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Monitoring gas and vapor concentrations

  • US 4,563,585 A
  • Filed: 09/23/1982
  • Issued: 01/07/1986
  • Est. Priority Date: 09/23/1982
  • Status: Expired due to Fees
First Claim
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1. In a method of monitoring low gas or vapour concentrations in a sample by correlating the behaviour thereof in respect of light at at least one first wavelength corresponding to at least one behavioural maximum of the gas being monitored with that in respect of at least one second adjacent wavelength at which the gas shows a behavioural minimum, the improvement wherein the first and second wavelengths are selected by passing light from a common entry beam through a spectrometer comprising slitted entrance and exit masks and an optically diffractive component, one of said masks having a plurality of slits determining different angles of diffraction of said first and second wavelengths, and selecting said first and second wavelengths alternately by permitting alternate passage of said light through slits in said mask with plural slits corresponding to angles of diffraction characteristic of said first and second wavelengths respectively, wherein light is selectively masked from slits in said mask with plural slits by movement of a slotted shutter, and movement of said slotted shutter is monitored and utilized to trigger a precision electronic gating signal operating to gate signals from a photodetector receiving light from the spectrometer for precisely controlled durations fully within periods when said selected slits are fully masked or unmasked, and wherein said light is passed through said sample between said exit slit and said photodetector.

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