Calibration vs Bump Testing


Here is the controversial subject. Not long ago we were having a discussion with some of our clients about this matter.

‘What is the difference between them?’

‘Should we be doing a bump test or a calibration check?

Well, here’s our explanation:

Literally, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy… Which in other words means just the act of comparison, and does not include any subsequent adjustment.

Did it help? If not, then a few more words.

A calibration of a monitor is a “resetting” of the detector’s response against a known concentration of target gas, in a balance of synthetic air or nitrogen. This includes exposing the instrument sensors and allowing the instrument to automatically adjust the readings to coincide with the known concentration of the calibration gas. Or, if necessary, the operator will manually adjust the readings to match the known concentration of the calibration gas.

The “Bump Test” is a quick check that the sensors are responding correctly to a known gas typically within ±10% accuracy.


So, with the “Bump Test” it is up to you to determine if the sensors are working properly by viewing the real-time readings. With the “Full Calibration” the instrument’s electronics determine if they pass or fail. The bump test does not check the accuracy of the instrument and does not calibrate the sensors. This is where the calibration comes in

What else?

Do you know how often you should calibrate your gas monitor and when carry out a bump test?

If the answer is no, then you need to know that calibration interval varies depending on the instrument you choose. For example, if you are using the Dräger X-am 2500 Gas Detector, it is recommended for the standard 4 gas monitor (LEL, CO, H2S, O2) be calibrated every 6 months. If you are wondering how often you should bump test your monitor is because you missed our last post about ‘bump test’. Do not worry, here a summery.

According to OSHA, a bump test of portable gas monitors should be conducted before each day’s use in accordance with the manufacturer’s instructions.

If you need more information or you have any enquiry, please contact us on 0845 3300 447 or email our team at

Posted by Ryan Jenkins

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