Why a logged bump test record matters after an incident
A bump record is the only evidence that a detector was proven responsive before an exposure, and it has to live outside the instrument to survive the event it is meant to explain.
Read Article→Learning Center
Plain-language explanations of the measurements, sensors and numbers behind environmental monitoring.
What calibration gas a detector needs, and how often it is due
A detector needs a certified mixture containing every gas it senses, a bump test before each day of use and a full span calibration at the interval its manufacturer publishes.
Read Article→Bump test against calibration, and why both exist
A bump test is a pass or fail check that an instrument still responds and alarms, while a calibration measures how far its reading has drifted from a certified reference and optionally corrects it, and neither procedure can substitute for the other.
Read Article→Bump testing, and why a gas detector that never alarms might be dead
A quiet detector is an ambiguous instrument, because clean air and a failed sensor produce exactly the same display, and only a deliberate exposure to gas can tell them apart.
Read Article→Converting between ppm and percent LEL for methane
For methane the whole conversion reduces to one constant, five hundred parts per million per percent of the lower explosive limit, provided the instrument is actually calibrated to methane.
Read Article→What a 10 percent LEL alarm point actually means in practice
A first alarm at a tenth of the lower explosive limit leaves a deliberate factor of ten of margin for sensor error, uneven mixing and the time people need to react, and it says nothing whatever about whether the air is safe to breathe.
Read Article→Why a percent LEL alarm is not a ppm leak locator
An atmosphere monitor answers whether a space is safe to occupy and a leak locator answers where gas is coming from, and the first will read zero beside a joint that the second can find in seconds.
Read Article→LEL and percent by volume, two gas scales that are not interchangeable
Percent by volume states how much of the air is the gas, while percent LEL states how far the mixture has travelled toward the leanest concentration that can ignite, and one number cannot be read as the other without knowing the gas.
Read Article→Why a wide measurement range can make an instrument less useful
A wider span spreads a fixed number of display counts and a fixed percentage class over more territory, so the readings you actually take land in the weakest part of the scale.
Read Article→How to read an accuracy figure written as percent plus digits
An accuracy specification written as a percentage plus a number of digits has a proportional term and a fixed term, and the fixed term is what decides whether a small reading means anything at all.
Read Article→How resolution and accuracy can disagree by a factor of twenty five
Resolution is the smallest change an instrument can show, accuracy is how close the shown value is to the truth, and because they are referenced to different things a published pair can differ by twenty five times or far more.
Read Article→Why 5 percent of full scale swamps a low gas reading, alarm point and all
Gas alarm thresholds sit near the bottom of a span where a fixed error band in absolute units can be as large as the threshold itself, which is why a modest sounding percentage of full scale destroys the useful part of the scale.
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