fieldbus Compatibility

The Honeywell XNX Universal Transmitter supports Relay, Modbus, and FOUNDATION Fieldbus as alternative optional interface configurations.

These three options cannot operate together through simultaneous installation.

The last two combinations require verification against the exact transmitter configuration.

The presence of an analog output terminal does not establish that every operating mode and diagnostic function remains available.

Final engineering recommendation

If your XNX-AMAV-RHIC1 currently uses a Relay Board and the project requires FOUNDATION Fieldbus, treat the upgrade as an interface replacement.

Do not purchase a second option board simply to install it alongside the existing module.

Before ordering, provide the following information:

• Complete transmitter nameplate photograph.
• Serial number and hardware revision.
• Photograph of the installed POD.
• Existing communication board part number.
• Sensor Personality Board identification.
• Required DCS communication and alarm functions.

These details help verify the correct replacement module and reduce compatibility risks during field maintenance.