United Sensor Sampling probes are made in three types:                 

Type A
Type A is uncooled, of welded construction, suitable for use up to 2000°F and is the smallest.

Type B
Type B can be used either as a heated or cooled probe.  The cooling passages are especially designed for unrestricted flow of cooling or heating fluids.  For some applications, it is important to keep the sampled gas above500°F to the analyzer to prevent condensation of evaporated hydrocarbons. In this case, the probe is heated by blowing hot air through the cooling passages.  This is more satisfactory than trying to heat it with anelectric coil because the variation of heat loss conditions from the surface of the probe makes it almost impossible to maintain an even temperature. For higher temperatures, the probe can be kept hot enough to prevent condensation but cool enough not to melt by blowing unheated shop air through the coolant passages.  Above 3000°, even with water cooling the stainless steel tip on the Type B probe it would burn out.  Therefore, Type C is recommended.

Type C
Type C probes have a copper tip, which has a high enough conductivity to prevent burning out at the highest temperatures and velocities.  Since the tip is easily damaged, it is not recommended for lower temperature applications.