Some common applications are:
– Leak Detection – Perimeter Monitoring – Spill Detection – Remediation – Arson Investigation – Diesel Fuel Threshold Limit Value Monitoring – Personal Protection Equipment – Decontamination – Law Enforcement – Drug Detection
Operation Principle Photoionization detection uses a specialized UV lamp that emits high energetic photons. The energy level of the photons depends on the gas fill of the lamp and is measured in electron volt (eV).
When the photons are absorbed by the gas atmosphere to be measured they excite the gas molecules causing the loss of an electron, resulting in ionization of the gas. The number of ionized gas molecules, which are measured as current generated from the movement of electrons in the detector, is proportional to the concentration of the ionized compound. This allows a quantitative measurement of concentration.
However photoionisation is not gas selective because all molecules with ionization potentials less than the photon energy of lamp are ionized. The technique is non-destructive so can be used in conjunction with other detectors for extending the analysis.
Heraeus manufactures a range of PID lamps with varying photon energies to enable a degree of compound selection. A recent introduction has been a dedicated 10.0 eV lamp which is particularly useful for measuring benzene, toluene, ethyl benzene and xylene (BTEX compounds).
Application Spotlight Measurement of Volatile Organic Compounds (VOCs) using portable Photoionization Detectors (PID) enables fast detection with high sensitivity. VOCs comprise numerous chemical compounds such as toluene and isobutylene and are found in many different industries. Exposure limits for these chemicals can be very low, when exposure occurs over a long period of time. Contact to these substances can present a serious health hazard not only in a manufacturing environment but on the streets as they are shipped. For this reason VOC detection is of paramount importance during emergency spill response actions and in industries where worker exposure must be limited.
While many VOCs are also flammable and can be detected with other technologies, such as a catalytic sensor, the levels of concern are typically at the parts-per-million (ppm) or parts-per-billion (ppb) level. For example, toluene has a lower explosive limit (LEL) of 1.2% and a permissible 8-hour exposure of 50 ppm. Exposures to LEL levels are 240 times higher than the shift exposure level (1.2% = 12,000 ppm).
Obviously, a technology capable of higher sensitivity is required to ensure worker or personnel safety. Photoionization detectors (PIDs) rely on specific physical properties of the VOCs, and many common VOCs have ionization potentials lower than 10.6 eV, which is a common energy level for PID UV lamps.
PID sensors, however, have limited specificity. With different lamp energies like 11.7, 10.6, 10.0, and 9.6 eV, some selectivity is afforded in detection. Despite this they will still only indicate that VOCs are present, but not what type. Many instruments with PID sensors have built-in conversion factors; if you know what type of VOC you are measuring, you can obtain a direct ppm reading on your display.
Heraeus Noblelight, a leading manufacturer of specialty light sources, supplies photoionization detector lamps (PID lamps) used in modern portable gas detection units. Using latest electronics and software, PID lamps can be used in durable and easy-to-use mobile gas alarm units delivering reliable detection results.
Design and Production Expertise Heraeus has extensively tested and selected materials to establish a quality standard in PID manufacture. Heraeus- proprietary manufacturing processes ensure unparalleled performance and consistency over the lifetime of the lamps. High purity of the gas spectrum is achieved throughout the life of the lamp by the use of a Heraeus-design internal cleanser.
Heraeus manufactures a wide range of PID lamps to standard and customer specific designs in both RF and DC versions. For hand-held detectors, RF versions provide the best solution due to demands for smaller size and low power drive circuitry, whereas DC operation is the preferred option for laboratory instruments.
