What happens when I turn my gas detector on?

Bump Test on a Gas Detector

Almost all gas detectors perform an automatic self-test at instrument turn on. Self-tests generally check the electronic circuit and that sensors are present.

They also typically light the display and sound the alarms and vibration mode so they can be verified by the user. Information such as the alarm levels set and the due dates for calibration may also be displayed during the start up process.

Self-tests do not confirm gas entries are free from any blockages or that the sensor or sensors are responding to gas. This is why you need regular bump tests.

Bump Tests

All sensors have a life span and at some time will fail. Some will fail suddenly and some will fail over a longer period. Bump testing alerts the user of non-functioning sensors. This failed condition could be a loss of sensitivity, a loss of response time or both that could be caused from various factors. One of these is gases or vapours being able to reach the sensor. Bump testing will alert the user if a gas inlet has become blocked, even if the blockage is not visible to the human eye.

What does it mean if a cell is described as blind?

It quite simply means that the cell is no longer able to have gases or vapours enter so that the cell can give a reading.

How long should a bump test take?

Bump tests are dependent upon the model and manufacturer, but can take as little as 15 seconds up to around 3 minutes.

Failed Bump on 3 or more sensors.

If you bump test your unit and all 3 or more sensors fail bump due to slow response times this is quite often that the filters are blocked, although some sensors may not be working correctly either. In the first instance change all of the sensor filters and re-bump, if this now results in a pass then the problem has been sorted.

If the bump test still fails return it to an authorised service centre.


All sensors have an amount of drift over time. A calibration will correct any degradation or drift that the sensor may have experienced during use and let you know that the readings are accurate. Without regular calibrations, the gas level readings will become less and less true as time passes.

Situations like over-exposure and the introduction of poisons can have heavy impacts, along with extreme environmental changes, all can cause sensors to be less accurate.

Calibration will correct for these potential uncontrollable effects and will verify that the sensors in your gas detector are responding to gas in the correct way against referenced test gases.