METHOD AND APPARATUS FOR MEASURING MOISTURE CONTENT

Abstract: Method for measuring the water content and a measuring apparatus. The method is based on the backscattering of infrared radiation. According to the invention the moisture content within the material can be reliably measured when the measuring detector is at least partially inside the material under examination. A radiation source (1) and infrared detector (5) are located within the frame (7) of the measuring head. The radiation is guided by a lense (2) through the window (3) to the material under examination. The backscattered radiation is conducted through a lense (4) to the infrared detector (5).

Description: METHOD AND APPARATUS FOR MEASURING MOISTURE CONTENT The present invention relates to a method for measuring the water content, i.e. the moisture content, or the con¬ tent of any other ingredient in a given material, which method is based on the backscattering of infrared radia¬ tion; the present invention also relates to an apparatus for realizing the said method. The measuring of moisture content by means of a method which is based on the backscattering of infrared radia- tion is generally known in the prior art, and in commer¬ cial distribution there are several devices which are operated according to the said method. These methods are, however, designed to measure the moisture content of a given material without touching the material itself, and the measurement is carried out by means of such equip¬ ment which is typically designed to be permanently in¬ stalled in connection to a conveyor band. The moisture content of any material can differ remarkably between the surface and the. inside, and this is a drawback when the measuring takes place on the surface. Moreover, a method which measures a given material without touching it is sensitive to any interference caused by surround¬ ing radiation, and consequently cannot be applied to portable apparatuses. Several different methods have been experimented for mea¬ suring the moisture content of a given material within the material itself; among them can be mentioned for in¬ stance a method which is based on the measuring of the dielectric constant, and a method which is based on mic- rowave absorption. All of these methods include, however, certain drawbacks from the point of view of operation ac¬ curacy, construction costs or work safety. The purpose of the present invention is to achieve a measuring method which eliminates the aforementioned drawbacks and which allows for a reliable, simple and accurate measuring of the moisture content of a given material, so that the measuring operation takes place within the said material. Apart from water content, the present invention is also suited for measuring other in¬ gredient contents in a given material. The purpose of the present invention is achieved by means of a method which is characterized by the novel features enlisted in the Patent Claim 1. Another purpose of the present invention is to realize a measuring apparatus, the operation whereof is based on the backscattering of infrared radiation, which appara- tus can be used within the material under examination, so that the measuring is carried out reliably, simply and accurately. In addition to water content, the apparatus of the present invention is also suited for. measuring other ingredient contents in a given material. This latter purpose of the present invention is realized by means of an apparatus which is characterized by the novel features presented in the Patent Claim 4. In the following the apparatus is described with refe¬ rence to the appended drawings, where Figure 1 shows a cross-section view of one preferred em¬ bodiment of the invention, and Figure 2 shows such a preferred embodiment of the inven¬ tion where optical fiber cable is used. Figure 3 shows another embodiment of the invention where optical fiber cab s used. Infrared radiation is transmitted from the radiation source 1 to the lense or lenses 2 and through the lense or window 3 right into the material 9 to be examined. The frame 7 of the measuring head of the apparatus pene- OMPI trates so deep into the said material, that the whole window or lense 3 is covered by the material 9. The infrared radiation which is scattered back from the ma¬ terial 9 is directed through the window or lense 3 and further through the lense or lenses 4 into a two-chan¬ nelled infrared detector 5. The electric signal recei¬ ved from the infrared detector 5 is processed in the electronic controlling and analyzing unit 8. The infrared radiation source 1 is electrically modula- ted, and the intensity of the modulated radiation is stabilized by means of a constant-controlling signal or on the basis of the signal received from the reference detector 6. The infrared detector 5 comprises two sepa¬ rate infrared detector elements, each of the said ele- ments having a separate interference filter, and a tem¬ perature-dependent member. The interference filters are used for separating the relevant wavelengths, which are to be analyzed in the measurement, from the infrared ra¬ diation scattering back from the material 9 under exami- nation. The temperature-dependent member is used for observing the temperature of the infrared detector 5, and, if necessary, for adjusting the temperature dependence of the electric signal received from the detector 5. By employing the above described, two-channelled infra- red detector 5 and the electrical modulation of the infrared source 1 , it is possible to make both the opti¬ cal and the mechanical structure of the measuring appa¬ ratus simpler, more endurable and better suited for field use than such prior art measuring apparatuses which are based on the backscattering of infrared radiation but where a rotating interference filter disc is used. That part of the measuring head which is stuck into the material can be constructed of pieces of optical fiber (10, 11), in which case the infrared radiation is direc- -gUREAl/ OMPI IS) t- t-* Cπ o cπ O

Claims: Claims 1. A method for measuring moisture content, the said method comprising an infrared radiation source (1), a system for guiding infrared radiation (2-4), a measuring head (7,14), an infrared detector (5) as well as an analyzing device (8) , c h a r a c t e r i z e d in that the measurement is carried out basing on the backscattering of infrared radia¬ tion so thatthe measuring detector is at least partially located inside the material under examination. 2. The method of claim 1, c h a r a c t e r i z e d in that the infrared raditation impulse is brought into the material from outside by means of a fiber optic cable (10), a mirror (12) and a lense or a window (13) and the back- scattered radiation is guided away from the material via the lense or the window (13), the mirror (12) and, the fiber optic cable (11) . 3. The method of claim 1 or 2, c h a r a c t e r i z e d in that the infrared radiation is created in the source (1) within the measuring head (7) which is pushed into the material. 4. An apparatus for applying the method of claim 1, the said apparatus comprising a radiation source (1) , means (2-4) for guiding radiation and means (5) receiving radia¬ tion, c h a r a c t e r i z e d in that the water content of the material under examination is measured by means of a measuring head pushed inside the said material, the said measuring head consisting of a frame (7) and of an infra¬ red radiation source (1) which source is located within the frame (7) and is electrically modulated and stabilized by standardizing the modulation signal or on the basis of the feedback signal received from the reference detector (6), of a lense or lenses (2,4), a window or lense (3) and of a two-channelled infrared radiation detector (5) consist¬ ing of two separate infrared detector elements, two sepa- rate interference filters OMPI and a temperature-dependent member, the measurement being-carried out so that infrared radiation.is con¬ ducted from the source (1) through the lense or lenses (2) and through the window or lense (3) into the mate- 5 rial (9) under examination, and the infrared radiation which is scattered back from the material (9) is con¬ ducted through the window or lense (3) and ' through the lense or lenses (4) to the infrared detector (5) , and • the temperature-dependence of the electric signal is ad- 10 justed by means of the temperature-dependent element installed within the said detector (5) , whereafter the ( ' - " ■ said signal is analyzed, in order to indicate the moistu¬ re content, by means of an analyzing device (8) which is electrically synchronized with the modulation signal 15 of the source (1). 5. The apparatus of Claim 4, c h a r a c t e r i z e d in that the temperature of the infrared detector (5) is stabilized by means of a cooling/heating element instal¬ led within the detector (5) . 20 6. The apparatus of Claim 4 or 5, c h a r a c t e r i ¬ z e d in that the infrared detector C5) which is employ¬ ed is provided with three or more channels. r 7. The method of claim 1, 2 or 3, c h a r a c t e r i z¬ e d in that the method is used for measuring other ingredien ^ 25 content than, water content in a given material

Inventors: HUTTUNEN PAAVO, HYVAERINEN TIMO, LAMMASNIEMI JORMA, HUTTUNEN, PAAVO, HYVAERINEN, TIMO, LAMMASNIEMI, JORMA
Applicants: VALTION TEKNILLINEN, VALTION TEKNILLINEN TUTKIMUSKESKUS
Application year: 1982
Main classification: G01N21
IPC codes: G01N21