M-AERI Purge Notes and Troubleshooting

  • The main goal of keeping the instrument purged is to avoid humid and salty air in the interferometer optics compartment.  RH above 30% can compromise the measurements.  Salt can deposit and contaminate the optics
  • Neither the interferometer enclosure, nor the M-AERI back-end enclosure are particularly air-tight
  • The purge gas is routed into the interferometer to purge the optics compartment, from where it leaks out to purge the M-AERI back-end, from where it leaks out to the environment
  • A trickle purge should be enough to maintain positive pressure and keep salty humid air out of the interferometer
  • Interferometer humidity may vary between 0-10% depending on the outside conditions, even with the purge running
  • 1.5 bottles of purge gas should (hopefully) be enough for a voyage
  • The desiccant in the interferometer doesn’t do much. It provides a buffer against high RH incursion. Desiccant alone cannot bring the interferometer RH down, the purge must be used
  • If the RH is high (>10%) inside the interferometer for a prolonged period, the desiccant may get saturated, at which point the desiccant becomes a source of humidity. Under these conditions, the desiccant should be changed, or removed entirely (tape over hole)