Dust measurement

Details Dust measurement Dust measurement

1981-02-12

1983-12-13

Sikes, William L.

Optics: measuring and testing

For size of particles

By particle light scattering

250565, 250574, 356341, 356343, G01N 1502

Patent

active

044202563

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a method for obtaining meaningful and utilizable electrical signals for measurements of flowing, substantially spherical particles (dust particles), using a light source which is adapted to illuminate the particles with light in a direction different from the direction of flow of the particles.
The environmental legislation and the process-technical development have led to an increased interest in instruments for continuous measurement of dust emissions. This applies to registration of the amount of emission to a recipient and to controlling its state as well as to supervision of operating conditions of dust emitters and the state of purification plants.
Existing instruments for continuous measurement of dust emission are substantially based on optical methods, where light used to illuminate a flowing medium containing particles is detected by a light detector disposed opposite the source of light. Otherwise a combined light source/detector unit is mounted at one end of the emission channel and the reflector unit at the opposite end. The damping of the light intensity caused by the dust is measured, and the obtained values is used as a measure of the particle concentration. However, damping will be considerably greater for fine particles than for large ones for the same mass concentration. Therefore, the correctness of the measurement values will be very dependent on the composition of the dust with respect to the particle size which often shows great variations.
The difficulties mentioned above are overcome by the invention. In accordance therewith, at least two light detectors are arranged in such a way that the light in the beam path from the light source to the first detector is substantially only influenced by as well loss by scattering as light absorption by the particles and this means that it is positioned on the opposite side of the sample from the light source on the axis of the incident beam, and that the light in the beam path from the light source to a second detector substantially only passes via reflections against the particles and this is provided by having the second detector positioned on the opposite side of the sample from the source on an axis angled with respect to the axis of the incident beam. Furthermore, the d.c. voltage component of the output voltage from the first detector related to the supply voltage to the light source is brought to act upon the d.c. voltage component of the output voltage from the said second detector, and the resultant signal is used to form a signal L. The a.c. voltage component from one of the said detectors is filtered out and the average value of the true R.M.S. value is formed and squared, and a signal R is formed on the basis of said squared average value of the true R.M.S. value. According to the invention, a signal A=.sqroot.L.multidot.R proportional to the concentration and/or a signal B=.sqroot.L/R to the average particle diameter are formed and constitute the utilizable signals.
On one hand, the method according to the invention will give a measuring result of the amount of dust particles that is independent of the particle size and of the flow rate, and on the other hand a measuring result of the average diameter of the dust particles in the measuring sample will be obtained and will be independent of the amount of dust particles.
The method is founded on the basic signals and on the placing of the elements necessary for the method which are described in the Swedish patent specification 7706320-4. (This is a third Swedish addition to a parent application that has further more matured into e.g. U.S. Pat. No. 4,110,044, the subject matter of which is specifically incorporated herein by reference. A method for obtaining a measure of the concentration of particles suspended in a liquid is described in the Swedish patent specification. Said method is very well suited for measuring particles above a certain size whether they are suspended in a liquid or are gas-carried. The new method according to the invention espec

REFERENCES:
patent: 4078863 (1978-03-01), Eriksson et al.
patent: 4110044 (1978-08-01), Pettersson et al.
patent: 4167335 (1979-09-01), Williams
patent: 4193692 (1980-03-01), Wynn

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