DE2333840A1 - DEVICE FOR ELECTROLYTIC ETCHING OF A WORKPIECE - Google Patents

Description

MITSUBISHI DENKI KABUSHIKI KAISHA, Tokyo, Japan

Device for electrolytic etching of a

Workpiece

The invention relates to a device for electrolytic Etching a workpiece, with a working gap between the Wei'kstück and an electrode one over a transformer and a working voltage provided by a rectifier is applied and wherein a test device is provided for determining an abnormal operation between the electrode and the workpiece.

An apparatus for the electrolytic etching processing of a Workpiece usually comprises a control device according to FIG Fig. 1. This device comprises a three-phase AC power source 1, a circuit breaker 2, a switch 3, a magnetic amplifier or a control throttle 4, a Step-down transformer 5, a rectifier 6 connected to the secondary winding of the transformer 5, an electrode 7, which is connected to the negative pole of the rectifier 6 via a shunt resistor S, a workpiece 9, which is connected to the positive pole of the rectifier 6 and the electrode 7 leaving a small gap opposite, a reference voltage generator 10, a device 11 for setting the reference voltage, a device 12 for setting the measured voltage, a comparator or comparator 13 for comparing the voltages of the

309882/1225

Devices 11 and 12, an amplifier 14, an ignition circuit

15 to control dec magnetic amplifier 4 and a thyristor

16 for driving a DC servomotor, a working vessel 17, a storage tank 18, an electrolyte 19, a pump 20 for supplying the electrolyte 19 from the storage tank 18 through a pipe 21 to the working gap, a dynamo 22 for displaying the speed, a DC servo motor 23 and a reduction gear 24.

An automatic control for constant voltage consists of a reference voltage generator 10, a device for setting the reference voltage 11, a device 12 for setting the measured voltage, a comparator 13, an amplifier 14, an ignition circuit 15, the thyristor 16 and the magnetic amplifier 4. An automatic control constant feed speed is achieved using a speed indicating dynamo 22, and a reference voltage generator 10, a device for setting the reference voltage 11, a device 12 for setting the measured voltage, a comparator 13, an amplifier 14, an ignition circuit 15 and a thyristor 16.

The devices according to FIGS. 2 and 3 serve to prevent damage of the electrode and the workpiece due to a signal indicating abnormal phenomena such as B. Sparking or unusual weakening of the current between the electrode and the workpiece (caused by the abnormal Formation of a strong oxidation membrane). In the device according to Pig. 2 will damage the electrode and the workpiece 9 thereby prevents such unusual Phenomena are detected by a test device 25, whereupon the circuit breaker 2 on the primary side the working voltage source is switched off via a safety switch signal line 26. In this device is the delay in actuation of the circuit breaker 2 from

309882 / 122S

REACHED

23338A0

- 3 -

When the abnormal phenomenon was detected by for switching off the working current source etv / a several 10ms, so that there is a risk of severe damage to the electrode 7 and the workpiece 9. When an abnormal occurs Phenomenon, it takes a long time to correct the electrode.

In the device according to FIG. 3, there is an automatic control intended for constant voltage. For this purpose, a group of thyristors 27 is used instead of the control throttle 4 Pig. 2 is used and the circuit breaker system according to Pig. will be improved. The working gap is created by a thyristor 28 bridged, which lies parallel between the electrode 7 and the workpiece 9, furthermore a diode 29 for Calibration of the voltage drop of the thyristor in the forward direction in series between the electrode 7 and the workpiece 9 switched so that the voltage drop in the forward direction of the diode 29 at the thyristor bridging the working gap 23 is applied, so that the thyristor 28 is ignited, even if the conditions at the working gap are so abnormal, that there is complete contact between electrode 7 and workpiece 9. The abnormal phenomenon is caused by the tester 25 detected and the thyristor 28 is triggered by a thyristor ignition signal, which is based on the test signal, Ignited via the signal line 30, so that the working gap is subjected to a voltage which corresponds to the voltage drop of the thyristor in the forward direction. The thyristor group 27 for automatic control under constant Voltage is turned off via the signal line 31 to turn off the thyristor and the switch 3 and the Circuit breakers 2 are through the signal line 32 for switching off the switch 3 and via the signal line 33 for Activation of the circuit breaker switched off. On this \ veic3 the working power source is switched off and damage to the electrode 7 and the workpiece 9 is prevented.

30988? / 1 ?? 5

With this device it only takes a few 10 ils to achieve the Voltage between the electrode 7 and the workpiece 9 ″ at To turn off the plague of an abnormal phenomenon. The voltage, however, which corresponds to the voltage drop of the thyristor 23 corresponds in the forward direction, remains between the Poland, so that the working current is not completely interrupted. A large number of thyristors must be connected in parallel when the operating current capacity of the thyristor 28 is in the range of several thousands to several tens of thousands Amperes. In this case it is difficult to turn all the elements on at the same time, and it is one large numbers of thyristors are required, so that the cost of the equipment is very large. In addition, it is necessary the diode 29 for calibrating the forward voltage drop of the thyristor in series with the electrode 7 and the workpiece 9 to switch. The diode 29 should have the same capacity as the rectifier 6 for the working current, so that this also reduces the cost of the apparatus similar to the thyristor 28 can be greatly increased and the working current cannot be completely interrupted will. If the thyristor 28 is ignited, there is a possibility that the thyristor 28 will be destroyed because none Device is provided to limit the current of the power source.

In addition, in a conventional apparatus for electrolytically etching a workpiece, an abnormal one becomes Phenomenon between the electrode and the workpiece during electrolytic processing by the test equipment 25 found. It is also known to detect spark formation between the electrode and the workpiece during electrolytic processing (abnormal phenomenon) by using a facility this determine which one generates a signal when the

30988? / 1225

set voltage by the sparking decreases compared to the predetermined reference voltage. For this purpose, the predetermined Reference voltage compared with the voltage at the working gap. This conventional device includes a transistor type voltage relay which operates at a voltage below the predetermined voltage is operated.

It is also known a device to a small voltage change the working voltage, which is caused by spark formation. Here is a combination a differentiating circuit and an integrating circuit are provided.

In the former system, however, it is necessary to use the predetermined Change reference voltage when the average working voltage is changed and it is difficult to understand the ripple component the working current source (pulsating component) and the voltage change component (caused by Sparks) in comparison with the average working voltage. With this conventional setup the accuracy of determining spark formation is extremely poor.

In the latter system, it is not necessary to change the predetermined reference voltage when the average working voltage will be changed. However, this device is due to the differentiating circuit by coming from outside random fluctuation or noise is greatly affected, so that it is very difficult to determine the ripple component the working voltage source and the voltage change component due to sparking compared to to identify average working voltage, so that here too the accuracy with which spark is determined v / earth, is very low.

30988? / 1225

So far, no satisfactory device has been found for the reliable detection of abnormal current weakening Known phenomena. · *.

It is therefore an object of the present invention to provide a device for electrolytic etching of a workpiece in which any disturbance due to abnormal current weakening phenomena is completely avoided. ■ -.y--

This object is achieved in that the primary side of the transformer with a diode and one of these thyristors connected in parallel is connected, which is controlled by das'Prüfgerät (25) so that the primary side of the transformer is short-circuited when an abnormal operation occurs.

The device according to the invention comprises a control throttle in an automatic control system according to FIG. 1 for constant voltage. Between the control reactor and the voltage drop transformer a diode is provided to reduce the size of the breaker thyristor and complete it Bring about interruption of the working current. It is a Three-phase all-wave rectifier provided and the interrupter thyristor is connected to the output of the rectifier, wherein the interrupting thyristor is triggered when an abnormal event is detected, so that a short-circuit of the three-phase 7/16 current between the control inductor is and the voltage drop transformer is forced and a feed between the workpiece and the electrode is stopped. The interrupter thyristor can be calculated within a few us detonated from the beginning of the abnormal event detected and the three-phase alternating current between "the control reactor and the voltage drop transformer is short-circuited. "- ■« ..,

3 0 9 a 8 2 ΙΛ 2 £ S-

In the inventive. Device becomes, the circuit part 'behind the control throttle forced to be short "agesch2Lcssen, so that the current capacity dec interrupter thyrictors due the current-limiting effect of the saturable reactor can be significantly reduced in comparison to conventional systems. Accordingly, it is possible to run the current only with a sub. breaker thyristor in combination with a rectifier diode and in particular a Droipho-sen-Allwellcn-Glcieh-, reht erdi ode. ouch Interrupt. 3 ^ i the interruption of the working current a delay is only caused by the Indu :: - Tanzkoaiponente des Spamiungsabfalltrancgormatora, the electrode and of the workpiece so that the tension is caused The voltage drop of the interrupter thyristor in the forward direction corresponds to »reduced to 1/10 to several tenths and the interruption of the working current continues with great speed.

In order to prevent an interruption from occurring when the work is interrupted due to the inductance component of the voltage drop transformer, the electrode and the sealing piece, a thyristor is provided in the device according to the invention. Working gap bridged, covic a biased capacitor for the working gap bridging thyristor between the work tick tmd- the 2-l lectr oeL.c, so that the cathode of the. Working gap bridging 2hyristor through the capacitor is negatively biased. The interrupter thyristor is ignited when an abnormal gate is set and at the same time the thyristor bridging the working gap is also ignited, with a delay in the interruption of the working current due to the inductance component of the step-down transformer. Electrode and the workpiece is avoided by forcing the current through the thyristor bridging the working gap * so that the working current flowing through the working gap is interrupted within a few us,

309882/1225

BAD ORIGINAL ° OPY

-S-

It was "previously necessary to use a diode to calibrate the Provide voltage drop of the thyristor in the forward direction when the thyristor bridging the working gap is provided between the electrode and the workpiece. In the present invention, however, it is unnecessary to use a diode Calibration of the voltage drop of the thyristor in the forward direction must be provided, since the thyristor by using the capacitor forced to bias the thyristor is ignited.

With the device according to the invention, abnormal processes determined as follows:

A sampling and holding circuit is provided with which samples are taken repeatedly during a certain period of time, whereupon the measured value is held for a certain time etc, this happens with a certain frequency (several KHz to several HHz). The frequency is higher than the frequency the ripple component of the working voltage. The output voltage of the sampling and holding circuit becomes the holding time from the input voltage to the hold time by means of a linear amplifier subtracted, forming a differential voltage during each of the short periods of time. This will make the Influence of the ripple component of the working voltage canceled, so that the accuracy and reliability of the detection of sparks is greatly increased. The sampling and Holding circuit generates an output voltage after a certain period of time during which an input voltage is input will. In the event of an abnormal process in the form of a sparkover at the working gap, a (small) Voltage change from which a sample is taken. Furthermore, the sampling and holding circuit stores the input voltage at the end of sampling based on a holding command signal and the output voltage is maintained until the next sampling command signal is received. the

30988? / 1225

Sampling takes place each time on the basis of a sampling command signal and the holding process is performed each time on the basis of a holding command signal.

In addition, with the device according to the invention, there is a small change in the working current due to an electrical shock determined by the sampling and quay circuit, so that a synchronization with the sampling and holding circuit to determine the small voltage change occurs in the event of a sparkover, with the sampling and holding of the voltage taking place and the sparkover is determined with great accuracy.

To increase döö? Working accuracy of the elektroiyticchen Etching is often carried out under a high gas pressure. In In this case, there are bubbles in the electrolyte and the working voltage and the working current change depending on the amount of vesicles. Accordingly, e3 has so far been difficult a change in work tension or work streak due to arcing from the change in working voltage and the working flow on the basis of the gas bubbles in a conventional manner. However, if according to the invention a sampling and holding circuit and a logic arithmetic circuit are used, so it is possible to use a small Increase in working voltage and low attenuation of the working flow due to the high pressure gas from a small voltage drop in the working voltage and a small increase in the working current due to dots to distinguish. In this way, the accuracy becomes essential even in systems which operate with high gas pressure elevated.

If the current is attenuated abnormally due to an abnormal Forming a strong oxide membrane, the working current becomes using a resistor into a voltage

309882/1225

converted, which is proportional to the working current and an abnormal damping of the current can be determined. In this case, the abnormal attenuation can be detected within several seconds to several tens of seconds, so that the length of time between the trial period and the hold period can be from about several seconds to several tens of seconds. The differential voltages in each period are determined to detect abnormal attenuation or weakening of the current.

In the following the invention is explained in more detail with reference to drawings.

Show it:

Fig. 1 is a block diagram of an embodiment of a conventional one Device for electrolytic etching of a workpiece;

Figures 2 and 3 are block diagrams of other embodiments of conventional ones Means for electrolytically etching a workpiece;

Pig. Fig. 4 is a block diagram of an embodiment of the invention Device for electrolytic etching of a workpiece;

Fig. 5 is a block diagram of another embodiment the device according to the invention;

6 shows a block diagram of a further embodiment of the device according to the invention;

Fig. 7 is a waveform of the working voltage in the case of the present invention Device for electrolytic etching a workpiece;

309882 / 122S

Fig. 8. a waveform of the working voltage as present Invention with periods of sampling and periods of maintaining the sampling value;

Fig. 9 is a waveform of the operating current in the invention Facility;

Fig. 10 is a waveform of the working current with alternate sampling and maintenance of the value at device according to the invention;

11 is a block diagram of a signal indicating spark formation in the device according to the invention;

Figure 12 is a block diagram of a circuit for detection an abnormal current weakening in the inventive Facility;

13 shows a waveform of the working current after passing through a filter in the device according to the invention;

Fig. 14 is an output waveform of the sample and hold circuit in the apparatus of the present invention and

Fig. 15 is a waveform of a signal of a subtraction circuit of the device according to the invention.

In Fig. 4, reference numeral 34 denotes a breaker diode group in parallel between a control inductor 4 and the primary side of a transformer 5. Reference numeral 35 denotes an interrupter thyristor, which is connected to both Poles of the diodes 34 is applied and the reference numeral 12 'denotes a signal line for the detection of an abnormal Signal formed by the phenomenon. A signal line 36 is used to forward the ignition signal of the interrupter thyristox 35. All other components are the same as the components

309882/1225

the conventional Pig. 2. Therefore, their description should be omitted. If between the Electrode 7 and the workpiece 9 an abnormal phenomenon is observed, the interrupter thyristor 35 is over '· the line 36 through the ignition signal, which is based on the test signal for the. abnormal. phenomenon is based, ignited, and the primary side of the transformer 5 is short-circuited, so that the working power source is switched off. At the same time, the breaker 2 is activated by an interrupt signal interrupted via line 33.

Another embodiment of the device according to the invention is shown in FIG. Here, a thyristor 28 is provided which bridges the working gap and is in series with a Yors voltage capacitor 37 for the thyristor 28 and between the electrode 7 and the workpiece 9 according to FIG. The capacitor 37 is charged via the signal line 39 by a capacitor charging signal which is formed in the charging circuit 38. If an abnormal phenomenon occurs at the _r working gap, this is .., .., determined by the test device 25 and the thyristor 35 is activated via the signal line 36 by the ignition signal, weL-. ches on the. a determined abnormal state associated test signal of the signal line 12 is based, ignited, so that those parts behind the control throttle 4 ·, ie the primary side of the transformer 5, is short-circuited. Thus, the working current source is switched off and at the same time the thyristor 28 is ignited via the signal line 30 by an ignition signal for the thyristor bridging the working gap, which avoids a delay in the interruption of the working current due to the inductance components of the transformer 5, the electrode 7 and the workpiece 9. At the same time, the interrupter 2 is switched off via the signal line 33 and the operating current source.

3Q98 82 / 122S ^;

GOPY

According to the invention, during the electrolytic etching. "in the event of an abnormal phenomenon, the Arbeltsctronource are switched off extremely quickly and safely by the test signal. According to the invention, a short circuit between the control throttle of the Arbeitsstromquelie and the step-down transformer is forced within a few µs due to the thyristor and the three-phase rectifier diode for all waves. In this Pail the current capacity of the diode and dc3 thyristor can be kept quite small due to the drop (current limitation) at the control choke as soon as the cable behind the control choke is short-circuited. The voltage, which corresponds to the voltage drop of the thyristor in the forward direction, falls at the step-down transformer so that deterioration is not observed.

In addition, according to the invention by the short-circuit. 3-thyristor and the capacitor negatively biasing the cathode. A delay between the electrode and the workpiece the interruption of the working current through the inductance Voltage drop transformer, the electrode and the workpiece can be reduced to a few ps. " so that the work stream compulsorily flows through the thyristor so that it does not is required to calibrate the voltage drop of the thyristor Use a diode in the forward direction.

In the following, the Pig. 6 shows a further Ausführungc- '- form of the device according to the invention described v / earth, v / ob position ν, the test apparatus 25 to the abnormal Pest a "phenomenon is improved This testing device for Peststellung an abnormal phenomenon is shown in Pig β, wherein the.. - 40 denotes Bezu33zeichen the Arbeitsspannung3quelle. the Bezugsseichen 41 denotes the working gap between electrode and workpiece, and reference numeral 42 denotes a Widers'jcnd for converting the load current into a voltage signal _r where the working voltage detected directly at the working gap v / ith

309882/1225

BAD LOCAL

'233384Q

.- ■■ 14 -

and where 'the Ά-r be its current separately ε * ΐΏ resistor 42' is determined- ν. ■ ""'"' ■■ - · - ' -lo :: -.-- ■" ■ .- ... ·,. ■

The reference numeral 43 denotes a reference pulse generator for sampling and holding for the setting of ' ! Sparking, This generator carries synchronous pulses ■ a_ · ,: " ^: circuit 44 for sampling and holding, the working voltage and a circuit 45 for sampling and holding the working current to .- 'the numeral 46 denotes a "subtraction circuit to form a" ifferenzspannung:. by subtracting the working voltage of the in stabbing - ^ v sample taken and held voltage "numeral · ~ ■ 47 denotes a subtraction circuit for forming a reference voltage by subtracting the voltage which is at the Υ / χάθϊν. stand 42 is tapped and corresponds to the working current -, '' ■ '■ ". (hereinafter referred to as the working current waveform), from the voltage of the working current waveform determined and maintained by sampling. The reference symbols 4S. and 49 denote level comparison circuits for comparing the differential output voltages of the Subtranktionskreis.se 46 and 47 with the predetermined reference voltage

50 denotes a logical one. Circuit for generating a Check signal "" when a spark occurs by determining ^ a spark component of the signal received from the level comparison circuits 48 and 49- is found ► The reference number 51 denotes a reference pulse generator for the Sampling and holding to detect abnormal Current change, or current monitoring v The generator

51 leads synchronous pulses to a circuit 52, which takes samples from the work stream and holds them (Sample and hold). The reference numeral 53 denotes a subtraction circle " to form a differential voltage by subtracting the operating current waveform after converting the Working current through the resistor 42 from the random sample determined and maintained voltage of the working

309882/1225

■■ · ■. 233384Q

current waveform and the reference symbol 54 denotes a level comparison circuit for comparison of the differential voltage at the output of the oubtra, ktionskreises 53 with a predetermined Reference voltage.

Fig. 7 shows the waveform of the working voltage, which at Working gap is present. And the reference numerals 55 and 56 denote voltage drops due to jumping sparks. Fig. 8 shows the waveform of sampling and holding the working voltage with the output of the circuit sampling and hold is given by tracking the input working voltage during the sampling time while di§ input voltage is maintained at the end of the sampling time during the hold time and as the output signal of the Circuit for sampling and holding.

Fig. 9 shows the waveform of the working current flowing through the resistance is generated by converting the operating current into a voltage and the reference numerals 57 and 53 denote Voltage increases caused by sparks. These correspond to the voltage reductions 55 and 56 according to Fig. 7. When a spark flashes, it falls the working voltage and the working current is increased.

Fig. 10 shows the sampling and holding waveform the working current waveform, with the output of the circuit being sampled and held by tracing the input— working strcms is given during the sampling period the detected value of the input waveform at the end of the. Sampling is recorded during the holding time.

11 shows the further processing of the signals indicating the formation of sparks. Reference numeral 59 denotes a signal after processing in the subtracting circuit 46 for the input voltage of the circuit for sampling and holding

309882/1225

233384Q

the signal voltage and the output voltage of the circuit for sampling and maintaining the tension. Numeral 60 denotes a level for setting a Voltage drop. When the voltage drops below the level, so a signal is generated by the level comparison circuit 48 in the next stage. The reference numeral 48 denotes a level comparison circuit for the working voltage drop in which the reference voltage and the level of the voltage drop are compared to voltage drops caused by sparking ascertain. Numeral 61 denotes a signal which is generated in the subtracting circuit 47 for the input waveform of the circuit for sampling and holding the waveform of the working current and for the output waveform of the circuit for sampling and holding. Reference numeral 62 denotes a level for detecting a current increase. When the voltage is increased above this level, the level comparison circuit 49 in FIG next stage a signal is formed. Numeral 49 denotes the level comparison circuit for the rise of the Working current in which the predetermined reference current and the current level increase compared v / ground to any detect current increases caused by spark formation. Numeral 50 denotes a logical one Circuit for processing the signal, which is caused by the lowering of the working voltage due to spark formation and to process the signal that occurs due to sparking caused by increasing the working current is caused. This logical circle has the function of the random fluctuations or coming from outside to separate the noise from signals that are traced back to sparking. The reference number 63 denotes a spark signal which has been processed by the logic circuit 50.

30988? / 1 2

Fig. 12 is a block diagram showing an electric circuit for detecting an abnormal change in amperage. The reference number 64 denotes a pilter circuit for separating a high-frequency ripple component of the working current waveform, which was converted into a voltage by the resistor. Numeral 51 denotes a reference pulse generator for sampling and holding for detection of abnormal change in current. Reference numeral 52 denotes a sampling and holding circuit for detecting an abnormal change in current. The reference numeral 53 denotes a subtraction circle. Numeral 54 denotes a level comparison circuit, and numeral 65 denotes an output pulse corresponding to the detected abnormal change in current. This circuit has a manually operated one Test circuit for determining a decrease in current strength with which a decrease in current intensity and an abnormal current weakening can be found. The reference number 66 denotes a working speed reference cell. The working current will be according to the change in working speed changed. Accordingly, if the potential of the reference cell for the working speed is changed manually is, the potential change is detected by a differentiating circuit 67 so that the sampling and holding takes place after the reference pulse generator 51 for sampling and holding to detect abnormal current weakening has been locked for a constant period of time by the device 68 to bring the operating current to a normal Stabilize value.

13 shows the waveform of the operating current after passing through the filter circuit 64.

Fig. 14 shows the output waveform of the sample and hold circuit.

309882/1225

233384Q

- 13 -

Fig. 15 shows that in the subtracting circuit 53 for the input working current waveform of the sampling and holding circuit and the output pulse of the sampling and holding circuit Signal. In Fig. 15, reference numeral 69 denotes abnormal current weakening, and reference numeral 70 denotes a level for detecting an abnormal current change or current weakening. When the voltage drops to a value below If this level drops, a signal is formed in the level comparison circuit 54.

The various embodiments for normal operation have been described above. To increase the working accuracy, devices with a high pressure gas charge are used used. Here, too, sparks and abnormal current weakening phenomena or current damping phenomena can easily be caused by the sampling and hold circuit, amplifier and logic circuit to be established.

According to the invention, sparks and abnormal current weakening can occur or current damping in electrolytic etching by use of the sampling and holding circuit of the amplifier and the logic circuit are detected, so that an abnormal Current weakening, which was previously very difficult and unreliable to determine, was determined with great certainty and accuracy can be. It is also possible to determine the ripple component of the working power source or the action of external random fluctuations in the voltage change components caused by arcing will be to distinguish. This is a particular advantage of the invention.

309882/1225

Claims (8)

233384Q - 19 PATEHTA! »'PROBLEMS 1. Setup sum electrolyte! See etching of a work piece, where at the working gap between the dome / head piece and an electrode an operating voltage provided via a transformer and a rectifier is applied, and where a Testing device for the detection of an abnormal process between Electrode and workpiece are provided, characterized in that the primary side of the transformer (5) with a diode (54) and one of these thyristors (35) connected in parallel is connected, v / which is controlled by the test device (25) so that £ the primary side of the transformer (5) when a abnormal operation is short-circuited. 2. Device according to claim 1, characterized in that that a thyristor (28) and a capacitor between the electrode (7) and the workpiece (9) are connected in line, the thyristor (28) being controlled by the test device (2i>) will. 3. Einrichtimg according to claim 1, characterized in that a thyristor (28) and a bias capacitor (37) in series between the electrode (7) and the workpiece (S) are connected, the thyristor (28) being controlled by the testing device (25) and the bias capacitor (57) is charged by a charging circuit (38). 4. Device according to one of claims 1 to 3, characterized characterized in that the tester (25) for 2-1 it solution of the working current for a short period of time each with a sampling and holding circuit (52) and a Computing amplifier (53,54) is equipped so that an abnormal Current weakening is detected. 8 82/122 * 5. Device according to claim 4, characterized in that that the test device (25) has a sampling and holding circuit (52) for the working current, and a reference pulse generator (51) for supplying a sampling and holding reference pulse to the sampling and holding circuit (52), as well as a Subtracting circuit to form a differential voltage from the operating current waveform and the output voltage of the Sampling and holding circuit (52), as well as a Yergleichsstromkreis (54) to compare the differential voltage and a predetermined reference voltage, as well as a logical one Circle for generating a signal in i'all an abnormal Current weakening. 6. Device according to one of claims 4 or 5, characterized by an udder (64) at the entrance of the sampling and holding circle (52). 7. Device imch one of claims 4 to 6, characterized by means of an adjustable working speed reference cell (66) and one which detects the change in potential Differentiating circle (6?) And a locking circle (66) to lock the reference pulse generator (51) for a certain period of time to stabilize the working current. S. Device according to one of Claims 1 to 3, characterized in that the test device (25) has a sampling and holding circuit (44 or / ^l ;! , 4S; 47,43) to determine spark.; .- formation. S. Device according to claim 3, characterized by one η Sampling and holding circuit (44) for the working voltage, a sampling and holding circuit (45) for the working current, a ? 33384Q JiezugGimpulsgenerator (43) for the supply of a sampling and Holding 3 reference pulse to the two sampling and holding circuits (44,45), a subtraction circuit (46) to form a .Differenzspannung between the working voltage and the Sampling and quay voltage, a subtracting circle (47) for the formation of an ulff erance voltage of the working current waveform: and the sampling and holding voltage, a level comparison circuit (45 or 49) for comparing the two differential voltages with a predetermined reference voltage and a logic circuit zui "Ex 'generation of a signal if due to the signal of the Level comparison circuit (48 or 4S) sparking is detected. 309882/12? 5