Coaxial probe for high temperature and high pressure applications

A probe defining a transmission line for use with a measurement instrument including a pulse circuit connected to the probe for generating pulses on the transmission line and receiving reflected pulses on the transmission line, the probe comprising:

• a center conductor for conducting the pulses;
• a conductive outer sleeve coaxial with the center conductor, the conductive outer sleeve having a process end and a connector end, the process end being exposed, in use, to a process environment being measured;
• a cylindrical ceramic seal element between the center conductor and the outer sleeve at the sleeve process end;
• and
• first and second cylindrical plastic seal elements between the center conductor and the outer sleeve disposed axially aligned between the ceramic seal element and the connector end.

A guided wave radar probe for use in high temperature high pressure process environments with a process instrument having a control housing assembly with a control connection comprising:

• an elongate cylindrical hollow seal adapter receivable in an opening of the process vessel;
• a conductive outer sleeve, the conductive outer sleeve having a process end and a connector end, the process end being connected to the adapter;
• a center conductor coaxial with the outer sleeve and the adapter and connectable to the control connection, in use, for conducting and guiding guided wave radar electrical signals;
• a first cylindrical seal element between the center conductor and the outer sleeve at the sleeve process end, the first cylindrical seal element being of a first material adapted to withstand a relatively high temperature;
• a second cylindrical seal element between the center conductor and the outer sleeve disposed between the first cylindrical seal element and the connector end, the second cylindrical seal element being of a second material adapted to withstand a lower temperature than the first cylindrical seal element;
• and
• elastomeric seals between the center conductor and the second cylindrical seal element and between the second cylindrical seal element and the outer sleeve.