DE2334167C3 - Method and device for ultrasonic measurement of the thickness of an elongated component - Google Patents

Description

3 4

The invention relates to a method for ultra-USA patents 34 07 352 and 35 00 185, sciiall measurement of the thickness of an elongated component, which magnetic coil or capacitance scanning probes the successive sections of which are shown relatively that act on bridge circuits. -move to an electric ultrasonic transducer, where- ultrasonic method for thickness measurement in body-

at first and second echo pulses from different 5 pers are known. One method is a pulse echo opposite Surfaces of the component from the process in which an impulse is emitted, noise is distinguished and unusable echoes and the returning echoes are evaluated. a second ultrasound procedure is a so-called

sound pulse is sent into the component, a first called resonance method. This method work-echo unpulse from a surface of the component and io tet according to the principle of the maximum amplitude of a an associated second echo pulse with minimal returning signal if the wavelength Jtopntudi from an opposite surface of the ultrasonic signal a whole multiple of that the component reaches the thickness of the object to be measured within a given period of time, receive and receive signals after receiving the first The ultrasonic pulse echo method is particularly

and a second echo pulse with a predetermined 15 ders useful for measuring the thickness and the minimum of excuses Amplitude are generated, the time-tricity of which is generated by cable sheaths. A crystal is through prefer distance in relation to the time between using a high voltage the reception of the first echo pulse stimulated by one of them to vibrate. The mechanical moving surface of the component and the reception of the train is then in the form of a sound wave through the ordered second echo pulse from the opposing 20 coupling means, for example the water of the customer The surface of the component stands, as well as the lead trough, transferred to the cable to be measured, directions for carrying out the procedure. Depending on the acoustic mismatch

In one type of communication cables, a me- solution between the coupling means and the cable-metallic moisture cover in the longitudinal direction is a portion of the sound wave energy at the Oberum a cable core is wound, said exceeded a reflecting surface _5, and a part continues. This division is repeated at every sloping edge of the moisture cover, forming the watertight seam. After that, a cladding echo signals are processed and allow a measurement of the thickness of the layers, depth cover to be extruded from plastic material over the core and the moisture. Then it is

sheathed cables for cooling by a relatively elongated material, such as a Konrlaneen Water trough passed through. line, strive for a crystal with a line focus,

It is desirable to keep both the mantle and the line focus parallel with the longitudinal axis wall thickness as well as the eccentricity of the jacket of the pipeline. In pipe production to monitor. Monitoring of the jacket, however, reveals the strength of the pipe in any way It may be possible to maintain uniform 35 greater lateral movement in succession Thickness of the jacket and a saving of artificial sections of the pipe. On the other hand, there are erosion materials by applying the minimum permissible lateral movements to when em IKA-Sn Eteldicke. The monitoring of the eccentric when moved through a cooling trough ^ is known The quote serves as an aid when setting up the extruder, ultrasonic measuring methods are, a den_USA patent to prevent the cable from being out of round. 4 <> writings 34 23 992, 34 74 664, 35 09 752 and

According to the prior art, the thickness of a 36 05 504 is described. over a metallic moisture cover extru- It is already a ™ T

This means that the plastic jacket is monitored by the fact that with a hand ^held you know capacity between the metal cover, with the, ie wall thickness, of ^^ and one in direct contact with the plastic 45 (DT-OS 19 60 514) . Measurement is carried out with the electrode placed in an uncovered position. For special problems. For example, after the formation of inner sheaths over the cable core without a gap between the WtrMchalhwnJ «· von de, J ^ rtdte, the presence of a metallic moisture cover and the surfaces * fa ^^^ jj ¹ such capacitance methods are, however, deposits ^, f ^ llwTdkr Benu and not usable and it must indirect tests ₅ o ^ therefore the re - ^^^ J ^^

KTÄÄ- control it is desirable- JK ^ r worth monitoring the jacket thickness as soon as possible, echo pulses is

If the sheath extrusion takes place, we improve ^a ^ ^Anz f ^lg f _pn ^nU J _p f _t ^a ""' _h ! "rn originally produced

essentially the feedback control system, which finer f st η Ze ^^ J ^^^ _ends . ^8th

connected to the extruder or with an impulse »rtemjrmnuna ν ^ _zy _

show used by an operator 65 of the invention ™ f ™ f Y _a ⁵ _{n a}

is used to make settings for monitoring the eccentric ^ei " _m ^ _{n C} ^C ^"" ^1C _component continuously

tricity and the jacket thickness.!. Examples moved multi-sensory u

of known measuring arrangements can be found in the, from jnei Vieizani

based impulses to determine the correct impulses echo measurement method applied, what at least are. To achieve the object, the invention requires a crystal 21 (see FIG. 2). The water from a method of the aforementioned the cooling trough 16 is used as a coupling medium for Type and is characterized in that the first transmission of ultrasonic energy to the cable echo pulse a first predetermined property to be 5 cloak 13. In order to ensure a meaningful exercise of the In addition to the minimum amplitude and the second echo thickness of the cladding 13, it is necessary to carry out an impulse a second, predetermined property, the jacket thickness round at various points borrowed to the minimum amplitude that the when to measure the circumference. This is also emergency reception of the first and second echo pulses necessary to the eccentricity of the cable jacket 13 generated signals to be able to determine uniqueness that can be distinguished from one another.

or off signals are that the on and off signals As best from FIG. 2 can be seen

a plurality of crystals 21-21 are used only due to the reception of the first and second, the

Echo pulses with predetermined properties around the circumference of the sheathed cable 12

are generated and that the off-pulse is only generated and arranged at a distance from it, wherein

is after a predetermined period of time after 15 each of the crystals in the cooling medium, for example

The beginning of the first echo pulse has passed. wise water, the cooling trough 16 is immersed. the

This ensures that only gül crystals 21-21 need to be selected so that

echo impulses and thus measured values, they determined as much energy as possible on a narrow

respectively are displayed so that an accurate and ma- rich focus, d. i.e., it is desirable that

Material-saving monitoring of the manufacturing process 20, the crystal has a line focus, the

in particular of sheathed communication cables line runs transversely to the cable 12. Must also

is possible. Selection made so that the crystal 21 for both

Developments of the invention as well as devices all of the cables expected in a manufacturing environment to carry out the process, counter sizes as well as for as many different ones as possible are required stood the subclaims. 25 materials can be used.

The invention is described below on the basis of another critical property is the damping

Embodiment and the drawings closer factor of the crystal 21. If the vibrations are not

explained. It shows quickly fading, does not result in a meaningful display

1 shows a perspective overall view of one of the sheath thicknesses, because the pulse echoes merge with one another for the extrusion of a cable sheath from 30 and become indistinguishable.
Plastic material on a core made of insulated The crystals 21-21 are excited by a chip wire with an ultrasonic device to the measurement impulse, which cyclic mechases of the thickness and eccentricity of the cable jacket causes niche tensions. The!" Tensions

F i g. 2 is a partially sectioned view of the high-frequency pressure gradient or white wave generated in

F i g. 1 shown water trough with four crystals in the coupling medium, which in this case

converters and the moving through the trough is the water of the cooling trough. The waves in shape

sheathed core as well as a view of a console of a damped sinusoidal oscillation migrate to

for displaying the thickness measurement and the eccentric surface of the cable jacket 13 (in time T,

Tricity of the cable jacket, see Fig. 6 a) where part of them due to the

3 shows the block diagram of one of four channels 40 acoustic impedance mismatch is reflected,

to carry out the ultrasonic measurement and construction This causes an external surface echo

parts that are common to all four channels (echo I, see Fig. 6 a) is generated.

F i g. 4 shows the partial circuit diagram of one in FIG. Part of the pressure wave also travels inward

placed pulse generator-receiver unit, in the cable jacket 13, with a second reflective

Fig. 5 shows the circuit diagram of the 45 tion shown in Fig. 2 on the inwardly located outer surface of the

Receiver logic circuit, cable jacket occurs. This determines the second

F i g. 6 waveforms to explain the working echo (see Echo II, Fig. 6 a).

wise of units of the in F i g. The expression "outside" as used here and in the

direction. Claims regarding the relationship between

In Fig. 1 is a device 10 used for covering 50 a surface and an object successive sections of a cable core is to be understood that the surface in the direction 11 is oriented towards the object with a plastic material such as polyethylene and shows the object, in order to adjoin or be in contact with a cable 12 with a jacket, abei put. The device 10 contains an extruder need not be.

14 and a cooling trough 16, which is attached to the extruder 55. It should be repeated that the measuring device used is connected. The core 11 is determined by means of a drive method, the time interval (2 1, see FIG. 6 a) between the device 17 through the extruder 14 forward echo signals. This distance is directly related to where the plastic material is extruded. with the thickness d of the cable jacket 13 in relation. The cable 12 is then moved through the cooling trough 16. Experiments have shown that this speed

The thickness of the jacket 13 (FIG. 2) is substantially uniform as possible. Thus, di <

to control effectively and to continue the eccentric use of the equation 2 d - vt allowed, mi

Controlling the tricity of the jacket is an ultrasonic d = jacket thickness, ν = speed of sound unc

Sheath measuring device 20 arranged. The device 65 t - echo spacing time. The echo gap time win

device 20 monitors the jacket thickness and measured eccentricity, ν is known (about 0.051 cm per micro

immediately after the covered core 11 in second), and d can then be easily determined

the water trough 14 is inserted. It gets the pulse There may be some irregularities in the off

7 8

spreading speed on the surface of the poly- 38 is capable of the thickness at the top and bottom of the cable-

Ethylene occur in front of the inside of the jacket jacket 13 in F i g. 2 as well as on the right and back

13 cools down. ken side to compare. Of course they need

Each of the crystals 21-21 is electrically connected for comparison measurements not along horizontal and

to be made with an assigned channel from a plurality of 5 vertical axes, but rather

Channels 22-22 (Fig. 3). Each of the channels 22-22 around- only at opposite intersections of the

summarizes a plurality of elements for converting axes of a related to the cable jacket 13

the time interval between the pulse echoes by the coordinate system.

The eccentricity measuring circuit 38 subtracts the

Arranged crystal 21 aligned materials recommend- io lower measurement from the measurement at the top of the mantle

have been caught to an output signal, wel- 13, where the result is multiplied by 100 and

Ches the thickness of the cable jacket 13 is proportional. is divided by the nominal value of the jacket thickness,

In addition, other components are provided to provide a percentage value with regard to the nominal jacket

which together with the four channels 22-22 result in a thick one. The same calculation is made

form electrical circuit 25. The output signal »5 carried out with respect to the thicknesses on the left and

the circuit 25 is on a console 26 (Fig. 2) on the right part of the cable jacket 13. Each of these

for an operator as thickness and eccentric measurements are made on a top-bottom gauge

indicated. 39 and a left-right measuring device 40 displayed,

Each of the channels 22-22 includes the associated ones associated with the eccentricity measuring circuit 38

Krislallwandler 21, which are with a pulse generator receiver.

catcher 27 is connected. The pulse generator-receiver The pulse repetition frequency circuit 30 gives

ger 27 initially gives a pulse in each cycle one pulse at a time PRF over the line

to the crystal converter 21 to the crystal with its device 31 to a connection point 43 (Fig. 5) for

To excite resonance frequency. Then, for example, receive the first channel and from there over

the pulse generator receiver 27 catches a line 44 in each cycle 35 to the input 47 of a pulse

pulse echoes from the cable under test 12. output device or optical isolator 48.

The pulse generator receiver 27 is via a line. The pulse generator 48 emits a pulse

device 28 with a receiver logic circuit 29 connects the pulse generator-receiver 27 to this so

bound, which on command of a pulse re-control that the associated transducer 21 pressure

Recall frequency circuit (PRF) 30 causes 30 waves to be transmitted.

the pulse generator receiver 27 the crystal converter. The pulse generator receiver 27 comprises one

21 pulses. The receiver logic circuit 29 is to trigger the trigger circuit 51 (FIG. 4) to which the im-

echo pulse received from the cable 12 to be tested is applied by the pulse generator circuit 48,

evaluate impulses and is able to evaluate those impulses in order to deliver a high-current impulse to the

divorce, which is used to measure the thickness of the jacket 13 35 control electrode 53 of a first controlled silicon

are not useful. Thus, the receiver logic rectifier (SCR) 54 must be used to ignite it.

circuit 29 both act between noise peaks and.

valid signals as well as between the first and The SCR 54 has a cathode 56 and anode

can distinguish the second echo signals. 57 on, the latter through a suitable external

Receiver logic circuit 29 is connected to a device such as positive voltage source 58, counter 32, which is forward biased a plurality of decade counters. The SCR 54 can measure into a conductive receiver logic circuit 29 via the control and the width of the output pulse of the electrode 53. The counter 32 state can be set.

is pulsed by an oscillator 34 (see oscillator- As can be seen in Fig. 4, the anode 57 of the input signal, F i g. 6 i). The pulse count is 45 first SCR 54 in series via a combiner Storage unit (not shown) stored, connection point 59 and a connection point 61 so that the signals received by the pulse generator receiver 27 are connected to the cathode 62 of a second SCR 63 Pulses through the receiver logic circuit. The connection point 61 is with the control 29 be rated. electrode 64 of the second SCR 63 connected. the

The stored digital counting 50 anode 66 of the SCR 63 is transferred via connection point value from the counter 32 to a digital-analog wall 67 and 68 with the cathode 69 of an SCR 71 verier 36, which binds the digital counting value. The connection point 68 is converted to an analog voltage to the control. This voltage electrode 72 of the SCR 71 is connected. Ultimately, there is a thickness specification for the assigned channel. is the anode 73 of the SCR 71 via connection. The continuous analog voltage is connected at points 74 and 76 to the cathode 77 of an SCR 7J suitable scale on a measuring device 37 (see FIG. 2), the connection point 76 being connected to dii is displayed that is assigned to this channel 22. This control electrode 79 of the SCR 78 is connected.
4, the anode 8: Thickness of the cable jacket on part of its circumference, the SCR 78 via a connection point 82 which is assigned to this channel, is to over- 60 earth 83 connected. The SCRs 54, 63, 71 and 7! watch. ^smc * resistors 84, 86, 87 and 88, respectively, are assigned to

Alternatively, the stored output can be connected in parallel to this. The connection point

signal are given to a digital computer and 82 is by means of a line 89 via a conn

such a data analysis can be carried out. connection point 91. at which the series circuit de

To measure the eccentricity of the cable jacket 65 resistors R4 and 86 to 88 are connected, un

13 is an eccentricity measuring circuit 38 with which then via a capacitor 92 with a connection Diftital-to-analog converter 36 of each of the channels connection point 93 connected. The connecting point 22-'2 connected. The eccentricity measuring circuit 93 is connected to the cathode 94 of a diode 96

ίο

the one whose anode "listens" for echoes via a connection point 98. This enables with regard to is connected to the associated converter 21. the sensitivity of device 20 to noise The diode 96 is used to reduce interference signals with a better operation of the video broadband amplifier, to block riger amplitude. If the diode 96 were the diode 96 is arranged in a line 89,

not available, there would be the possibility that 5 the pulse generator of the circuit 27 with the Vi noise signals low amplitude from the ignition part of the deo broadband amplifier 106 connects, so that the Circuit blocks via the connection point 93 on the line in a first direction and in the Line 98 and echo signals from the assigned other direction (to the left in FIG. 4) passed through Converter 21 deteriorate. Depending on the flow of a current, the assigned With low-level noise signals, the diode io converter 21 has a pulsating effect.

96 for either positive or negative displacement The detector arrangement is based on the properties

as an idle circuit. tailored to the expected signals. For example

The blocking diode 96 is over the connection is because of the known distance between the point 98 by means of a line 101 via a Wi converter 21 and the cable 12 together with the derstand 102 also with a connection point 103 15 speed of propagation of sound waves in connected and from there with the inlet 104 of a water the time interval generally known, Wideband Video Amplifier 106. To avoid expecting pulse echo signals during this time that at the input 104 of the amplifier 106 a large can. Therefore, the ultrasonic device is 20 negative voltage appears, which destroy it, designed so that it only emits pulse echo signals would, a diode 107 is in a line 108 so assumes during this time interval that follows, which with the connection point 103 is referred to as "window width" in the following. Connection. Two acoustic properties of polyethylene that

The low-noise broadband video amplifier 106 propagation speed and the acoustic Im of the usual type receives, amplifies and transmits echo-pedance are particularly important. Both depend on signals from the cable 12. The weak echo signals a ₅ depend on the temperature and therefore need to be amplified to around 1 to 3 volts. The extended examinations

Broadband video amplifier 106 is chosen so that the equation for the speed of the longi-

that the semiconductor components used in it are tudinal sound waves (shear waves are not here have low noise properties. important) in a medium is given as:

Facilities in the pulse generator-receiver 30
circuit 27 to be provided to reduce the Kc + -u

Noise level during a time period in which y ₂ _ L__

Echo signals through the circuit 25 for checking for- * ~ ρ

is particularly important when it means device 20 for measuring the thickness of an inner 35

Mantle is used. The from the inner jacket ι ⁼ longitudinal velocity,

received pulse echoes are with regard to their Am- ^μ ~ Sdiermodul,

plitude lower than that of an outer cladding _V ^Q ~ density,

received. This is because the poly- ^c ~ modulus of the volume elasticity,

Ethylene surface on the inner jacket is more irregular 40 The acoustic impedance of polyethylene is important. _{T he} slight elevations and depressions of the tig, as it affects the size of the echo signal. The inner cladding reduces the Z, e range of the Ka equation for acoustic impedance is the following and thus causes a smaller rise: ^F

edge amplitude of the echo signals. Also cause Z = ρ V ₁

the slight elevations and depressions phase 45 with the symbols used above The strength de.

differently drawn. Although the echo ^ "ΪΪΙ ^^^^^^,? *. The signal strength between the inner and outer sheaths impedance mismatch determines the EchoampU and fluctuates between different cable sizes, 50 tuden. The interface! between ™ water and poly

^ zsgsjufjsszs? * ssÄ ^ ΐ fs

The inner MaBK ₁ draw, * h «the K _? be _lk e, n & K &

together and shows a somewhat irregular echo after the second

outward facing outer surface. In contrast, 55 experimental data showed that the acoustic!

.st the outer jacket via a tubular metal impedance for polyethylene ürhöheTe temperature,

shielding «is handed down which contributes to the decrease, in particular, its ectoin

the outwardly directed outer surface of the outer amnitude, much w _P m »V 7 ~, ·. Su «-« ouch

Coat is rather uniform. This makes it necessary ^ S & ^ tt ^ SJ ^^^^ USi

60 th Polväthvlcnn ^ rn ·· ^, u? α u ι, Ι da

ask what again the possibility of inclusion «J ^ SSSS ^ S ^ t ^^

tS wash the pulse gen- EÜä2ft befd

Ratorteil of the circuit, which the SCRs 54, 63, 71 tSS ^ SSa ^^^ SS

and 78, and the broadband video amplifier 6 ₅ at the inside ManS h? T ί

106 of the pulse generator receiver 27 is arranged on the basis of Let mJ% 1 * ⁶ " ^die

serves to increase the impedance level during SfchüSJvaSenS i ^

the period of time during which the receiver 27 received the 32 £ SS

If the minimum value falls, there is no incorrect measurement. Rather, the last good measurement is stored in memory for counter 32 to maintain a correct caliper output.

The receiver logic circuit 29 is capable of testing the following expected signal properties:

(1) the signal echoes occur in a predetermined period of time (called the window width) after the transmitted pulse,

(2) is the initial polarity of each echo

connection points 136 and 137 to an inverter 138 and from there via a line 139 to a flip-flop 141 in order to set this.
The flip-flop has a clear or reset input 142, which is connected to the pulse repetition frequency circuit 30 and one output 143 of which via a connection point 144 with an input 146 of a holding pulse generator 147 designed as a monostable multivibrator and

ίο is connected via a line 148 to a confirmation pulse generator 149 designed as a monostable multivibrator.

An output 151 of the multivibrator 149 is connected to an input 153 via a line 152

(3) the first echo pulse has a short duration compared to the second echo

(4) ^{(zwiSh 8} en ^6a the first and second echo * NAND gate 154 is connected. As shown in Fi g. 5 to exist a time interval of at least 200 ns, ^ice? 'F' ^{hen lst d} .f connection point 136 "The one

(5) the amplitude of the second Echoinipulses is ^ ¹ ™ ⁸ "? Nut to the other input 157 of the connected greater than that required by the first echo micro NAND gate 154. Thus, llth positive Sinimumfs Fi e. 6 a) and ^gnale g ^leichzem 8 ^to inputs 153 and 157 of the

(6) the second echo pulse has a duration of ²⁰ NAND gates 154 , a low level appears at at least 700 ns output 158 of this gate, at least / uu ns. _{The output 15g of} NAND gate 154 is over

If these properties are connected to a set input 161 of a sequence of first and second flip-flops 162 assigned to one another for a particular line 159 . The flip-flop 162 will match echo pulses, the receiver logic is reset by a delayed PRF signal. This circuit 29 is a command in the form of a read by applying a reset signal to a pulse to the counter 32 to the during the
Time 2 t (see Fig. 6 h) stored count value as
to store valid information.

Below throw all the logical elements, i. H. 3 " NAND and NOR gates, the flip-flops and the monostable multivibrators, in general Hand described in positive logic, where high voltage is a binary "1" and low voltage is a binary "1" represents binary "0".

The connection point 43 is connected to an input 111 of a monostable multivibrator 112 (see FIG. 5), which generates a delay pulse which is sent via a line 113 to a second mono input 163 of the flip-flop, namely through the rear edge of the delay pulse from output 115 of multivibrator 112.

An output 164 of the flip-flop 162 is connected by means of a line 166 via a connection point 167 to an input 168 , which is designated as the D input of a flip-flop 169 . A clock input 171, referred to as a ^ input, of the FHp flop 169 is fed from the output 173 of the multivibrator 149 via a line 173.

The flip-flop 169, which is cleared by a pulse repetition frequency signal (IRF) that is applied to the input 170 , is generated at the unstable multivibrator 114 and a signal at a 4th gear 174 that is transmitted via line 176 appears on output 115 . An output 116 of the multi-input 177 of a NAND-Ga.rci-s 178 over travibrators 114 is via a line 117 via a gene. The connection point 137 is connected by means of a connection point 118 to an input 119 of a line 179 via a connection point 181 to a detector or comparator 120 for a positive voltage threshold value and to an input 121 45 to a second input 182 of the NAND batters 178.

a negative span comparator 122. The output 183 of NAND gate 178 ^; st over

connected. a line 184 to an input 186 a. Flip

The threshold detectors 120 and 122 throw flops 187 attached.

of a comparator part 123 of the receiver logic- The flip-flop 187 has a with the Imp. ¹ S-

circuit 29 includes. As can be seen in FIG. 5, the 5 ° repetition frequency circuit 30 connected to the comparator portion 123 of the circuit 28 includes a reset input 188 on. However, the reset is delayed until the trailing edge of the pulse generated by the multivibrator 112. An output 189 of the flip-flop 187 is connected to an input 192 of a NAND gate 193 via a line 55 191 . The connection point is also 144

an RF input port 124 connected to wideband video amplifier 106 . The input 124 is led to inputs 126 and 127 of the threshold value detectors 120 and 122 , respectively.

The detectors 120 and 122 have a negative output signal when their threshold values are exceeded. As shown in FIG. 5 can be seen, an output 128 of the threshold value detector 120 is led to an input 129 of a NOR gate 131 with negative logic. This nomenclature is intended to mean that when either input 129 or the other input 133 is fed a low level, output 134 of the

g gp

connected by line 194 to the other input of NAND gate 193 , and the NAND gate produces a low output pulse as shown in FIG. 5 is shown.

Another output 197 of the flip-flop 187 is connected via a line 198 to an input 199 of a monostable multivibrator 201, which acts as a generator of a hold pulse for checking the Ehf il di Ei

NOR gate 131 has a high level. One serves the properties of the second pulse echo

Output 132 of the detector 122 is to the other output 202 is by means of a line 203 via a

Input 133 of NOR gate 131 is performed . The connection point 204 and a line 206 with

Output 134 of NOR gate 131 leads via input 207 of a second echo confirmation

pulse generator 208 connected. The generator 208 is also a monostable multivibrator.

The output 209 of the multivibrator 208 is via a line 211 with an output 212 NAND gate 213 connected, another input 214 of the NAND gate via a line 216 · is connected to the connection point 181. The NAND gate 213 can have a negative signal at an output 217 and then to give a line 218 to a flip-flop 219 ίο to be set via its input 221.

The flip-flop 219 has one with the pulse repetition frequency circuit 30 connected reset input 222. It generates a signal at its output 223, which is then via a line 224 to a Input 226 of a NAND gate 227 goes. NAND gate 227 generates high signals when applied at both inputs 226 and an input 228, which is connected via a line 229 to the connection point 167 is connected, a low signal which is via a line 231 to the input 232 of a Pulse generator in the form of a monostable multivibrator 233 runs to set it.

The connection point 204 is via a line 236 to an input 237 of an amplitude comparator 238 of the detector circuit 123 is connected. An output 239 of the comparator 238 is via a line 241 connected to a flip-flop 242. The flip-flop 242 has one having the pulse repetition frequency circuit 30 connected reset input 240. An output 243 of the flip-flop 242 is connected to an input 246 via a line 244 of the multivibrator 233 connected, the other input 247 via a line 248 with a Input 249 of the multivibrator 114 is connected.

On command, the multivibrator 233 generates a read pulse at the end of the "window width", which causes that the count is stored in the memory unit (not shown).

It is important to note that there is about 3.8 to 7.6 cm of water above the cable 12 for the device 20 to function properly. The underside of the crystal converter 21-21 must also be immersed. A cylindrical device can be used for this purpose, which is placed above the uppermost V.'andler 21 and is arranged in the immediate vicinity of the cable 12. Then the container can be vacuumed connected to draw water up and submerge the lower part of the crystal.

It should be noted that with the one used here Expression "measurement" or "test" or "monitoring" the comparison of a quantity with a reference quantity is meant. For example, threshold detectors 120 and 122 check whether the At least the silence amusement echoed exhibit. On the other hand, the comparator 238 determines whether the peak amplitude of the second echo pulse is greater than a predetermined amplitude. Of course, the device 20 could be refined so that the actual values of the time intervals and the amplitudes can be determined.

Depending on the permissible error rate, the device 20 can also be less expensive be designed. For example, channel 22 can contain the thresholds of both pulses and the peak amplitude of the second echo pulse, checking any recorded second Impulse is allowed after a pre-set time. For this it is of course assumed that the first echo pulse that has the required threshold is a valid pulse. This can be right or not. Alternatively, the device 20 may be designed to determine whether the threshold values of both pulses are above a predetermined amplitude, whether the peak amplitude of the second echo pulse is greater than a predetermined value and whether the duration of the first echo pulse is less than a preset value.

The preferred embodiment described herein records a time count between the echo pulses on. if a sequence of first and second echo pulses is valid. The first impulse is valid, if the amplitude is above a certain threshold and the duration is less than a preset value is. The second pulse is valid if its peak amplitude is above a preset Size and the duration is greater than a preset duration. A valid sequence a first and a second echo must occur in the so-called window width.

A refinement of the present system takes into account the use for dynamic cable sheath thickness measurement, so while the cable 12 is moved forward. In contrast to the measurement of pipe wall thickness, the lateral movement of the cable and deformations in the jacket 13 are included. In some known devices manual adjustments must be made if the cable dimensions or other parameters can be changed. The embodiment of the invention described here represents automatically adapts to these changes.

Way of working

In the description of the working method of the ultrasonic measuring device 20 according to the invention, let Reference is made to FIGS. 4 and 5. The pulse repetition frequency circuit 30 gives a pulse via the line 41 to the connection point 43 and then via the line 44 to the pulse generator device 48. The optical isolator 48 then sends a trigger pulse to the trigger circuit 51.

The trigger circuit 51 gives a positive potential to the control electrode 53 in order to ignite the first SCR 54 to effect. This leads to an increased anode-cathode potential at the second SCR 63, which ignites. The SCRs 71 and 78 are fired in the same way.

The four SCRs 54, 63, 71 and 78 are able to withstand the applied potential when it is is evenly divided by resistors 84 and 86-88. However, if the first SCR 54 is conductive the remaining three cannot withstand the applied potential and ignite, as above described.

This firing of the four series SCRs 54, 63, 71 and 78 causes the capacitor to discharge 92 so that a pulse is applied to the associated transducer 21. This impulse is a negative pulse of 200 to 250 V and a duration of about 60 nanoseconds. The feed this pulse to the transducer 91 causes the generation of pressure waves, which on the encased Cable 12 act.

¹⁵ 16

A moment after the SCRs 54, 63, 71 the circuit takes the noise signal first

and 78 ignite, the potential at the connection echo is up and waiting for the real first echo

point 91 failed, practically zero, while on the ver when the appearance of the second echo was confirmed,

connection point 93 approx. 200 to 250 V available. Should this happen, the receiver logic

are. This causes a discharge of the capacitor 5 device 29, which has the expected positive-negative sequence

92 through the SCRs until prak- does not receive through the capacitor, no generation of the read pulse

table the voltage is zero. cause.

Current is then supplied by the source 109. In addition, the pulse repetition frequency controls

to recharge the capacitor 92. Frequency circuit 30 controls the operation of channels 22-22

How the receiver ^{logic circuit works 10 and more} ? Working together. To do this

^{r ö 6 6} generates the pulse repetition frequency circuit 30

The receiver logic circuit 29 (Fig. 5) is thus four pulse repetition frequency signals, one for each

constructed to deliver a positive pulse each of channels 22-22, each soft for a period of time

if the received by the pulse generator receiver 27 of one millisecond. The four impulses are

f received echo pulses within a predetermined offset of about 250 microseconds (Fig. 6 j),

th amplitude range. what the relocation of the working sequence of the 4 channels

In one of the pulse generator-receiver 27 received. This is how all essentials run

caught valid set of echo pulses, these processes in the upper channel lie within the first

a time 2 t apart, as shown in FIG. 6, from 250 microseconds, i.e. before the generation of the

where the first echo pulse is denoted by I and the shifted Im-

about 40 to 120 microseconds after the start of the pulse. Then the left and right KanpJ follow.

Cycle occurs. The first echo pulse occurs when the PRF circuit 30 conditions the circuit

by the associated transducer crystal 21 29 for each cycle. A defined as negative impulse

transmitted pulse to the outward-pointing nated pulse PRF from the PRF circuit

Surface of the jacket 13 meets. The second echo "5" to the "1" inputs 142, 170, 222 and 240 of the

pulse, labeled II, arises when the non-flip-flops 141, 169, 219 and 242 are given to

to reduce the reflected part of the outputs emitted by the converter crystal to a «low level,

deten impulse the inward-facing surface The delivery of the FKF impulse is the beginning

of the jacket 13 meets. of a test cycle. The PRF circuit 30

The amplitude of the echo pulse I is a radio 30 also controls the circuit 29 to generate echoirc pulses

tion of the acoustic impedance mismatch between associated transducer 21 only during the

see the hot polyethylene jacket and the water absorbing predetermined length of time, which is

water in the cooling trough 14. The amplitude of the echo pulse width (FIG. 6 b) is indicated. The impulse of

ses II is a function of the acoustic impedance- the PRF circuit 30 is applied to the input 111 of the

Mismatch between the hot polyethylene 35 multivibrators 112 given.

shell and the core 11. In addition, the first The multivibrator 112 causes a freeze delay

Echo pulse with respect to amplitude and duration reduction (Fig. 6 b) of predetermined duration, and

lower than the second echo pulse. this pulse is sent to reset input 163 of the

Given during the "window width" of about 90 to flip-flops 162 to cause the-

120 microseconds duration (Fig. 6 b) a hold 40 sen "0" output 164 will have a high level,

pulse (Fig.6d) when receiving a first echo In addition, the delay pulse is on a

generated by the receiver logic circuit 29. A reset input 188 of flip-flop 187 is given,

Valid pulse (Fig. 6e) begins immediately after to bewixken that output 197 has a low

the end of the first sustaining pulse. The level is weaker and the output 189 has a high level

It is worth seeing that the first valid pulse after the 45 assumes.

Decrease in amplitude of the first echo pulse occurs. Conces- the rear edge of the through line 113

When the receiver logic circuit 29 sends a positive Vej delay pulse, the multivibrator

tive output 158 shows, it is known that a validator 114 for generating a window pulse (Fig. 6).

ger first impulse occurred. Then becomes The so-called "window width" of the window pulse

The beginning of the second echo pulse, a second hold, is the period of time in which the channel 22 is valid

pulse is generated and a second valid pulse that receives with pulse echoes and thus eliminates scattered pulses

begins at the end of the second sustaining pulse. Im preventing. The end of the window pulse is called

In contrast to the first valid pulse, the second end of a test cycle should be considered.

Valid pulse during the decay of the second echo separates the receiver logic circuit 29 whether an

impulse occur. As a result, the two should pulse for further processing control

th valid pulse assigned circuit part one of measurements that the reception of echo pulse

give negative output 217 , which indicates that sen are assigned, generated or not,

second echo pulse outside of the predetermined window pulse is transmitted from output 116

Limits of the threshold value band is. gen and the connection point 118 supplied to

It should be noted that the receiver logic circuitry, 60 to enable detectors 120 and 122 ,

when it has a negative output at a detector circuit 123 includes devices

receives first echo, no second echo expected to perceive a positive or a negative

and thus no read pulse for the first cycle of the echo pulse transmitted by the amplifier 106

generated. has been applied to the input terminal 124 .

The valid pulse also avoids the wrong response. 5 it can be seen that the amplitude

acquisition of noise signals, which on air bubble threshold detectors 120 and 122 only then

can be based in the water of the cooling trough 16. If enabled, when the window signal on the connection

a noise signal leads the first echo pulse, formation point 118 appears. _{6Q9 615 /} , ₂₆₃

π ¹⁸

. The amplitude threshold detector 120 g see % ^> \ ^ ΤΨ £ ^

a negative confirmation signal to the input , 129 ^ " _m ^ f high level and causes som,

of NOR gate 131 when present * ieu «^ valid output; 1 »^ ^ ^ _s . _gnais ^ ^

positive echo pulse at input connection 1124 aas _{NANr> gate 193} . _{This leads} to £

the threshold value detector circuit 123 other- 5 IW ^^, _{193 a negative} output ^

On the other hand, the Ampbtud ^ threshold value detector 12i gives the 'Jf ^ ^ _{the B inn of the measurement k}

XS »123 is so, ο rs * reason for the age of one

designed to be single- ^ - ^ "^ '^"? ^ ⁸ ^ L

SST ZRtÜ & ttZZZ ,

at least ^ the TOrout determined threshold value 192 of the NAND gate 198 appear. D, it has been amplitude the negative signal cnchrrt a negative short duration pulse at NAND _nic £ _t '20 have the effect of gate 193. However, if the flip

When the polyethylene jacket 13 cools down, flop 141 is reset, the output 143 increases the amplitude of an ecitio pulse from the jacket. a low level, which at the output 196. The present system is for the thickness and eccentricity to cause a low level, whereby the tricity measurement was placed as close as possible to the extruder output pulse of the NAND gate 183 and thus placed. Thus the measurement takes place on the hot poly- «5 the orallator impulse payment was interrupted ^ ethylene jacket material. The detectors 120 and 122 To avoid this, a delayed FKF-

are designed and set to receive pulses at the input 188 of the frlip-hop 187, which only give a predetermined mini. This delays the resetting of the output malamplitude, which corresponds to that which is expected at the 189 at a high level to a high level outwardly facing surface of the polyethylene 30 at the input 192 of the NAND gate 193 jacket 13 is expected. until after output 143 of the

The receiver logic circuit then checks flip-flops 141 by means of at least one partially valid 29 first echo pulse in order to determine whether the term threshold value pulse I.

first echo pulse no longer than a pre- The appearance of a high level at the connection

is the correct length of time. Investigations have started at 144 shows an at least partially validity that the first echo, from the interface of the water, is the first. A test is started, and the outward-facing surface of the poly- to check this assumption for correctness, and the expected pulse of ethylene is very short, although by determining that its duration is about duration, for example in the range of half a 500 nanosecond and that a microsecond thereafter. In contrast, the second echo time interval occurs without a signal. For this purpose, the impulse from the interface between the inwardly high level at the junction 144, the facing surface of the polyethylene and that also causes a high level at the input 146 of the core or the shielding layer of a duration in the first sustaining pulse multivibrator 147 is given. ranging from 1 to 2 microseconds. This is because the signal at junction 144 indicates that polyethylene tends to filter out high frequency energy presence of a valid echo pulse and the greater reflection of the amplitude caused by one of the thresholds at the second interface. Hence, some value detectors 120 or 122 must be determined.
The application of a signal to the connection point in terms of time duration and amplitude result 144 lets the hold multivibrator 147 fill you up. 50 time delay or hold pulse (Fig. 6 d)

Should the amplitude of the first echo pulse testify to determine whether the first pulse exceeds a predetermined value, the valid time period, for example ¹ Zs microsecond, threshold value detector ISO or 122 is a signal to be considered a valid first echo pulse. The input terminal 129 or 133 of the NOR gate hold pulse multivibrator 147 generates a hold meter 131. This in turn brings the NOR gate 131 55 pulse of a predetermined length, which in this case sends a high voltage signal to the Vt Microsecond long. After the V * micro tie point 136 and the inverter 138 give. Second causes the trailing edge of the hold pulse. Inverter 138 then gives a negative signal that valid pulse multivibrator 149 generates a pulse on line 139 to flip-flop 141. This goes (Fig. 6e) of about 500 nanoseconds.
the output 143 of the flip-flop 141 at high 60. This pulse has the effect that at the input 153 of the voltage level, which appears at the connection point 144 to the NAND gate 154, a high level appears. to operate the NAND gate. Should the echo

The flip-flop can only be cleared by a pulse to the sustain pulse duration exceeding applying the PRF Signalis have at the beginning of the following, is fed via line 156 Link measurement cycle. 65 point 136 a high level at input 157 of the

The high voltage level is applied to the connection point of NAND gate 154 . This causes a low level input to input 196 at output 158 of the NAND gate. of the NAND gate 193 given. As in Fig. 5 to If the echo pulse is still present, then means

this, that no valid echo pulse I because of too large also shows the end of the counting cycle m (Fig. 6). The

^ Duration has been received, and the measurement of setting the flip-hop 187 results in a

the signal is abandoned; in the other case the level at output 189 becomes low and consequently a

the signal is saved. negative signal at input 192 of the NAND gate

The output 164 of flip-flop 162 will appear through 5 193 to disable the gate and grounds delayed PRF pulse, if this at the generation of a low level at the output too uninput 163 is created, break back. This causes an interruption of the NAND gate is operated so that there is a low count of the oscillator output signal through the has rigen level at the output 158, which is fed to a counter 32 (FIG. 6 h).

Echo impulses that are longer than 500 nanoseconds. The remainder of the cycle is used to determine the

the flip-flop 162 is set to validate the second echo, which has the consequence

to cause a low level at its output 164. that the count value is in the buffer memory (not

The low level at output 164 appears on the shows) is being transmitted.

Connection point 167 and at the D input 168 of the For the second echo pulse, a valid

Flip-flop 169. _l5 used festätigung that of the Gültigbestäti-

If the D input of the flip-flop 169 is low, the first echo pulse is the same. Let it be level when the positively directed trailing edge reminds you that the second echo pulse has a duration of the valid pulse generated by the multivibrator 149 in the order of magnitude of Vs to 2 microseconds at the clock or C-output 171 . As a result, the portion of the receivers the output 174 as appears low. This corresponds to logic circuit 29, which checks the second pulse, a non-gap situation - the first echo pulse with a built-in delay of 1 micro is invalid. If the output 174 is marked as low second. Only then does the pulse appear, the NAND gate 178 is checked not actuated, and if it is still the threshold amplitude and the output 174 remains low. The next one has, the pulse is stored.
The FRF pulse seeks to reset the flip-flop 169. The setting of the flip-flop 187 has the effect that since the output 174 is already low, the low level at the output 197 remains low at the high level. goes and is given on line 198. the

On the other hand, if the echo pulse is after the rising edge of the pulse from the flip-flop 187

Hold pulse appears (which results in a valid first that the second hold pulse generator 201

Echo pulse), a pulse with a duration of about 1.0 micro-

NAND gate 154 not high. That generates NAND seconds.

Gate 154 is not actuated and sets the flip-flop when the hold delay pulse passes through the

162 picht, and the high level is generated at the output 164 of the multivibrator 201, a signal of

appears at the D input 168 of the flip-flop 169. The connection point 204 appears via the line 236

D is high when the clock C at the input 171 to an input 237 of the threshold value detector 238

occurs, output 174 is high, which is given high to enable that detector. The posi-

Level at input 177 of gate 178 causes tive amplitude of the second pulse is through the

to release the gate. Threshold value detector 238 remains checked via output 174 in order to determine

until the next working cycle, when the PRF im- whether the amplitude of the second echo has a

pulse resets flip-flop 169 and causes 40 to exceed preset value, which is much larger

the output is low. is than that of the original threshold.

Should a high threshold value detector shown in FIG Level occur, the first echo pulse with respect to 236 only checks positive signals; however, it can Time and duration confirmed as valid. This also allows another threshold detector to be included in the switching circuit 29 expect a second echo pulse. 45 tion 123 for checking the signal for negative

The high steering appearing at connection point 167 are included.

Level causes a high level at input 228 In the event that the maximum amplitude of the

of NAND gate 227 to enable the gate. Threshold value is exceeded, the detection

Enabling NAND gate 227 enables gate 238 to go low on line 241

if the second received pulse is valid 5 "to an input of the flip-flop 242 to activate the flip-

is asserted, the generation of a read pulse to flop and cause a high level

cause the count value stored in counter 32 to appear at its output 243. The high level

is chert. at output 243 is given on line 244,

When the second echo pulse from input 124 of the order the signal on input 246 of the multivibra circuit 29 is received, causes one of the thresholds to lead 55 gate 233 and release the multivibrator, value detectors 120 or 122 that the NAND gate The trailing edge of the multivibrator 201 er gate a high level pulse generated at its output 134 appears at the multivibrator 208 testifies. This has the consequence that a high level and has the consequence that the second pulse validity the line 139 and via the connection point multivibrator 208 a validity pulse (Fig. 6 g) 181 on the input 182 of the already released 6 "of about 500 nanoseconds. The second NAND gate 178 is given to the NAND valid pulse multivibrator 208 causes a Press gate. high level from output 209 via path 211

The actuation of the NAND gate 178 - which is transmitted and transferred to the input 212 of the NAND

is partly performed on the receipt of the second echo pulse gate 213.

This is based - causes a low level at the 65 As in FIG. 5 can also be seen when ent input 186 of FHp-flop 187 appears, by which neither the positive nor negative threshold value select flip-flop to put. The receiver logic circuit rend the duration of the valid pulse exceeded 29 then awaits the second echo pulse. This will be a signal from junction 137 across

233 indicates that the first Im- _{a5 is} based on the thickness of the one to be tested

ώίβΑ asÄSsaa

If the window pulse is over, a decision is made regarding the generation of the most stop It does not matter whether the read pulse is generated or and the validation is designed so that Only this passing of the window pulse is possible per microsecond. Ä Sn sLna ° indicated by the monostable, for example, the holding pulse multivibrator

SvibmÄ SEafiig 248 generate a hold pulse at the input 157, which wemg en σηηΐ 247 of the multivibrator 233 is given. The 35 is equal to the decay time of the associated crystal Sivfbrator M3 is the pre-animal through an input 21. It is possible to fuss a crystal, 2 ^ 6 was released by the MultWibrator 242, which had a decay time of less than 0.5 micro an input signal from the NAND gate will now have 227 seconds.

The multivibrator 233 is now activated. Then the Gidtigimpulsgenerator 149 must men

^? to cause the counter 32 to generate the pulse width 40 pulse of a duration which is at least glucti Ts pulse from NAND gate 193 on receipt of a penode of the oscillation of the "organized Kj ^" the edge of the window pulse at the entrance stalls 21 is. The crystal 21 can be given with * MgJ «£ 247 to save. oscillate so that the pulse width is 200 nanosimn

The oscillator 34 generates pulses, which is through the.

the zaSsTgezählt be, wherein the initial 45 If these two time periods specified ^ started nd so puricfdes first sustain pulse and on, the successful operation of the front ^C hyng Kigspunkt of the second echo pulse ended 20 thereof from that the second echo (Echo IGIN CHT mediaVinci 4d The difference between these is received before the end of the first hold and validity measure for the time interval between the echo pulse confirmation for the first echo. The counter 32 comprises three decade counters, 50 this requirement cannot be met are, if changed, tens and ones, with a 4-bit storage device for measuring ummantehinge ^ rather which is assigned to each of the decade counters, whose thickness is of the order of magnitude if with regard to the echo pulses I and Π of less than 0.5 mm is «Micha

correct impulses in a positive-negative sequence. Of course, when using some ubhch £

Then a read pulse is generated at the 55 plastic ^insulation material for the thin% ™ _h ° end "window width" of the window pulse. This has the consequence that the pulses in the counter's memory are longer, because the speed of the number value stored by * 32 is transferred from the counting part of the counter sound pressure wave in the respective material to the memory part of the counter. Darger can be. In hot polyethylene the expected value is given from the memory to the digital 60 tete speed 0.5 mm per ^Μι1 ^ ^05ε1π1 "^ _ _ν1 analog converter 36, which has a continuous For a given thickness in hot Pοlyvmy

Liehe output voltage is generated, which the cladding chloride can reduce the time between echoes 1 to 1 dTckeSt be longer than with polyethylene, so that one exercise

It should be noted that the pulses stored in the buffer memory are reduced, and that even the increased count value is not changed until the next 6 ₅ jacket is thinner than 0.5 mm. . _H

The following validation pulse is generated around the There is a possibility to zmscbe the thickness

associated count in the buffer memory to a first surface and a second gpn transfer. The circuit 25 is so complicated that overlying surface becomes too

when there are several layers of different materials in between. Instead of measuring a Cable sheath thickness can also be measured the thickness of a covering layer, which successive Includes portions of a solid core or a hollow core such as tubes.

It should be noted that in some cable constructions in which, for example, an inner jacket is attached a core winding or another material clings to the surface, the second echo pulse of each echo pulse pair is stretched. However, it should be

innert that during the thickness measurement the off signal through the NAND gate 193 upon receipt of the initial part, of the second echo pulse is generated.

The peak value and duration properties of the second echo pulse are met. When the Kerri turn on the other hand has a distance from the inwardly facing surface of the jacket. the air acts as a barrier for the ultrasonic impulses. In this case too, the test and use generation of the second echo pulse in the thickness measurement is not deteriorated.

In addition 5 sheets of drawings

Claims (7)

Claims. 1. Method for ultrasonic measurement of the thickness of an elongated component, its successive Sections move relative to an electrical ultrasound transducer, with first and second echo pulses of different opposite surfaces of the component distinguished from noise and unusable Echo pulses are invalidated by sending an ultrasonic pulse into the component a first echo pulse from a surface of the component and an associated second echo pulse with minimum amplitude from an opposite surface of the component within of a given period of time and receive signals after receiving the first and second Echo pulse with a predetermined minimum amplitude are generated, the time Distance in relation to the time between the reception of the first echo pulse from the one Surface of the component and the reception of the assigned second echo pulse from the ent- »5 opposite surface of the component is, characterized in that the first Echo pulse a first predetermined property in addition to the minimum amplitude and the second Echo pulse has a second predetermined property in addition to the minimum amplitude, that the signals generated when the first and second echo pulses are received from each other distinguishable on and off signals are that the on and off signals are only due to the Receiving first and second echo pulses are generated with ** predetermined properties and that the off-pulse is generated only after a predetermined period of time from the start of the first echo pulse has passed. 2. The method according to claim 1, characterized in that after the validation of the first and second echo pulse a control pulse is generated and that the measurement of the elapsed time is processed when the control pulse is generated. 3. The method according to claim 2, characterized in that the property tested for Declaration of validity of a qualified first echo pulse a duration less than a predetermined one Time span is. 4. The method according to claim 2 or 3, characterized in that the property tested for Validation of a second echo pulse • a peak amplitude and a duration above of or greater than specified values. 5. The method according to any one of claims 2 to 4, characterized in that upon receipt of the first echo pulse, the time measurement is started and when the second is received Echo pulse is interrupted and that the measured time value is only accepted as a valid measured value and stored after the validity of the second echo pulse has been determined is. 6. Apparatus for performing the method according to claim 1, characterized by a Device that generates an on-signal when a first echo pulse is received and initiates the checking of a test property of the first echo pulse which is required for the validity, a device which, if valid of the first echo pulse and when a second echo pulse is received, the test of test properties required for the validity of an assigned second echo pulse initiates a device which causes the generation of an off signal, such that the period between the on-signal and the off-signal depends on the time span between receiving the first echo pulse from one surface and receiving the associated one second echo pulse depends on the opposite surface, a device for measuring the length of time between the on and off signal, a device used at confirmed validity of the first echo pulse a device for generating a control pulse prepared and if the validity of the assigned second echo pulse is confirmed operated for the purpose of generating the control pulse, and a device for processing the measured Period of time due to the generation of the control pulse. 7. Apparatus according to claim 6 with a comparison device for checking the amplitude properties the first and second echo pulses, characterized by means for checking the duration of the first pulse, the has a required amplitude property, means for checking the duration of a associated second pulse, this test causing the comparison device, the To examine the peak amplitude of the second pulse, a generating device for the on-signal upon receipt of the first echo pulse with the required amplitude and for the off signal if the first echo pulse is valid and while a second pulse is being received, a Initiating device which initiates the further processing of the measurement, a first logic device, upon receipt of the first echo pulse with the required amplitude, the generating device and the device for Checking the duration of a first pulse in action sets a second logic device on Reason for the valid first echo pulse and an associated second echo pulse with the required duration activates the initiating device, a third logic device, which, in response to the first echo pulse, the second logic device for generating of the off signal and to actuate the confirmation device for the second pulse puts into action, confirming the validity of the second pulse with reference to the Peak amplitude actuates the inducing device further, and a device that has a The test cycle for actuating the initiating device begins when it is at the end of the Test cycle is actuated, and the circuit is prepared for another operating cycle.