What Is A PID Gas Detector And How Do They Work?

PID stands for “Photo-Ionization Detector.” PID (Photoionization Detection) sensors are essential tools for monitoring air quality.

They can be incorporated into a hand-held, personal, or fixed detector for detecting volatile organic compounds (VOCs) and some inorganic compounds.

What is a PID Gas detector?

A PID gas detector measures and monitors volatile organic compounds (VOCs) at very low concentrations and other gases in the air. It relies on a process called photoionization to detect and quantify these substances.

How Does a PID Gas Detector Work?

Photoionization detectors use high-energy ultraviolet light from a lamp housed within the detector as a source of energy used to remove an electron from neutrally charged VOC molecules, producing a flow of electrical current proportional to the concentration of the contaminant.

Applications of the PID gas detector

  • Personnel safety
  • Industrial hygiene
  • Soil contamination and remediation
  • Unintended emissions
  • Law enforcement
  • Emergency response
  • Leak detection
  • Perimeter monitoring
  • Refineries and petrochemical
  • Air quality monitoring

Advantages of Photoionization Detectors

  • High sensitivity
  • No poisoning problems.

Disadvantages of Photoionization Detectors

  • non-selective.
  • Greatly affected by humidity,
  • The short life of UV lamps, and
  • Expensive.

How to Choose the Right PID Sensor for Your Application

Choosing the right PID gas detector for your application is the key to ensuring safety for everyone involved; here are three things I consider when selecting the PID detector.

The main VOC in the environment

PID detectors use three lamps: the 9.8 eV lamp, the 10.6 eV lamp, and the 11.7 eV lamp.

If I know that the main VOC is Benzene, I will pick the 9.8 EV lamp, and for general VOC, I will pick the 10.6 eV lamp, and for very specific gases and applications, I will pick the 11.7 eV lamp.

Portable or Fixed

Another question you must ask yourself is whether you want personal protective equipment or portable equipment that users wear when they visit the site. Or do you want a Fixed unit that will stay in a fixed location but will alert users when there is a dangerous VOC in the environment? 

Single or Multigas

You can have a PID gas detector that detects only VOCs or combine it with other sensors, such as H2S, O2, LEL, and CO.

What Types of VOCs Can PID Sensors Detect?


PID gas detectors are not selective, meaning they can detect a broad spectrum of VOCs, including solvents, fuels, pesticides, and other organic compounds.

Factors Affecting PID Detectors

Many factors affect PID sensors, such as humidity and dirt. Environmental humidity can cause leakage currents or scatter ultraviolet light, reducing sensitivity.

If the sensor’s sensitivity has been impaired too much, which can be ascertained during calibration, then the lamp should be cleaned to improve its functionality.

PIDS that use electrode stack designs are better choices as these can be designed to reduce humidity interference.

However, the electrode stack is extremely sensitive and can shorten its life span if situated within heavily contaminated sites.

As it is disposable, a spare electrode stack can be kept in service facilities to replace it after PID use in dirty environments when required. After the electrode stack is replaced, the PID should be recalibrated.

Calibration of PID gas detector

PID sensors need to be calibrated to ensure safety and accuracy. Two types of calibration are available: zero calibration and span calibration. 

Zero calibration

This is called fresh air calibration, when you perform a zero calibration in the ambient air. If you are in a contaminated area, you can use a zero gas cylinder or a nitrogen gas cylinder to perform zero calibration.

Span calibration

Span calibration involves applying a known concentration of the VOC and recalibrating the gas detector. Isobutylene is the most common calibration gas used to calibrate PID sensors.

If you want to detect a specific VOC such as Benzene, the recommendation would be to calibrate the unit with that specific target gas, but if you are targeting general VOC, then calibrate with Isobutylene.

The calibration frequency depends on the manufacturer’s recommendation; most manufacturers recommend calibrating at least once per year. Regular calibration ensures accurate readings.

PID detectors are the best choice for detecting multiple heavy gases and solvents in a specific environment.

If the gas is known in that environment, Calibrate the PID for that gas type instead of giving it a general calibration.

Bump Test 

You should perform a bump test before using your PID gas detector to ensure the sensors are functional before entering a potentially hazardous area.

The bump test will test the functionality of the sensors and alarms. The recommended concentration to bump test your detector is that the concentration should be above the lowest alarm level. This will ensure that the unit will go into alarm when you bump test.

What Is A Bump Test In Gas Detection?

FAQ: PID Gas Detector

What does PID mean in gas detection?

PID stands for PhotoIonization Detector, and this device measures the presence of volatile organic compounds (VOCs).

Is VOC the same as PID?

A PID sensor is a device used to measure and monitor volatile organic compounds (VOCs) to very low concentrations and other gases in the air. It relies on a process called photoionization to detect and quantify these substances.

VOCs are chemical compounds with significant vapor pressures that can seriously affect our health and the environment.

Can a PID detect H2S?

No, PIDs detect only those substances that the UV photons can ionize.

Can I use a PID gas detector to detect Benzene?

Yes, you can use a PID gas detector for a Benzene-specific measurement. For benzene-specific measurements, selective benzene detection can be carried out using the standard PID detector in combination with the benzene tubes. This pre-tube filters out all hydrocarbons present except for benzene.

Can PID Sensors Detect Combustible Gases?

While PID sensors are primarily designed for VOC detection, some models can detect combustible gases indirectly by measuring changes in VOC concentration.

What is the best PID single gas detector?

Many great PID detectors are on the market, but the ToxiRAE Pro PID is the best. It is easy to manage and detect up to 300 VOCs; you can read about ToxiRAE Pro PID here.

Conclusion

PID gas detectors are valuable tools for detecting and quantifying VOCs in various applications.

Understanding their operation, maintenance, and suitability for different industries is crucial for effective use.

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