(see WP #6332)

~0605 - 0630 hrs. local -> Kyle in and out of LVEA 

Attempted to de-energize PT180 by removing the fuse at terminal #111 in the Y-arm vacuum rack.  Noted that the old PT180A signal wiring had been lifted from the terminal strip and was deliberately zip-tied out of the way.  The cabling to PT180B was still landed having only the black conductor fused at terminal #111.  Curiously, the indicated pressure value on the MEDM screens did not change as the result of removing this fuse.  Next, I removed the external gauge electronics, isolated PT180 from the site vacuum volume via closing the 1 1/2" metal-sealed isolation valve and then opened the pump port valve so as to pump the PT180 volume with the locally mounted turbo.  Heating was started with the initial variac settings of 20%.

Unfortunately, we are using the BPG402-SE version of this gauge - where the "S" indicates "short" nipple.  This limits the gauge bake temperature to a modest 80C as measured at its CF flange as the internal PCB can't be thermally radiated at greater temps.  This may be a significant limitation as the current theory is that water vapor is the source of the undesired gauge behavior and a relatively short duration bake at relatively low temperatures won't likely remove very much water.  (I can cheat a little and adjust the non line-of-site surfaces to much higher temps.)  

SUMMARY:  

Disregard the indicated pressure value shown for PT180 as it is not valid (the value at the time of gauge de-energization is latched in Beckhoff?) 
Also, I will need access to the LVEA later this evening and twice tomorrow, Friday, to make measurements and adjustments.