1835 Series Submersible Pressure Sensor with Internal Lightning Protection - DESCRIPTION
by Druck

The PTX 1835 is identical to the PTX1830 except for the additional internal lighting protection. 

The lightning Surge Arrestor is an Integral lightning protection assembly certified to Standard IEC 61000-4-5 (Level 4).  Basically the sensor can withstand most indirect lightning strikes (the exception being a direct strike on the sensor).