DE2730049A1 - METHOD OF MONITORING THE CONDITION OF ELECTRODES SUBMERSED IN A BULK OF HEAT SOFTENING MATERIAL - Google Patents

Description

OR —ING. DIPI ING. M. SC. DII-L-PHVS. DR. DIPL.-PHYS.

HÖGER - LEGAL RIGHTS - GRIESS3ACH - HAECKER

PATENT LAWYERS IN STUTTGART

-S-

A 42 397 m

a - 168

June 28, 1977

Owens Corning Fiberglas Corporation

Fiberglass tower

Toledo, Ohio 43 659 / USA

Method for monitoring the condition of heat-softening substances in a mass Material submerged electrodes

The invention relates to a method for monitoring the condition of in a mass of heat-softening material, preferably glass, for heating it by adding Joule heat submerged electrodes.

In general, the present invention is concerned with a monitoring method and monitoring devices that monitor changes in state determine, in the most general case, a change in position of a submerged in the molten mass Determine the electrode, but in particular are able to

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also determine the special type of change in position, for example sagging or tilting of the upper part can. The material that softens when heated is preferably glass. The electrodes in which are inside A material located in a melting tank is used to heat this material by supplying Joule heat. By the invention addresses both initial electrode failure and possible damage to the furnace determine yourself early on and avert it as far as possible.

The electrical heating of heat-softening material by the application of Joule heat involves the establishment of a electrical current-carrying connection to the one to be melted Material with the help of electrodes. A typical heat softening material, namely glass, must be at or above the usual working temperatures, i.e. kept at around 1427 ° C by dipping one or more pairs of electrodes into the molten glass and controlling the electrodes Supplies pulses of electrical power that flow through the glass. Very often such electrodes are designed so that essential Parts of their surfaces in contact with the glass to the walls of the container or of the melting furnace for the glass are kept at a distance so that the amount of heat transferred to the walls can be reduced and the service life 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 protect the electrode and the refractory floor, it has been found that there is a tendency of the electrodes to continuously corrode in the area where they pass through to the wall and to cause erosion phenomena to show.

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In the case of cylindrical electrodes, around the electrodes are below of the furnace bottom cooling jacket has been placed so that the electrode temperature outside of the furnace on a Maintain a level which is so low that it can be influenced by components of the free atmosphere and the resultant 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 construction / glass melt boundary layer and slightly below. Such erosion can lead to the electrode breaking off in the melt. With such a cancellation of the Electrode, the bottom wall in the adjacent area of the remaining electrode stub is attacked and developed Leaks very quickly if it is not possible to take corrective action immediately.

The present invention represents a further development of a method for monitoring the heating of molten glass by supplying Joule heat and a device for Implementation of this method, both of which are described in German patent application P 25 45 532.7, and is therefore also an addition to the subject matter of this patent application.

In this patent application mentioned, it is pointed out that changes in the cross-sectional area of an electrode, for example by constriction of the electrode by erosive influences and the formation of breaks in the constricted area to characteristic changes in the electrical parameters

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lead this electrode, which takes into account threshold value systems can be monitored, with an alarm being issued if the predefined set values are exceeded or Display means are operated.

In this connection it has recently been found that melting tanks heated by the application of Joule heat and contain molten glass, broken or perforated by sagging or overturning electrodes can be, namely of electrodes that extend vertically through the bottom of the melting tank in the normal state. These breakthroughs and damage to the melting tank are due to electrical, physical and Thermal erosion of the bottom wall of the melting tank due to the tipped or sagged electrodes. The type of sagging the electrode affects the detrimental effects on the furnace and its operation, as in some cases adjacent ones Electrodes can sag or tilt away in such a way that a short circuit is effectively formed between them. It is It has also been observed that electrodes which have continued to operate even after they have sagged develop the tendency to in the vicinity of the turn from the desired normal vertical orientation to be eroded to such an extent that the Completely break off electrodes. It is therefore extremely desirable to prevent electrodes from tipping or sagging in the opaque To be able to determine the mass of the thermally softened material in order to take appropriate corrective measures are suitable for avoiding the undesirable consequences of such an electrode sagging during continuous operation.

The present invention is therefore based on the object of providing a method which can be used not only in the

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Can detect short-term damage to the electrodes, as described in German patent application P 25 45 532 is described, but with which also in long-term operation, i.e. with monitoring processes that take place over weeks, months and years, a gradual change in the orientation of the electrodes, i.e., in short, their sagging in the heated glass mass.

To solve this problem, the invention is based on the method mentioned at the beginning and, according to the invention, consists in that with initial use of the electrode in the material electrical parameters of the electrode and the one in the vicinity The material located on the electrode is detected and these electrical parameters are monitored during the life of the electrode and a shift as a function of the rate and magnitude of change in the electrical parameters being monitored of the electrode is determined from its original orientation in the mass heated by it.

In general, the present invention encompasses a system with which an incipient electrode damage with electrodes that are are in a molten mass heated to a considerable temperature, can be detected, as well as a displacement of the electrode (s) from their preferred vertical upright position. Have such electrode changes been detected? then countermeasures can be taken in good time without interrupting the melting process.

It has been found that an incipient electrode damage or an incipient displacement of the electrode from her preferred orientation is reflected in a change, usually an increase in resistance between

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a pair of electrodes, from a suitable supply source the required power for a heat emission is supplied by Joule's heat generation. Relocation an electrode, that is, its tilting, sagging, tilting away or the like, differs from erosion or a fraction by the rate, i.e. by the speed and size of the increase or change of initial values starting from that have been determined while the electrode was still in its correct orientation Has. Such a change in resistance, which is related to an electrode displacement, can last for weeks, months and even Years of use of the electrode.

A feature of the present invention is that current and voltage in the electrode pair comprising electrical Circuit scans or measures, thus determining resistance and as a result of reaching a predetermined resistance actuates a display device.

Another feature is that the accuracy of the resistance determination is increased by sampling the rms values of current and voltage and using these values, to determine the associated resistance.

A third feature of the present invention is that it uses circuitry associated with a comparator and which generates signals that represent relatively very precisely the true rms values of current and voltage, thus the beginning of a critical current / voltage ratio or critical resistance levels (critical with reference on an electrode displacement) can be determined.

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In the present invention, a shift or change in the orientation of an electrode in a mass is arranged from heat-softening material, determined from their preferred orientation out by that one samples and detects the change in the current-voltage ratio of a pair of electrodes. This pair of electrodes also has the Electrode, which is to be monitored for its displacement. The change in the current-voltage ratio of the observed Pairs is related to the current-voltage ratio which this pair of electrodes has delivered at a point in time at which At the beginning of their use, the two electrodes will be in their preferred orientation, i.e. usually perpendicular up, have found.

Another inventive feature is finally that one pair of electrodes from a plurality of Electrode pairs a resistance measuring device selectively assigned, likewise a display device, the one beginning Indicates damage or sagging of the electrode. The measuring system is also designed so that the pair of electrodes, which has undergone such a change that the display device has been actuated, at the position of the overall system can be determined and identified.

In summary, the invention is that a method to determine an electrode displacement in an opaque melt of a heated by supplying Joule heat Material is created, the heating of the material takes place through the electrode. Man monitors the electricity that Voltage and other electrical properties of the assembly of electrodes and of the heat-softened material, relating to an electrode displacement can be significant.

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A relatively rapid change in the monitored resistance is often an indication of resulting changes in the geometric relationships between an electrode and the heat-softening material and other electrodes, where such changes can accelerate system failure if corrective action is not taken. Alarm devices, printed instructions for carrying out repairs and / or process control arrangements can be activated are as a result of a given change in current / voltage or a change in resistance.

The sagging or overturning of electrodes and the direction of this overturning movement can be determined by the type and the size of changes that are determined on a long-term basis, with at least time intervals in on the order of days. Several electrodes and pairs of electrodes are monitored by following Art a multiplex process the parameters between each to monitoring electrode pairs cyclically and repeatedly scanned. Since the current and voltage supply to the electrodes is very is often done by controlled silicon rectifiers so that the heating runs in the desired paths, with the Electrodes are supplied with selective subranges of power pulses, resulting in complex waveforms. In this way Any resulting distortions in the current and voltage values can, however, be kept small and their influence eliminated be that one for the present inventive measurements the true rms values of current and voltage are used based on the values determined with the help of converters or converters can be generated that convert the rms values into direct current values. In this Connection one also uses circuits that output

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deliver DC voltage signals that closely approximate the measured current and voltage values in their effective relationships correspond.

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 greater detail below. Included demonstrate:

Fig. 1 is a flow chart showing the monitoring process on represents an incipient electrode damage,

Fig. 2 is a schematic representation of a plan view of a glass melting furnace and associated electrical circuit elements to monitor the electrodes arranged in the glass melting furnace for possible damage, the electrodes are arranged in the form of electrode pairs and connected to associated supply sources,

3 shows a further one in a schematic block diagram Embodiment of a monitoring circuit for at least a typical pair of electrodes, monitoring voltages that approximate the rms values of current and voltage corresponding to the Pair of electrodes are supplied; these proportional voltages are compared with set values, thus either short-term deviations in the current-voltage ratio of electrodes or discrepancies can be detected from actual or extrapolated initial values show a long-term deviation represent.

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Figures 4, 5, 6 and 8 represent alternative exemplary embodiments regarding the connection of electrodes and at the same time give possible embodiments regarding sinking and tipping of electrodes. For the electrode patterns shown in these figures Resistance models have been developed that are used in the evaluation of observed changes in resistance and which then provide information on which electrode changes will occur on a long-term basis. Figures 4,5, 6 and 8 correspond to a section along the line 4-4 of FIG FIG. 7, which shows another paired electrode pattern, corresponds to a section taken along line 7-7 of FIG.

Finally, FIG. 9 shows a schematic representation of a Top view of a glass melting tank as well as a typical one Driving pattern for electrodes arranged in this, which leads to, notwithstanding a tilting of individual electrodes in any direction, a relatively uniform change in resistance, namely an increase in resistance results.

Based on measures according to the invention, it has been determined that an imminent or incipient failure and damage to an electrode, which in a fluid mass of heat-softening Material is submerged, to which the electrode conveys an electrical current flow to achieve Joule heat, is indicated by an increase in resistance between corresponding pairs of electrodes carrying that current. It is believed that this phenomenon is due to erosion of the electrode, which reduces its cross-section, and to development due to fractures in the constricted erosion area.

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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 concluded from this circumstance that the beginning of the finally to a 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 with electrodes in the area which is contiguous or contiguous to the exit area of the electrode from the refractory wall of the container containing the molten material. Characteristically, the rate of increase in resistance increases over time. It turned out that a 20% increase is a reliable indicator of trouble ahead, so a feature according to the invention, such a rise as a criterion for actuating a device indicating these difficulties used.

It should be noted here that during long-term operation of containers heated by means of Joule heat, a certain erosion of the Electrodes occurs over relatively long periods of time. This long-term erosion and the resulting long-term increase in the resistance value between electrode pairs there is no indication of an incipient electrode breakage or damage the electrodes. For example, in the case of a glass melting device, there is one used for the manufacture of glass wool Sodium borosilicate type glass, the glass being heated to a melting and refining temperature of around 1427 ° C, the resistance between vertical, round, cylindrical molybdenum electrodes with a diameter of 7.62 cm, which are extend through the furnace floor and contact the glass for a length of about 102 cm, at about 0.04 ohms if

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the electrodes are a distance across the furnace floor 1.83 m.

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 every three months to a 20% higher value compared to the current resistance then existing.

The operation of a display according to this system can be used in such a way that an automatic switch-off of this Electrode pair, at which an increased resistance value has been scanned, supplied power is effected. Preferred In practice, however, the operation is such that an alarm is issued continuously until the alarm is confirmed and the responsible personnel have been instructed to respond to the alarm with an inspection or investigation of the electrodes, their circuits and the oven to react in order to determine the cause of the change and either to eliminate the cause by repairing it, to switch off the power of the area in question, or to make sure there are no difficulties or problems.

There are now a number of variables that exist for any given System, which by means of the above-mentioned procedure

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wakes, affect the electrode pair resistance. in the In the case of glass melting, there is a steep temperature coefficient in the range of the temperatures of interest here for melting, refining and processing the glass. The composition of the glass is also used to determine the resistance significant. In addition, as mentioned, 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 remain without further consideration. The initial electrode drain is predetermined, and the gradual change in dimension or size can be adjusted as explained above if there is 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.

In practice, the glass is heated on the basis of Joule shear Heat with a multitude of pairs of electrodes. The electrodes of these pairs can consist of single or multiple elements exist. Effective monitoring of this system includes selective monitoring of the resistance of each a variety of electrode pairs. According to a preferred embodiment, this takes place in that in cyclical Follow the electrode pairs to be scanned. Where several elements are used to form a pair of electrodes, the individual electrode elements can be scanned when pairing with another electrode or a other electrode element is made. This element scan is desirable because the increase in resistance that occurs on a Change in the state of one of the elements is due, masked by the other elements connected in parallel

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could be. Such parallel-connected electrode elements have a tendency to the current that was previously assigned by the associated Element has been led to pick up when that element degrades and increases its own resistance value.

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 of 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 flow of current between the pairs can be neglected. The waveforms, especially the Waveforms that are influenced by a phase or time control for the supplied power deviate from the pure Sinusoidal. For a precise determination of the electrode pair resistance value, signals representing current and voltage can be used processed as true rms values. This is particularly true because if the glass is heated by the Joule effect, essentially all of it occurs Impedance is ohmic, i.e. purely resistive.

Wherever it is possible to calculate the resistance value with the help of calculators or computers, the true rms values of current and voltage are designed, reduced or dimensioned in such a way that they meet the requirements of the input of the computer are adapted.

The illustration in FIG. 1 shows that the monitoring an impending electrode breakage is carried out by including a resistance value of an electrode pair the electrode, is developed and that this resistance

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value is compared with a set point, and if there is a match, an on a damage report responsive mechanism is operated. The resistance value is developed by connecting a pair of electrodes applied voltage or a measured, 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 that lead to the electrodes.

Although the mentioned comparison with a preset point is useful for the automatic operation of a display device, for printing or for influencing and bringing about a change in a process control, a direct display and reading of a given resistance value can also be used as an indication of an incipient failure. The illustration of Fig. 2 shows a device for heating molten glass by supplying Joul ¹ shear heat, wherein a monitoring circuit is provided for a plurality of electrode pairs, which is operated so that an automatic scanning, the development of resistance values, the alarm when reached of alarm levels and the determination of the current and voltage value is carried out for a pair of electrodes determined by a code. The illustration in FIG. 2 shows in more detail 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 13. Each electrode of the electrode pair 16 has two electrode elements 21, 22 and 23,

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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 the electrode elements which are in turn arranged in pairs 21, 22 and 23, 24.

Each pair of electrodes 12 to 16 is provided with a source for supplying electrical power pulses of opposite polarity connected, two anti-parallel, controlled silicon rectifiers (SCR 26 and 27) for example the pair of electrodes 12 are provided, which are triggered by an ignition controller 28; the ignition regulation or control circuit to trigger the rectifier can contain current-limiting circuit arrangements, not shown, to the Selectively trigger rectifier when an alternating current is supplied to them via the power transformer 19. in the In the case of the pair of electrodes 12, the power they require is supplied to them via connecting cables 31 and 32. in the In the case of the pair of electrodes 16, the electrode elements are connected to an AC power source that is formed from the secondary winding of a power transformer 33; the current flow also takes place via two controlled silicon rectifiers 34 and 35, to which an ignition control system 36 corresponding to the control circuit 28 is assigned. Here extend there are respectively parallel connecting lines 37, 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 the supply of power pulses of opposite polarity, which are not shown, however, provided; these systems correspond to the transformer 29, the controlled rectifiers 26 and 27 and the control circuit 28.

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The resistance of the pair of electrodes 12 is determined by using a transformer 44, the voltage across the electrode leads 31 and 32 scanned, one connection of the secondary winding of the transformer 44 to ground and the other side via a line 45 and a contact of a relay R1 with a so-called bus line, that is to say one common line 47 is connected. The bus line 47 applies the voltage waveform fed to it to a converter 48, which converts the true rms value into a direct voltage, such a converter can be called, for example 4128 purchased from Burr Brown. This represents the rms voltage and, if necessary, subdivided it or measured direct current signal, is fed via lines 51 and 53 from converter 48 to a computer 51 and there processed by the computer together with a correspondingly dimensioned or reduced signal, which represents the effective current represents flowing through the pair of electrodes; this calculation is done to develop a resistance value for the Pair of electrodes 12. The pair of electrodes 12 for heating the molten material 18 by Joule's heat from a Current supplied to the power source is from a stroke transformer or transducer 54, which has turns wound around line 32 and a downstream transformer 55 supplies a signal. To reduce or dimension this current signal, use the secondary winding of the Transformer 55 connected a resistor 5G, the one Connection of the secondary winding is connected to ground and the current signal via a line 57 to a signal contact 5 8 of the Relay R1 and from there to a further bus line 59 is fed; this bus line then connects the current signal supplied to it with a further converter 61, which corresponds to the converter or converter 48 and is able to supply the one supplied to it

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Convert voltage or current rms value into a direct voltage. The correspondingly reduced direct current signal representing the rms value of the current then passes over Lines 62 and 63 to the computer 51 to be there with the corresponding "Voltage signal" to be processed for the respective resistance value. The normal resistance value for a The electrode pair can be determined by calculation or measurement.

Once an equilibrium has been established in the processing conditions in the melting furnace 11, of the Calculator from the determined voltage rms values and current rms values a resistance value can be developed. A set point or a set value is then established as an alarm threshold and an input value provided in the computer Comparator supplied. The other input of the comparator is then subjected to the resistance value (R = E / I), which is derived from the voltage and current rms value is.

The functional processes of the converter or converter are thereby used 48 and 61 and the processing ability of the calculator 41 used for a plurality of electrode pairs, if a plurality such couples need to be monitored. This is done by a time divider circuit or by means of a time division multiplex method; the time division multiplex basis is stored or programmed internally in the computer so that the computer periodically a coded address is sent to the various circuits whose resistance value must be monitored. In usual For example, an IBM 1800 computer can be used here, which is anyway for a variety of other process control and monitoring functions used in such a way that it has a multi-channel

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plex circuit connected to the electrode pairs in succession will. During the scanning, the fourth is usually monitored and calculated for each pair of electrodes in a time interval of about 2 seconds. During this 2 second period, the voltage and Current rms values are sampled and a resistance calculation is carried out. A coded output signal is then output, whereby the multiplex circuit is connected to the next circuit, whose values are determined and compared Need to become. The computer can be designed in such a way that the evaluation takes place in a continuously cyclical cycle subordinate circuits are scanned that in mutually spaced periods of time complete scanning cycles be performed, or that a selective detection of predetermined circuits at more frequent intervals, compared with other circuits.

The computer 51 outputs the coded addresses for the circuit in four binary signals which are transmitted via lines 64, 65, 66 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 4 8 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. Will therefore the relay R1 energizes, it then closes its contacts 46 and 48 and connects the pair of electrodes 12 to calculate its Resistance value. In the same way, energizing the associated relays in the scan sequence will energize the others Electrode pairs are monitored and their resistance values are calculated.

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The computer 51 which generates the code signal for the electrode pairs can also use a corresponding pair code Feed display device 71, which is a digital or an in may be another code translated code, for example also a letter code, which is displayed in the display window 72 of the display device 71 is displayed while the current values I and the voltage values E are then displayed in the display windows 73 and 74 will. The result is a resistance value that is too large or excessive for the area being monitored at this point in time is viewed, an alarm display can appear in window 75 and / or another alarm can be given, for example, a printout can be made using a typewriter or a display on a cathode ray tube containing the following instructions: Electrode pair X, switch off power and call monitoring 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 16 or, if one looks in the illustration of FIG. 2 from left to on the right counts, fifth heating zone for the material in the melting furnace over two elements in the form of closely spaced one from the other arranged, straight, round, cylindrical rods,

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which extends vertically upwards from the bottom of the furnace extend, wherein the electrode elements are arranged in pairs, so that a monitoring of the individual elements is possible. It is true that a common power source for supplying power to the heating area 5 is electrically connected in parallel linked to these individual elements, but only one such element is always given Polarity monitored in a sampling interval. The elements 21 and 23 are with respect to their voltage values of one Transformer 76 monitors, v / obei this transformer with his Primary winding is connected to the power supply cables 37 and 41; the current monitoring is carried out with a Winding 77 in the connecting line 37 to a transformer 78. This monitoring is due to the addressing the decoding circuit 68 operates in such a way that the decoding circuit 68 only energizes the relay R5 and therefore the contact 81 for the determined voltage value to the converter 43 and the contact 82 for the determined current value to the converter 61 closes. At this point in time, the computer calls up the entered threshold value resistance for this pair of electrodes forming elements and actuates the display device; there is also a separate sampling interval provided for the other two elements 22 and 2 4 forming the pair of electrodes of zone 5, which then takes place when the computer issues a corresponding address for energizing relay R6 in a coordinated sequence.

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 electrode pair indicating changes in the current and voltage values at 73 and 7 4 indicated if they subsequently change at the start of the alarm.

In addition to the relatively short-term changes in resistance, which have just been discussed above, has been found to extend over long periods of time Changes in resistance (long-term effects) between electrodes that utilize Joule's heat generation used for heating of heat-softening materials, of considerable importance in the display of the State of the melting and refining device as well as its individual components are, therefore, also with appropriate Monitoring can increase the service life of the facility. In particular, it has been found that changes in resistance or changes in the current-voltage ratio between electrodes, which, as electrode pairs, are the main supply current source to heat a material area located between them, in which they are immersed, serve, a Show electrode displacement if such changes are seen as long-term effects, i.e. over periods of at least a few weeks and occur more frequently over months and even years. Deviations from the initial values are defined as changes, which result and can be observed when the electrodes are put into operation, in the direction of values, the at least 15 and up to 50% of these initial values differ.

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For example, electrodes mounted upright in a body of molten glass change their position in the vertical direction (paired) electrode resistance related to the electrode pair when they gradually move out of their vertical orientation experience a decrease or a sag, from the initial value in a gradual change over a long period of time, where deviations, namely increases in resistance and / or decreases between 15 and 50% occur; this behavior stands in contrast to the relatively abrupt change behavior described above. These long-term changes will and must can therefore be measured and determined against their initial values, in contrast to the comparative or set points that are used when an incipient electrode failure is detected.

In the system shown in Fig. 2, sagging, e.g. a bending or falling over of the electrodes can be monitored by looking at the current, current one Resistance values or current voltage ratios with the original value compares the zone resistance between paired electrodes. If one observes that over a period of at least several weeks if the change is noticed gradually and exceeds 15% of the original value, then a Display means are operated. One can therefore use a subroutine or a subroutine to get current resistance values to sample and process between paired electrodes with initial values between the same electrodes, where then the computer 51 and its associated alarm-generating arrangement 75 as well as a current value display device 74, a voltage value display device 73 and a display device 72 for the pair behavior can be operated.

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The display of an electrode slump has proven to be meaningful there with regard to the direction of the Drawdown highlighted where changes related to inter-pair electrical parameters for more than one electrode are available in the area in which a lowered electrode is indicated. It has been found that the lowering of an electrode, in particular there, the current-voltage ratios adjacent pairs of electrodes, where there is a certain phase relationship between the different There is power supplied to electrode pairs.

The illustration of FIG. 3 shows the plan pattern of an electrode arrangement in a typical tank or container 101 which looks like that there are six rows of four electrodes each, which are uniform to one another are spaced along the longitudinal axis of the rectangular tank. In particular, the electrodes can be used to supply energy be arranged in the form of working pairs so that there are either adjacent electrodes 116 and 117 in one Tank, or alternating or respectively one electrode skipping pairs of electrodes 102 and 104 as well as 103 and 105 in a row; it is also possible to have pairs of electrodes in different rows either parallel to the longitudinal axis of the tank, in this case, for example, to arrange electrodes 102 and 106 or to run obliquely to the longitudinal axis of the tank, for example the electrodes 102 and 107, which then form a common working pair. A commonly used arrangement is in Fig. 3 shown; in this case the main currents run between alternating electrodes or each skipping one electrode in a row Electrodes, as can be taken from the power supply from the secondary winding 108 of the transformer 109, the controlled rectifier 111 connected in anti-parallel

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and 112 returns to the secondary winding. Here are the Controlled rectifiers 111 and 112 under the control of an ignition controller 113, the corresponding drive signals to their gate electrodes feeds. With a typical alternating trigger control or ignition control for a melting container or Tank to which a multiphase power is supplied, the electrodes of a row are connected to a common phase, then successive rows of electrodes with different Phases are switched. However, this common phase per row does not exist when referring to the transformers providing the power supply and controlled rectifiers made inter-row connections are, as is the case, for example, between the electrode pairs 102 and 106 in the aforementioned alternating relationship is. In addition, it is possible to have adjacent electrodes from a common phase via their main supply arrangements to couple, as is the case with the electrode pairs 116 and 117 as well 118 and 119 adjacent to the floor channel 115 in the area of opening 114 lying under glass is the case.

Adjacent, i.e. adjacent, electrode pairs 116 and 117 and 118 and 119 are controlled in the same way and supplied with power like a typical pair of electrodes 103, 105, namely with the aid of a phase adjustment control principle based trigger circuit 121 for the anti-parallel connected controlled rectifier 122 and 123, which with the secondary winding 124 of a transformer connected in series are.

The change in resistance, which manifests itself as a change in ratio from current to voltage in the heat-softening material results, which with the help of the electrodes using the

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developed Joule heat is heated through determine a variety of metrological measures. As already with reference to Figures 1 and 2 and from the through phase lock / triggered, controlled rectifier The resulting waveform has been explained, the resistance can be determined and specified as precisely as that Current-to-voltage ratio of the rms values of these two Sizes. The ignition control causes distortion in the waveforms used in the power circuitry for the the Joule effect using external electrodes predominate as well as in the interphase currents within the bulk of the heat softening material. However, the impedance is the Joule's thermal effect developing circuits in the essentially ohmic, and therefore other current and voltage values can also be used, especially where the change their relationship is important. The instantaneous values can therefore also be used after the controlled rectifier has been ignited or the maximum values or the mean values can be used. So are the current and voltage values determined with the aid of effective value converters or converters (cf. converters 48 and 61 of FIG. 2) for purposes of determination of changes in resistance in the sense of changes in the current-to-voltage ratio, however, other circuit means can also be used be used.

Advantageously, however, these other, electricity and Circuits and switching means that detect voltage values that are approximately the same as the r.m.s. values, since these r.m.s. values are then also used in other measurements that differ from the ratio measurements required to practice the present invention. One Circuit that is able to produce a very close proportional

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Relation to rms values is the one in Fig. 3 shown circuit, which is used to detect current and voltage. This circuit includes a voltage divider, which generates a voltage via a resistor-capacitor combination that is closely proportional to the true rms values. A similar circuit is made for each of the current and the Voltage sensing circuitry such as decoding circuit 6 8 of FIG. 2, which, like the Specify relays R1 ... R6 that shifts voltage and current sensing circuits between different electrode pairs.

FIG. 3 shows as an exemplary embodiment that a sampling or detection of the voltage applied to lines 125 and 126 to the electrodes 103 and 105 is carried out by means of a transformer 127, the secondary winding 128 of which is grounded once and on the other hand is connected to an effective value measuring circuit; this circuit is designed so that from him at least one signal proportional to the rms value is created. This circuit "simulates" an effective value formation comprises a charging circuit with two time constants, which provides an output signal on its output line 129, which is a sum of signals representing different time constants. It is about the resistance 131 with the Capacitor 132 in conjunction with a diode 133 formed time constant as well as a time constant that is based on the resistor 134, the same capacitor 132 and diode 135 are based. The circuit is designed so that there is a current division corresponding to the values of the resistors 131, 136, 134 and 137. In one embodiment, for the resistors have the following resistance values: resistor 131 390 ohms, resistor 136 1000 ohms, resistor 131 560 ohms and

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Resistor 137 300 ohms; the capacitor 132 has a capacitance of 20 uV. In this way, an output signal is produced on the output line 129 which, in the closest approximation, corresponds to voltage values which have a constant proportionality to the actual rms value voltage values applied to the lines 125 and 126, respectively. By suitably adjusting the voltmeter 138, it is therefore possible to read the effective voltage across the electrodes directly.

By means of a further circuit 139, it is possible to acquire current signals which are proportional to the effective current. For this purpose, a current coil 141 is provided, which is connected to a line leading to the electrodes or assigned to it in such a way that, for example, a signal can be obtained from line 126 and via a transformer or current converter 142, which signal can be obtained at the secondary winding 143 of the transformer is present. The secondary winding is grounded on one side and has a resistor 144 connected in parallel. The corresponding connection of the secondary winding operates on a circuit 139 which is similar to the circuit used for determining the effective value of the voltage. An ammeter 145 is connected to this circuit, which. ¹ ; is adjusted so that the effective current carried by the output line 146 is indicated in a proportional proportion.

The two lines 146 and 129 are connected to an analog divider circuit 147 connected, which on their output line 14Ü a resistance value from the supplied current and voltage signals or derives the current-to-voltage ratio. The output line 140 is connected to a comparator 149,

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which has an adjustable potentiometer 1j1 with which standard values can be set, which then serve as comparison points with which the analog divider circuit calculated ratio signal (with respect to the resistance) is compared. If the set comparison standard is reached by the output signal on line 148, an alarm is then issued via an alarm-generating circuit 150.

The overall system can be designed so that a large number of electrode pairs by means of a relay, for example based selection system, such as the type shown in Figure 2, scanned v / ground; it is also possible to use a (not shown) Provide optical display to identify the pair of electrodes, which from its predetermined area falls out. The optical display can be designed in the form of a row of lamps, each of which has an associated locking system to the effect that the display of the electrode pair exceeding the permissible limit values also then still takes place and is recorded if the multiplexed working scanning device scans the next and the following pairs of electrodes.

Finally, the system also has a manual control, which is not shown and which is designed so that the automatic continuous scanning can be switched off and the system can be set to the selection of the electrode pair, which caused the alarm.

It has been found to be beneficial for each pair of electrodes to use the same proportional circuits (i.e. the circuits that in close proportionality to the Ef-

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supply corresponding output signals) so that changes can be made and deviations in the fourth displayed, which can be attributed to differences in the individual circuits, be avoided. Wherever different standard resistance values have to be monitored, for example on electrodes, that are located in tank areas that have different temperature properties are the set points different for the comparator 149 for the different base resistance values from which the given deviation then takes effect. One way to adjust the individual setting points by scanning the electrode pairs accordingly carry along, results from the switching (not shown) to different handle positions on the potentiometer 151. This can be done by switching to different taps, each with the appropriate setting. made v / ground, with switching means not shown provided are; but it is also possible to set the individual setting points for the respective electrode pairs at different To feed tank areas to the comparator by switching to separate potentiometers, each in corresponding Way are adjusted.

The explained, simplified, securing a proportional relationship Circuits are beyond the phase angle adjustment range not quite as accurate as the real rms value conversion, which in 2, although they are able to provide a more precise indication of the current-voltage ratio or the resistance for the range of values for different phase settings in phase-controlled triggering is derived compared to averaging circuits. However, these circuits are accurate enough to avoid deviations within a few percent of the true rms

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determine and thus the monitoring options available Invention ensure that for short-term / changes are feasible to prevent an incipient failure due to an internal crack in the electrode or a constriction of a Display electrode before breaking the electrode tip. Long-term changes in resistance, indicating a sagging or sagging of the electrode, are scanned and detected, and then not in these spouts there is a need to set the set points or comparison value again after the one representing a limit Signal deviations with respect to the comparator 149 have been fixed. With these long-term resistance changes one obtains the reference value of the ratio of current and Voltage or resistance originally at the start of work or initial setting in the tank or due to the Assembly of the pair of electrodes in question.

A connection between long-term resistance losses and the shift or /. Dislocation of electrodes within the heat softening mass has also been observed. In certain tanks or melting tanks intended for melting glass, in which heat is supplied by Joule 'see Effect-creating electrodes were installed that extended vertically up through the Tnnkbodeii, such electrodes have tilted downwards, they are sacked and in this way have the working parameters of the system changes.

In general, molten glass, which ^{is subjected to a melting process based on Joule L'} s heat input, has a thermal gradient starting from a colder surface, which is caused by the depth of the batch coverage,

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extends through the boundary layer molten glass and through the depth of the molten glass. Glass is on Transition area or in the intermediate layer between glass and tank bottom, hundreds of temperature degrees (F) cooler than glass at and near the top or head of the electrodes. Due to the steep negative temperature coefficient of resistance of molten Glass, when an electrode sags or falls over, it now has an orientation in one adopts a higher resistance material. If one takes this effect into consideration, then the result is by the presence of the electrode there is a tendency for the glass to be heated by Joule's heat which surrounds the electrode concentrated, so that there is a heating of the glass adjacent to the tank bottom, to the extent to which the higher resistivity of the cooler molten glass does not prevent this.

In this context, volumetric effects must also be taken into account because where one or both of two electrodes arranged in pairs have sagged and bent, there is a change in resistance in the circuit between this pair of electrodes and the associated molten glass area includes, because when the electrode is approaches the bottom of the tank, at the same time they tend to have their radial current flow patterns in those surrounding the electrode melted glass cylinder loses and only the volume of melted glass remains above the electrode remains, into which the current can be directed. In effect, this results in a volume reduction in relation to that of a power line available mass, since the sagged electrode is now near the bottom of the melting tank.

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It is desirable to prevent the electrodes from dislocating or sagging from their preferred orientation when heated of glass by Joule's heat to be determined, for sagging interrupts the desired thermal pattern in the molten glass and therefore also changes the melting and refining parameters. In addition, the refractory linings of the furnace walls erode at a relatively high rate when they are exposed to undesired electrical potentials which cause a current to flow in them. It therefore increases in size then, as an electrode sags towards the bottom of the furnace, the rate of both thermal and electrical erosion is significant, to such an extent that rupture and damage to the Melting tank wall gives rise to the operation of this melting tank must be set prematurely. An early detection of a sagging electrode therefore enables the maintenance personnel of this melting tank to take corrective measures. that maintain the processing parameters and ensure the useful life of the entire system. That's the way it is then possible in the usual way to remove the bagged electrode from its area of activity within the melting tank, for example by disconnecting them from their electrical supply line or by replacing them with them, that they can be passed through the furnace in front of a replacement electrode pushes inwards without interrupting the operation of the melting tank. In certain cases you can do the Also take account of sagging of the electrode by rearranging the electrodes and their power supplies. It is therefore extremely desirable to determine the sagging per se and the type of sagging.

Figures 4 to 8 show different patterns of an electrical

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denbeeinleßigung, which so far and in the following also as Sagging is called. For these samples, the resistance change characteristics are measured and various Connections to the supply source are made, such as the dashed lines between the electrode pairs demonstrate. FIGS. 4, 5, 6 and 8 show, viewed over the cross section 4-4 of FIG. 3, an electrode that skips over one electrode in each case or alternating control, in such a way that the dashed lines 152 and 153 connect the Specify controlled power sources that feed their power to the electrode pairs 105-103 and 104-102. The boundary layer between the molten glass and the furnace bottom is indicated by line 154 which are cross-sections sized so that the molten glass has a greater depth than the height of the upright electrodes 104 and 102 of the Fig. 4, based on the transition layer 154, has.

If a working pair of electrodes in an alternating row of electrodes supplied with current sag towards one another as in FIG. 4, the pair of electrodes 105-103 sag, i.e. the upper electrode area tilts downwards, then the resistance of the area between these electrodes increases. If the electrodes tilt towards one another relatively quickly, ie in a period of hours compared to the more usual period of weeks or months, this resistance increases by about 30%. This is due to the thermal inertia of the molten glass mass. The greatest current density and the greatest Joule's heating result in a thin glass envelope area around the electrodes. In the case of a group consisting of molybdenum, a diameter of about 7.62 cm having electrode ^e ^ ⁿ is obtained predominant energy consumption within a sheath portion with a wall

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thickness of about three electrode diameters, the largest being Energy consumption in the warmer material above the bottom of the melting tank occurs. It is theoretically assumed that if an electrode sags and bends very quickly, this causes the electrode to fall out of its high temperature surrounding envelope and then completely or is partially surrounded by cooler glass with a higher specific resistance value, which also increases the resistance of the glass between the electrodes is enlarged.

In those cases where the electrodes of FIG. 4 are slow collapse towards each other, an increase in resistance between the collapsed electrodes of about 20% is observed. Remains however, the other pair of electrodes 104, 102 in its preferred vertical orientation, then the decrease Resistance between them around 25%. This drag reduction is due to the reduction in the effective length-to-space area of the current flow lines between the Electrodes, as the opposing electrical poles of the bagged electrode pair are removed from the main line area are.

Another change or sagging pattern of electrodes is shown in FIG. 5, where the electrodes of both electrode pairs 105, 103 and 104, 102 are tilted towards one another. With regard to the chronological sequence of the sagging or tilting of the electrode pairs, the following relationships result. When the pair of electrodes, which has been tilted in the second position, moves towards one another, its resistance zone increases from an initial value by about 15%; the first pair of sagging electrodes reduces its zone resistance by about 5 to about 15 % of its initial value; It means that

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this pair of electrodes from an initial 20% increase relative to the initial reference value a reduction of 5% in relation to makes this initial reference value.

In FIG. 5, the electrodes 103 and 104 are shown in such a way that they did indeed move towards one another when they were tilted, without moving however to touch. It goes without saying, moreover, that the tipping and sagging of the electrodes can take place in any direction can take place and that the embodiments shown in the figures of a tipping or sagging in general Level of the cross-sectional representation only for the sake of better understanding and better representation have been chosen. Where the electrodes 104 and 103 are up to an actual or almost reached contact contact and are effectively electrically interconnected by a low resistance path like this 8, such electrodes also connect the secondary windings of their supply transformers at the same time and connect these in series with respect to the outer electrodes 102 and 105, so that the predominant current path is now runs over the outer electrodes 105 and 102. The resistance value of each of the two zones increases remarkably in an order of magnitude which corresponds to about half of its initial values.

If a pair of electrodes sags in opposite directions and moves away from each other, as is the case for the electrodes 6, the resistance of each zone increases by about 33% over the initial zone resistances. This is due to the larger effective electrode spacing in the molten glass, to the repositioning of the electrodes in a colder part of the melt and on the volumetric efficiency

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effect of the reduced space for effective conduction of current in the melt due to the approximation the sagged or tipped electrodes to the floor and the refractory lining of the melting tank. It results there is little effect on the zone resistance of an adjacent zone in the series when the second Pair of electrodes, which sags and tips away, move away from each other, since in this case, too, their resistance increases by about Enlarged 33% of the original value. It is believed that the tilting of the first, tipping away from each other Electrode pair has a small influence on the zone resistance of the electrode pair, which in its preferred vertical Orientation remains because like electrical polarities are close to each other, as is the case with respect to electrodes 105 104 and 103 hold true with respect to 102, so that the change in the cell constant in the melt is canceled.

An outward tilting of electrode pairs, which are connected to the supply circuit next to one another are, as is the case for the electrode pairs 116, 117 and 118, 119 corresponding to the dashed lines 110 and 120 in FIG 7 applies, leads to an increase in the zone resistance of about 30% based on the original resistance in the preferred one vertical electrode orientation. As in the case of electrodes 102 and 104, which are assigned to one another in pairs, where likewise only a voltage-sensing transformer 152 and a current-receiving coil 153 are shown, which then the approximate values for the current and voltage circuits supplying the rms numbers are assigned as for the transformer 127 and the coil 141 apply, are also in the paired electrodes 116, 117 and 118, 119 the voltage and current circuits in the appropriate

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se of voltage transformers 154 and 155 and current receiving coils 156 and 157, which are supplied with the respective circuits for the approximate determination of the respective effective values are connected.

An illustration of a row of electrodes and a switching pattern supplying the electrodes with current is given in FIG. wherein the circuit pattern is formed so that as a result of electrode sagging in any direction uniform Zone resistance changes or uniform electrode pair resistance changes be achieved. The circuit pattern of Fig. 9 is designed so that crossed to the longitudinal axis the melting tank result in diagonally oriented zones, so that relatively long main conduction paths in the in the melting tank located melt 162 are formed. These long, current paths formed by the resistors 163, 164, 165 and 166 indicated in dashed lines result from the increased resistance of the melt at the current work temperatures, so that the required amount of electrical Power can be supplied to the limited volume of the melt with high voltage and low current. To this In this way, it is possible to keep the losses in the power supply arrangements low, in particular the Transformers and connecting cables.

2 conditions to be kept low, in particular the losses V = I R in the

A typical melting tank has a length of 12.5 m, is 4.87 m wide and has six rows of four electrodes each. The one with respect to the outlet opening below the glass The electrode row 167 furthest away from 168 is at a distance of 1.37 m from the rear wall 169; the distance between the individual rows of electrodes is 1.82 m Electrodes are in a spaced relation to the fusible

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ne arranged in total in each row as applies to row 167 in which the outer electrodes 171 and with their centers 91 cm away from the correspondingly close side walls 175 and 176. The distance between the The electrode center points along a row is approximately 1 m. The molybdenum electrodes 171 used have have a diameter of 7.62 cm and are exposed to the glass to be heated, i.e. the melt 162 over a length of 102 cm. In the illustrated distribution pattern of electrodes and associated Power supplies, there is a 25% greater resistance in the diagonal zones, designated 163 to 166 are, based on the electrode pairs arranged in the same geometry, which are shown in FIG. 3 and in each of which an electrode in the pairing row is skipped. It is theoretically believed that this increased Zone resistance is the volume of the melt in the vicinity of the electrodes at which the predominant Joule heat input occurs, so that volumetric influences on the zone resistance change can be reduced as they result from electrode sagging and tilting. In addition, the absence of electrodes reduces other electrode pairs in the melt volume between each pair of electrodes the cell effect of the displacement or displacement of such electrodes on the change in resistance in the zone. In practice it has been found that a zone that has a tilted or sagging electrode in a system shown in Fig. 9 has a resistance increase above its initial state, with both electrodes arranged vertically and upright away from the bottom of the melting tank, of about 30% for each tilt direction. The illustration in FIG. 9 shows that a single-phase (phase A) supply voltage source coupled to the first two rows of electrodes

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in such a way that all electrodes of each row have the same instantaneous polarity distributions from the secondary windings of the supply transformers. Similarly, the two rows of electrodes 177 and 173 a different phase is supplied individually; the same applies to the electrode rows 179 and 181. The power supply for each zone is carried out as described above.

The zone 163 between the electrode 171 of the row 167 and the Electrode 184 of row 186 is connected to secondary winding 187 of the transformer 188 controlled via anti-parallel connected Rectifiers 191 and 192 supplied by an ignition controller 190 are controlled. Each zone is monitored with regard to its electrical parameters as described above, in that a current pickup coil 194 is associated with a cable leading to an electrode; also will a voltage sensing transformer 195 is used, the electrical with both the electrodes supplying power Lines is connected.

There are then further the current sensing arrangements 196 and the voltage sensing arrangements 197 are provided that the Forward signals from the current pick-up coils, for example 194, and from the voltage transformers such as 195. more precisely transpose and supply analog divider circuits that a comparator a resistance signal or a Apply the current / voltage ratio signal, as above overall already described. The initial setting point or the reference potential supplied to the comparator 199 is obtained taking into account the initial resistance of the assigned pair of electrodes and its zone area as setting on Potentiometer 201, with an alarm-generating arrangement 202 on a preset deviation of the resistance from the original

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worth responding. In FIG. 9, these circuits are only given in a typical block diagram; the power pickup coils and the voltage transformers are only shown for the first zone to be detected in the drawing. It understands that sampling means are provided in a preferred multiplex circuit in a suitable manner, as has already been done with With reference to FIG. 2 was explained. In this way, the resistance and its limit values for each zone of the respective Detect electrode pairings as well as for the other zone areas 177, 178 and 179, 181, there is only one detection circuit required and the identification of the zone and the assignment of the reference point circuit can be done with the Sampling function of the decoding circuit are coordinated. Through the scanning sequence and the selection of the setting points, so far desired, both increasing and decreasing resistance values with respect to the original zone resistance values can be detected.

The magnitudes or amplitudes of long-term changes in the zone resistance, caused by a displacement of the electrodes from their preferred orientation are a function of one Numerous factors, apart from the directions of the tipping process already mentioned above, the speed of the Sag, the temporal tipping relationships between pairs of electrodes that make the zone main current available, and the tilt relationships or the lack of tilt between electrodes of multiple pairs. Particularly notable influences The control configurations also respond to the changes in resistance of the electrodes, their relative instantaneous polarity distribution and their phase relationships. In any case it is a long-term change in resistance in a zone in the range between 15% to about 50%, based on the original zo-

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an indication and an indication that a Electrode sags or tips over that the electrode has been shifted from its preferred orientation. In many cases there are the magnitudes of the change in resistance and the relationships of the changes in resistance in one another associated electrode pair areas a relatively precise indication of the nature and direction of the electrode displacement from their preferred orientation.

Especially with regard to the many possible electrode orientations in a heating system that uses Joule heat supply to a material that softens in heat, and the innumerable possibilities of individual and combined electrode displacement It goes without saying that the present explanation only makes the invention understandable in its basic features could and is therefore not to be understood in a restrictive sense.

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Claims (13)

OR.-ING. DIPL.-INS. M. SC. DIt L-P. IVS. DR. DIPL.-PHVS. HÖGER - STELLrecht- GR.ESSSACH - HAECKER PATENTANWÄLTE IN STUTTGART A 42 397 m a - 168 June 28, 1977 Owens-Corning Fiberglas Corporation, Fiberglas Tower, Toledo, Ohio 43 659 / USA Patent claims: 1.) Method for monitoring the state of in a mass \ / made of heat-softening material, preferably glass their heating by applying Joule heat submerged electrodes, characterized in that when the electrode is initially used in the material, electrical parameters of the electrode and the material in the vicinity of the electrode are determined and these electrical parameters are monitored during the life of the electrode and as a function the rate of change and the magnitude of change in the monitored electrical parameters, a displacement of the electrode in the mass heated by it is determined from its original orientation. 2. The method according to claim 1, characterized in that the heating by supplying Joule heat is used electrical energy of the electrode in the form of voltage pulses of non-sinusoidal waveform and alternating of opposite polarity and the monitored electrical parameters are current and voltage values that correspond at least approximately to the effective values. 3. The method according to claim 1 or 2, characterized in that that the resistance of the electrode and of the material that is in its vicinity and heated by it at the initial level Use of the electrode detected and during the 809813/0674 ORIGINAL INSPECTED June 28, 1977 Electrode life is monitored and then a displacement, displacement or sagging of the electrode is indicated Display arrangement is actuated when the change in magnitude of the monitored resistance is at least 15%, based on the originally determined resistance is with a long-term monitoring interval of at least several weeks electrode usage. 4. The method according to claim 3, characterized in that the resistance between zv / ei initially in a body of immersed by heat to be heated material and in this vertically upward extending electrodes determined and a long-term change in the determined resistance is used with respect to the originally determined resistance to actuate a display device which sagging or tilting of the electrode (s) from their vertical position, indicates upright orientation. 5. The method according to claim 4, characterized in that the display device is based on an increase in resistance responds to the originally determined resistance. 6. The method according to claim 4, characterized in that the display device is based on a resistance reduction responds to the originally determined resistance. 7. The method according to claim 4, characterized in that the size of an electrode displacement or an electrode sagging The specified change in resistance is between 15 and 50%, based on the originally determined resistance. 8. The method of claim 3, wherein the to be softened in heat 809813/0674 June 28, 1977 Material (glass) in a longitudinal axis and a testicle having melting tank is heated and the electrodes designed as a vertical elongated electrical conductor extending from the bottom of the melting tank in an upright direction and in rows, each consisting of at least two pairs of electrodes, in the transverse direction to the longitudinal axis of the Melting tank are arranged, characterized in that the electrodes combined in pairs alternate with Forming main conduction paths between them within the heat softening material are so arranged that at least one further electrode of another pair is located between each electrode pair and that one Long-term decrease in resistance between the first pair of electrodes, based on its original resistance for actuation the display device is used to the effect that one electrode of the other, arranged between the first pair of electrodes Couple sinks in or tips over. 9. The method according to one or more of claims 1 to 8, characterized in that a resistance increase, based on the initial resistance, between a first paired Electrode arrangement, associated with a decrease in resistance, again based on the initial resistance between a another paired electrode arrangement in which the first paired electrode arrangement and an electrode between them Arrangement containing row is an indication that the electrode of the first pair of electrodes, which is between the second pair of electrodes is, has tipped or sunk. 10. The method according to claim 9, characterized in that the increase in resistance between the first pair of electrodes between 809813/0674 A 42 397 m a - 168 - 4 - June 28, 1977 see 20 and 30%, based on their initial resistance, and the decrease in resistance between the other pair of electrodes at about 25%, based on their initial resistance, lies. 11. The method according to one or more of claims 1 to 10, characterized in that in rows of at least two electrode pairs arranged electrodes within a melting tank a resistance increase above the initial resistance with a pair of electrodes of about 15%, at least one of the pair of electrodes tipping away or sagging forming electrode in the direction of the other. 12. The method according to one or more of claims 1 to 11, characterized in that adjacent electrodes are different Electrode pairs are supplied with voltages of different polarity for the majority of the time and that a decrease in resistance between electrodes combined in pairs, each with an external intermediate electrode in the order of 50%, based on their initial resistance value an indication of this is that adjacent electrodes of different pairs are in close proximity have tilted or sagged towards each other. 13. The method according to one or more of claims 1 to 12, characterized in that a resistance increase between a pair of electrodes by about 33% above their initial resistance an indication of this is that the electrodes in this pair have tilted or sagged in one direction away from each other are. 809813/0674