DE2545532A1 - DEVICE FOR MONITORING INITIAL ELECTRODE DAMAGE IN A MELTING DEVICE - Google Patents

Description

DR.-tNG. DIPI ING. M. SC DMo-PHY »OB DIPL.-PHVS. HÖGER - LEGAL RIGHT - GRIESSEACH - HAECKER PATENT LAWYERS IN STUTTGART

A 41 418 m

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October 9, 1975

Owens-Corning Fiberglas Corporation Toledo, Ohio 43659, USA

Device for monitoring incipient electrode damage a melting device

The invention relates to a method and an apparatus for monitoring the heating of molten glass by Jouleteche heat, especially for monitoring when it occurs Electrode damage, with electrodes in electrical connection with the molten glass with voltage pulses cyclically applied.

The electrical heating of heat-softening material by applying Joule heat includes the establishment of a electrical current-carrying connection to the material to be melted with the aid of electrodes. A typical warm softener Material, namely glass, must be kept at or above the usual working temperatures, i.e. around 1427 ° C

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by inserting or into the molten glass dips several pairs of electrodes and supplies the electrodes with controlled pulses of electrical power that flow through the glass. Very often such electrodes are designed so that substantial parts of their surfaces which are in contact with the glass to the walls of the container or the melting furnace for the glass are kept at a distance, so that the on the walls The amount of heat transferred can be reduced and the service life of the furnace walls is extended. For example, includes one electrode shape is a straight, round cylinder that extends through the bottom of the furnace. Though considerable Efforts are made to ground the electrode and To protect the refractory floor, it has been found that there is a tendency for the electrodes in the passage area to To corrode the wall continuously and show signs of erosion.

In the case of cylindrical electrodes, around the electrodes are below of the furnace floor cooling jackets have been arranged so as to to keep the electrode temperature outside of the melting furnace at a level which is so low that it is affected due to components of the free atmosphere and the resulting damage are not possible. In addition, it is not uncommon inside the jacket and around the electrode to maintain an inert atmosphere so that the electrode is in the length range in which their temperature is within of the furnace, is protected. However, even with such precautions, the electrodes tend to develop to erosion phenomena, usually in the area of the melting furnace floor / glass melt boundary layer and slightly

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down. Such erosion can lead to the electrode breaking off in the melt. If the electrode breaks off in this way the bottom wall in the adjacent area of the remaining electrode stub is attacked and very developed quick leaks, if it is not possible to take corrective action here immediately.

The invention is based on the object of a method and a device for monitoring such a melting furnace create, in which heat-softening material is melted by applying Joule heat, so that a beginning Failure of electrodes can be detected in good time and such conditions can be displayed. In this way it is possible take corrective action in a timely manner that will prevent greater harm.

To solve this problem, the invention is based on the method mentioned at the beginning and, according to the invention, consists in determining the effective value of the voltage applied across the electrodes and the effective value of the current flowing through the electrodes and, on the basis of the determined effective values, determines the electrical resistance value on which they are based, as well as a is actuated to a predetermined value of resistance ^to ~ speaking display device.

It has been found that an incipient electrode damage is heralded by an increase in the resistance between the pair of electrodes to which electrical power is supplied ^{for Joufe 1 shear heating ".}

A feature of the present invention is therefore that in

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the circuit of the power supply for the electrode pair current and voltage are sampled and the resultant Resistance is detected, whereupon a display device is actuated as a result of a predetermined resistance.

Another feature is that the accuracy of the resistance determination is increased by the fact that the RMS values of current and voltage and uses these values to determine the associated resistance.

Another inventive feature is that each Electrode pair with an existing plurality of such electrode pairs selectively assigned a resistance measuring arrangement will, together with an indication system for an incipient damage; there is also a display device for this Electrode pair provided so that this particular pair can be selectively determined from the plurality of electrode pairs.

The invention therefore consists in that possible electrode damage is determined in advance by monitoring the current, voltage and resistance between the respective electrode pairs in a heating system based ^{on the generation of Joule 1 shear heat.} A very rapid change in the monitored resistance is an indication of incipient damage or incipient failure; the monitoring system is designed so that alarming means, corresponding message-printing arrangements and / or process rule controls can be actuated in order to be able to carry out a display as a result of a predetermined voltage ratio or a change in resistance. Usually a large number of

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Electrode pairs using a time division multiplex method in such a way that the parameters of current and voltage assigned to each pair are monitored in a repetitive cycle or resistance can be scanned. Distortions of current and voltage values can be kept low by using selective Subranges of the usual power pulses or power values are processed in gates to regulate the heating; complex voltage forms that may be present are thereby subjected to a utilization that special converters are used, which the true effective values of Record current and voltage and convert them into DC voltage values.

Further refinements of the invention are the subject of the subclaims and laid down in these.

The structure and mode of operation of exemplary embodiments of the invention are explained in more detail below. Included demonstrate:

FIG. 1 is a flow chart which shows the monitoring process for incipient electrode damage and

FIG. 2 shows a schematic representation of a plan view of a glass melting furnace and associated electrical ones Circuit elements for monitoring the electrodes arranged in the glass melting furnace for possible Damage.

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In accordance with the present invention it is found that an impending or incipient failure and damage to an electrode, which is in a fluid mass from in Heat-softening material is immersed, to which the electrode conveys an electrical current flow to achieve Joule heat, is indicated by an increase in the resistance value between corresponding pairs of electrodes that carry this current to lead. It is believed that this phenomenon is due to erosion of the Electrode, which reduces its cross-section, and on the development due to fractures in the constricted erosion area.

Because there is a considerable increase in the resistance value between electrode pairs up to 24 hours before the actual electrode break could be observed, one has inferred from this circumstance that the beginning of finally to one The process leading to damage or rupture is a decrease in cross-sectional area along the length of the electrode. This decrease or this constriction has often been observed in the case of electrodes in the area adjoining or adjacent to the exit area the electrode extends out of the refractory wall of the container containing the molten material. In characteristically, the rate of increase in resistance increases over time. It turned out to be. that a 2O% increase is a reliable indicator of coming Difficulty is, therefore, according to an inventive Feature such an increase is used as a criterion for actuating a device indicating these difficulties.

It should be noted here that during long-term operation of containers heated by means of Joule heat, a certain erosion of the

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Electrodes occurs over relatively long periods of time. This long-term erosion and the resulting long-term increase in Resistance value between electrode pairs is not an indication of the beginning of an electrode break or damage to the electrodes. For example, in the case of a glass shingling device for a glass of the sodium borosilicate type used in the manufacture of glass wool, wherein the glass is heated to a melting and refining temperature of about 1427 ° C, the resistance between vertical, round, cylindrical molybdenum electrodes with a diameter of 7.62 cm, which extend through the furnace floor and contact the glass for a length of about 5.8 cm, at about 0.04 ohms if the electrodes are at a distance of 1.83 m above the furnace floor.

A determined increase in resistance to 0.05 ohms over a relatively short period of time was then used to establish a to indicate upcoming or beginning damage. In order to keep false advertisements small, a working time range is created while which changes in resistance due to normal erosion are not compensated for, is set to about three months. Therefore, if the resistance between electrode pairs is compared with reference to a set value, then this set point can all three itonates compared to a 20% higher value with the then existing current resistance, can be readjusted.

The operation of a display by this system can be used in the manner v / ground that an automatic switch-off of this pair of electrodes, has been sampled at which a rise in the price resistance value causes wild.Bevorzugte practice, the power supplied is, however, to the effect at ¹¹¹ service that a continuous The alarm is issued until the alarm is confirmed and the responsible personnel are instructed accordingly

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has been given to respond to the alarm by inspecting or examining the electrodes, their circuits and the oven, so as to determine the cause of the change and divert the cause by repairing that Turn off the performance of the area in question or make sure there are no difficulties or problems are present.

There are now a number of variables that exist for any given system which, by the above mentioned method is monitored, affect the electrode pair resistance. In the case of glass melting, there is a steep one Temperature coefficient in the range of the temperatures of interest here for the melting, refining and processing of the Glass. The composition of the glass is also important for determining the resistance. In addition, also have how mentioned that the dimensions of the electrodes and their condition have an influence on the resistance. During normal operation there are glass mixes and temperature are stabilized and can therefore be ignored. The initial electrode dimension is given and the gradual change in dimension or size can be adapted as explained above, if there is a change in the electrode pair resistance. Therefore, there can be a relatively abrupt change in the resistance value of a pair of electrodes with abrupt, i.e. short-term changes in the state of the electrodes.

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In practice, the glass is heated due to it Jouie heat with a multitude of pairs of electrodes. The electrodes of these pairs can consist of single or multiple elements. Effective monitoring of this The system includes the selective monitoring of the resistance of each of a plurality of electrode pairs. This is done according to a preferred embodiment in that the electrode pairs are scanned in a cyclical sequence. There, where several elements are used to form an electrode pair, the individual electrode elements can be scanned when pairing with another electrode or electrode element. This element sampling is desirable because the increase in resistance, which is due to a change in the state of one of the elements by the others connected in parallel Element could be masked. Such parallel-connected electrode elements have a tendency to the current, which before has been guided by the associated element to record when that element deteriorates and its own Resistance value increased.

Another factor to consider when monitoring an electrode pair resistance value What needs to be considered is the current flow between the pairs and the complex waveform the input power for the melting furnace, from which the current and voltage values for displaying the resistance are derived are. In a stable system, the inter-pair current flow can be neglected. The waveforms, in particular the waveforms produced by phase or timing control for the supplied power are affected, deviate from that

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pure sinusoidal shape. For an exact determination of the electrode pair resistance value signals representing current and voltage can be processed as true rms values. This is especially true because in the case of heating of the glass by the Jouls fencing effect essentially the entire occurring impedance is ohmic, i.e. purely resistive.

There where a calculation of the resistance value with the help From calculators or computers in question, the true rms values of current and voltage can be made smaller or be dimensioned so that they are adapted to the input requirements of the computer.

The illustration in FIG. 1 shows that the monitoring of an impending electrode break is carried out as a result that a resistance value of a pair of electrodes is included the electrode, is developed and that this resistance value is compared with a set point, wherein then, if there is agreement, a mechanism responsive to a damage report is actuated. The resistance value is developed in that the voltage applied to a pair of electrodes or a dimensioned, approximately reduced Part of this voltage is determined, this voltage " serves to heat the molten material to be processed and that continues to be the current or a measured one, to scale a reduced part of this current flowing through the pair of electrodes is determined. This voltage and current monitoring can be carried out on the cables or lines,

which lead to the electrodes.

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Although the mentioned comparison with a preset point for the automatic operation of a display device, useful for printing out or for influencing and bringing about a change in a process control, but also a direct one Display and reading of a given resistance value can be used as an indication of an incipient failure, The illustration in FIG. 2 shows a device for heating molten glass by supplying Joule heat, wherein a monitoring circuit for a plurality of electrode pairs is provided, which is operated in such a way that automatic sampling, the development of resistance values, the alarm signal when an alarm level is reached and the current and voltage value determination for one by one Code specific electrode pair is made. The illustration in FIG. 2 shows more precisely a glass melting furnace 11, which has five pairs of electrodes 12, 13, 14, 15 and 16, which protrude upward through the bottom wall 17 of the melting furnace and are submerged in the molten glass 18. Every Electrode of the electrode pair 16 has two electrode elements 21, 22 and 23, 24, as can be seen more precisely on the right-hand side of the melting furnace in the plane of the drawing. The resistance monitoring is carried out for the electrode pairs 12 to 15 and for those again arranged in pairs Electrode elements 21, 22 and 23, 24.

Each pair of electrodes 12-16 is provided with a source for supply electrical power impulses of opposite polarity connected, whereby two antiparallel connected, controlled Silicon rectifiers (SCR 26 and 27) are provided, for example, for the pair of electrodes 12, which are controlled by an ignition

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control 28 are triggered; the ignition regulation or control circuit for triggering the rectifier can contain current-limiting circuit arrangements, not shown, to selectively trigger the rectifiers when their over the power transformer 19 is supplied with an alternating current. In the case of the pair of electrodes 12, these will be theirs Required power is supplied via connecting cables 31 and 32. In the case of the electrode pair 16, the electrode elements are connected to an AC power source formed by the secondary winding of a power transformer 33; the flow of current also takes place via two controlled silicon rectifiers 34 and 35, which have an ignition control system 36 is assigned in accordance with the control circuit 28. In this case, parallel connecting lines 37 extend in each case, 38 and 41, 42 to the electrode elements 21, 22 and 23, 24. Also for the electrode pairs 13, 14 and 15 are controlled Sources for supplying power pulses of opposite polarity, but not shown, provided; these Systems correspond to transformer 29, controlled rectifiers 26 and 27, and control circuit 28.

The resistance of the pair of electrodes 12 is determined by that with the help of a transformer 44, the voltage across the electrode leads 31 and 32 is sampled, one of which Connection of the secondary winding of the transformer. 44 to ground and the other side via, a line 4 5 and a contact 46 of a relay R1 is connected to a so-called bus line, that is to say a common line 47. The bus line 47 applies the voltage waveform fed to it to a converter 48 which converts the true RMS value into a DC voltage converts, such a converter can, for example, under

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the designation 4128 from the company Burr Brown. This representing the rms voltage and, if applicable subdivided or measured direct current signal is sent from converter 48 to a computer 51 via lines 52 and 53 fed and processed there by the computer together with a correspondingly sized or scaled-down signal, which the Represents rms current flowing through the pair of electrodes; this calculation is made to develop a resistance value for the pair of electrodes 12. That of the pair of electrodes for heating the molten material 18 by Joule's marriage Heat from a power source supplied current is sensed by a current transformer or converter 54, which is via Has turns wound around the line 32 and supplies a signal to a downstream transformer 55. To reduce the size or measurement of this current signal, a resistor 56 is connected across the secondary winding of transformer 55, wherein the one terminal of the secondary winding is connected to ground and the current signal via a line is fed to a signal contact 58 of the relay R1 and from there to a further bus line 59; this bus line connects then the current signal supplied to it with a further converter 61, which corresponds to the converter or converter 48 and is able to convert the voltage or current rms value supplied to it into a direct voltage. That accordingly The reduced direct current signal representing the rms value of the current then passes via lines 62 and 63 to the computer 51 to be processed there with the corresponding "voltage signal" for the respective resistance value to become. The normal resistance value for a pair of electrodes can be determined by calculation or measurement.

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Once in the melting furnace 11 a balance in terms of the processing conditions has been established, the computer can use the determined effective voltage values and RMS current values a resistance value can be developed. A set point or a set value is then used as a Alarm threshold established and fed as an input value to a comparator provided in the computer. The other entrance of the The resistance value (R = E / I) is then applied to the comparator, which is derived from the effective voltage and current value is.

The functional sequences of the converter or converter and 61 and the processing capability of the computer 41 for a Multiple pairs of electrodes are used if multiple pairs of electrodes need to be monitored. This is done through a Time divider circuit or by means of a time division multiplex method; the time division multiplex basis is stored internally in the computer or programmed so that the computer periodically transmits a coded address to the various circuits, their resistance value must be monitored. In the usual way, an IBM 1800 computer, which is already used for a large number of other process control and monitoring functions is used so that it can be accessed via a multiplexing circuit is connected to the pairs of electrodes in succession. Monitoring takes place during scanning and Calculation of the values for each pair of electrodes usually in a time interval of about 2 seconds. During this For a period of 2 seconds, the voltage and current rms values are scanned and a resistance is calculated carried out. An encoded output signal is then output, whereby the multiplex circuit with the next

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Circuit is connected, the values of which must be determined and compared. The computer can be designed in this way be that the circuits subject to the evaluation are scanned in a continuously cyclical cycle, that complete sampling cycles can be carried out in time periods spaced apart from one another, or that a selective one Detection of given circuits occurs at more frequent intervals compared to other circuits.

The computer 51 gives the coded addresses for the circuit in four binary. Signals transmitted via lines 64, 65, and 67 are supplied to a decoding circuit 68. The decoder circuit 68 generates individual relay actuating signals and feeds them to relays that have normally open contacts in their circuits, i.e. normally open contacts; these Working contacts are between the signal voltage source and the converter 48 for the voltage signals and the signal current source and the converter 61 for the current signals, the corresponding code being assigned to each pair of electrodes. Therefore, when the relay R1 is energized, it closes its contacts 46 and 48 and connects the pair of electrodes 12 for calculation its resistance value. In the same way, by energizing the associated relays in the scan sequence, the other pairs of electrodes are monitored and their resistance value is calculated. The computer 51 which generates the code signal for the electrode pairs can also have a corresponding one Apply pair code to a display device 71, which may be a digital code or a code translated into another code can, for example, also a letter code that is displayed in the display window 72 of the display device 71, select

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The current values I and the voltage values E are then displayed in the display windows 73 and 74. Results in a Resistance value for the monitored at this point in time Area is considered too large or excessive, an alarm indication may appear in window 75 and / or otherwise An alarm can be given, for example a printout using a typewriter or a display on a Cathode ray tube containing the following instructions: Electrode pair X, switch off power and call surveillance personnel.

Since the resistance value can be different between electrode pairs or between electrode element pairs, has each pair has a separate set value or threshold. This setting value is at the point in time at which the pair of electrodes in question is monitored and its resistance value is calculated, retrieved from the memory of the computer 51. The setting value can be shifted in any suitable way (for example, it can be 120% of the normal resistance), so as to form an alarm threshold for indicating a failure of one of the electrodes in the electrode pair.

It should be pointed out that the fifth pair of electrodes or, if one looks from the left in the illustration in FIG counts to the right, fifth heating zone for the material in the melting furnace over two elements in the form of closely spaced arranged in a straight line, round, cylindrical rods, which extend in a vertical direction upwards extend from the furnace bottom, the electrode elements are arranged in pairs, so that a monitoring of the

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individual elements is possible. So there is a common power source for supplying power to the heating area 5 linked in electrical parallel with these individual elements, but it is always just one Element of predetermined polarity monitored in a sampling interval. The elements 21 and 23 are monitored with respect to their voltage values by a transformer 76, which Transformer is connected with its primary winding to the power supply cables 37 and 41; the current monitoring takes place with a winding 77 in the connecting line 37 to a transformer 78. This monitoring is due to the Addressing by the decoding circuit 68 is effective in such a way that the decoding circuit 68 only uses the relay R5 energized and therefore the contact 81 for the determined voltage value to the converter 48 and the contact 82 for the determined Current value to converter 61 closes. At this point in time, the computer calls the threshold resistance entered into it for the elements forming this pair of electrodes and actuates the display device; überhihaus is then a separate sampling interval is also provided for the other two elements 22 and 24 of FIG Zone 5, which occurs when the computer assigns a corresponding address in a coordinated sequence to energize relay R6 issues.

The programming of the computer 51 can also include, as a subroutine, an alarm signal when the electrode is damaged. Such a subroutine then keeps the display indicating an alarm condition as a result of a resistance value that is on has found the alarm threshold. In this way

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the display remains for the code of the electrode pair which caused the alarm condition and the scanned ones Current and voltage values displayed by the display device. Alternatively, the computer can use the address of the alarm condition holding the indicating pair of electrodes, changes in the current and voltage values at 73 and 74 displayed v / earth if they subsequently change at the start of the alarm.

The above discussion related to special conditions in electrode pairs, those with electrical values on the order of magnitude of 3000 amps and 150 volts work to heat glass by Joule heat, which leads to a resistance value came from about 0.05 ohms; it goes without saying, however, that the measures according to the invention also apply to others, in heat emollient materials that have different electrical parameters and are heated by Joule heat is. In addition, it goes without saying that the proposed computer functions can also be changed, in order to be able to carry out other display or control processes, for example a reading of the respectively existing Resistance value of each pair of electrodes can be made. The description given above is corresponding to be understood only as an exemplary embodiment and not as restrictive with regard to the invention.

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Claims (1)

October 9, 1975. ^ Claims 1.] Procedure for monitoring the heating of molten Glass by Joule heat, especially for monitoring electrode damage that occurs, with electrical Electrodes connected to the molten glass are cyclically applied with voltage pulses, characterized in that the effective value of the applied across the electrodes Voltage as well as the effective value of the current flowing through the electrodes are determined and based on the determined RMS values of the underlying electrical Resistance value is determined and a display device responding to a predetermined value of the resistance is actuated will. 2. The method according to claim 1, characterized in that the resistance determined from the current and voltage values available at the electrodes has a predetermined value a resistor is compared and an alarm is issued when the threshold value is exceeded. 3. The method according to claim 1 or 2, characterized in that the determination of the electrical resistance value of a predetermined pair of electrodes carried out at time intervals , with an alarm relating to the beginning of electrode damage being issued when a certain change in resistance takes place from a predetermined value. 309817/0892 A 41 418 m Oct. 9, 1975 - 3 4. The method according to one or more of claims 1 to 3, characterized in that the predetermined resistance value (Threshold comparison resistance) 20% greater than that Normal electrode resistance is. 5. The method according to one or more of claims 1 to 4, characterized in that the effective values of current and Voltage at the electrodes can be scanned cyclically. 6. The method according to one or more of claims 1 to 5, characterized in that a plurality of electrode pairs is cyclically supplied with electrical power pulses and their respective state is monitored, with current and voltage effective values applied over certain electrode pairs scanned in a cyclical predetermined sequence and a display identifying the respective electrode pair is made, for which an incipient electrode damage can be determined. 7. The method according to one or more of claims 1 to 6, characterized in that a preset resistance value is specified and then electrode damage begins is established when the determined resistance value in a predetermined ratio to the preset resistance value. 8. The method according to one or more of claims 1 to 7, characterized in that a predetermined normal resistance value is established and for each individual pair of electrodes is compared with the determined resistance value. 6G9817 / 0S92 A 41 418 m Oct. 9, 1975 - # - 9. The method according to one or more of claims 1 to 8, characterized in that an effective electrode is one The electrode pair is formed from a large number of parallel-connected and simultaneously with cyclic power pulses supplied elements, whereby the resistance value of each individual element is determined and with the threshold resistance value is compared to issue an alarm. 10. Device for monitoring incipient damage to electrodes which can be used when melting a material softening in heat by supplying Joule ¹ shear heat, in particular for monitoring the electrode state in a glass melting furnace, characterized in that at least one pair of electrodes (12, 13, 14, 15, 16) are provided and submerged in the heat-softened material (glass 18) that the at least one pair of electrodes via connecting lines (31, 32, 37, 38, 41, 42) with an electrical power source (26, 27, 28, 29; 34, 35, 36, 33) that monitoring devices (44, 54, 55, 48, 76, 77, 61) are provided that monitor the voltage between the electrode pairs (12, 13, 14, 15, 16) and monitor the current supplied to each pair of electrodes, and that a circuit (51) processing the resistance value based on the voltage and current value is provided, to which a display device (71) is assigned to give an alarm if a On the basis of a given resistance value, the beginning of electrode damage can be determined. 609817/0892 A 41 418 m 11. The device according to claim 10, characterized in that the current monitoring arrangements converter circuits (48,61) which convert the applied rms values of voltage and current of the electrode pairs into direct current signals . 12. Apparatus according to claim 10 or 11, characterized in that that at least two pairs of electrodes (12, 13, 14, 15, 16) are provided, which have separate monitoring arrangements are assigned for the selective determination of the respective resistance values. 13. Apparatus according to claim 10 or 11, characterized in that that in each case one converter (48) converting rms voltages into direct current signals and one rms current signals converter (61) which converts direct current signals is provided that scanning arrangements (68; R1, R5, R6; 46, 58, 81, 82) are provided, which preferably scan the electrode pairs cyclically in the time division multiplex process and for each pair of electrons simultaneously determine the voltage and current values and feed them to a computer circuit (61) Determination of the respective resistance value, the computer circuit (51) being designed in such a way that an alarm is issued takes place when a predetermined resistance threshold is reached. 14. The device according to one or more of claims 10 to 13, characterized in that depending on the cyclical A circuit arrangement is provided which has a predetermined resistance value for each individual electrode pair issues. 609817/0892 Oct. 9, 1975 - & - 15. The device according to one or more of claims 10 to 14, characterized in that a circuit arrangement is provided which, with reference to the scanning arrangements, a signal identifying each individual electrode pair outputs as a function of the predetermined resistance values assigned to each pair of electrodes. 16. The device according to one or more of claims 1 to 15, characterized in that the time division multiplex sampled, respectively associated DC output signals the rms value converter (48, 61) are fed to a computer (51) which is used for cyclical scanning of a downstream Decoding circuit (68) supplies addresses belonging to each pair of electrodes, simultaneously with the determination of the resistance value assigned to a pair of electrodes from a memory, a predetermined threshold resistance value is called up and compared with the calculated resistance value. 17. The device according to claim 16, characterized in that when the threshold resistance value is exceeded, an associated one Display device is caused to give an alarm, at the same time one of this pair of electrodes identifying Coding and the associated current and voltage values are displayed. 609817/0892 L e e f s e ί t e