Some sensors can be fitted directly into the process by means of an
integral process connection or by using an appropriate compression
fitting. Other applications require a pocket or thermowell which is a
permanent fitting into the process yet allows the sensor to be inserted
or removed without interruption.
Pockets
invariably increase the response time and obviously the thicker and
heavier the pocket the more the response time will be increased. Some
styles use spring loading which keeps the inset in permanent contact
with the pocket. However, it is the radial clearance between the inset
and pocket which has the greatest influence on response time.
For
improved response the inset should be assembled into the pocket using
thermally conductive grease. The following illustrations show the two most popular styles of pockets/thermowells.
Note: Pocket immersion lengths are relative to the probe lengths shown.