A Solid State Gas Density Monitor for Gas Insulated Substation Equipment

A solid state gas density monitor has been developed for SF6 service in gas-insulated substation equipment that is based on principles and construction techniques similar to ionization-type fire alarms. The monitor has a resolution of .7kPa (.1 psi) at 20°C. and, depending on ion chamber voltage and geometry, exhibits a linearity of ±1. to ±4. kPa (±.15 to ±.6 psi) at 20°C. over the density range 0.20 to 0.66 MPa (30 to 95 psia) at 20°C. The monitor incorporates two level contact closure actuated by gas density falling below one of two pre-set alarm limits, and an LCD read-out for visual monitoring and instrument calibration. The display presents density in terms of equivalent psia at 68°F (20°C.).