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Gas Monitor Calibration - What, Why, How Often

What does it mean to calibrate a gas monitor? Why is calibration even necessary? How often is calibration to be performed?

Calibration of Gas Detector


Gas Monitor Calibration

A gas monitor calibration determines if a sensor can accurately read the known concentration of a calibration gas. If it can't, the calibration electronically adjusts the gas monitor to account for the difference. Simply put, a calibration aligns a sensor with a calibration gas.


Calibration Drift

Calibration is needed because of Calibration Drift. Calibration Drift occurs when the sensor can't accurately read the calibration gas.

A number of factors cause Calibration Drift in gas monitors (from OSHA):

  • AGE - Gradual chemical degradation of sensors and drift in electronic components that occur naturally over time.
  • ENVIRONMENT - Chronic exposures to, and use in, extreme environmental conditions, such as high/low temperature and humidity, and high levels of airborne particulates.
  • SENSOR POISONING - Exposure to high (over-range) concentrations of the target gases and vapors.
  • MONITOR ABUSE - Harsh storage and operating conditions, such as when an instrument is dropped onto a hard surface or submerged in liquid. Normal handling/jostling of the equipment can create enough vibration or shock over time to affect electronic components and circuitry.

When a sensor can no longer be aligned to the calibration gas during calibration, a sensor failure occurs. This failure is due to calibration drift. The sensor will need to be replaced.


Calibration Frequency

OSHA does not give any detailed recommendation concerning gas monitor calibration frequency. OSHA simply says, "follow the manufacturer's recommendations with regard to calibrating the instruments."

RKI Instruments, in a effort to be helpful, outlines two extremes of calibration frequency:

  • Example 1 - Users who require the readings to hold up in court as data for certain legal applications must calibrate both before and after each test or each series of tests, in order to remove all doubt of the proper functioning of the instrument.
  • Example 2 - The other extreme is someone who only uses the instrument a couple times a year for non-critical applications. This type of user should calibrate their instrument before each use.

Most users will be in the middle of these two extremes. RKI, for example concludes that "typical calibration frequencies for most applications are between 3 and 6 months, but can be required more often or less often based on your usage". Honeywell BW recommends calibration at least every 6 months.

Calibration Frequency is ultimately determined by the end user based on OSHA's requirement to follow the manufacturer's guidelines. Neither the manufacturer nor a distributor can make a specific recommendation.


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