Calibration standard for infrared absorption gauge
First Claim
1. A calibration standard for an infrared absorption gauge, said gauge having a source of infrared radiation, an exit to enable said radiation to reach a sample zone and an entrance to transmit the radiation reflected from the sample zone whereby the amount of sorbed substance on a sample, located in the sample zone, can be measured, the calibration standard comprising an assembly which includes spectrally selective absorption means to receive infrared radiation from said exit when said calibration standard co-operates with said absorption gauge, said spectrally selective absorption means having an infrared absorption spectrum resembling that of the substance to be measured, and optical means to return infrared radiation, which has passed through said spectrally selective absorption means, to said entrance substantially along the same path as that followed by infrared radiation from the sample zone to said entrance in the absence of the calibration standard.
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Accused Products
Abstract
The calibration standard is attached to a sensing head of an infrared absorption gauge for the purpose of calibrating the gauge. The calibration standard includes spectrally selective absorption means having a spectrum closely resembling that of a substance to be measured, such as water sorbed onto a paper sample. The calibration standard also includes optical means for returning infrared radiation, which has passed through the absorption means, to the absorption gauge substantially along the same path as would normally be followed by the radiation reflected from the sample in the absence of the standard. The spectrally selective absorption means is preferably made of anhydrous material, such as glass containing a rare earth substance, or polypropylene, which is stable. The optical means may include diffusing means and a reflective plane. According to one arrangement, the calibration standard comprises a housing with a window at one end, a plurality of diffusing elements attached to a central portion of the window and a reflective plane spaced from the diffusing elements. The window and/or the diffusing elements and/or the reflective plane may comprise or include the spectrally selective absorption means. Various arrangements are described.
29 Citations
33 Claims
- 1. A calibration standard for an infrared absorption gauge, said gauge having a source of infrared radiation, an exit to enable said radiation to reach a sample zone and an entrance to transmit the radiation reflected from the sample zone whereby the amount of sorbed substance on a sample, located in the sample zone, can be measured, the calibration standard comprising an assembly which includes spectrally selective absorption means to receive infrared radiation from said exit when said calibration standard co-operates with said absorption gauge, said spectrally selective absorption means having an infrared absorption spectrum resembling that of the substance to be measured, and optical means to return infrared radiation, which has passed through said spectrally selective absorption means, to said entrance substantially along the same path as that followed by infrared radiation from the sample zone to said entrance in the absence of the calibration standard.
- 20. A calibration standard for an infra-red absorption gauge comprising a window for transmitting infra-red radiation, diffusing means for diffusing the infra-red radiation, a reflective plane, and spectrally selective absorption means having an infra-red absorption spectrum resembling that of the substance to be measured, said spectrally selective absorption means being arranged to transmit the infra-red radiation therethrough, and said reflective plane being spaced from said diffusing means and arranged to return the infra-red radiation to said window.
Specification