What is the difference between suction and diffusion type detection?



A suction type detector incorporates a pump and allows for the connection of an incoming and an outgoing sample line. The detection unit continuously draws an air sample from a location, which is normally within a range of 15 meters from the gas detector. The sample line can easily be entered into an installation or cabinet to be monitored. Using two connectors (in and out) the detector can be linked to for example the exhaust of a gas cabinet.


A diffusion type detector consists of a sensor and a detector body. The sensor is either united with the body or connected via a cable (e.g. TX-KFP with RX-WAD). With a diffusion type detector it is essential to locate the sensor element (or sensor element and detector body) in the area of monitoring. For example for environmental monitoring the detector is placed on the wall in the area of monitoring and for cabinet exhausts monitoring the sensor is mounted on the exhaust pipe with a NW-40 flange and a KF-40 clamp.


When choosing between suction and diffusion type detection the following issues have to be considered:


Ease of installation. Using a suction type detector in general requires no or minimum adaptations to existing installations. The sample line is just entered or linked to the monitored installation.


Ease of performing periodical maintenance. Is it possible and safe to enter the monitored installations or areas for detector maintenance? A suction type detector can be placed outside the area allowing an easy and safe access to the detector.


Pyrolyzer requirement. Some target gases require the detector to have a pyrolyzer. Pyrolyzers require a constant airflow, which can only be achieved with a suction type detector. Pyrolyzers are used in the detection of e.g. SF6, NF3, C4F8, TEOS and Acrylonitrile. Investment cost of the systems. A diffusion type detector requires in general a smaller investment than a suction type detector.


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