Why your meter is reading — and why that reading might be wrong. A training exploration of sensor technology and cross-sensitivity by instrument type.
Before cross-sensitivity makes sense, you need to understand what each sensor is actually doing. Select each card to reveal the explanation.
Think of it like a tiny battery that runs on gas. The target gas enters the sensor, reacts with an electrode, and that reaction produces an electrical current. The meter measures the current and converts it to a reading.
The problem is the electrode doesn't care which gas caused the reaction — it only cares that a reaction happened. Any gas that triggers a similar reaction will produce a current. The meter has no way to tell the difference.
Two tiny beads — one heated with a catalyst, one without. When combustible gas reaches the hot bead, it burns on the surface. That burn raises the temperature of the bead, which changes its electrical resistance. The difference in resistance between the two beads is your LEL reading.
It's calibrated to methane by default. Every other combustible gas burns differently — some hotter, some cooler — so the reading is already an approximation unless you apply a correction factor.
A UV lamp fires high-energy light at the air sample. If a gas molecule absorbs enough energy, it loses an electron and becomes an ion. The meter collects those ions and measures the current — that current is your reading.
Calibrated to isobutylene. Every other chemical ionizes at a different efficiency. The ratio between isobutylene's efficiency and the target chemical's efficiency is the correction factor. Without it, your reading is directionally useful but numerically wrong.
Choose the instrument you're working with, then select a chemical environment to see how each sensor responds — and why.