I am looking for a solution to monitor and log ambient He levels down to 50-100ppm.
The detector is meant to be installed in an experimental hall where a large number of Photo Multiplier Tubes are in use. PMTs ageing speed increases with the He concentration. We consider 100-50ppm a safe limit for the PMTs and we want to make sure that the ambient level of He does not exceed that threshold. Unfortunately there is a (normally sealed) device in the same area that could leak Helium so we need to actively monitor the He level.
The only solution I could think of is to look for a Thermal Conductivity Detector, such as those used in handheld gas sniffers. But a TCD will give only a reading related to the overall difference between sample and reference. Can you suggest any other solutions?