| Description: | The time of flight ACSM had two problems during the deployment of AMF 3 at SGP. The first
was a problem with a short in the pulser. This is the ion steering element that
accelerates the molecules into the time-of-flight detector. This problem was intermittent. I
replaced the pulser and the instrument seemed to work. The second problem was a persistent
clogging of the critical orifice. This caused the inlet pressure to drop and reduced the
total ion current. The orifice was cleaned several times, but the problem reoccurred. I
decided to have the instrument removed and shipped back to BNL to determine the cause of
these problems. I took the instrument to Aerodyne where we found a loose screw in the vacuum
chamber. This screw was located directly above the pulser and explained the intermittent
cause of the short as well as the observation that when the unit was reassembled it
seemed to work. It was only after the unit was run long enough for it to heat up that the
problem appeared.
The orifice clogging problem seems to have been caused by a small fragment of Teflon tape
that was on one of the NPT fittings used in the Nafion dryer. A small shredded filament
of the tape was outside the threads and in the sample stream. Small pieces of the Teflon
appear to have been introduced into the sample stream and lodged in the orifice. The
fitting was cleaned and reinstalled and the instrument run over the weekend with no
reoccurrence of the clogging problem. The instrument was shut down and shipped to Alaska for
installation during the August installation trip. |