Photoionization detector
Principle
A Photoionization detector (PID) uses an ultraviolet (UV) light source to ionize chemicals to positive and negative ions that can be easily counted with a detector. Ionization occurs when a molecule absorbs the light energy. The gas becomes electrically charged. These charged particles produce a current that is then amplified and displayed on the meter as "ppm" or even "ppb".
Benefits
- modern type (3D) is not affected by temperature and humidity changes
- one detector can detect broad range of gases
- high sensitivity (ppb's)
- quick response (< 3 s)
- high precision at very low levels
Weaknesses
- low selectivity for most compounds
