Honeywell XNX-AMAV-RNCB1 Relay Board Specifications

Honeywell XNX-AMAV-RNCB1 Relay Board Specifications: Understanding the CB1 Code

The Honeywell XNX-AMAV-RNCB1 is a configurable gas transmitter for industrial gas detection applications. It combines a millivolt sensor interface with an optional relay board and an MPD-CB1 catalytic bead sensor configuration.

However, its model number contains several configuration codes that buyers must interpret correctly. The most important distinction concerns the R and CB1 identifiers.

R identifies the relay option, while CB1 identifies the MPD-CB1 catalytic bead sensor configuration. CB1 does not describe the relay board or its electrical ratings.

This distinction matters when purchasing replacement components or configuring gas detection systems. Incorrect interpretation can lead to incompatible parts, unnecessary replacement costs, and commissioning delays.

1. XNX-AMAV-RNCB1 Model Number Breakdown

Honeywell uses a structured product coding system to identify XNX transmitter configurations. Each section describes a particular hardware, interface, or sensor option.

Two codes deserve particular attention during procurement:

• R: Identifies the XNX relay interface option.
• CB1: Identifies the MPD-CB1 catalytic bead sensor configuration.
• N: Indicates that the separate Local HART option is not installed.

Therefore, buyers searching for a replacement relay board should specify the XNX Relay Option Board. They should not use CB1 as the relay board identification.

Always verify the complete transmitter configuration and applicable hardware revision before ordering replacement components.

2. Honeywell XNX Relay Board Specifications

The XNX Relay Option Board provides three Form C contacts for alarm and fault indication. Each relay uses a single-pole double-throw configuration, commonly called SPDT.

Each contact group provides three connection points:

• NO (Normally Open): The contact remains open in its normal de-energized condition.
• NC (Normally Closed): The contact remains closed in its normal de-energized condition.
• C (Common): The shared switching terminal connects to either NO or NC.

Honeywell specifies the following relay contact ratings in its installation documentation:

These ratings describe specified contact limits. They do not guarantee identical switching performance across every load type.

Inductive loads, such as solenoid coils and contactors, can generate switching surges. Check the applicable load ratings and suppression requirements before connecting them directly.

For demanding loads, an appropriately rated interposing relay can provide additional electrical separation and protection.

3. Understanding the Three XNX Relay Functions

The three relays perform different monitoring functions. They provide separate signals for gas alarms and transmitter faults.

Relay 1: Level 1 Gas Alarm

Relay 1 responds when the measured gas concentration reaches its configured first alarm threshold. Engineers can connect this signal to a PLC digital input or external alarm circuit.

Typical applications include preliminary warnings, operator notifications, and ventilation activation. The actual response depends on the site's approved alarm philosophy.

Relay 2: Level 2 Gas Alarm

Relay 2 responds when the gas concentration reaches the configured second alarm threshold. This output supports more advanced alarm and response functions.

For example, a plant may use this signal for additional audible alarms or predefined equipment shutdown logic. However, the final action must follow the approved Cause and Effect matrix.

Relay 3: Fault and Special Status

Relay 3 reports transmitter faults and designated special operating conditions. Honeywell recommends using this output for equipment fault monitoring.

Connecting this signal to the DCS allows operators to distinguish equipment problems from actual gas concentration alarms. This distinction improves fault visibility and maintenance response.

My recommendation is to connect the Fault Relay to a dedicated PLC or DCS diagnostic point. This prevents maintenance faults from remaining unnoticed during normal operation.

4. XNX Relay Board TB3 and TB4 Terminal Wiring

Correct terminal identification is essential when installing or replacing an XNX relay board. Never rely exclusively on existing wire colors or handwritten terminal labels.

Honeywell assigns TB3 to the three relay contact groups. TB4 provides the remote reset connection.

How does this arrangement benefit industrial control systems?

Separate contacts allow engineers to distribute different alarm signals to independent control circuits. A typical arrangement uses three dedicated PLC or DCS inputs.

• Level 1 connects to the preliminary alarm input.
• Level 2 connects to the high-level alarm input.
• Fault connects to the transmitter diagnostic input.

TB4 supports remote resetting through a momentary switch. A momentary closure between its two terminals performs the corresponding remote reset function.

However, remote reset does not replace the need to identify and correct the original fault. Follow the approved operating procedure before resetting alarms or faults.

5. MPD-CB1 Catalytic Bead Sensor: Measurement Range and Application

The CB1 suffix identifies the MPD-CB1 catalytic bead sensor configuration. This sensor detects combustible gas concentrations and supports %LEL measurements.

The nominal measurement range is 0–100% LEL. The transmitter processes the sensor signal and provides the configured measurement and alarm functions.

Catalytic bead technology detects combustible gases through a controlled oxidation reaction. The sensing element responds to combustible gas concentrations within its designed operating range.

This technology supports applications in refineries, gas processing facilities, chemical plants, and other hazardous industrial areas.

However, correct gas selection and calibration remain essential. Different combustible gases have different lower explosive limits and sensor response characteristics.

• Confirm the target gas before selecting calibration parameters.
• Verify the approved gas calibration procedure.
• Check sensor condition and environmental operating limits.
• Use suitable certified calibration equipment and test gas.
• Follow Honeywell recommendations for inspection and sensor replacement.

Do not assume that two identical sensor models automatically have identical calibration requirements. Verify the target gas and configuration against the applicable Honeywell documentation.

6. Installing or Replacing the XNX Relay Option Board

Replacing an XNX relay board requires electrical isolation and proper electrostatic discharge protection. The procedure involves accessing the transmitter POD and its internal option-board connections.

Follow these general preparation steps before installation:

1. Obtain the approved maintenance procedure and verify the replacement part.
2. Isolate the XNX transmitter power supply.
3. Disconnect externally supplied power from TB3 at its source.
4. Confirm that all relevant circuits are electrically safe.
5. Apply suitable ESD precautions before handling electronic components.
6. Remove the transmitter cover and carefully extract the POD.
7. Install the relay board with its connector pins correctly aligned.
8. Reassemble the POD and restore the wiring according to the drawings.

One important detail deserves special attention: the relay contacts may receive power from an external source. Switching off the transmitter alone does not guarantee that TB3 has no voltage.

Always isolate external circuits before servicing the relay board. Follow the hazardous-area certification and installation requirements for the actual site.

7. Troubleshooting Fault 152 After Relay Board Installation

Some technicians encounter Fault 152 after installing a new XNX option board. This alarm does not automatically mean that the replacement relay board has failed.

Fault 152 indicates an option module configuration error. The transmitter may need to recognize and accept the newly installed option.

Honeywell's Relay Board Installation Guide describes the option recognition procedure.

Recommended configuration procedure:

1. Allow the transmitter to complete its startup sequence.
2. Open the Information Menu.
3. Navigate to Transmitter Data.
4. Open the Option Revision screen.
5. Select the newly detected relay option.
6. Choose Accept New Option using the front-panel magnetic interface.
7. Confirm that the transmitter updates its option configuration.
8. Verify the transmitter status and relay operation.

If Fault 152 remains, inspect the board installation and connector alignment. Also confirm the correct option-board type and consult the applicable technical manual.

Do not repeatedly reset the transmitter without investigating the option recognition problem.

8. Testing the XNX Relay Outputs Before Commissioning

After installation, engineers should verify both local relay operation and external signal transmission. A normal display does not independently prove that every contact works correctly.

Use the approved XNX test procedure and available Force Relays function to check the outputs.

Recommended verification sequence:

• Inspect TB3 wiring and confirm every NO, NC, and Common connection.
• Verify the external circuit supply and electrical protection.
• Test the Level 1 relay response.
• Test the Level 2 relay response.
• Test the Fault Relay response.
• Verify the corresponding PLC or DCS input indications.
• Check the TB4 remote reset function.
• Restore normal operating conditions and document the results.

Relay forcing should only occur under an approved test plan. Notify affected operators and temporarily manage any bypassed alarm or interlock functions.

For safety-related applications, complete the required functional testing according to the project's safety procedures.

9. Relay Option Compatibility: Relay, Modbus, and Foundation Fieldbus

The XNX transmitter supports several optional communication interfaces. However, the relay, Modbus, and Foundation Fieldbus option boards cannot operate together as interchangeable simultaneous POD options.

Honeywell documentation identifies these options as mutually exclusive. Therefore, engineers must select the required interface during equipment configuration.

If a plant requires digital communication instead of hardwired relay signals, review the complete transmitter configuration. Do not assume that installing another interface board will preserve the original relay functionality.

For existing installations, check the actual system architecture before changing the interface option. Consider PLC or DCS compatibility, wiring modifications, commissioning requirements, and operational downtime.

10. Practical Application: Connecting XNX Relays to a PLC or DCS

Consider a refinery with several XNX gas transmitters distributed across process areas. The control system needs separate indications for low-level alarms, high-level alarms, and transmitter faults.

The three XNX relay outputs can provide independent hardwired signals to the control system. Engineers can assign each signal to a dedicated digital input.

For example:

• Level 1 triggers an operator warning and preliminary response.
• Level 2 initiates the approved higher-level alarm sequence.
• Fault identifies a transmitter diagnostic or special operating condition.

The final control actions must follow the site's Cause and Effect documentation. A relay contact alone does not establish a complete safety instrumented function.

Engineers should also consider contact supervision, cable integrity, input-card compatibility, and the control system's fault detection strategy.

11. Engineer's Insight: Avoid Confusing Sensor Codes with Interface Options

Product coding errors can create unnecessary procurement problems in industrial gas detection projects. The XNX-AMAV-RNCB1 provides a useful example.

Buyers sometimes focus on the CB1 suffix when searching for relay board replacements. However, CB1 identifies the catalytic bead sensor configuration, not the relay interface.

The R code identifies the relay option. This distinction should guide spare-part identification and compatibility checks.

My recommendation is to verify three items before placing an order: the complete transmitter configuration, the required option-board type, and the applicable hardware revision.

For critical gas detection systems, also verify certification requirements and the sensor's target gas compatibility. A physically similar replacement does not automatically meet the original application's technical requirements.

12. Frequently Asked Questions

Q1: Can the XNX-AMAV-RNCB1 relay board be replaced with a Modbus or Foundation Fieldbus board?

A: These interfaces are mutually exclusive XNX option configurations. A replacement requires an assessment of the complete transmitter configuration and control-system requirements. Modbus or Foundation Fieldbus cannot simply be added alongside the existing relay option as another simultaneous POD interface.

Q2: Can any Honeywell XNX relay board replace the original board?

A: Do not assume universal compatibility across every hardware revision or transmitter configuration. Verify the XNX-specific option board, connector arrangement, transmitter revision, and applicable installation documentation. For a critical installation, select a replacement that matches the original configuration.

Q3: What should engineers check when the relay outputs fail after board replacement?

A: Start with external power, TB3 wiring, terminal identification, and the option recognition status. Check Fault 152 and complete the Accept New Option procedure when required. Then use the approved Force Relays test to verify each contact and its corresponding PLC or DCS input.

13. Procurement Checklist for Honeywell XNX-AMAV-RNCB1

Purchasing teams should verify the following specifications before ordering a complete transmitter or replacement option board.

Important purchasing recommendations:

• Confirm whether you need a complete transmitter or an individual relay option board.
• Request the full model number and hardware revision.
• Verify the required hazardous-area certifications.
• Confirm the sensor type and target gas application.
• Check relay interface compatibility before ordering.
• Request supporting technical documentation for replacement verification.

Conclusion

The Honeywell XNX-AMAV-RNCB1 combines a millivolt sensor personality, relay interface, and MPD-CB1 catalytic bead sensor configuration.

The R code identifies the relay option, while CB1 identifies the combustible gas sensor configuration. This distinction prevents common procurement and replacement errors.

The relay board provides three SPDT contacts for Level 1, Level 2, and Fault indications. Its specified contact ratings are 250 VAC at 5 A and 24 VDC at 5 A.

Before installation, verify TB3 and TB4 wiring, external power isolation, and option-board recognition. After installation, test every relay and confirm the corresponding control-system inputs.

Accurate model identification and systematic commissioning help maintain dependable gas detection and industrial safety monitoring.