NPL's Controlled Flow Air Sampler is an accurate air quality sampler that can be easily installed at any monitoring site.

The system was developed by NPL for the UK's Department for the Environment, Food and Rural Affairs (DEFRA) to meet the benzene monitoring requirements of the EC Directive and has been in service in this role since 2001.

It has been validated using NPL's Controlled Atmosphere Test Facility (CATFAC) and by parallel monitoring at four UK sites over a period of a year.

System Specification

The system pumps controlled air samples alternately through two Perkin Elmer-type sampler tubes. The use of two samplers allows measurement repeatability to be checked. The sample is taken through a 1/8 inch, electro-polished stainless steel tube at a flow rate of approximately 2 litres per minute. This avoids sample losses to the walls of the pipe.

The system performs a number of diagnostic tests. Circuits continuously monitor the power supplies, reference voltages, and the internal clock, and also compare the measured flow with the set point of the mass flow controller. In the event of a failure in any of these an indicator LED ceases to flash.

The specifications of a system to measure benzene are given as an example of performance:

• System dimensions : Height 0.50 m : Width 0.44 m : Depth 0.24 m.
• Measurement repeatability: the average difference between analysed duplicate tubes is approximately 0.02 ppb (3.1%).
• Measurement uncertainty: the estimated overall uncertainty in the benzene measurements is ± 12%, at the 95% confidence level.
• Operating conditions: the system is intended for indoor operation in the temperature range 10°C to 30°C.

If you would like further information please contact us.