Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1996-06-04
1998-02-10
Glick, Edward J.
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
25033911, 2503418, G01N 2101, G01N 2149, G01N 2185
Patent
active
057172102
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a measuring device for measuring the amount of solids contained in a liquid.
BACKGROUND OF THE INVENTION
There is a need in many processes to know the amount of solids contained in a liquid. In some instances, very small quantities of particles contained in a liquid, i.e. concentrations of a few p.p.m., must be measured, such as in water treatment plants for controlling the purity of drinking water. In other instances, the concentration of fibers suspended in water used in paper mills must be measured to control the various stages during the paper making process. In other industries, such as the food industry there is an interest in measuring the moisture content in food products.
It is known in the art to use photometrical measuring devices by using pulsating light, most often infrared (IR) light, to measure the concentration of particles in liquids. For example, the Swedish Patents Nos. SE-B-382 116, SE-B453 015 and European Patent No. EP-A-96 696 disclose such devices. However, the drawbacks of the earlier devices are many.
When a light beam is passed through a material, the optical radiation is attenuated according to the following formula: when the beam has travelled a distance 1, or, when used for measurement of concentration, the concentration of particles, and .mu. (.lambda.) is the attenuation coefficient. The attenuation coefficient is composed of two components: the absorption coefficient .lambda. and the scattering coefficient s so that .mu.=.lambda.+s. Of these two components, .lambda. is very dependent on the wavelength. Thus, the choice of wavelength is important and therefor infrared fight is chosen for which the absorption is low.
This is important according to the known transmission techniques, because the light transmitted through a suspension is measured, and the difference between the emitted and detected light is a measure of the concentration of solids in the liquid. Too much light must not then be absorbed, leading to low measurement signals.
However, problems with the known technologies stiff remain, because the transmitted energy detected depends exponentially on the concentration according to the formula above so that the detected energy is drastically reduced for higher concentrations of solids. In order to obtain reasonable measurement value signals, it is necessary to use high energies and to transmit short pulses at long intervals in order not to overload the IR-diodes.
The exponential relation also provides further problems such as a need for post treatment of the signals detected to obtain signals that vary according to a linear relationship.
The transmission technology and the exponentially decreasing energy values detected in relation to the concentration of solids implies that the measuring device often cannot be used directly in the process because the distance between transmitter/detector and/or the concentration would be so large that no light could be transmitted. This is solved, as described in Swedish Patent No. 453,015, by diverting a portion of the current and forcing this through a pipe with a defined diameter and with the transmitter/detector positioned opposite each other to provide a "two-dimensional measurement." This requires extensive pipeline constructions for diverting a portion of the current to be measured.
Drawbacks in the form of signals that are not related to the concentration, such as reflection disturbances, temperature dependence of the IR-diodes for the exchange of light, deposits on the sensors and so forth i.e. noise, are difficult to compensate for with the known two-dimensional transmission technologies. In Swedish Patent No. 453,015, a reference device is disclosed that consists of a measuring reference unit in heat transmitting contact with a liquid feeding pipe, wherein the unit is devised to compensate for the temperature dependency of the IR-diodes and the remaining components in the system as well as for any incoming scattered light. These reference units do not measure through the
Bexelius Per
Todor Andreas
Bednarek Michael D.
Glick Edward J.
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