DE900725C - Adjustable capacitor - Google Patents

Description

Adjustable capacitor In low-current technical. , Devices need Capacitors are often built in, with regard to their constancy and accuracy the highest demands are made on their capacitive value. With electrical Filters as they are e.g. B. are used in carrier current devices, as well as in Dekäadenkonderisatoren and in generator circuits for measurement purposes, the capacitors must meet the highest demands concerning. Immutability and low tolerance of their electrical value are sufficient.

Accuracies of about o "i ° / o and above are required. Such Up to now, capacitance values have been achieved by using a capacitor with relative a large margin of its actual value (about T 2% of its nominal value) Adjustment capacitor, which is selected according to its value, switched in parallel. The additional capacitor is usually relatively smaller Capacity and may accordingly have a larger percentage tolerance.

Instead of fixed additional capacitors there are also changeable ones Capacitors used. However, it occurs with commonly used adjustable trimmer capacitors the disadvantage in appearance that an electrical connection to a movable electrode takes place and that in connection therewith the trimmer capacitor, z. B. at. occurring high voltages, usually of a relatively large size.

It was already suggested that the adjustable capacitor, who, if applicable, as mentioned, used as an additional capacitor is built up in such a way that it is rigid from a dielectric body, z. B. ceramic material, on which the electrodes as surface metallizations are upset. The capacitance adjustment of this capacitor is done by grinding made of electrode covering parts. This procedure, of course, continues in the case the use; of the capacitor as additional balancing capacitance: that the Main capacitor, to: the former is connected in parallel with its actual Value below: the target value.

The latter method is different from the previously mentioned method basic advantages. However, it still remains as a major disadvantage left that sanding; of electrode covering parts. a time consuming process and furthermore: that the capacitor treated by grinding is often unsightly will.

The suggestions outlined below are aimed at eliminating or Reduction: addressed these disadvantages.

To shorten the process it is suggested: the electrode surface of the adjustable capacitor: the area of which can be reduced by grinding should, lattice-like, d. H. to dissolve into interconnected partial areas. Herewith the not inconsiderable advantage is gained that the adjustment is only possible by Grinding in a parting line needs to exist, namely such a parting line "the a; Covering part to: whose capacitive part the total capacity to: is large, from: the remaining effective electrode coating.

If this measure already takes the time and effort of grinding reduced to a fraction of what was previously necessary, so it is still beneficial to provide the following improvements to the adjustment capacitor, namely, this Improvement make it easier to determine the excess capacity amount. If: the variable capacitor is interconnected with a main capacitor and put together, as both are to be built into: the finished device, and connected to a measuring bridge in this! state, it is disadvantageous! that the initial (the capacitance value of the two capacitors eats too high. One would have to now change the frequency of the measurement voltage to get out of the frequency difference on: to close the capacitance value to which the capacitor arrangement to achieve the exact target amount must be reduced. Changing the measuring bridge frequency is inexpedient. It is definitely more advantageous to use one and the same measuring frequency to work and: to determine the capacitive excess amount by other measures. To make this possible in a simple manner, it is proposed that the. Main part of the Metallization covering, the area of which is to be reduced for capacity adjustment, through a parting line from the metallization part connected to the electrode connection point to be separated, namely by a parting line: the one after the measurement or after the Installation of the capacitors in the device is easy. electrically bridged by means of solder can be. This measure enables a calibrated capacitor in the measuring arrangement to be provided, which is connected in parallel to: the capacitor arrangement. Through the The joint is by far the largest part of the Abgleiohkapazi. so that the capacitor arrangement initially has a shortfall. Through the calibrated Rotary capacitor of the measuring arrangement, the shortfall is determined exactly, whereupon .the shortfall on the bypass capacitor through appropriate .dimensioning of the electrode coating and then by bridging the parting line on -dem Adjusting capacitor is connected. There is no problem with ground purely empirical experience without further intermediate measurements of the adjustment capacitor to give a required target value in each case by removing excess covering parts can be eliminated by applying appropriate separating joints. The explained Measures result in a very considerable saving in terms of time and effort with the exact: adjustment of capacitance values, which either: by an adjustable Capacitor alone or: by a capacitor connected to the adjustable capacitor Capacitor relatively large capacity can be formed.

The figure explains: the proposed measure on a platiform trained capacitor. i is the rigid dielectric sheet on which the Electrode coatings 2, 3 and 4 are applied as surface metallizations. 4th is the main part of the electrode coating, the area of which has to be reduced for adjustment target. Between 3 and 4, which in and of themselves belong to the same electrode coating. is: a parting line is switched on, which after .the adjustment of the capacitor through a soldering point is to be bridged at the point io. The electrode pad 4 is in: dissolved in a grid-like manner,: that the metallization-free strips. 5, 6, 7 are provided. The external connection of the electrodes is made through the soldering lugs 8 and g, which are soldered onto the electrode metallizations. With this capacitor now does not need to bring about a certain capacitance value, the total Sanding off parts of the surface, but it is only necessary .an a suitable Make a narrow parting line to create a necessary large area of the grid-like dissolved electrode coating is switched off and thus capacitive becomes ineffective.

The strips 5, 6 and 7 created by the metallization-free strips Partial areas are of different widths, so that any one can be easily Can achieve accuracy when matching.

Instead of metallization strips running in parallel, you can of course even. different partial areas are formed by a grid-like dissolution, so can it e.g. B. be advantageous to provide triangular metallization lugs.

Another very practical addition and training to what has been described ab: the same capacitor can consist of the external covering with a scale and scale value information to be printed, so that each: desired (capacity value find it immediately and read off the position of the necessary parting line without further ado leaves.

To protect against the effects of the weather, the adjustable capacitor be provided with a varnish coating; the coating can be colorless. to the structure to keep the grid-like dissolved surface visible and thus to find it to facilitate the grinding point.

Claims (1)

PATENT CLAIMS: i. Abgleidhbaren capacitor, on its rigid dielectric layer metallized electrode coatings are applied and its Capacity adjustment by grinding off parts of one electrode metallization is made thereby. characterized in that the metallization, its Area for capacity balancing is to be reduced, like a grid, d. H. in each other connected partial areas, is dissolved. a. Adjustable capacitor according to claim i, characterized in that the main part of the metallization, its surface should be reduced for capacity adjustment, by a simple way (soldering) electrically bridgeable parting line from. the one connected to the electrode connection point Metal lining part is separated. 3 (. Adjustable capacitor according to claim i or z, characterized in that, the electrode coating, the surface of which for the capacitance comparison is to be reduced, is printed with scale information that indicates the point at which a Interruption of the metallization in order to achieve a desired capacity adjustment must be made, allow immediate reading.