GB1582673A

GB1582673A - Ice detector

Info

Publication number: GB1582673A
Application number: GB627078A
Authority: GB
Original assignee: Apparatebau Gauting GmbH
Current assignee: Apparatebau Gauting GmbH
Priority date: 1977-02-18
Filing date: 1978-02-16
Publication date: 1981-01-14
Also published as: FR2381288B3; FR2381288A1

Description

(54) ICE DETECTOR (71) We, APPARATEBAU GAUTING GmbH., a German company of Ammerseestrasse 31, D-8035 Gauting, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to an ice detector, for example for aircraft, comprising a sender which generates radiation directed against a detection surface susceptible to icing, and a receiver which receives the radiation reflected by the detection surface as a function of its condition of icing, and an evaluvation circuit which evaluates a signal generated by the receiver for determining the icing condition.

One embodiment of this type of ice detector is known from U.S. Patent 2 359 787.

Light is used here as the radiation; and the detection surface consists of glass. The deector apparatus operates according to the principle of the Snellius computation law.

When ice settles on the detection surface, the total optical density of the detection surface (glass and ice) alters also, whereby the angle of refraction is altered. Less light then falls on to the receiver than in the case of an un-iced detection surface.

The known ice detector has the disadvantage that it responds only after actual icing has occurred. However, it is desirable, in particular when using the ice detector in aircraft, to have a warning even before the actual icing.

According to the present invention there is provided an ice detector comprising a sender for generating radiation which is directed against a detection surface susceptible to icing, a receiver which is arranged to receive radiation reflected by the detection surface as a function of its condition of icing and which is operable to generate a corresponding signal, and an evaluation circuit for evaluating the signal generated by the receiver for determining the icing condition, wherein the detection surface is provided with a cooling device for accelerating artificially the formation of ice thereon.

With this cooling device, it is possible to simulate on the icing surface a condition which does not yet obtain but which may occur shortly. An icing alert can be given when the icing tendency begins to increase while the cooling of the detection surface remains unchanged. It is of advantage that, with artificial icing, specific parameters may be taken into consideration. In an aircraft, for example, the danger of icing is not the same at all points. It also depends on the shape of the aircraft as well as, in addition to the meteorological conditions, the height and the speed of the aircraft. Parameters such as the location in the aircraft where the danger of icing is to be determined, the shape of the aircraft, the height and the speed may be taken into consideration when artificial icing is employed. This makes the ice detector universally usable.

The artificial icing on a relatively small detection surface does not impair the aerodynamic properties of an aircraft. Since, on the other hand, the ice dectetor warns before an immediately imminent icing, heating elements can be introduced at the endangered locations in good time before icing, so as to forestall the icing.

An advantageous development of the invention may consist in that a rising or fall ing temperature curve is generated by the cooling device above the detection surface and that the chronological dependence of the icing at points of variable temperature is determined as the measure for the speed of icing, and a measure for the intensity of icing is derived from the integration of the icing speed over time.

To obtain the rising or dropping temperature curve above the detection surface, the cooling device may be formed of a plurality of thermoeiectrical cooling elements (Peltier elements) which are preferably distributed on the irradiated side of the detection surface and disposed at a distance from each other, making possible variable cooling of different areas of the detection surface as well as their heating in a reversing operation. With heating, it is possible to thaw out the ice that has formed on the detection surface due to the artificial icing, and the ice detector may thereby be again made ready rapidly for measurements under new conditions.

The thermoelectrical cooling elements may f ;r example be disposed on the detection surface in the form of concentric rings.

In this instance, the desired rising and falling temperature curve can be generated along cycloids.

Another advantageous modification of the invention may consist in that the frequency band of the sender and/or the receiver is narrow and selected so that in this frequency band the influence of ice on the reflection factor of the detection surface is different from that of water, sodium chloride crystals, or other impurities. This measure starts out from the known fact that, due to their different molecular structure and, insofar as they also have a crystalline structure (ice and sodium chloride), the individual media have different absorption coefficients and thereby variable reflection factors for various frequencies of electromagnetic waves, particularly for light.Experiments have shown that an ice detector can differentiate particularly well between ice and water if the radiation is infrared light and if the sender and/or the receiver operate preferably at a wavelength of 12 or 14 ,um.

A further practical development may consist in providing, in the ray path between the sender and the reflection surface, a test layer which is normally radiationpermeable and whose reflection characteristics are definably changeable for testing the ice detector. If light is used for radiation, the test layer may be formed of a liquid crystal plate or a plate of ferroceramic material disposed between the sender and the detection surface.

As a practical matter, the deflection surface is integrated into the skin of the aircraft when such is its intended use. Natural icing conditions are thereby simulated; further, the aerodynamic properties of the aircraft remain unaffected by the ice detector, this being of importance for example if it is built into helicopter rotor blades.

In order to prevent adverse influences due to external light which can fall through the detection surface if it is made of glass, it is further proposed that the amplitude or intensity and/or the frequency and/or the phase of the radiation emitted by the sender be modulated, and that the receiver have a demodulation member by means of which reflected radiation emitted by the sender may be distinguished from external radiation.

It is further proposed to provide an auxiliary reference signal receiver which is irradiated directly by the sender, and to use the reference signal generated by the reference signal receiver in evaluating the reflected radiation, in order to compensate changes in amplitude or intensity of the radiation emitted by the sender.

A practical construction of the evaluation circuit may provide for receive cells to be connected with a multiplexer by means of which it is possible to obtain a chronologically staggered evaluation of the reflection signals generated by the individual receive cells in order to determine the icing tendency, the icing intensity, and the icing speed An embodiment of the invention is described herein-below in connection with the drawings, by way of example.

There is shown in: Fig. 1 A section through an ice detector which operates with radiation having oscillatory characteristics, in this case electromagnetic radiation in the form of infrared light; Fig. 2 A view from above onto the ice detector shown in Fig. 1; Fig. 3 A block circuit diagram of the ice detector with evaluation circuit; Fig. 4 A graphic representation of the dependence of the absorption coefficient of water and ice on the wavelength of light.

The ice detector as shown in Figs. 1 and 2 is located in a housing 12, which is covered over with a detection surface 1 made of a material which is permeable to the radiation used. On the inside of the detection surface 1, annular thermoelectric cooling elements (Peltier elements) 7 are provided, between which free sections 14 are disposed.

The detection surface 1 is fitted into the skin of an aircraft 3 so that it is flush with the latter.

In the housing 12, an infrared light source 2 is disposed which radiates light with a wavelength of about 12 ,um. The rays which emerge radially from the light source 2 are deflected by a biconvex lens 16, so that they fall onto the deflection surface 1 vertically, substantially parallel to each other. At the free sections 14, the light rays penetrate through the material of the detection plate 1. When ice crystals 15 have formed on the detection plate 1, a part of the light is reflected and arrives, through the free sections 14, back in the interior of the ice detector. In the reflection range of the free sections 14, receiver elements 10 in the form of pyroelectrical crystals are disposed, which respond to the infrared light.

Further, a reference light receiver 9 is disposed in the housing 12 and is irradiated by light coming directly from the light source 2.

On the inside of the detection surface 1, there is further provided a temperature sensor 4 which measures the temperature of the detection surface and acts as a true-value indicator for the detection surface in a temperature control loop.

Between the detection surface 1 and the biconvex lens 16, there is further provided a liquid crystal plate 6 whose transparency is changeable in order to thereby simulate icing and test the functioning of the ice detector.

In order that the receiver elements 8 should react only to reflected infrared light originating from the light source 2, optical filters 8 are further provided between the receiver elements 10 and the detection surface 1.

With the thermoelectrical cooling elements 7, it is possible to adjust a temperature curve above the detection surface 1 rising from the center towards the edge, the curve being indicated by the decreasing density of the ice crystals from the center towards the edge.

Further, the housing 12 contains the electronic evaluation circuit 11 which is illustrated in greater detail in Fig. 3.

As will be seen in Fig. 3, the light generated by the light source 2 is sent through an intensity modulator 19 which is controlled by a modulation control member 20.

The output signals generated by the receiver elements 10 are fed to a multiplexer 18 which is controlled by a time control member 26. Further, the output signal of the reference receiver 9 is fed to the multiplexer 18. The output signals of the receiver elements 10 are conveyed by the multiplexer 18 in chronological succession to a frequency-selective signal amplifier 24. The phase of the amplifier 24 is changed by the modulation control member 20 via a phase shift member 25 in the rhythm of the modulation. The output signal of the amplifier 24 is fed to a discriminator 27 which simultaneously receives a time control signal from the time control member 26.

The output signal generated by the discriminator 27 is tested for icing tendency in a computer section 28. The icing intensity is determined in a computer section 29, and the icing speed is determined in a computer section 30. The data or signals corresponding to the icing intensity and the icing speed are processed in a further computer section 31. At its output 33, this further computer section 31 delivers the information whether icing is to be expected and what icing speed and icing intensitay are to be expected.

The operational parameters, such as for example height, speed, meteorological conditions, location of the ice detector in the aircraft, etc., can be fed into an input 32 of the computer section 31. These data are fed to a control section 22 for a current source 21 with which the thermoelectrical cooling elements 7 are operated. The output signal of the temperature sensor 4 is also fed to the control section 22.

An instruction to test can also be fed into the input 32 of the computer section 31. When this is the case, the liquid crystal plate 6 is obscured and thereby icing is simulated for testing the ice detector.

Further, a thawing signal may be fed into the input 32 of the computer section 31. When this is the case, the thermoelectric cooling elements 7 are operated in reverse and heat the detection surface 1, so that ice that has accumulated thereon is thawed off.

From the graphic representation shown in Fig. 4 it may be seen that the- absorption coefficients of liquid water and ice, given the wavelength of 12 ,am here used, exhibit considerable difference for infrared light.

As a result of this difference, the ice detector is in a position to discriminate whether ice or liquid water or other substances have settled on the detection surface 1. The reflection factor is reversely proportional to the absorption coefficient.

WHAT WE CLAIM IS: 1. An ice detector comprising a sender for generating radiation which is directed against a detection surface susceptible to icing, a receiver which is arranged to receive radiation reflected by the detection surface as a function of its condition of icing and which is operable to generate a corresponding signal, and an evalution circuit for evaluating the signal generated by the receiver for determining the icing condition, wherein the detection surface is provided with a cooling device for accelerating articficially the formation of ice thereon.

2. An ice detector in accordance with claim 1, wherein the cooling device is operable to generate a rising or falling temperature curve beyond the detection surface, and the evaluation circuit is operable to determine the chronological dependence of the icing at a point of variable temperature as the measure for the speed of icing, and to derive a measure for the intensity of icing from the integration of the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. a part of the light is reflected and arrives, through the free sections 14, back in the interior of the ice detector. In the reflection range of the free sections 14, receiver elements 10 in the form of pyroelectrical crystals are disposed, which respond to the infrared light. Further, a reference light receiver 9 is disposed in the housing 12 and is irradiated by light coming directly from the light source 2. On the inside of the detection surface 1, there is further provided a temperature sensor 4 which measures the temperature of the detection surface and acts as a true-value indicator for the detection surface in a temperature control loop. Between the detection surface 1 and the biconvex lens 16, there is further provided a liquid crystal plate 6 whose transparency is changeable in order to thereby simulate icing and test the functioning of the ice detector. In order that the receiver elements 8 should react only to reflected infrared light originating from the light source 2, optical filters 8 are further provided between the receiver elements 10 and the detection surface 1. With the thermoelectrical cooling elements 7, it is possible to adjust a temperature curve above the detection surface 1 rising from the center towards the edge, the curve being indicated by the decreasing density of the ice crystals from the center towards the edge. Further, the housing 12 contains the electronic evaluation circuit 11 which is illustrated in greater detail in Fig. 3. As will be seen in Fig. 3, the light generated by the light source 2 is sent through an intensity modulator 19 which is controlled by a modulation control member 20. The output signals generated by the receiver elements 10 are fed to a multiplexer 18 which is controlled by a time control member 26. Further, the output signal of the reference receiver 9 is fed to the multiplexer 18. The output signals of the receiver elements 10 are conveyed by the multiplexer 18 in chronological succession to a frequency-selective signal amplifier 24. The phase of the amplifier 24 is changed by the modulation control member 20 via a phase shift member 25 in the rhythm of the modulation. The output signal of the amplifier 24 is fed to a discriminator 27 which simultaneously receives a time control signal from the time control member 26. The output signal generated by the discriminator 27 is tested for icing tendency in a computer section 28. The icing intensity is determined in a computer section 29, and the icing speed is determined in a computer section 30. The data or signals corresponding to the icing intensity and the icing speed are processed in a further computer section 31. At its output 33, this further computer section 31 delivers the information whether icing is to be expected and what icing speed and icing intensitay are to be expected. The operational parameters, such as for example height, speed, meteorological conditions, location of the ice detector in the aircraft, etc., can be fed into an input 32 of the computer section 31. These data are fed to a control section 22 for a current source 21 with which the thermoelectrical cooling elements 7 are operated. The output signal of the temperature sensor 4 is also fed to the control section 22. An instruction to test can also be fed into the input 32 of the computer section 31. When this is the case, the liquid crystal plate 6 is obscured and thereby icing is simulated for testing the ice detector. Further, a thawing signal may be fed into the input 32 of the computer section 31. When this is the case, the thermoelectric cooling elements 7 are operated in reverse and heat the detection surface 1, so that ice that has accumulated thereon is thawed off. From the graphic representation shown in Fig. 4 it may be seen that the- absorption coefficients of liquid water and ice, given the wavelength of 12 ,am here used, exhibit considerable difference for infrared light. As a result of this difference, the ice detector is in a position to discriminate whether ice or liquid water or other substances have settled on the detection surface 1. The reflection factor is reversely proportional to the absorption coefficient. WHAT WE CLAIM IS:

1. An ice detector comprising a sender for generating radiation which is directed against a detection surface susceptible to icing, a receiver which is arranged to receive radiation reflected by the detection surface as a function of its condition of icing and which is operable to generate a corresponding signal, and an evalution circuit for evaluating the signal generated by the receiver for determining the icing condition, wherein the detection surface is provided with a cooling device for accelerating articficially the formation of ice thereon.

icing speed over time.

3. An ice detector in accordance with claim 1 or 2, wherein the cooling device comprises a plurality of thermoelectrical cooling elements which are disposed at a distance from each other, making possible variable cooling of different areas of the detection surface.

4. An ice detector in accordance with claim 3, wherein said thermoelectrical cooling elements are distributed on the side of said detection surface which is to be irradiated by the sender.

5. An ice detector in accordance with any one of the preceding claims, wherein the cooling device is operable as a heating device.

6. An ice detector in accordance with claim 3 or 4, or claim 5 when appended to claim 3 or 4, wherein the thermoelectrical cooling elements are disposed on the detection surface in the form of concentric rings.

7. An ice detector in accordance with any one of the preceding claims, wherein the frequency band of the sender and/or receiver is narrow and selected so that in this frequency band the influence of ice on the reflection factor of the detection surface is different from that of water, sodium chloride crystals, or other impurities.

8. An ice detector in accordance with claim 7 wherein the radiation is infrared light.

9. An ice detector in accordance with claim 8, wherein the sender and/or the receiver operate at a wavelength of 12 or 14 ixm.

10. An ice detector in accordance with any one of the preceding claims, wherein there is provided, in the ray path between the sender and the reflection surface, a test layer which is normally radiation permeable and whose reflection characteristics are definably changeable for testing the ice detector

11. An ice detector in accordance with claim 10, in which the radiation is light and the test layer is formed of a liquid crystal plate or a plate of ferroceramic material disposed between the sender and the detection surface.

12. An ice detector in accordance with any one of the preceding claims, in which the radiation is light and, between the sender and the detection surface, a lens is provided for converting the light rays emerging radially from the sender into substantially parallel light rays which fall substantially vertically on the detection surface.

13. An ice detector in accordance with any one of the preceding claims, wherein there is provided on the detection surface a temperature sensor which acts in a temperature control loop as a true-value indicator for adjusting the temperature of the detection surface.

14. An ice detector in accordance with any one of the preceding claims, and comprising modulating means for modulating the amplitude or intensity and/or the frequency and/or phase of the radiation emitted by the sender, and the receiver comprises a demodulation member by means of which reflected radiation emitted by the sender may be distinguished from external radiation.

15. An ice detector in accordance with any one of the preceding claims, and comprising an auxiliary reference signal receiver which is arranged to be irradiated directly by the sender, whereby in use of the ice detector a reference signal generated by the reference signal receiver is used in evaluating the reflected radiation in order to compensate changes in amplitude or intensity of the radiation emitted by the sender.

16. An ice detector in accordance with any one of the preceding claims, wherein the receiver comprises a plurality of receive cells which are connected to a multiplexer by means of which it is possible to obtain a chronologically staggered evaluation of the reflection signals generated by the individual receive cells in order to determine the icing tendency, icing intensity, and icing speed.

17. An ice detector in accordance with any one of the preceding claims, which is adapted for use with said detection surface integrated into the skin of an aircraft.

18. An ice detector substantially as hereinbefore described with reference to Figures 1 to 3 of the accomanpying drawings.

19. An ice detector in accordance with claim 17 or 18, when said detection surface is integrated into the skin of an aircraft.