The Fisher 2100 on/off pneumatic switch and 2100E electric switch sense high or low liquid levels. Typically, these switches pneumatically or electrically operate safety shutdown systems for field processing equipment in oil and gas production applications. The 2100 and 2100E switches use a displacer-style sensor located in an external cage that mounts on the outside of a vessel. Unless otherwise noted, all NACE references are to NACE MR0175-2002.