Calibrations

Calibration - the act of adjusting the accuracy of a measuring instrument by comparison with a known standard. Calibration refers to an instrument's measuring accuracy relative to a known concentration of gas. Gas detectors measure the concentration of a gas in an air sample by comparing the sensor's response to the response generated by a calibration gas of a known concentration. The instrument's response to the calibration gas serves as the measurement scale or reference point.

EnviroMed offers only high-quality, certified, NIST-Traceable calibration gas. In order to meet the standard, the gas is mixed, tested with NIST-traceable instruments, set aside for a specified time period and retested.

Why calibrate?

Gas sensors need to be calibrated and periodically checked to ensure sensor accuracy and system integrity. If the instrument's reference point has shifted, the reading will shift accordingly and be unreliable. This is called "calibration drift" and it happens to all detectors over time. An instrument that experiences calibration drift can still measure the quantity of gas present but it cannot convert this information into an accurate numerical reading. Regular calibration with a certified standard gas concentration will update the instrument's reference point, ensuring that the instrument will produce continued, accurate readings.

Causes of Calibration Drift

Over time, the accuracy of gas detection instruments can diverge from their calibration settings in several ways:

• Gradual chemical degradation of sensors and drift in electronic components that occur naturally over time
• Chronic exposures to, and use in, extreme environmental conditions, such as high/low temperature and humidity, and high levels of airborne particulates.
• Exposure to high (over-range) concentrations of the target gases and vapors.
• Chronic or acute exposure of catalytic hot-bead LEL sensors to poisons and inhibitors. These include: various volatile organic vapours, silicones, hydride gases, halogenated hydrocarbons, and sulfide gases.
• Chronic or acute exposure of electrochemical toxic gas sensors to solvent vapors and highly corrosive gases.
• 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 & circuitry.

Often, after exposure to the more extreme conditions above, when calibration is attempted, the detector will either display a failure message or it will not allow the user to fully adjust the display reading. At this point, the severely damaged sensor must be replaced and/or the detector serviced by qualified personnel.

What is the value in a regular calibration schedule?

Gas detectors are designed for the detection and measurement of potentially life threatening atmospheric conditions. Hazards such as oxygen deficiencies, explosive atmospheres, and toxic gases and vapors regularly kill as many as three-hundred workers per year in the United Sates, many of them during confined space entry procedures. The atmospheric conditions which lead to these accidents and fatalities are usually invisible to the workers who are involved. The only way to insure conditions are safe is to use an accurate atmospheric monitor. The only way to know that the readings are accurate is to expose the instrument to known concentration test gas; in other words, to check the accuracy of the instrument on a regular basis.

Secondly, regular calibration provides a means by which maximum sensor life expectancy can be reached. The cost of replacing a spent sensor due to lack of maintenance far exceeds the cost of maintaining it.