TVOC Monitor: Difference Between FID and PID Detectors

TVOC (Total Volatile Organic Compounds) monitors are core equipment for VOCs monitoring, widely used in petrochemical, chemical, environmental protection, and other industries. FID (Flame Ionization Detector) and PID (Photoionization Detector) are the two primary...

Stream detection technology. This article provides a detailed comparison of two approaches and key selection criteria.

I. FID Detector

How it works

The FID detector measures VOC concentrations by ionizing organic compounds in a hydrogen flame.

Detailed process:

1. Sample gas enters the flame ionization detector.

2. Organic compounds produce ions when burned in a flame.

3. Ions form an electric current under the influence of an electric field.

4. Calculate VOCs concentration from current measurement

Benefits

• Fast response times, up to seconds

• Wide measurement range: 0-10000 ppm

• High stability with minimal long-term drift

• Responds to most organic compounds

• Can serve as evidence for law enforcement monitoring

Cons

• Hydrogen source required; safety hazard present.

• Large device size

• Higher price

• Complex to maintain

• No response to inorganic materials

Use Cases

• VOCs Monitoring for Petrochemical Enterprises

• Online Monitoring for Chemical Industrial Parks

• Environmental Law Enforcement Monitoring

• Fenceline VOC Monitoring

II. PID Detector

How it works

PID detectors measure VOC concentrations by ionizing organic compounds using ultraviolet light.

Detailed process:

1. Sample gas enters the ionization chamber.

2. The UV lamp emits ultraviolet light to irradiate the gas.

3. Organic molecules absorb energy to become ionized.

4. Ions form an electric current under the influence of an electric field.

5. Calculate VOCs concentration from current measurement

Benefits

• Compact and portable

• No gas required. Safe to use.

• Fast response times, up to seconds

• Lower price

• Easy to maintain

Cons

• Narrow measurement range: 0-2000 ppm

• Highly sensitive to humidity

• The bulb has a limited lifespan and requires regular replacement.

• Different responses to different organic compounds

• Cannot be used as a basis for law enforcement monitoring

Use Cases

• On-site Emergency Monitoring

• Occupational Health Inspection

• Indoor Air Quality Testing

• Leak Detection and Repair (LDAR)

3. Comparison of Two Technologies

IV. Selection Recommendations

1. Petroleum and Chemical Enterprise Online Monitoring → Select FID

2. Environmental Law Enforcement Monitoring → Select FID

3. On-site Emergency Detection → Select PID

4. Occupational Health Testing → Select PID

5. Fenceline Monitoring → Select FID

6. Indoor Testing → Select PID

V. Usage Precautions

FID Usage Notes:

• Keep hydrogen cylinders away from ignition sources and regularly check the gas line for leaks.

• Replace hydrogen cylinders regularly to prevent insufficient pressure.

• Regularly clean the combustion chamber to prevent carbon buildup.

• Check the igniter and gas line if ignition fails.

PID Usage Notes:

• Do not use in high-humidity environments

• Regularly clean the ionization chamber and UV lamp.

• Replace the tube promptly when its lifespan expires.

• Avoid measuring corrosive gases