Selection depends on the nature of the medium being sensed and cost requirements. Direct immersion of a probe into a liquid requires a fitting with a pipe thread, which may be adjustable or welded on the probe.
Figure shows a typical assembly, with one thread for mounting the probe and another for a connection head. Connection heads provide a transition between probe leads and external signal wires.
Mounting in a solid material is best accomplished with a spring-loaded holder, which may be fixed or adjustable.
Spring loading provides good contact of the probe tip against the bottom of the hole and dampens potentially damaging vibration. When liquids are particularly corrosive, under high pressure, or fast-flowing, a thermowell may be necessary.
A thermowell is a tube, closed at one end, which protects the probe and allows its removal without breaking the liquid seal.