XNX Gas Detector Calibration and Testing

First of all, we will look at the calibration procedure and after that, we will go through testing so that you can understand everything easily.

Basics of XNX Gas Detector Calibration

Before going into the specific calibration procedures, it’s important to understand the basics of calibrating an XNX gas detector.

What is Calibration?

Calibration is the process of adjusting the readout of a gas detector to match a known concentration of test gas. It establishes a baseline reference point to ensure the accuracy of measurements. Calibrations account for sensor drift over time.

Why is Calibration Important?

Frequent calibrations are critical for occupational safety, especially in potentially hazardous environments. Calibrations ensure the gas detector is providing accurate readings and can properly activate alarm setpoints if a dangerous gas leak or exposure occurs.

Types of Calibration

There are two main types of calibration performed on XNX gas detectors:

Zero Calibration

Sets the baseline reference with a zero-gas that has no traces of the target gas. This accounts for any inherent background electrical noise in the sensor.

Span Calibration

Exposes the sensor to a gas concentration at a known alarm setpoint level, usually the sensor’s full measurement range. This verifies and adjusts accuracy across the sensor’s detection band.

Most sensors require both zero and span calibration. Oxygen sensors only require a span calibration.

Calibration Equipment

Proper calibration requires the following equipment:

1. Certified calibration gas cylinder with an analytically verified concentration at or near the sensor detection range.
2. Fixed flow regulator with reproducible flow rate around 300-375 mL/min.
3. Teflon tubing to connect the regulator to the detector with minimal gas absorption.
4. Calibration adapter to interface tubing with specific XNX detector housing.

Frequency of Calibration

The recommended calibration frequency varies by sensor type, but at minimum follow these guidelines:

1. Toxic Gas Sensors – Calibrate every 6 months
2. Oxygen Sensors – Calibrate every 12 months
3. Combustible Gas Sensors – Calibrate every 3 months

It’s also good practice to calibrate after any sensor replacement, prolonged exposure to target gas, or major environmental changes, and before performing a bump test.

XNX Universal Gas Transmitter Calibration Procedure

Calibrating the versatile XNX fixed gas detector follows a standardized procedure outlined in the detector’s operating manual. Here is an overview of the step-by-step calibration process:

1. Connect the flow housing outlet tubing to the sensor housing. For remote sensors, attach tubing to the auxiliary calibration adapter.
2. Access the calibration menu on the XNX detector’s touchscreen interface.
3. For zero calibration, apply zero gas to the sensor and allow the signal to stabilize. Initiate calibration through the menu once stabilized.
4. For span calibration, enter the span gas concentration into the detector interface. Apply span gas and initiate calibration once the signal is stabilized.
5. If calibration passes, the detector will display a “Passed” message. If calibration fails, a “Failed” message will appear and you must repeat the process.

The minimum total calibration time is around 10-15 minutes, including 5 minutes of gas exposure and stabilization time per calibration stage. Be sure to use dry, VOC-free air as your zero gas.

Special Calibration Considerations by Sensor Type

While the overall XNX calibration procedure remains constant, certain sensor types require additional provisions:

Combustible Gas Sensors

• Must use methane-in-air calibration gas certified to 50% LEL concentration.
• Combustible sensors are susceptible to poisons which may affect sensitivity over time.

Toxic Gas Sensors

• Each toxic gas sensor has an optimal calibration gas concentration near its detection range.
• Humidity can impact readings for sensors like hydrogen sulfide. Use dry-span gas.
• For sticky gases like hydrogen chloride, use minimal tubing lengths with mostly Teflon construction.

Oxygen Sensors

• Do not require a zero calibration. Can use ambient clean air (20.9% O2) for span procedure.
• Avoid oxygen-deficient environments under 6% v/v O2 concentration.

After finishing calibration, be sure to properly store and re-certify calibration gases at regular 6-month intervals. Always cautiously vent calibration gases to a safe location.

Functional Bump Testing XNX Gas Detectors

Along with periodic calibrations, functional “bump tests” add another layer of confirmation that the XNX detector can accurately respond to real-world gas leaks.

What is a Bump Test?

A bump test briefly exposes the calibrated sensor to a low concentration of target gas to verify it can detect gas and trigger alarms at setpoints. The readings don’t need to be accurate. The goal is confirming functionality, not recalibrating.

Why Bump Test?

Bump tests ensure the entire gas sampling system is working properly, an advantage over routine calibrations alone. They can catch issues like blocked sample lines, sensor degradation, and readout electronic failures. Honeywell recommends periodic bump testing every 30 days.

Performing an XNX Bump Test

Follow this straightforward sequence to functionally test your XNX with a bump test:

1. Calibrate the detector fully before introducing the test gas.
2. Access the Bump Test menu section under Gas Calibration.
3. Briefly expose sensors to a low concentration of target gas, between 10-30% of the full scale range.
4. Verify that the detector responds to the gas and triggers configured alarm setpoints.
5. Ensure readings return to normal baseline when gas exposure stops.

Troubleshooting XNX Calibration Failures

Calibrations can sometimes fail, displaying error messages on the XNX interface. Here is some troubleshooting guidance for specific calibration failures:

Issue	Potential Causes	Solutions
Span Calibration Fails	Incorrect span gas concentration enteredBlocked or leaking sample tubingSensor reached end of operational lifeElectronics failure	Verify span gas value input correctlyCheck tubing connections with soapy bubble testAttempt calibration with fresh sensorContact Honeywell service for electronics testing
Reads Scaling Errors During Calibration	Gas concentrations outside sensor detection band Defective sensor unable to reach calibration point	Ensure gas concentrations are within 70-130% of range <br>- Run diagnostics on sensor replacement needed
Fails to Hold Calibration Long Term	Environmental factors like temperature/humidity shiftsSensor drifting downwards out of calibration	Improve temperature/humidity stabilityIncrease calibration frequencyTest sensor for shortened operational life

Maintaining Optimal XNX Gas Detector Performance

Like any analytical instrument, an XNX gas detector depends on regular maintenance and testing to sustain peak performance. Follow this preventative maintenance checklist:

1. Perform calibrations and bump tests on the recommended intervals
2. Keep detailed logs of all tests, calibrations, errors, and servicing records
3. Visually inspect sensors and sample line filters for contamination or damage
4. Ensure temperature/humidity remains stable at the detector location
5. Review sensor lifespans and proactively replace expired sensors
6. Follow all manufacturer-recommended maintenance items
7. Enroll in on-site service plans to catch issues early

FAQs – XNX Gas Detector Calibration and Testing

Conclusion

Regular XNX gas detector calibration and bump testing provide the bedrock for reliable safety monitoring. Always utilize the sensor-specific best practices outlined in the XNX operating manuals. Confirm that technicians have the necessary training for servicing the detectors before personnel assignments. With robust XNX instrumentation with competent technicians and rigorous calibration/testing standards, organizations can rest easy knowing even the smallest gas hazards won’t go undetected.