How can I calculate relative humidity in helium?

[Telefunken123]

Hello,
I want to calculate the relative humidity in Helium. I only have the variables "dew point temperature", "gas temperature" and "gas pressure". So I tried with Magnus and Antoine equation. But I read that the Antoine equation is very unprecise. So do you know how to calculate the relative humidity in Helium with these variables?

Best regards
Telefunken

 

[Tom.G]

Haven't done it, but here are a few clues.
https://brownell.co.uk/datasheets/basics_humidity.pdf
https://www.google.com/search?&q=Psychrometric+Chart+of+Helium

 

[BvU]

I only have the variables "dew point temperature", "gas temperature" and "gas pressure".

You do, we don't. Are we talking milliKelvin cryogenics or STP here ?