Optical transmission cell with minimized spurious absorption
A spectroscopic measuring device for minimizing spurious absorption due to undesired gases. The device includes a probe body, or a transmission cell formed from a central measurement cell and first and second probe bodies. Each probe body is subject to leakage of undesired gas, especially over time in the presence of high pressure gas. Each probe body includes a bore located between a primary window disposed at or near a distal end and a secondary window located at or near the proximal end. It being observed that the absorbance is proportional to the pathlength and inversely proportional to the volume as long as the pressure in the probe body remains low compared to that in the measurement cell, a glass filler rod is located in the bore and a is void located adjacent to the filler glass rod, thereby minimizing spurious absorption even in the presence of leakage.
1. A spectroscopic measuring device for minimizing the effect of undesired gases that that interferes with measurement, comprising:
a central section for receiving a gas passing through the central section to be analyzed;
first and second probe bodies that are inherently subject to leakage of undesired gas, wherein the first and second probe bodies are attached to the central section with one injecting light into the central section and one collecting light from the central section in order to measure a characteristic of the gas passing through the central section, and wherein each probe body
comprises:
an axis, a distal end, a proximal end, and an interior;
a primary optical window disposed at or near the distal end of the probe body and sealed with respect to the probe body;
a secondary optical window located at or near the proximal end of the probe body and sealed with respect to the probe body, a bore in the interior of the probe body that defines an optical path between the primary optical window and the secondary optical window, the bore having a nominal length and a nominal volume;
a filler rod located in the bore and capable of transmitting light entering the primary optical window along the nominal length of the bore; and
a void in fluid communication with the bore and located adjacent to the filler rod and outside of the optical path, the void increasing the nominal volume of the bore and providing a location for holding undesired gas outside of the optical path;
wherein each filler rod fits tightly within a first portion of the bore and wherein each void comprises an expanded space in a second portion of the bore.
2. The spectroscopic measuring device of claim 1 , wherein the primary optical window of each probe body is sealed with respect to the respective probe body by a high pressure seal comprising a “C”-ring.
3. The spectroscopic measuring device of claim 1 wherein each filler rod is a glass rod.
4. The spectroscopic measuring device of claim 1 wherein each void comprises an expanded space around a portion of the filler rod.
5. The spectroscopic measuring device of claim 1 wherein the first portion is a distal portion of the bore and wherein in the second portion is a proximal portion of the bore.
6. The spectroscopic measuring device of claim 5 wherein each bore has a first diameter in the distal portion and a second larger diameter in the proximal portion, the void being formed by the second larger diameter in the proximal portion.
7. The spectroscopic measuring device of claim 1 wherein the central section comprises a cross fitting.
8. The spectroscopic measuring device of claim 1 wherein the light comprises near-infrared radiation.