| Description: | The nafion membrane failed allowing water to leak into the saturation air system and
eventually into the vacuum system. It is not unusual for Nafion membranes to fail since they
are delicate.
Unfortuanately this was just the latest in a series of problems with the HT-DMA:
1. The SEMS unit (the HT-DMA is made of 3 units) was not entirely communicating with HSEMS
unit. The HSEMS could talk serially to the SEMS but the SEMS was not talking serially to
HSEMS. This was a software issue which needed to be resolved by recoding.
2. The laminar flow elements used in both the HSEMS and SEMS unit are very sensitive to
the presence of condensed water droplets in the sample and compressed air supply. The water
droplets give a false signal that the flow is low and the control circuit tries to
compensate. The flows become erratic. There are about 8 laminar flow elements in the HSEMs and
two in the SEMS. It appears most were being effected.
3. The vacuum and air supplies started to degrade. If the HT-DMA does not have sufficient
vacuum, it starts to fail. |