Sample
Ambient gas enters the ionisation chamber by diffusion or controlled flow. Filters and flow design protect the lamp and make the response more repeatable.
Volatile organic detection
PID
Photoionisation detection provides fast, broad-range measurement of volatile organic compounds in air. It turns molecules with suitable ionisation energies into a proportional electrical signal, making changing exposure conditions visible in real time.
Introduction
A PID (Photoionization Detector) sensor is a gas detector used to measure volatile organic compounds (VOCs) and other gases in the air. It operates based on the principle of photoionization, where gas molecules are ionized by ultraviolet light, producing positive ions and electrons. The sensor detects the generated ions and measures the resulting current, which is proportional to the concentration of the target gas.
PID sensors have high sensitivity and can detect a wide range of VOCs, making them valuable in industrial environments, environmental monitoring, and safety applications. They are commonly used in industries such as chemical manufacturing, petrochemicals, environmental protection, and emergency response. PID sensors provide real-time measurements and can detect gases at low concentrations, making them highly effective for identifying potential hazardous substances in various environments.
Technical principleTalk to a technology expert
Use ultraviolet energy to reveal VOC concentration.
A pump or diffusion path brings the gas sample into a small ionisation chamber. Ultraviolet photons from the PID lamp transfer energy to compounds whose ionisation potential is below the lamp energy, creating temporary positive ions and electrons.
An electric field collects these charged particles and produces a current related to the amount of ionisable vapour present. Electronics stabilise and amplify the signal, while calibration and correction factors translate it into a concentration reading. The molecules normally recombine after measurement, so the technique is non-destructive at the sensing stage.
A PID is a broad-band VOC detector, not a compound identifier. Lamp energy defines the detectable chemical window, and the displayed concentration depends on calibration gas, response factor, humidity, contamination and the composition of the atmosphere.
Signal path
A direct path from vapour to live concentration.
The PID sensing cycle is rapid and repeatable, which suits personal, portable and fixed monitoring. Interpretation still depends on knowing what the instrument can ionise.
Ionise
Ultraviolet photons ionise molecules below the lamp’s energy threshold. Compounds above that threshold pass through without producing a PID response.
Measure
Electrodes collect the ions and convert their movement into a small electrical current. Signal conditioning stabilises the reading across the required range.
Interpret
Calibration converts current into concentration and alarm logic evaluates exposure or process limits. Correction factors can improve estimates when the likely compound is known.
Engineering considerations
Broad response requires disciplined interpretation.
PID instruments are highly useful for finding and trending VOCs, provided lamp selection, calibration and environmental effects are made explicit in the method.
Lamp energy
The ultraviolet lamp sets the ionisation window and therefore the compounds that can be detected. A higher-energy lamp may broaden coverage but also changes selectivity and maintenance needs.
Calibration basis
Readings are relative to the calibration gas unless a compound-specific response factor is applied. Reports should state that basis so concentration data is interpreted correctly.
Field condition
Humidity, lamp fouling, flow restriction and mixed vapours can alter response. Routine bump tests, cleaning and contextual measurements protect confidence in the trend.
Key information
Technology Features
High sensitivity, strong compound selectivity
High sensitivity : PID technology has high sensitivity, capable of detecting very low concentrations of volatile organic compounds (typically in the range of ppb to ppm), making it suitable for monitoring trace pollutants in the air
Broad response: a PID responds to compounds whose ionisation potential is below the lamp energy. A conventional PID does not identify individual compounds in a mixture, and its response can be affected by humidity, quenching gases, lamp contamination and the selected response factor
Real-time response
Real-time capability: PID technology enables real-time monitoring of volatile organic compounds, facilitating the timely detection of pollution sources and events in the air, thus contributing to environmental protection and human health
Fast response time: PID technology exhibits a rapid response time, capable of detecting the presence of pollutants within seconds. It can quickly adjust and react, facilitating timely alarms and control measures
Portable and easy to use
Portable design: Many PID detectors feature a portable design, small in size, lightweight, easy to carry and operate, suitable for on-site real-time monitoring and mobile detection
Simple operation: PID detectors typically come with a simple operating interface and user-friendly operation methods, requiring no complex training to use, making them suitable for various environments and operators
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