Fluid monitoring

Details Fluid monitoring Fluid monitoring

1994-07-28

1997-03-25

Porta, David P.

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

250345, G01N 2135

Patent

active

056147198

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

This invention relates to apparatus for and a method of monitoring for the presence of a fluid and is especially, but not exclusively, related to the monitoring of a gas in a dirty environment, such as, a mine or other high particle-contaminated environment.
Such inventive apparatus and method may also be used for the detection and/or qualitative and/or quantitative analysis of a fluid.
Any fluid exhibits a characteristic light absorption spectrum which can be used to monitor the presence and quantify the amount of the fluid in a given sample. The precise configurations of such absorption spectra vary from fluid to fluid but generally consist of both fundamental and derived overtone absorption bands. Thus, a choice of wavelength region for a fluid to be monitored is usually available. Additionally, some fluids also exhibit regular comb-like absorption spectra structures around their primary absorption lines, examples of such fluids being methane, carbon monoxide and oxygen.
A conventional gas monitoring arrangement consists of a light source, wavelength band filter and an appropriate detector plus a gas sample cell through which light from the source is passed.
If a DC system of monitoring is employed, then a reference beam is required for calibration purposes. In a "dirty" environment, such as, a coal mine, there is considerable scope for measurement errors, in that it is difficult to ensure that the sample and reference beams are equally affected by any contamination.
Also, such known arrangements tend to lack sensitivity and, hence, are not suitable for use in monitoring low level fluid leaks.
It is an object of the present invention to provide apparatus for and a method of monitoring for the presence of a fluid which overcome, or at least substantially reduce, the disadvantages associated with the known fluid monitoring arrangements discussed above.
Accordingly, one aspect of the invention resides in fluid monitoring apparatus comprising electromagnetic radiation sources arranged to provide respective reference and sample beams of electromagnetic radiation, the wavelength of the electromagnetic radiation preferably being matched with that of the absorption spectrum of a fluid to be monitored, a first cell which contains a reference sample of the fluid to be monitored and through which the reference beam of electromagnetic radiation is passable, a second cell which is capable of containing a working sample of the fluid to be monitored and through which both the reference and sample beams of electromagnetic radiation are passable, means arranged to detect the reference and sample beams independently of each other after they have passed through the second cell and to provide respective signals representative of the independently-detected beams, and means arranged to compare said signals in order to determine the presence, and preferably also the concentration, of any working sample of fluid to be monitored in the second cell.
In accordance with a second aspect of the invention, there is provided a method of monitoring for the presence of a fluid, comprising passing through a first cell containing a reference sample of the fluid to be monitored a reference beam of electromagnetic radiation, passing through a second cell capable of containing a working sample of the fluid to be monitored the reference beam of electromagnetic radiation and a sample beam of the electromagnetic radiation, the wavelength of the radiation preferably being matched with that of the absorption spectrum of the fluid to be monitored, detecting the reference and sample beams independently of each other after they have passed through the second cell, providing respective signals representative of the independently detected beams and comparing said signals to determine the presence, and preferably also the concentration, of any working sample of fluid to be monitored in the second cell.
The reference and sample beams may be of any suitable form, as long as they can be detected independently of each other. For example, they

REFERENCES:
patent: 3005097 (1961-10-01), Hummel
patent: 5155545 (1992-10-01), Rinke
patent: 5160843 (1992-11-01), Lehto

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