Precautions for Using PID (Photoionization Detector) Sensors

PID (Photoionization Detector) sensors measure gas concentration by utilizing ultraviolet (UV) light to ionize target substances. They are highly sensitive and widely used for detecting volatile organic compounds (VOCs).

The UV lamp in a PID sensor typically has energy levels of 9.8 eV, 10.6 eV, or 11.7 eV. The selection of lamp energy depends on the ionization potential (IP) of the target gas. The lamp energy must be higher than the IP of the gas for effective detection. For example, formaldehyde (HCHO) has an IP of 10.87 eV. To measure formaldehyde, an 11.7 eV lamp must be used, as a 10.6 eV lamp cannot detect it.

High humidity conditions (>90% RH) may cause condensation to form on the UV lamp window, affecting the accuracy of readings. Therefore, PID sensors are typically used in dry environments or designed with moisture-proof features.

Exposure to high concentrations (e.g., >1000 ppm) or high-boiling-point VOCs (such as oils, aldehydes, and aromatic hydrocarbons) can lead to the accumulation of ionized products and non-volatile residues (e.g., silicone oil, H₂S) on the UV lamp window. This can reduce UV light transmittance, resulting in signal attenuation, longer response times, and decreased sensitivity. Prolonged exposure may permanently damage the UV lamp. To mitigate contamination, minimize impact, and extend the sensor’s lifespan, it is recommended to use a pump-sampling device when operating a PID sensor.