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.