Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1996-07-01
1999-01-26
Hannaher, Constantine
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
250373, G01N 2159
Patent
active
058641408
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus for measuring characteristics of a liquid. In particular, but not exclusively, the invention relates to an ultraviolet (UV) absorbency-based monitor for measuring the amount of organic pollution in a liquid, and is of application for on-line monitoring of water quality at locations such as industrial or water treatment plant effluent outlets, rivers or reservoirs.
2. Description of the Prior Art
A number of methods are available for determining the biological or organic pollution in water, involving the measurement of parameters such as BOD (biochemical oxygen demand), TOC (total organic carbon) or COD (chemical oxygen demand). The parameter that is usually of most interest is the BOD.
A number of on-line, continuous BOD monitors are available that operate by measuring the absorbency of ultraviolet (UV) light by a sample. These monitors are based on the principle that a particular substance will absorb light of a particular wavelength (or wavelengths), so that the reduction in intensity of light of that wavelength, when transmitted through a sample containing the substance, can be related to the concentration of that substance. Aromatic organic compounds, and other organic compounds that have conjugated double bonds, absorb light in the UV wavelength region and research has shown that absorbency measurements taken in that region, and in particular at 254 nm, can be related to BOD (and also to TOC and COD).
In one such monitor, the amount of organic matter in a liquid sample is determined by passing a liquid sample through a flow cell, passing UV and visible light through the sample and making measurements of the absorption of UV light by the sample and the absorption and scatter of visible light. The amount of organic matter in the sample is determined from the measured absorption of UV light, with the visible light measurements being used for compensation purposes.
One disadvantage of the known monitor is the tendency of the flow cell to become fouled by substances in the liquid sample, which can result in the windows for the UV and visible light monitors becoming obscured. This reduces the accuracy and efficiency of the monitor and can eventually prevent operation. It is necessary, therefore, to clean the flow cell at regular intervals, which is costly and time-consuming and can prevent automatic operation of the monitor.
OBJECTS AND SUMMARY OF THE INVENTION
There is a need, therefore, for an apparatus for measuring characteristics of a liquid, that resists fouling by substances in the liquid and which can clean itself when fouling occurs.
According to the present invention there is provided an apparatus for measuring characteristics of a liquid, the apparatus including a channel through which, during operation, the liquid flows and a plurality of sensors for measuring characteristics of the liquid as it flows through the channel, the cross-sectional area of the channel being substantially constant so that, during operation, liquid flows through the channel at a substantially uniform speed.
This reduces turbulence in the liquid, which in turn helps to reduce fouling of the channel by substances in the liquid.
Advantageously, the cross-sectional shape of the channel varies along its length, according to the requirements of the different sensors. The cross-sectional shape of the channel may vary to accommodate one or more sensors located within the channel. By varying the shape of the channel while keeping its cross-sectional area constant, the needs of the different sensors can be met, without causing turbulence in the liquid.
Advantageously, the two transverse axes of the channel are of different lengths, at least one sensor being arranged to measure a characteristic of the liquid between points at opposite ends of one of the transverse axes and at least one other sensor being arranged to measure a characteristic of the liquid between points at opposite ends of the other transverse axis.
Advantageously, at le
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Acer Consultants Limited
Hannaher Constantine
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