Fire Weather Geotechnical Historical Pres. The TGA100 Auxiliary Dewar, an optional accessory for the TGA100 Trace Gas Analyzer , extends the TGA100's liquid nitrogen hold time from 15 hours to 4 days. Unlike an automatic fill system that senses the liquid level in the laser dewar and controls a valve to refill the dewar, the TGA Auxiliary Dewar maintains a constant liquid level in the TGA100 laser dewar. It has no need to measure the liquid nitrogen level, and no moving parts, so it can provide reliable performance at a reasonable cost. An access port in the top of the cover allows the auxiliary dewar to be filled without removing the cover.
Liquid nitrogen flows by gravity into the laser dewar.
A sealed chamber around the fill tube forces the displaced gas to bubble back up the fill tube. When the liquid nitrogen in the laser dewar rises to the bottom of the fill tube, gas can no longer escape. This causes the laser dewar to be slightly pressurized by the weight of the liquid nitrogen in the auxiliary dewar. As the liquid nitrogen boils in the laser dewar, the liquid level drops to the end of the fill tube, allowing the gas to bubble up through the fill tube. This maintains the level of the liquid nitrogen in the laser dewar at the bottom of the fill tube.