CA1338766C - Method and apparatus for measuring propagation time with ultrasonics in liquid or solid materials according to the impulse reflexion method - Google Patents
Method and apparatus for measuring propagation time with ultrasonics in liquid or solid materials according to the impulse reflexion methodInfo
- Publication number
- CA1338766C CA1338766C CA000604654A CA604654A CA1338766C CA 1338766 C CA1338766 C CA 1338766C CA 000604654 A CA000604654 A CA 000604654A CA 604654 A CA604654 A CA 604654A CA 1338766 C CA1338766 C CA 1338766C
- Authority
- CA
- Canada
- Prior art keywords
- threshold
- echo
- time
- height
- adjustable
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
- G01S15/06—Systems determining the position data of a target
- G01S15/08—Systems for measuring distance only
- G01S15/10—Systems for measuring distance only using transmission of interrupted, pulse-modulated waves
- G01S15/101—Particularities of the measurement of distance
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
- G01S7/523—Details of pulse systems
- G01S7/526—Receivers
- G01S7/527—Extracting wanted echo signals
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Computer Networks & Wireless Communication (AREA)
- General Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
Abstract
In the method of ultrasonic transit-time measurement in liquid or solid materials by the pulse-reflection method, a test head transmits a pulse, if possible in the form of a shock wave, which travels through a buffer zone and partly enters the test piece and is partly reflected from its surface. The entry or back-wall echo reflected from the surface into the test head (the starting echo) is used to derive an echo-start signal for starting a transit-time measurement (echo-start), which is stopped by a subsequent back-wall echo (useful signal provided its amplitude exceeds an adjustable threshold value. The height of the threshold value in connection with the echo-start signal is progressively altered in dependence on the amplitude and variation in time of the starting echo; the threshold value initially has a high value during a first, adjustable-height threshold and then decreases along a slope, in accordance with a preset function and within an adjustable time, to a second threshold, which is also adjustable in height.
Description
The present invention relates to a method and device for ultrasonic measurement of transit time in liquid or solid materials, by the pulse reflection method.
In the known method of this Icind and the device operating by the method, it is conventional to extract interfering reverberations from the starting echo by preventing the transit time measurement from being stopped during a measurement-blocking time. The measurement-blocking time (idle time) is adjustable in duration, and must be shorter than the transit time to be measured. Any useful signals within the measurement-blocking time cannot be detected and are therefore left out of consideration. As a resuLt, the shortest measurable transit time is determined by the length of the measurement-blocking t;me. Transit times can be detected only if they are longer than the measurement-blocking time.
The measurement-blocking time itself must be adjusted so that reverberations of the starting echo cannot stop the transit-time measurement. Accordingly, in the known method and the device operating in accordance therewith, the amplitudes and the variation in time of the reverberations substantially determine the shortest measurable transit time. However, the reverberations depend on various factors, mainly the attenuation of the test head, which if possible should be of the nature of a shock wave, and on the nature of the surface of the test piece or the material of which it is made. The rougher the surface of the test piece, the more extensive are the starting-echo signal and the subsequent back-wall echoes, and the measurement-blocking time has to be set correspondingly longer. In the known method and the device operating in accordance therewith, therefore, problems occur e.g. when the test piece has rough, more particularly corroded, surfaces. When for example the known method is used for testing piping, particularly for internal testing by a scraper, a relatively long idle time has to be set owing to corrosion and the rough surfaces, with a disadvantageous effect onthe minimum residual-wall thickness which can be resolved.
The invention aims to solve this problem. Its object is to improve the method of the initially-mentioned kind and the device operating by the method, so that it is possible to detect a useful signal which occurs during the reverberations, provided the useful signal is at a sufficiently higher level than the background caused by the reverberations, i.e. provided there is an adequate useful signal-to-noise ratio.
According to the present invention there is provided a method of ultrasonic measurement of transit time in liquid `h "
, ,~
-or solid test pieces, using a pulse reflection method, in which a test head transmits a pulse, which travels through a buffer zone and is partly reflected by the surface of a test piece and partly enters the test piece and is reflected from the real surface thereof, eventually after one or more reciprocating passages,into the test head, wherein an echo start signal for starting a transit time measurement is derived either from the entry echo or a back-wall echo reflected into the test head and wherein the transit time measurement is later on stopped by a subsequent echo signal used as wanted signal provided its amplitude exceeds an adjustable threshold value, characterised in that the height of the threshold value is varied in time in connection with the echo start signal and in accordance with the variation in amplitude and time of the starting echo, the threshold value initially having a high value during a first threshold of adjustable height, and then decreasing along a slope in accordance with a preset function and within an adjustable time to a second threshold likewise adjustable in height.
Preferably the pulse transmitted by the test head is in the form of a shockwave.
According to the present invention, there is also provided a device for ultrasonic measurement of transit time in liquid or solid test pieces, using a pulse reflection method, comprising a comparator connected to a main amplifier and having an output at which a pulse for stopping the transit-time measurement appears, characterised in that the comparator is connected to an adjusting device which is triggered by the echo start signal, and initially generates an analog or digital voltage having a value as per the first - 3a -threshold, followed by a voltage which decreases down a slope and finally delivers a voltage having a value as per a second threshold.
The second threshold corresponds to the threshold value occurring immediately after the measurement-blocking time in the know method.
The invention therefore enables the measurement-blocking time to be dispensed with under some circumstances. It proposes that the amplitude and duration of the threshold value should be chosen and altered in accordance with the variation of the starting echo, so that reverberations in the starting echo are not incorrectly interpreted as a useful signal, i.e. connot stop the transit-time measurement. Accordingly, if a measurement-blocking time is completely dispensed with, the first threshold is set so high that it is greater than the amplitude of the first half-wave of the starting echo. The progressively decreasing slope following the first threshold has a voltage curve and a duration such that the subsequent half-waves remain underneath it, i.e. do not reach the threshold value.
After the reverberations have died away, the second threshold remains constant, and is chosen substantially so that other interfering signals cannot stop the transit-time measurement.
Basically the invention uses the fact that if the test conditions are the same or similar, e.g. if the same type of test head is used and the test pieces are comparable, the reverberations or the decay characteristics are substantially constant, so that the variation in time of the threshold value according to the invention does not need to be readjusted during a test and, if the test serves similar purposes, the same variation in threshold value can be set as before.
i~`
- 3b -According to a preferred feature of the invention, the subsequent processing of the signals is completely blocked initially by the echo start signal during a measurement-blocking time tt of adjustable duration and subsequently the signal is evaluated by means of the periodically altered threshold values.
The resulting measurement-blocking time t1 is appreciably shorter namely between zero and 300 ns than the measurement-blocking time in the known method, and therefore haspractivally no influence on the measureable residual wall thickness. The measurement-blocking time can be obtained by setting a short, stepped, substantially higher prethreshold value before the first threshold value, or can be obtained in known manner by complete blockage as per the known method.
t 338766 ., The method accordin~ to the lnventlon operates substantially only durlng the reverberetion6. After the reverberatlons ttle sltuatlon 18 the 6ame as ln the known method (second threshold). The dlfference from the known method, however, i8 that 61gnal proce6sing can also occur durlng the reverberatlons atld tlle decaylng vlbrfltlons.
Provlded a useful 61gnal ls sufflclently above the thre~tlold value, whlch varles ln tlme ln controlled manner, lt i6 detected and stop6 the tran61t-tlme meesurement.
The maln edvantege of the mettlod accordin~ to the inventlon and the devlce6 operatln~ in accordance wlth the method ls ln the slmple con6tructlon. The cost of equlpment ls small. As compared wlth the kl-own devlces, the addltlonal flrst threshold and the sloping decrease ln the threshold velue have to be provlded, but the requlred circultry ls not expensive, slnce a comparator for the second threshold velue 15 present ln the known device. The comparator ls 6upplled lnitlally wlth the first thre6hold valùe, then wlth the slopln~ voltage curve and finally wlth the second threshold value Admlttedly, ~erman patent speclflcetlon 33 39 984 dlsclo6es a sonlc or ultrasonlc dlstance mea6urlng devlce ln whlch, when used for alrborne sound and operatlng wlth a 61ngle head, after every transmltter pulse the ampllflcatlon of the ampllfler ls controlled ln dependence on tlme and ln accordance wlth a stored functlon establlshed ln accordance wlth the dec~y characterlstlcc of the test head. The function 16 cho6en so that the ele~l L~ ~ Lv~
orlginating from the free vibration of the test head cannot slmulate 8 useful signal.
This known distance-measurlng devlce is intended only for airborne sound; lt does not contaln a buffer zone for sound to travel or consequently en echo start, and the ad~ustment of ampllflcatlon ls simple since the speed of sound in air is small compared wlth the speed in solld or liquld bodles. It ls impossible or expensive to transfer thls principle to measurement of translt times in solld or liquld bodies.
Other adventages and features of the lnventlon wlll be clear from the other claims and from the followin~ descrlptlon of a non-llmitative embodlment of the invention, described ln detail hereinafter with reference to the drawings in whlch:
Flg. 1 is a block circuit dlagram of a device according to the invention, showin~ only the details necessary for explainlng the inventlon;
Flg. 2 shows the varlatlo~ m tlme of the voltages at point U in detall, from the block clrcult dlagram ln Fig. l;
Fig. 3 shows the varlatlon ln tlme of the voltage U~ of themeasurin~ gate triggered by echo start, the translt-tlme measurement belng stopped by a useful slgnal;
Flg. 4 is a graph of the varlatlon in tlme of the threshold value synchronlzed wlth Flgs. 2 and 3, and Flg. 5 ls a U-t graph of the surface echo signal (corresponding to Flg. 2) and of the variation in tlme of the threshold voltage U~.
In the devlce ln Fig. 1, ultrasonic pulses are directed by a test head 24 across a buffer zone 22 to a test plece, which in the drawing is shown as a pipe 20 but can be a plate or the like. In known manner, some of the pulses enter the wall of pipe 20 whereas some are reflected by the entry surface and travel directly through the buffer zone 22 back to the test head 24. This process wlll be described in detail.
The test head 24 is connected to a transmitter 26 and also to a preamplifier 28. The transmltter 26 is trig$ered by a clock control sy6tem (not shown here) and delivers a transmitter pulse SI. The pulse and the varlous subsequent echo slgnals are picked up by the preamplifier 28 and dellvered to a main amplifier 30. The total ampliflcation of the circuit comprislng the preampllfier 28 and main amplifier 30 is ad~ustable but remains constant during the test.
The ampllfled slgnals at the output of the main ampllfler 30 are sent on the one hand to the posltive lnput of a comparator and on the other hand to an echo start devlce 34. The separatlon occurs at a ~unction point U. The input of the echo start device 34 constltutes another comparator 36, whose positlve lnput ls connected to the ~unction point U, whereas its negative input is supplied wlth an ad~ustable voltage vla a potentlometer 38. Consequently a signal appears at the output of comparator 36 only when the slgnal voltage from the functlon polnt U exceeds the comparatlve volta~e set at potentlometer 38. The settin~ ls such that the comparator delivers a signal lf the starting-echo signal occurs at the ~unction point U, resulting in known manner in the "echo-start". The echo-start signal is transmltted through a line 40 to an ad~ustment devlce 42.
In a variant embodiment, shown in chain lines in Flg. 1, the echo-start signal is delayed by sultable devices behind comparator 36.
The duratlon of the delay ls ad~ustable vla a potentlometer 44. The ~ - 7 - 1 338766 delay results ln a measurement-blocking time adJustable between 0 and 300 ns.
Imrnediately at`ter the echo-start pulse (delsyed lf required) is received on line 4~, the output 46 of the ad~ustlng device 42, whlch is connected to the negative input of comparator 32, flrst dellvers a voltage briefly (for 0 to 150 ns, e.g. for 30 ns) at the flrst threshold value. The voltage ls adJustable at a potentiometer 48.
After the preset time, the ad~ustln~ device 40 delivers a volta~e which slopes downwards, the duration of the downwards slope bein~
ad~ustable by a potentiometer 50. This time is deflned by the time required for the sloping voltage to decrease from the first threshold level to a second threshold level. The value of the second threshold is set by the third potentiometer 52. The second threshold corresponds to the threshold normally present in devices of the aforementioned kind. In the known devices of the kind in question here, the threshold is present after the "longer" measurement-blocking time. The second threshold ls made such that the measured result cannot be influenced by any other kinds of interference occurring when the reverberations have ended.
Accordingly, l~mediately after receiving the echo-start si~nal (delayed if required) the comparator 32 initially blocks all slgnals below the level of the hi~h first threshold. It then blocks all signals varying in time and below the sloping curve and flnally, at the end of the downward slope, it blocks all signals below the level of the second threshold. Consequently a signal appears at the output 54 of comparator 32, whlch is connected to the circuit (not shown here) for measuring the transit tlme (construction of measurin~ gate) only if the respective threshold values are exceeded at the given tlmes.
Instead of the analog construction shown by way of example in Fig. 1, the signal processing can be partly or completely digltal. In the _ -- 8 partly digital form, potentiometers 48 to 52 are omltted and a store, more partlcularly an E-PROM, is provided in the adJustment devlce 42 and stores the height of the flrst threshold 58, the duration and the functlon governing the slope 60, and the helght of the second threshold 62. This lnformatlon can be called ln via the transmitter pulse EI, which is supplied through a line 70.
In a completely digital embodiment, D/A converters are dlsposed between the main amplifier 30 and the ~unction point U. The subsequent signal processing ls dlgital ln known manner, l.e. by means of a digital comparator 36 or the like, in whlch case potentiometers 38 and 44 are also omitted.
The processes discussed hltherto with reference to the block circuit diagram in Fig. 1 will now be explained with reference to the graphs in Figs. 2 to 4, which show variations of voltage wlth time. A test cycle of the kind ln question beglns with a transmltter pulse Sl, beginning at time t0 and shown diagrammatlcally only as a rectangle in the graph in Fig. 2, which shows the voltage curve at the ~unction point U. At the time tO an ultrasonic pulse starts from test head 24 through the buffer zone 22. At the time tl the part of the pulse reflected from the entry surface of pipe 20 returns to the test head 24, and the signal received thereby and subsequently amplified results in a signal curve 56 at the ~unction point U. An echo start signal is derived in known manner (at time tl) in the echo-start device 34 from the flrst half-wsve, which has the highest amplitude.
The time t0 to tl is therefore the time for outward and reeturn travel of the pulse in the buffer zone 22 ~marked 122 in Fig. 2). At the time tl also, the measuring gate for measuring the transit time is opened (see Fig. 3). Beginning at the time tl also, the ad~usting device 42 outputs a brief high voltage at the level of a first threshold (reference 58 in Fig. 4). Shortly thereafter at time t2, the starting voltage of the ad~usting device 42 slopes downwards ~the slope has the reference number 60) until at tlme t3 the voltage g reaches the level of a second threshold which then remains constant (reference 62). As a comparlson between Figs. 2 and 4 shows, the second threshold occurs towards the end of the decay time of the signal curve 56, i.e. of the entire start-echo signal.
At the time t4 the useful signal, i.e. the first stopping back-wall echo (signal curve reference 64 in Fig. 2) exceeds the value of the second threshold 62, at which tlme it stops the time measurement, and consequently the time gate is closed (see Fig. 3). The time tl to t4 is the translt time of the pulse from the entry surface to the back wall and back to the entry surface of pipe 20. It ls marked 120 in Fig. 2. The same duration 120 can also be measured between the first and the second back-wall echo (64, 65) if the first back-wall echo 64 is used as an echo start signal and the second back-wall echo 65 is used as a useful signal. Slgnal 56 is then blanked out.
Before the time tl, the output voltage of the ad~ustlng device 42 is zero as shown in Flg. 4.
The variations in the signal at the time of the starting echo wlll be described in detail wlth reference to the graph in Fig. 5. At the time tl the echo signal exceeds the threshold set in comparator 36, thus opening the measuring gate (see Fig. 3). During a subsequent measurement-blocking time t~, comparator 32 remains completely blocked. To this end, in the example shown here, a blocking signal ls supplied to the negative input of comparator 34 for a time ad~ustable between 0 and 300 ns. At the end of the measurement-blocking time t~, the voltage is at the first threshold 58 during the ad~ustable period until time t2. As Fig. 5 shows, this value is appreciably above the reverberations of the echo-start signal. This situation is maintained. The subsequent progressive descent of slope 60 is at a voltage such that the reverberations 66 remain below the corresponding voltage values of the progressively changing threshold.
At the time t3 the slope reaches the level of the second threshold 62, at a time when the reverberations have substantially decayed.
o - I 338766 If a useful signal 68 occurs at a tlme t4 before time t3, the measuring gate is closed at that time if, as shown, the useful slgnal 68 is at a higher voltage than the progresslvely changlng slope. In that case, therefore, comparator 32 outputs a signal which closes the measuring gate. It should be explained that the measuring ~ate is started by a prior-art method.
Instead of the straight-line descent of the slope 60 shown in Figs. 4 and 5, a different curve could be chosen, e.g. a descent in accordance with a quadratic function or an e function or the like.
Instead of the potentiometers 38, 44 and 48 - 52 shown in the embodiment, other suitable ad~usting elements could be provided for the corresponding voltage values or durations.
In the known method of this Icind and the device operating by the method, it is conventional to extract interfering reverberations from the starting echo by preventing the transit time measurement from being stopped during a measurement-blocking time. The measurement-blocking time (idle time) is adjustable in duration, and must be shorter than the transit time to be measured. Any useful signals within the measurement-blocking time cannot be detected and are therefore left out of consideration. As a resuLt, the shortest measurable transit time is determined by the length of the measurement-blocking t;me. Transit times can be detected only if they are longer than the measurement-blocking time.
The measurement-blocking time itself must be adjusted so that reverberations of the starting echo cannot stop the transit-time measurement. Accordingly, in the known method and the device operating in accordance therewith, the amplitudes and the variation in time of the reverberations substantially determine the shortest measurable transit time. However, the reverberations depend on various factors, mainly the attenuation of the test head, which if possible should be of the nature of a shock wave, and on the nature of the surface of the test piece or the material of which it is made. The rougher the surface of the test piece, the more extensive are the starting-echo signal and the subsequent back-wall echoes, and the measurement-blocking time has to be set correspondingly longer. In the known method and the device operating in accordance therewith, therefore, problems occur e.g. when the test piece has rough, more particularly corroded, surfaces. When for example the known method is used for testing piping, particularly for internal testing by a scraper, a relatively long idle time has to be set owing to corrosion and the rough surfaces, with a disadvantageous effect onthe minimum residual-wall thickness which can be resolved.
The invention aims to solve this problem. Its object is to improve the method of the initially-mentioned kind and the device operating by the method, so that it is possible to detect a useful signal which occurs during the reverberations, provided the useful signal is at a sufficiently higher level than the background caused by the reverberations, i.e. provided there is an adequate useful signal-to-noise ratio.
According to the present invention there is provided a method of ultrasonic measurement of transit time in liquid `h "
, ,~
-or solid test pieces, using a pulse reflection method, in which a test head transmits a pulse, which travels through a buffer zone and is partly reflected by the surface of a test piece and partly enters the test piece and is reflected from the real surface thereof, eventually after one or more reciprocating passages,into the test head, wherein an echo start signal for starting a transit time measurement is derived either from the entry echo or a back-wall echo reflected into the test head and wherein the transit time measurement is later on stopped by a subsequent echo signal used as wanted signal provided its amplitude exceeds an adjustable threshold value, characterised in that the height of the threshold value is varied in time in connection with the echo start signal and in accordance with the variation in amplitude and time of the starting echo, the threshold value initially having a high value during a first threshold of adjustable height, and then decreasing along a slope in accordance with a preset function and within an adjustable time to a second threshold likewise adjustable in height.
Preferably the pulse transmitted by the test head is in the form of a shockwave.
According to the present invention, there is also provided a device for ultrasonic measurement of transit time in liquid or solid test pieces, using a pulse reflection method, comprising a comparator connected to a main amplifier and having an output at which a pulse for stopping the transit-time measurement appears, characterised in that the comparator is connected to an adjusting device which is triggered by the echo start signal, and initially generates an analog or digital voltage having a value as per the first - 3a -threshold, followed by a voltage which decreases down a slope and finally delivers a voltage having a value as per a second threshold.
The second threshold corresponds to the threshold value occurring immediately after the measurement-blocking time in the know method.
The invention therefore enables the measurement-blocking time to be dispensed with under some circumstances. It proposes that the amplitude and duration of the threshold value should be chosen and altered in accordance with the variation of the starting echo, so that reverberations in the starting echo are not incorrectly interpreted as a useful signal, i.e. connot stop the transit-time measurement. Accordingly, if a measurement-blocking time is completely dispensed with, the first threshold is set so high that it is greater than the amplitude of the first half-wave of the starting echo. The progressively decreasing slope following the first threshold has a voltage curve and a duration such that the subsequent half-waves remain underneath it, i.e. do not reach the threshold value.
After the reverberations have died away, the second threshold remains constant, and is chosen substantially so that other interfering signals cannot stop the transit-time measurement.
Basically the invention uses the fact that if the test conditions are the same or similar, e.g. if the same type of test head is used and the test pieces are comparable, the reverberations or the decay characteristics are substantially constant, so that the variation in time of the threshold value according to the invention does not need to be readjusted during a test and, if the test serves similar purposes, the same variation in threshold value can be set as before.
i~`
- 3b -According to a preferred feature of the invention, the subsequent processing of the signals is completely blocked initially by the echo start signal during a measurement-blocking time tt of adjustable duration and subsequently the signal is evaluated by means of the periodically altered threshold values.
The resulting measurement-blocking time t1 is appreciably shorter namely between zero and 300 ns than the measurement-blocking time in the known method, and therefore haspractivally no influence on the measureable residual wall thickness. The measurement-blocking time can be obtained by setting a short, stepped, substantially higher prethreshold value before the first threshold value, or can be obtained in known manner by complete blockage as per the known method.
t 338766 ., The method accordin~ to the lnventlon operates substantially only durlng the reverberetion6. After the reverberatlons ttle sltuatlon 18 the 6ame as ln the known method (second threshold). The dlfference from the known method, however, i8 that 61gnal proce6sing can also occur durlng the reverberatlons atld tlle decaylng vlbrfltlons.
Provlded a useful 61gnal ls sufflclently above the thre~tlold value, whlch varles ln tlme ln controlled manner, lt i6 detected and stop6 the tran61t-tlme meesurement.
The maln edvantege of the mettlod accordin~ to the inventlon and the devlce6 operatln~ in accordance wlth the method ls ln the slmple con6tructlon. The cost of equlpment ls small. As compared wlth the kl-own devlces, the addltlonal flrst threshold and the sloping decrease ln the threshold velue have to be provlded, but the requlred circultry ls not expensive, slnce a comparator for the second threshold velue 15 present ln the known device. The comparator ls 6upplled lnitlally wlth the first thre6hold valùe, then wlth the slopln~ voltage curve and finally wlth the second threshold value Admlttedly, ~erman patent speclflcetlon 33 39 984 dlsclo6es a sonlc or ultrasonlc dlstance mea6urlng devlce ln whlch, when used for alrborne sound and operatlng wlth a 61ngle head, after every transmltter pulse the ampllflcatlon of the ampllfler ls controlled ln dependence on tlme and ln accordance wlth a stored functlon establlshed ln accordance wlth the dec~y characterlstlcc of the test head. The function 16 cho6en so that the ele~l L~ ~ Lv~
orlginating from the free vibration of the test head cannot slmulate 8 useful signal.
This known distance-measurlng devlce is intended only for airborne sound; lt does not contaln a buffer zone for sound to travel or consequently en echo start, and the ad~ustment of ampllflcatlon ls simple since the speed of sound in air is small compared wlth the speed in solld or liquld bodles. It ls impossible or expensive to transfer thls principle to measurement of translt times in solld or liquld bodies.
Other adventages and features of the lnventlon wlll be clear from the other claims and from the followin~ descrlptlon of a non-llmitative embodlment of the invention, described ln detail hereinafter with reference to the drawings in whlch:
Flg. 1 is a block circuit dlagram of a device according to the invention, showin~ only the details necessary for explainlng the inventlon;
Flg. 2 shows the varlatlo~ m tlme of the voltages at point U in detall, from the block clrcult dlagram ln Fig. l;
Fig. 3 shows the varlatlon ln tlme of the voltage U~ of themeasurin~ gate triggered by echo start, the translt-tlme measurement belng stopped by a useful slgnal;
Flg. 4 is a graph of the varlatlon in tlme of the threshold value synchronlzed wlth Flgs. 2 and 3, and Flg. 5 ls a U-t graph of the surface echo signal (corresponding to Flg. 2) and of the variation in tlme of the threshold voltage U~.
In the devlce ln Fig. 1, ultrasonic pulses are directed by a test head 24 across a buffer zone 22 to a test plece, which in the drawing is shown as a pipe 20 but can be a plate or the like. In known manner, some of the pulses enter the wall of pipe 20 whereas some are reflected by the entry surface and travel directly through the buffer zone 22 back to the test head 24. This process wlll be described in detail.
The test head 24 is connected to a transmitter 26 and also to a preamplifier 28. The transmltter 26 is trig$ered by a clock control sy6tem (not shown here) and delivers a transmitter pulse SI. The pulse and the varlous subsequent echo slgnals are picked up by the preamplifier 28 and dellvered to a main amplifier 30. The total ampliflcation of the circuit comprislng the preampllfier 28 and main amplifier 30 is ad~ustable but remains constant during the test.
The ampllfled slgnals at the output of the main ampllfler 30 are sent on the one hand to the posltive lnput of a comparator and on the other hand to an echo start devlce 34. The separatlon occurs at a ~unction point U. The input of the echo start device 34 constltutes another comparator 36, whose positlve lnput ls connected to the ~unction point U, whereas its negative input is supplied wlth an ad~ustable voltage vla a potentlometer 38. Consequently a signal appears at the output of comparator 36 only when the slgnal voltage from the functlon polnt U exceeds the comparatlve volta~e set at potentlometer 38. The settin~ ls such that the comparator delivers a signal lf the starting-echo signal occurs at the ~unction point U, resulting in known manner in the "echo-start". The echo-start signal is transmltted through a line 40 to an ad~ustment devlce 42.
In a variant embodiment, shown in chain lines in Flg. 1, the echo-start signal is delayed by sultable devices behind comparator 36.
The duratlon of the delay ls ad~ustable vla a potentlometer 44. The ~ - 7 - 1 338766 delay results ln a measurement-blocking time adJustable between 0 and 300 ns.
Imrnediately at`ter the echo-start pulse (delsyed lf required) is received on line 4~, the output 46 of the ad~ustlng device 42, whlch is connected to the negative input of comparator 32, flrst dellvers a voltage briefly (for 0 to 150 ns, e.g. for 30 ns) at the flrst threshold value. The voltage ls adJustable at a potentiometer 48.
After the preset time, the ad~ustln~ device 40 delivers a volta~e which slopes downwards, the duration of the downwards slope bein~
ad~ustable by a potentiometer 50. This time is deflned by the time required for the sloping voltage to decrease from the first threshold level to a second threshold level. The value of the second threshold is set by the third potentiometer 52. The second threshold corresponds to the threshold normally present in devices of the aforementioned kind. In the known devices of the kind in question here, the threshold is present after the "longer" measurement-blocking time. The second threshold ls made such that the measured result cannot be influenced by any other kinds of interference occurring when the reverberations have ended.
Accordingly, l~mediately after receiving the echo-start si~nal (delayed if required) the comparator 32 initially blocks all slgnals below the level of the hi~h first threshold. It then blocks all signals varying in time and below the sloping curve and flnally, at the end of the downward slope, it blocks all signals below the level of the second threshold. Consequently a signal appears at the output 54 of comparator 32, whlch is connected to the circuit (not shown here) for measuring the transit tlme (construction of measurin~ gate) only if the respective threshold values are exceeded at the given tlmes.
Instead of the analog construction shown by way of example in Fig. 1, the signal processing can be partly or completely digltal. In the _ -- 8 partly digital form, potentiometers 48 to 52 are omltted and a store, more partlcularly an E-PROM, is provided in the adJustment devlce 42 and stores the height of the flrst threshold 58, the duration and the functlon governing the slope 60, and the helght of the second threshold 62. This lnformatlon can be called ln via the transmitter pulse EI, which is supplied through a line 70.
In a completely digital embodiment, D/A converters are dlsposed between the main amplifier 30 and the ~unction point U. The subsequent signal processing ls dlgital ln known manner, l.e. by means of a digital comparator 36 or the like, in whlch case potentiometers 38 and 44 are also omitted.
The processes discussed hltherto with reference to the block circuit diagram in Fig. 1 will now be explained with reference to the graphs in Figs. 2 to 4, which show variations of voltage wlth time. A test cycle of the kind ln question beglns with a transmltter pulse Sl, beginning at time t0 and shown diagrammatlcally only as a rectangle in the graph in Fig. 2, which shows the voltage curve at the ~unction point U. At the time tO an ultrasonic pulse starts from test head 24 through the buffer zone 22. At the time tl the part of the pulse reflected from the entry surface of pipe 20 returns to the test head 24, and the signal received thereby and subsequently amplified results in a signal curve 56 at the ~unction point U. An echo start signal is derived in known manner (at time tl) in the echo-start device 34 from the flrst half-wsve, which has the highest amplitude.
The time t0 to tl is therefore the time for outward and reeturn travel of the pulse in the buffer zone 22 ~marked 122 in Fig. 2). At the time tl also, the measuring gate for measuring the transit time is opened (see Fig. 3). Beginning at the time tl also, the ad~usting device 42 outputs a brief high voltage at the level of a first threshold (reference 58 in Fig. 4). Shortly thereafter at time t2, the starting voltage of the ad~usting device 42 slopes downwards ~the slope has the reference number 60) until at tlme t3 the voltage g reaches the level of a second threshold which then remains constant (reference 62). As a comparlson between Figs. 2 and 4 shows, the second threshold occurs towards the end of the decay time of the signal curve 56, i.e. of the entire start-echo signal.
At the time t4 the useful signal, i.e. the first stopping back-wall echo (signal curve reference 64 in Fig. 2) exceeds the value of the second threshold 62, at which tlme it stops the time measurement, and consequently the time gate is closed (see Fig. 3). The time tl to t4 is the translt time of the pulse from the entry surface to the back wall and back to the entry surface of pipe 20. It ls marked 120 in Fig. 2. The same duration 120 can also be measured between the first and the second back-wall echo (64, 65) if the first back-wall echo 64 is used as an echo start signal and the second back-wall echo 65 is used as a useful signal. Slgnal 56 is then blanked out.
Before the time tl, the output voltage of the ad~ustlng device 42 is zero as shown in Flg. 4.
The variations in the signal at the time of the starting echo wlll be described in detail wlth reference to the graph in Fig. 5. At the time tl the echo signal exceeds the threshold set in comparator 36, thus opening the measuring gate (see Fig. 3). During a subsequent measurement-blocking time t~, comparator 32 remains completely blocked. To this end, in the example shown here, a blocking signal ls supplied to the negative input of comparator 34 for a time ad~ustable between 0 and 300 ns. At the end of the measurement-blocking time t~, the voltage is at the first threshold 58 during the ad~ustable period until time t2. As Fig. 5 shows, this value is appreciably above the reverberations of the echo-start signal. This situation is maintained. The subsequent progressive descent of slope 60 is at a voltage such that the reverberations 66 remain below the corresponding voltage values of the progressively changing threshold.
At the time t3 the slope reaches the level of the second threshold 62, at a time when the reverberations have substantially decayed.
o - I 338766 If a useful signal 68 occurs at a tlme t4 before time t3, the measuring gate is closed at that time if, as shown, the useful slgnal 68 is at a higher voltage than the progresslvely changlng slope. In that case, therefore, comparator 32 outputs a signal which closes the measuring gate. It should be explained that the measuring ~ate is started by a prior-art method.
Instead of the straight-line descent of the slope 60 shown in Figs. 4 and 5, a different curve could be chosen, e.g. a descent in accordance with a quadratic function or an e function or the like.
Instead of the potentiometers 38, 44 and 48 - 52 shown in the embodiment, other suitable ad~usting elements could be provided for the corresponding voltage values or durations.
Claims (15)
1. A method of ultrasonic measurement of transit time in liquid or solid test pieces, using a pulse reflection method, in which a test head transmits a pulse, which traces through a buffer zone and is partly reflected by the surface of a test piece and partly enters the test piece and is reflected from the real surface thereof into the test head, wherein an echo start signal for starting a transit time measurement is derived either from the entry echo or a back-wall echo reflected into the test head and wherein the transit time measurement is later on stopped by a subsequent echo signal used as wanted signal provided its amplitude exceeds an adjustable threshold value characterised in that the height of the threshold value is varied in time in connection with the echo start signal and in accordance with the variation in amplitude and time of the starting echo, the threshold value initially having a high value during a first threshold of adjustable height, and then decreasing along a slope in accordance with a preset function and within an adjustable time to a second threshold likewise adjustable in height.
2. A method according to claim 1, characterised in that the pulse transmitted by the test head is in the form of a shock wave.
3. A method according to claim 1, characterised in that the pulse is reflected after at least one reciprocating passage into the test head.
4. A method according to claim 1, characterised in that the subsequent processing of the signals is completely blocked initially by the echo start signal during a measurement-blocking time tt of adjustable duration and subsequently the signal is evaluated by means of the periodically altered threshold values.
5. A method according to claim 4, characterised in that the measurement-blocking time tt is between zero and 300 ns.
6. A method according to claim 1, 2, 3, 4 or 5, charac-terised in that the height of the first threshold, the height of the second threshold and the duration of the slope decreasing from the height of the first threshold to the height of the second threshold are adjustable.
7. A method according to claim 1, 2, 3, 4 or 5, charac-terised in that the duration of the first threshold is adjustable in the range from zero to 150 ns.
8. A device for ultrasonic measurement of transit time in liquid or solid test pieces, using a pulse reflection method, comprising a comparator connected to a main amplifier and having an output at which a pulse for stopping the transit-time measurement appears, characterised in that the comparator is connected to an adjusting device which is triggered by the echo start signal and initially generates an analog or digital voltage having a value as per the first threshold, followed by a voltage which decreases down a slope and finally delivers a voltage having a value as per a second threshold.
9. A device according to claim 8, characterised in that the echo start signal is delayed.
10. A device according to claim 9, characterised in that the adjusting device comprises a potentiometer for adjusting the voltage of the first threshold, a potentiometer for adjusting the duration of the decrease in voltage to the height of the second threshold, and a potentiometer for adjusting the height of the second threshold.
11. A device according to claim 8, characterised in that the adjusting device comprises a store in which the voltage value of the first threshold, the duration and the function determining the decrease along the slope, and the voltage value of the second threshold are stored in digital form, and the contents of the store is called in by the transmitter pulse.
12. A device according to claim 11, characterised in that the store is a freely programmable store.
13. A device according to claim 11, characterised in that an A/D converter is provided between the main amplifier and the junction point U and the subsequent signal processing is digital.
14. A device according to claim 8 or 10, characterised in that the adjusting device also comprises an adjusting element for setting a measurement-blocking time tt beginning with the echo start signal.
15. A device according to claim 14, characterised in that the adjusting element is a potentiometer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3822699.5 | 1988-07-05 | ||
| DE3822699A DE3822699A1 (en) | 1988-07-05 | 1988-07-05 | METHOD AND DEVICE FOR MEASURING RUNTIME BY MEANS OF ULTRASOUND IN LIQUID OR SOLID MATERIALS BY THE IMPULSE REFLECTION METHOD |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1338766C true CA1338766C (en) | 1996-12-03 |
Family
ID=6357986
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000604654A Expired - Fee Related CA1338766C (en) | 1988-07-05 | 1989-07-04 | Method and apparatus for measuring propagation time with ultrasonics in liquid or solid materials according to the impulse reflexion method |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0423153B1 (en) |
| CA (1) | CA1338766C (en) |
| DE (2) | DE3822699A1 (en) |
| WO (1) | WO1990000745A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10241084B2 (en) | 2014-03-10 | 2019-03-26 | Ge Sensing & Inspection Technologies Gmbh | Ultrasonic-pulse-echo flaw inspection at a high testing speed on thin-walled pipes in particular |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4040190C2 (en) * | 1990-12-15 | 1994-08-04 | Kernforschungsz Karlsruhe | Method for measuring the transit time of ultrasound using the pulse reflection method |
| GB9103867D0 (en) * | 1991-02-25 | 1991-04-10 | Salubre Investments | A circuit for processing pulses |
| KR0168087B1 (en) * | 1993-06-29 | 1999-05-01 | 김광호 | Apparatus and method for measuring the distance of obstacle with supersonic sensor |
| EP0971242A1 (en) | 1998-07-10 | 2000-01-12 | Cambridge Consultants Limited | Sensor signal processing |
| DE10230587B4 (en) * | 2002-07-05 | 2012-04-12 | Ge Sensing & Inspection Technologies Gmbh | Method and apparatus for ultrasonic testing of spot welded joints, in particular of body panels |
| RU2490533C2 (en) * | 2009-04-30 | 2013-08-20 | Ниссан Мотор Ко., Лтд | Device and method to control continuously variable transmission of belt type |
| GB2572215A (en) * | 2018-03-23 | 2019-09-25 | Short Brothers Ltd | Detection of kiss bonds within composite components |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4169263A (en) * | 1976-07-23 | 1979-09-25 | Rockwell International Corporation | Variable threshold signal detecting apparatus |
| DE2726981C2 (en) * | 1977-06-15 | 1984-11-22 | Fried. Krupp Gmbh, 4300 Essen | Device for measuring time between pulses |
| DE2853170A1 (en) * | 1978-12-08 | 1980-06-19 | Deutsch Pruef Messgeraete | Ultrasonic technique for metrology - using peak value sensors responding to test piece end surfaces to operate flip=flop, gate element and counter |
| US4315325A (en) * | 1980-07-02 | 1982-02-09 | Purecycle Corporation | Echo ranging pulse discrimination circuit |
| GB8422022D0 (en) * | 1984-08-31 | 1984-10-24 | Atomic Energy Authority Uk | Electrical signal discrimination |
-
1988
- 1988-07-05 DE DE3822699A patent/DE3822699A1/en not_active Withdrawn
-
1989
- 1989-06-06 DE DE8989906704T patent/DE58905333D1/en not_active Expired - Fee Related
- 1989-06-06 EP EP89906704A patent/EP0423153B1/en not_active Expired - Lifetime
- 1989-06-06 WO PCT/DE1989/000373 patent/WO1990000745A1/en active IP Right Grant
- 1989-07-04 CA CA000604654A patent/CA1338766C/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US10241084B2 (en) | 2014-03-10 | 2019-03-26 | Ge Sensing & Inspection Technologies Gmbh | Ultrasonic-pulse-echo flaw inspection at a high testing speed on thin-walled pipes in particular |
| US10488367B2 (en) | 2014-03-10 | 2019-11-26 | Ge Sensing & Inspection Technologies Gmbh | Ultrasonic-pulse-echo flaw inspection at a high testing speed on thin-walled pipes in particular |
Also Published As
| Publication number | Publication date |
|---|---|
| DE58905333D1 (en) | 1993-09-23 |
| WO1990000745A1 (en) | 1990-01-25 |
| EP0423153A1 (en) | 1991-04-24 |
| EP0423153B1 (en) | 1993-08-18 |
| DE3822699A1 (en) | 1990-01-11 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1296094C (en) | Filling level meter | |
| US5877997A (en) | Pulse echo distance measurement | |
| US4079315A (en) | Method and apparatus for measuring time interval between two pulse signals | |
| US3454922A (en) | Ultrasonic pulse distance measuring device | |
| US4910717A (en) | Apparatus for measuring distances | |
| US4675854A (en) | Sonic or ultrasonic distance measuring device | |
| US3427866A (en) | Ultrasonic thickness gauge and flow detector | |
| GB2282886A (en) | Flow measurement | |
| GB1587617A (en) | Method of and arrangement for measuring the level of filling in a container or the height of loose material on a storage place | |
| CA1338766C (en) | Method and apparatus for measuring propagation time with ultrasonics in liquid or solid materials according to the impulse reflexion method | |
| GB1210476A (en) | Recording volume flowmeter | |
| GB1102491A (en) | Device for sonic and ultrasonic internal scanning of solid and fluid media | |
| US5155472A (en) | Contact type liquid level sensing system | |
| US5201225A (en) | Instrument for measuring thickness of coated plate and method thereof | |
| US3863198A (en) | Doppler sonar utilizing period measurement with thresholded receivers | |
| GB1577620A (en) | Distance measurement | |
| GB1092531A (en) | Liquid presence detector | |
| GB1129655A (en) | Improvements in or relating to ultrasonic measuring apparatus | |
| GB1226987A (en) | ||
| US3431550A (en) | Ultrasonic presence detectors | |
| JPH0943360A (en) | Water infiltration detecting method | |
| US3710310A (en) | System for determining depth of water | |
| GB1130958A (en) | Material tester | |
| US3449710A (en) | Controlled threshold detector for sonar applications | |
| GB2284053A (en) | Detecting presence or absence of liquid in a vessel |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |