Abstract: According to various embodiments, a sensing device for measuring oxygen concentration cycles in breath is disclosed. The sensing device includes a laser configured to emit light at an A-band of oxygen, a lens configured to collimate the light, and a multi-pass cell configured to contain a replaceable sample cell. The light passes through the multi-pass cell and is attenuated by oxygen in the sample cell. The sensing device further includes a photodetector configurated to convert the attenuated light into an electrical signal, and a lock-in amplifier or an equivalent processing circuit configured to determine oxygen concentration from the electrical signal.

Abstract: A lightweight pup joint comprising a length of pipe with male and female union subs on the ends and having integral metallic fluid contacting components. The pipe is formed with a minimum wall thickness required for the intended pressure rating and includes a radially enlarged portion on one end to form a male sub. The other end of the pipe includes a small radial flange sized so a union nut can be moved over the flange. A split female sub is assembled over the flange and held together by a snap ring. An annular sealing member seals gaps between portions of the female sub, seals an interface between the flange and the female sub, and seals a gap between the flange and a male sub of an adjacent pipe. At least one ear on the pipe fits into a slot in the female sub to prevent rotation of the female sub when the union nut is threaded onto the female sub.