Introduction to the OXY2 measurement system
Inert gas welding requires the exclusion of oxygen from the weld
zone during the welding process. The shield gas ( typically argon ) needs to be
free of oxygen from air leaks into the feed hose and the back side of the weld
needs to be protected with a purge, or backing,
ensure a low or controlled oxygen concentration on the back face of the weld.
On the front face of a weld the the inert gas stream (provided it is free of
leaks ) efficiently excludes oxygen from the weld zone. On the back side of the
weld special precautions must be taken to prevent oxidation. This involves the
isolation of the back side of the weld with fixtures that provide for the purging of this area
with an inert atmosphere. The OXY2 instrument works with these fixtures to
continuously sample the purge gas and to monitor the oxygen concentration.
Monitoring the weld gases with an OXY2 adds a quantifiable element of quality
control to the inert gas welding process. It also provides an economic benefit
by giving the welder the information he needs to accurately judge the purge gas
flow rate and purge period.
Principle of Operation of the weld gas analyzer
The unit contains a small pump which draws a continuous sample
from the purge gas in the welding zone. This sample is passed into a special
zirconium detector that is very sensitive to the presence of oxygen. A
zirconia sensor is an electrochemical oxygen concentration cell with a solid
ceramic electrolyte. It has the property of producing a small emf (voltage) in
the presence of oxygen. The relationship between the emf produced by the
detector and the oxygen concentration is well understood and highly repeatable.
This means that the detector can be calibrated directly in oxygen concentration
units. Sensors of this type can be used to measure concentrations from a few
ppm all the way up to 100% oxygen. They are very reliable, the calibration is
stable over long periods (years) and a detector calibrated for use with low ppm
concentration as in the welding application will not saturate or show any
degradation when exposed to high oxygen concentrations (air for