What are the differences between the principles of PID (Photoionization Detector) and FID (Flame Ionization Detector) in VOC (Volatile Organic Compounds) detectors?
1. Different detection principles
When a VOC detector based on the PID (Photoionization Detector) principle detects the sample gas, it uses ultraviolet light to ionize the sample gas to monitor the concentration of VOCs. After the sample gas is discharged, a secondary analysis of the sample gas can still be carried out. However, when a VOC online monitor based on the FID (Flame Ionization Detector) principle detects the sample gas, it uses a hydrogen flame to ionize the sample gas. After the burned sample gas is discharged, the components and concentration of the VOC gas have changed, and a secondary analysis cannot be performed.
2. Different types of detected gases
The VOCs detected by the PID principle include saturated and unsaturated hydrocarbons, aromatics, amines, halogenated hydrocarbons, thiohydrocarbons, alcohols, esters, and hydrazine gases. The FID principle is widely used for the detection of volatile hydrocarbons and many carbon-containing compounds.
3. Different installation and usage methods
In terms of installation and usage, a VOC gas detector using PID is compact and easy to carry, simple to install, and has a relatively low cost. However, since a VOC gas detector based on the FID principle requires a hydrogen cylinder or an online hydrogen generator, its installation difficulty and technical requirements are higher, and the cost is also higher than that of the PID principle.
4. Different monitoring ranges
The monitoring range of the FID principle is 1-50,000 ppm, while the monitoring range of the PID principle is 1-4,000 ppm or 0.1-10,000 ppm. When the concentration of VOCs is higher than 10,000 ppm, the FID has better linearity. Therefore, when users choose the principle of a VOC gas detector, they need to decide according to the on-site VOC concentration.
