Device and method for examining materials by means of acoustic spectroscopy

Abstract

A device for examining a test material via acoustic spectroscopy, including a measuring distance which is formed from a reference material and the test material an ultrasonic transmission device for transmitting an ultrasonic transmission signal having an initial amplitude (A0) through the measuring distance, a first ultrasonic reception device for receiving the transmitted ultrasonic reception signal after the signal has passed through the measuring distance, and a second ultrasonic reception device for receiving the ultrasonic receiving signal reflected on the boundary surface between the test material and the reference material after the signal has twice passed through the reference material or test material, the transmission device being configured for giving ultrasonic transmission signals having different frequencies (f) and the two reception devices being configured for receiving corresponding ultrasonic reception signals having different frequencies.

Claims

1. A device for examining a test material via acoustic spectroscopy, comprising a measuring distance which is formed from a reference material and the test material, at least one of a density (.sub.R), a sonic transmission speed (c.sub.R), an acoustic attenuation coefficient (.sub.R) or an acoustic impedance (Z.sub.R) of the acoustic material being known for different frequencies, and the length (x.sub.R) of the reference material being known, and the length (x.sub.M) of the test material being known, and comprising: an ultrasonic transmission device for transmitting an ultrasonic transmission signal having an initial amplitude (A.sub.0) through the measuring distance, configured for transmitting ultrasonic transmission signals having different frequencies (f); a first ultrasonic reception device for receiving a transmitted ultrasonic reception signal after said transmitted ultrasonic signal has passed through the measuring distance; a second ultrasonic reception device for receiving an ultrasonic reception signal reflected on a boundary surface between the test material and the reference material after said ultrasonic reception signal has twice passed through the reference material or the test material, the first and second reception devices being configured for receiving corresponding ultrasonic reception signals having different frequencies, a first processing device configured to measure a time of flight (t.sub.G) of the transmitted ultrasonic reception signals after said signals have passed through the measuring distance, and a second processing device configured to identify an amplitude (A.sub.T) of the transmitted ultrasonic reception signals after said transmitted ultrasonic reception signals have passed through the measuring distance, and a third processing device configured to identify an amplitude (A.sub.R) of the ultrasonic reception signals reflected on the boundary surface between the test material and the reference material after said ultrasonic reception signals have twice passed through the reference material or the test material, and an evaluation device configured to calculate at least one of a density (.sub.M), a sonic transmission speed (c.sub.M), an acoustic attenuation coefficient (.sub.M) and/or an acoustic impedance (Z.sub.M) of an acoustic material for different frequencies (f) from the time of flight (t.sub.G), the amplitude (A.sub.T) of the transmitted ultrasonic reception signal and/or the amplitude (A.sub.R) of the reflected ultrasonic reception signal.

2. The device according to claim 1, wherein the time of flight (t.sub.G) is identified with a resolution of at least 100 picoseconds in the first processing device.

3. The device according to claim 1 wherein the first processing device comprises a time-to-digital converter configured to identify the time of flight (t.sub.G).

4. The device according to claim 1, wherein the second ultrasonic reception device is configured for receiving the ultrasonic reception signal reflected on the boundary surface between the test material and the reference material, after said ultrasonic reception signal has twice passed through the reference material or the test material, via switching the ultrasonic transmission device from a transmission mode to a reception mode.

5. The device according to claim 1, wherein the reference material consists of a solid body.

6. The device according to claim 1, wherein a cavity exists between the boundary surface of the reference material and the first ultrasonic reception device, a liquid or gaseous test material being able to fill or flow through said cavity during examination.

7. The device according to claim 1, wherein the device is connected to a container in which oil or an operating material is contained, said oil or operating material from the container filling or flowing through a cavity between the boundary surface of the reference material and the first ultrasonic reception device during examination, and at least one of the density (.sub.M), the sonic transmission speed (c.sub.M), the acoustic attenuation coefficient (.sub.M) or the acoustic impedance (Z.sub.M) of the oil or the operating material being able to be identified.

8. The device according to claim 7, wherein the operating material comprises transformer oil, and wherein in the evaluation device, a water content and/or an acidity level in the transformer oil is derived from at least one of the density (.sub.M) of the transformer oil, the sonic transmission speed (c.sub.M) in the transformer oil, the acoustic attenuation coefficient (.sub.M) of the transformer oil or the acoustic impedance (Z.sub.M) of the transformer oil.

9. A transformer for converting an AC input voltage to an AC output voltage, said transformer comprising a housing filled with transformer oil, wherein the device according to claim 1 is provided in or on the transformer for an online examination of the transformer oil.

10. A method for examining a biological or non-biological test material via acoustic spectroscopy, comprising a measuring distance which is formed from a reference material and the test material, at least one of a density (.sub.R), a sonic transmission speed (c.sub.R), an acoustic attenuation coefficient (.sub.R) and/or an acoustic impedance (Z.sub.R) of an acoustic material being known for different frequencies, and a length (x.sub.R) of the reference material being known, and a length (x.sub.M) of the test material being known, and comprising the steps of: transmitting an ultrasonic transmission signal having an initial amplitude (A.sub.0) through the measuring distance using an ultrasonic transmission device, said transmission device being configured for transmitting ultrasonic transmission signals having different frequencies (f) into the measuring difference, and receiving the transmitted ultrasonic reception signal at a first ultrasonic reception device after said transmitted ultrasonic reception signal has passed through the measuring distance, and receiving an ultrasonic reception signal reflected on a boundary surface between the test material and the reference material at a second ultrasonic reception device after said ultrasonic reception signal has twice passed through the reference material or the test material, the first and second reception devices being configured for receiving corresponding ultrasonic reception signals having different frequencies (f), and a) measuring a time of flight (t.sub.G) of the transmitted ultrasonic reception signals for each of the different ultrasonic transmission signals after said transmitted ultrasonic reception signals have passed through the measuring distance, b) identifying an amplitude (A.sub.T) of the transmitted ultrasonic reception signals for the different ultrasonic transmission signals after said ultrasonic reception signals have passed through the measuring distance, c) identifying an amplitude (A.sub.R) of the allocated ultrasonic reception signals reflected on the boundary surface between the test material and the reference material for the different ultrasonic transmission signals after said ultrasonic transmission signals have twice passed through the reference material or the test material, d) calculating at least one of a density (.sub.M), a sonic transmission speed (c.sub.M), an acoustic attenuation coefficient (.sub.M) or an acoustic impedance (Z.sub.M) of the acoustic material, for different frequencies from the time of flight (t.sub.G), the amplitude (A.sub.T) of the transmitted ultrasonic reception signals or the amplitude (A.sub.R) of the reflected ultrasonic reception signals.

11. The method according to claim 10, wherein the time of flight (t.sub.G) is identified with a resolution of at least 100 picoseconds.

12. The method according to claim 10, wherein at least one of the density (.sub.M) of the transformer oil, the sonic transmission speed (c.sub.M) in the transformer oil, the acoustic attenuation coefficient (.sub.M) of the transformer oil or the acoustic impedance (Z.sub.M) of the transformer oil are identified.

13. The method according to claim 12, wherein a water content or an acidity level in the transformer oil, is derived from at least one of the density (.sub.M) of the transformer oil, the sonic transmission speed (c.sub.M) in the transformer oil, the acoustic attenuation coefficient (.sub.M) of the transformer oil and/or the acoustic impedance (Z.sub.M) of the transformer oil.

14. The method according to claim 10, wherein longitudinal ultrasonic waves are generated by the ultrasonic transmission device in the MHz range.

15. The method according to claim 10, wherein the ultrasonic transmission signals having different frequencies (f) are modulated onto or added to a shared carrier signal and are subsequently transmitted together in the ultrasonic transmission device.

16. The device according to claim 1, wherein the time of flight (t.sub.G) is identified with a resolution of at least 10 picoseconds in the first processing device.

17. The device according to claim 1 wherein the reference material comprises at least one of plastic and glass.

18. The device according to claim 6, wherein the test material is transformer oil.

19. The method according to claim 10, wherein the time of flight (t.sub.G) is identified with a resolution of at least 10 picoseconds.

Description

(1) In the following, the invention is described in an exemplary manner by way of an embodiment schematically illustrated in the drawings.

(2) In the figures,

(3) FIG. 1 illustrates a device according to the invention having different functional modules in a schematic diagram;

(4) FIG. 2 illustrates the measuring distance of the device according to FIG. 1 in an enlarged view;

(5) FIG. 3 illustrates the formulary for calculating the acoustic material parameters;

(6) FIG. 4 illustrates the evaluation device of the device according to FIG. 1 having the formulas stored therein for calculating the acoustic material parameters of the test material to be examined.

(7) FIG. 1 illustrates in a schematic diagram the basic setup of a device 01 according to the invention, as it can be utilized for the online examination of a test material 02. The test material 02 is a transformer oil 30 (cf. FIG. 2) from a transformer 31. A cavity 35 is connected to the transformer 31 via connecting tubes 32 and 33 and via an operation of a pump 34 so that the transformer oil 30 can be pumped from the inside of the housing 36 in circulation through the cavity 35.

(8) The setup of the measuring distance 37 when carrying out the actual examination of the test material 02 is to be briefly described in the following by way of the sketch in FIG. 2.

(9) The measuring distance 37 consists, on the one hand, of a reference material 38 and the test material 02 to be examined, which is the transformer oil 30 in the illustrated embodiment. The reference material 38 can be a solid body made of glass or plastic, for example, the acoustic material properties of the reference material 38, i.e. the acoustic attenuation coefficient .sub.R, the acoustic impedance Z.sub.R, the density .sub.R, the sonic transmission speed c.sub.R, having to be at least partially known. Moreover, the length x.sub.R of the reference material 38 and the length x.sub.M of the test material, i.e. the clear span of the cavity 35 in the signal direction, are known.

(10) An ultrasonic transmission device 39, by means of which ultrasonic transmission signals can be generated having an initial amplitude A.sub.0 and can be coupled into the measuring distance, is arranged at the beginning of the measuring distance 37. The ultrasonic transmission device 39 is a combined apparatus which can also function as an ultrasonic reception device 40 by being switched. An ultrasonic reception device 41, by means of which ultrasonic signals can be received, is also arranged at the end of the measuring distance.

(11) During the actual examination of the test material 02, the transformer oil 30 first flows through the cavity 35 via the operation of the pump 34. In this context, the transformer oil can be measured online without having to open the housing 36. As soon as the cavity 35 is completely filled with transformer oil 30, the ultrasonic transmission device 39 generates an ultrasonic transmission signal having an initial amplitude A.sub.0 and couples said transmission signal into the measuring distance 37.

(12) As schematically illustrated in FIG. 2, the ultrasonic transmission signal 42 first passes through the reference material 38 until it reaches the boundary surface 43 between the reference material 38 and the test material 02. A part of the ultrasonic transmission signal runs through the boundary surface 43 and passes through the test material 02 until it reaches the ultrasonic reception device 41 as a transmitted ultrasonic reception signal 44. By evaluating the transmitted ultrasonic reception signal 44, the time of flight t.sub.G, which the transmitted ultrasonic reception signal has required for passing through the entire measuring distance 37, and the amplitude A.sub.T of the transmitted ultrasonic reception signal 44 can be measured or identified.

(13) The portion of the ultrasonic reception signal 44 reflected on the boundary surface 43 passes through the reference material 38 a second time in the opposite direction until said portion reaches the ultrasonic reception device 40 realized by switching the ultrasonic transmission device 39 as a reflected ultrasonic reception signal 45. By evaluating the measuring values of the ultrasonic reception device 40, the amplitude A.sub.R of the reflected ultrasonic reception signal 45 can be identified. The manner in which the measuring signals of the two ultrasonic reception devices 41 are further processed is further described in the following by way of the sketch in FIG. 1.

(14) Other than the combined ultrasonic transmission device and ultrasonic reception device 39/40 as well as the ultrasonic reception device 41, the device 01 comprises a signal preparation module 05 for generating the ultrasonic signals to be emitted from the ultrasonic transmission device 39. Further a signal generator 06 and a signal amplifier 07 are provided.

(15) The signal paths recorded by the ultrasonic reception device 40 or 41 are first amplified using signal amplifiers 08. The transmitted ultrasonic reception signals 44 are subsequently split in a signal splitter 09 and are distributed to a first processing device 10 and a second processing device 11 for parallel processing. The first processing device 10 serves for determining the time of flight, which the transmitted ultrasonic reception signal 44 has required for passing through the measuring distance 37 for each correspondingly set frequency. After passing through a signal processing module 12, the transmitted ultrasonic reception signal 44 enters a time-to-digital converter 13, by means of which the time of flight of the ultrasonic signal, i.e. the time between emitting the signal from the ultrasonic transmission device 39 and receiving said transmitted ultrasonic reception signal 44 at the ultrasonic reception device 41, can be measured.

(16) The functionality of the time-to-digital converter 13 is based upon the fact that the time of flight of an electric signal through a plurality of electronic circuits 14 contained in the time-to-digital converter 13 is known.

(17) For measuring the time of flight, the trigger signal of the ultrasonic transmission signal is directed to the time-to-digital converter 13 simultaneously with the emission from the ultrasonic transmission device 39 in order to initiate the time-measuring process. The trigger signal of the ultrasonic transmission signal then passes through the consecutively arranged circuits 14 in the time-to-digital converter 13. Each passing through an electronic circuit 14, which corresponds to a predetermined time of flight, is added up by a counter 15. As soon as the ultrasonic reception signal 44 is directed to the electronic circuits 14, the counter 15 stops and multiplies the number of added passages by the known time of flight of the individual electronic circuits 14. The result is the overall time of flight t.sub.D for the corresponding measurement. A time of flight (t.sub.G) 16 is yielded for each transmission frequency and is stored with the corresponding allocated transmission frequency in a storage device 17 in each instance.

(18) Parallel thereto, the transmitted ultrasonic reception signal 44 is evaluated in the second processing device 11 and the amplitude A.sub.T of the transmitted ultrasonic reception signal 20 is identified. For this purpose, a signal processing module 18 is provided in the second processing device 11, said transmitted ultrasonic reception signal 44 being processed and said amplitude (A.sub.T) 20 of the ultrasonic reception signal 44 being identified using said signal processing module 18. The ultrasonic reception signal 44 is split and indexed using the signal splitter 19. In a third processing device 46, the reflected ultrasonic reception signal 45 is processed by means of a signal processing module 18 and the amplitude (A.sub.R) 47 of the reflected ultrasonic reception signal is identified. The amplitude values 20 and 47 are each identified in the processing devices 11 and 46 in a frequency-dependent manner and the results data are stored with the corresponding frequency in the storage device 17 in conjunction with the corresponding time of flight 16.

(19) The results data stored in the storage device 17, namely the time of flight (t.sub.G) 16, the amplitude (A.sub.T) 20 of the transmitted ultrasonic reception signal 44 and the amplitude (A.sub.R) 47 of the reflected ultrasonic reception signal 45, are subsequently read out from the storage device 17 and are forwarded to an evaluation device 48 for further calculating the results data.

(20) FIG. 3 shows the formulary for calculating acoustic material parameters as they are required by the evaluation device 48 for calculating the results data.

(21) FIG. 4 schematically illustrates the evaluation device 48, by means of which the results data for the acoustic impedance Z.sub.m of the test material, the degree of reflection R on the boundary surface 43, the acoustic attenuation coefficient .sub.M of the test material, the sonic transmission speed c.sub.M of the test material, the density .sub.M of the test material and the compressibility of the test material can be calculated from the measuring values, namely the time of flight t.sub.G, the amplitude (A.sub.T) of the transmitted ultrasonic reception signal 24 and the amplitude (A.sub.R) of the reflected reception signal 45, with the aid of the formulas shown in FIG. 4.

(22) After determining the acoustic material parameters of the transformer oil 30 by calculation in the evaluation device 38, the water content or the acidity level can be determined in the transformer oil 30 in a subsequent step. Additionally, further insulation parameters, such as the breakdown voltage (according to BDV) as well as the dissipation factor (tangens delta), can be determined.