|Publication number||US3764883 A|
|Publication date||Oct 9, 1973|
|Filing date||Oct 26, 1972|
|Priority date||Oct 28, 1971|
|Also published as||CA960294A, CA960294A1, DE2251568A1, DE2251568B2, DE2251568C3|
|Publication number||US 3764883 A, US 3764883A, US-A-3764883, US3764883 A, US3764883A|
|Inventors||Braun Staad F, Ribnitz P|
|Original Assignee||Gema Ag|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (5), Referenced by (20), Classifications (18), Legal Events (2)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent 11 1 [111 3,764,883
Staad et al. Oct. 9, 1973 MONITORING APPARATUS FOR 3,217,207 11/1965 Webb 317/51 PREVENTING SPARK-OVERS AT A HIGH i g i i ams... VOLTAGE INSTALLATION 3,665,253 5/1972 Stefani 317/31 X  Inventors: Franz Braun Staad; Peter Ribnitz,
both of St. Gallen, Switzerland Primary Examiner-William M. Shoop, Jr.  Assignee: Gema AG Apparatebau, St. Gallen, AttorneymKarl mocks Sw1tzerland ABSTRACT  Filed: 1972 A monitoring apparatus for preventing a spark-over at  AppL No; 301,149 7 V a high voltage installation for corona electrodes comprising a high-frequency voltage source and a high voltage transformer, the secondary winding of which is Fmeign Application Priority Data coupled through the agency of a high voltage cascade Oct. 28, 1971 Switzerland 15725/71 with the corona electrode. The high-frequency voltage source is connected via a power amplifier, which start-  US. Cl 321/11, 204/312, 250/324, ing from a certain value of its output current exhibits 317/27, 330/51 current limiting and decreasing output voltage charac-  Int. Cl. H02m 1/18 teristics, with the primary winding of the high voltage  Field of Search 204/312, 317, 327; transformer. A comparator has its inputs coupled with 250/324, 325, 326; 317/27 R, 31, 51; the input and output respectively of the power ampli- 330/51; 321/11 fier and in the event the output voltage of the power amplifier is smaller than its input voltage interrupts  References Cited the current circuit to the corona electrode through the UNITED STATES PATENTS agency of a cutoff mechanism.
2,066,522 H1937 Doherty 330/51 6 Claims, 2 Drawing Figures 2 25 15 1 asc/mroe E g M64 VGZTAGE .7 5456x9092 0156/1015 5 TEA/YSRJR/If? 7 MONITORING APPARATUS FOR PREVENTING SPARK-OVERS AT A HIGH VOLTAGE INSTALLATION BACKGROUND OF THE INVENTION The present invention relates to a new and improved construction of monitoring apparatus for preventing spark-overs at a high voltage installation, especially for corona electrodes, with a high-frequency voltage source and a high voltage transformer, the secondary winding of which is coupled through the agency of a high voltage cascade circuit arrangement with the corona electrode.
Prior art apparatuses for monitoring the high voltage at corona electrodes in equipment for spray painting or lacquering are only then generally effective when there has already occurred a spark-over owing, for instance, to the corona electrode and the object undergoing treatment approaching one another too closely. A great prevalent danger is the possible explosion of the sprayed powder cloud. Additionally, during each spark-over the surface of the sprayed coating is impaired. Therefore attempts have been made to reduce to the greatest possible extent the energy of the sparkover by employing an alternating'current voltage of as high as possible frequency, so that the high voltage transformer and the capacitances at the high voltage cascade circuit arrangement can be selected to be small and thus store very little energy. Other monitoring devices contemplate reducing the electrode voltage as soon as a spark-over condition arises.
SUMMARY OF THE INVENTION It is therefore a primary object of the present invention to provide a new and improved construction of monitoring apparatus which effectively prevents sparkovers at a high voltage installation.
Another and more specific object of the present invention relates to a new and improved construction of monitoring apparatus which is relatively simple in construction and design and which removes the voltage from the corona electrode before a sparkover condition arises.
Now in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the inventive monitoring apparatus of this development is manifested by the features that the high-frequency voltage source is connected via a power amplifier, which starting from a certain value of its output current exhibits current limiting and decreasing output voltage characteristics, with the primary winding ofa high voltage transformer. A comparator has its inputs connected with the input and output respectively of the power amplifier and in the event that the output voltage of the power amplifier is smaller than its input voltage the comparator, through the agency of a cutoff mechanism, interrupts the current circuit to the corona electrode.
BRIEF DESCRIPTION OF THE DRAWING The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawing wherein:
FIG. 1 is a schematic circuit diagram of monitoring apparatus designed according to the teachings of this development wherein a portion of the circuit diagram is depicted in block configuration and another portion thereof depicted with its individual components; and
FIG. 2 is a graph showing the dependency of the output voltage of the power transformer upon the output current with constant input voltage.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Describing now the drawing, in FIG. 1 there is illustrated an exemplary embodiment of the inventive monitoring apparatus embodying a high-frequency voltage source in the form of an oscillator 1 which generates an alternating-current voltage at a fequency of 17 kHz with a constant voltage of 12 volts. The output of the oscillator 1 is electrically coupled with a first terminal 20 of a first potentiometer R,, the second terminal 21 of which is grounded. The sliding tap 30 of potentiometer R is coupled through the agency of a rest contact a belonging to a relay A defining a cutoff mechanism with the input 22 of a known power amplifier 2 and with the anode 23 of a first diode D,. This power amplifier 2 possesses a large current gain; its voltage gain normally amounts to approximately 1. The output voltage U appearing at the amplifier output 24 corresponds to the input voltage U, when the output current la does not exceed a certain value. On the other hand, if the output current I exceeds the value la then the output voltage U, decreases approximately in linear fashion, as best seen by referring to FIG. 2, and amounts to zero at the time of maximum possible output current Ia" (short-circuit condition). The output 24 of the amplifier 2 is coupled with the primary winding 25 of a high-voltage transformer 3 and with the anode 26 of a second diode D The secondary winding 27 of the high-voltage transformer 3 is coupled with the input 28 of a high-voltage cascade circuit arrangement 4 which delivers a direct-current voltage of about kV to a corona electrode 5.
The first terminal 31 of a second potentiometer R and a terminal 32 of a capacitor C the other terminal 33 of which is grounded, are connected with the cathode 34 of the first diode D The second terminal 35 of the potentiometer R is connected to ground via a resistor R The sliding tap 40 of the potentiometer R is connected to the non-inverting input 41, also designated by reference character with a comparator 6. The cathode 29 of the second diode D is connected with the inverting input 42, also designated by reference character of the comparator 6 and a terminal 43 of a grounded capacitor C The base 44 of a switching transistor T is coupled through the agency of a resistor R, with the output 45 of the comparator 6. At the collector current circuit of transistor T there is ar ranged the relay A.
With the foregoing background in mind there will be now considered the mode of operation of the previously described monitoring apparatus. During normal operation, that is to say, when the output current I of the amplifier is smaller than Ia then the voltage U which corresponds to the rectified output voltage Ua and is applied to the inverting comparator input 42, is more positive than the voltage U, at the non-inverting comparator input 41. The voltage U corresponds to the rectified amplifier input voltage U,,, but attenuated by the combination of the potentiometer R and resistor R The output voltage U, of the comparator 6 is negative if the voltage U applied to the inverting input 42 is more positive than at the non-inverting input 41 of the comparator 6. The switching transistor T in the normal condition is therefore non-conductive, the relay A in its rest state, and the rest contact a is closed.
Before a spark-over appears at the corona electrode 5 the electrode current and accordingly also the current at the primary winding 25 of the high voltage transformer, which approximately corresponds to the output current Ia of the amplifier 2, begins to rise. Upon exceeding the value Ia, which is dependent upon the design of the amplifier, the output voltage Ua begins to drop and therefore also the voltage U In the event that the voltage U becomes more negative than the voltage U,, then the output voltage of the comparator 6 becomes positive, the transistor T conducts, the relay A is actuated and the rest contact a opens, so that the current supply to the corona electrode 5 is interrupted.
With the aid of the potentiometer R and the resistor R it is possible to regulate the relationship of the amplifier input voltage to the amplifier output voltage, at which the monitoring apparatus is to respond. The resistor R serves the purpose of preventing the voltage U from dropping to zero. If this should happen then the equipment will be erroneously completely disconnected so that even with a spark-over it will not respond.
With the aid of the potentiometer R it is possible to regulate the input voltage Ue of the amplifier and therefore indirectly also the high voltage of the corona electrode. An advantage of this monitoring device is that it is not dependent upon the adjusted value of the input voltage Ue rather upon the relationship between the amplifier input voltage to the amplifier output voltage. In this way there can be realized a positive cutoff or disconnection whenever the corona electrode voltage has dropped to a certain percentage of a reference value.
While there is shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims. ACCORD- INGLY,
What is claimed is:
l. A monitoring apparatus for preventing spark-overs at a high voltage installation for corona electrodes, comprising a high-frequency voltage source, a corona electrode, a high-voltage transformer having a primary winding and a secondary winding, a high-voltage cascade arrangement connected in circuit with the corona electrode, the secondary winding of said high-voltage transformer being coupled with the corona electrode via said high-voltage cascade arrangement, a power amplifier means, which starting at a certain value of its output current exhibits current limiting and decreasing output voltage characteristics, said high-frequency voltage source being electrically coupled with the primary winding of the high-voltage transformer through the agency of said power amplifier means, comparator means having a first input, a second input and an output, said power amplifier means having an input and an output, one of the inputs of said comparator means being connected with the input of the power amplifier means and the other input of said comparator means being connected with the output of said power amplifier means, cutoff means for the corona electrode, said comparator means interrupting the current circuit to the corona electrode via said cutoff means when the output voltage of the power amplifier means is smaller than its input voltage.
2. The monitoring apparatus as defined in claim 1, wherein the high-frequency voltage source comprises oscillator means with adjustable output voltage.
3. The monitoring apparatus as defined in claim 1, further including a first rectifier arranged between the input of the power amplifier means and said one input of the comparator and a second rectifier arranged between the output of said power amplifier means and said other input of said comparator.
4. The monitoring apparatus as defined in claim 1, further including potentiometer means electrically coupled between the input of the power amplifier means and said one input of the comparator means for adjusting the relationship between the amplifier input voltage to the amplifier output voltage at which the monitoring apparatus responds independent of the value of the amplifier input voltage.
5. The monitoring apparatus as defined in claim 1, wherein said cutoff means comprises a relay which can be actuated by said comparator means, said relay having a switching contact arranged in circuit between the high-frequency voltage source and the power amplifier means.
6. The monitoring apparatus as defined in claim 1, wherein the current value at which there occurs limiting of the output current can be adjusted by changing two components at the power amplifier means.
' UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTEON PatentNo. 3,764,883 Dated October 9, 1973 l fi srk Franz Braun and Peter Ribnitz It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
 l'nventorsz Franz Braun, Staad; Peter Ribnitz, St. Gallen,
' Switzerland Signed and sealed this 19th day of February 197M.
EDWARD M.FLE TCHER,JR. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-105O (10-69) USCOMM-DC GOING-P69 u.s. sovuunzn-r rnm'rme ornc: ID" o-acd-au,
w U Wm v .-w ;w
I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent: No; 3 764 5 883 D g d October. 9 1973 Inveha g Franz Braun' and Peter Ribnit z It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
 Inventors-Q Franz Braun, Staad; Peter Ribnitz, St. Gallen,
' Switzerland Signed and sealed this 19th day of February 197A.
c. MARSHALL DANN Commissioner of Patents EDWARD MIFLETQCHER, JR. A ttesting Officer FORM PO-105O (10-69) uscoMM-Dc coon. U. S. GOVIINIIENT PRINTING OF"; 1
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|U.S. Classification||363/53, 422/186.15, 330/51, 250/324, 361/86|
|International Classification||H02M3/24, H02H3/28, B05B5/08, H02H3/26, H02H7/00, B05B5/10, H02M3/28|
|Cooperative Classification||H02H3/28, B05B5/10, H02H7/003|
|European Classification||H02H7/00D, H02H3/28, B05B5/10|
|Aug 30, 1982||AS02||Assignment of assignor's interest|
Owner name: GEMA AG APPARATEBAU, A CORP. OF SWITZERLAND
Owner name: RANSBURG-GEMA AG, KUNKLERSTRASSE 9, 9015 ST. GALLE
Effective date: 19820823
|Aug 30, 1982||AS||Assignment|
Owner name: RANSBURG-GEMA AG, KUNKLERSTRASSE 9, 9015 ST. GALLE
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:GEMA AG APPARATEBAU, A CORP. OF SWITZERLAND;REEL/FRAME:004052/0993
Effective date: 19820823