Gas Detection Sensor - Tec Trek Web Site

Tip of the Week

Burn In or Burn Out

A recent call from an undisclosed offshore location has prompted me to post this information for distribution to field personnel who calibrate hydrocarbon gas detectors.

While conducting calibration of catalytic bead gas detectors, a failed attempt required that the sensor assembly be replaced, either due to age, damaged sensor bridge, or contamination.  After replacement, the calibration procedure was immediately attempted without complications and the technician departed for another structure. Two hours later, I received a call, not from the technician, or the facility operator, but from an inspector who was on location at the time. " The sensor was just recently replaced and all indicators were clear, now we are showing a fault condition what would you say is the problem" was his comment to me. PINC P-154.

Damn!!

Although a sensor fault can be cause by a variety of issues, the fact that the sensor was just replaced told me one thing. The appropriate burn in time was not observed.

A catalytic bead sensor works on the diffusion method, meaning the gas comes into contact with and literally is ignited by the active bead which then causes a resistance change on the Wheatstone Bridge. For this to occur, the bead must be at operating temperature. Sensor resistance values change when in a shelf state vs. when in operation, therefore being aware of the operating characteristics is critical for any field technician. PINC P-106 and/or G-856.

When in doubt regarding burn in time, it is always recommended to contact the manufacture of the equipment for their input. The manufacturer stated that 24 hours was the recommended burn in time prior to calibration.  Now we all know that waiting a day for a sensor to become stable will not be realistically possible, so I will share a method for sensor preparation.

After sensor replacement, wrap the sensor with neoprene insulation, the same type used when protecting your water pipes during winter is perfect. Based on past experiences, in about 2 hours the sensor should have stabilized at operating temperature and ready for calibration. Keep in mind the longer the burn in time the better.  Also ensure that the insulation is clean and free of contamination  that may damage the sensor.

The above information does not apply when IR Gas Detectors are used.

If you require more information regarding the terms and explanations above, contact me by email or phone for assistance.

The above information is covered in the following Tec Trek class segments: Awareness Training (FG-01A), Basic Technical Training (FG-01)

For more information regarding training schedules and course curriculum, please visit our Web Site at www.tectrek.org

or Contact Todd Olivier at (337) 298-7959.

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Email: todd@tectrek.org