"Ported To Atmosphere" Caisson Gauge - 160mm Diameter Waterproof Case

160mm diameter caisson gauge designed to have the  internal reference chamber ported outside the hyperbaric chamber to atmospheric. This gives potentially greater accuracy than a conventional caisson gauge as the balance reference chamber is always using live atmospheric pressure rather than a pre-trapped value. 

Chamber pressure enters the gauge via a special port at the bottom of the gauge which is protected with an air filter. This port is connected to the bourdon tube measuring element inside the gauge. 

The process connection at the bottom of the gauge, which is open to the internal void of the gauge, is used to connect the gauge to a vent pipe leading outside of the hyperbaric chamber thus venting the gauge to atmosphere. Please note this thread connection port should not be used when calibrating the gauge.    

The gauge, with accuracy 0.25% full scale, is designed to be surface mounted within the hyperbaric chamber and is constructed around the workings of a conventional bourdon tube pressure gauge. This design allows the instrument to be bench calibrated in a similar fashion to other oxygen cleaned bourdon tube pressure gauges. Calibration is carried out by removing the air filter and connecting the female threaded port a suitable pressure source.