DE760088C - Parallel switch, especially for crank capacitors - Google Patents

Description

Parallel switch, especially for crank capacitors When building a Parallel switch, especially for crank capacitors for measurement purposes, is one Number of conditions, some electrical, some mechanical, to be observed, which are to be explained in the following.

When using crank capacitors in measuring bridge circuits, it is important that the connection and disconnection of the individual capacitors, z. B. a decade, occurs continuously and during the switchover, so while the brushes slide from one position to the next, no interruption or any other value of the capacitance appears set at the terminals. For this reason, all designs with shift drums are ruled out. If the shift drum according to Fig. I (shift drum drawn unwound), assuming four capacitors in the size ratio i: 2: 2: 5 (e.g. o, ooi, o, oo2, o, oo2, o, oo5, uF) , i: 2: 3: 4 or the like brought about from position i to position 2, then in position z ... o, ooi, uF, in position 2 ... o, oo2, uF , in the position between the two contacts, as long as both brushes are still in contact, 0.003, uF switched on. Similar discontinuities arise when switching from position 3 to 4, 4 to 5, 6 to 7 and 8 to g. This is not allowed in the aforementioned bridge circuits, as more and found a larger deviation during Urnschaltens the capacitor in .Nullinstrumetlt must "-erden and adjustment of the bridge is inaccurate uncomfortable and might.

A frequently used construction of a parallel switch is shown Fig. -2, in which, by turning clockwise, one drawn in the zero position, approximately semicircular disk i around an axis 2 perpendicular to the image plane the individual capacitors (e.g. i i X o, ooi l..F) are constant one after the other via brushes 3 or 4., j etc. and via terminals 6 and; to- or switched off.

It is necessary for measurements with direct current. that the switched off Capacitors of a decade always short-circuited «-ground, so the next time Switching on a capacitor is not caused by incorrect measurements due to residual charges can be. This requirement is relatively easy to meet constructively and is known per se. A second approximately semicircular disk b (in Fig. 2), which is offset from disk i by iSo # "in the image plane and at the same time with the disk i can also be rotated about the axis 2 «- is in contact with the brush g, which in turn is connected to a coating of all the capacitors. In the drawn zero position of the crank, all capacitors are short-circuited. When rotated by one step, the first capacitor is switched on, while all the rest still remain short-circuited. The same applies to the other positions the crank.

Electrostatic shielding is required for measurements in the audio frequency range necessary in order to especially reduce the influence of the hand capacity when operating the crank remove.

Another requirement is that zero capacitance. so the between the capacitance occurring between terminals 6 and 7 (Fig. 2) in the zero position of the crank assumes the smallest possible value. This capacity is particularly important in executions with shielding so large that they generally oppose the permissible deviations of the individual stages of the capacitor are no longer neglected by their setpoint can be. Usually one helps oneself in such a way that this value is measured once. possibly entered in a test certificate and taken into account for every measurement.

In the case of crank switches for larger capacitors, e.g. B. 10 X 0, i yF, and higher frequencies, e.g. B. 10000 Hz, it is necessary that the contact resistances at the brushes are below a certain value, which results from the requirement that the angle tgb = R ") C caused by the contact resistance R (in front of the capacitor C) is significant is smaller than the angle caused by the losses in the dielectric of the capacitor.

The insulation materials used must take into account the Requirements for direct current measurements high isolation. for alternating current measurements have low loss angles.

In addition to the electrical requirements shown above for a useful parallel switch design There are still some mechanical requirements, namely: The crank switch must, despite the large brush surface and the high brush pressure, as possible to ensure small contact resistance, can be easily adjusted and a have good locking.

The usual crank switch for resistors (with a brush or a pair of brushes :) has a relative in the manufacture of such devices significantly higher proportion than the parallel switch. So it is also in the interest A saving in tools, etc. is desirable, with the parallel switch as possible to use many parts of the series switch.

The switch designs known up to now usually only suffice for one Part of the specified conditions. A new switch will now be described below "-earth. mainly to meet the requirement of the smallest possible zero capacitance and the use of as many parts of a series switch as possible are significant improvements having. -The parallel switch, especially for crank capacitors with a fixed contact circle and rotating brush groups, is characterized in that the circle division of the contacts and brushes is different in size.

The contact circuit is on the base plate i i made of insulating material 12 and the axis 13 attached. On the axis are the crank i-. with the numbering and the latching device, not shown, is rotatably mounted. -With the crank it is the insulating washer 15 on which the brushes are attached, mechanically connected.

The brushes of the two brush groups 16 and 17 are with each other electrically connected. The circle division of the brushes is smaller than the division of the Contacts and so g e selected that taking into account the brush and contact width in the intermediate position during switching (according to Fig._1) in the direction of rotation between the first brush of the brush group 16 and the last brush of the other Brush group 17 just a contact 1 2 remains free and no short circuit between the brush groups and thus between the terminals occur can. The various divisions of the brush and contact circle still have the significant advantage that a brush after the others run up against the contacts and an easier and safer operation of the switch is guaranteed.

In Fig. 5 the position of the switch is shown in which the first capacitor is switched on, while the rest remain short-circuited. The connection of the capacitor takes place on the one hand via the apparatus terminal and the connected 'supply line, via the contact part 18, via two brushes of the brush group 16 and via a corresponding connection contact 12 of the capacitor, on the other hand via the other terminal and via the common supply line for all capacitors takes place immediately.

In order to achieve zero capacitance despite the intended electrostatic shielding To keep it small (in the position o of the switch shown in Fig. 3) is the Contact 18 is divided and the first brush i9 of the brush group 16 is correspondingly shorter. This has the advantage that only the capacity of one half of the Contact and the connected supply line comes into consideration. Would this contact are not divided, then the capacity of the entire brush group is in the zero position 16 and the connected contacts against the shield or against earth to the Clamps. Only when the first contact is switched on does this capacity come in added to the value of the first capacitor, d. H. the capacitance value of this capacitor is adjusted taking this switch capacity into account.

Claims (2)

PATENT CLAIMS: i. Parallel switch, especially for crank capacitors, with a fixed contact circle and rotating brush groups, characterized in that that the circle division @ of the contacts and brushes is different in size. 2. Parallel switch according to claim i, characterized in that it has an electrostatic shield and to reduce the zero capacitance that of the position zero corresponding Contact divided and the associated brush different in length compared to the length of the rest of the brushes.