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Vacuum-Variable-Capacitors-Jennings-Datasheets.pdf
Jennings variable vacuum capacitor. Two sets of concentric cylinder plates, one adjustable and the other fixed, are enclosed in an evacuated ceramic.
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vacuum variable capacitor products for sale – eBay
JENNINGS VACUUM VARIABLE CAPACITOR CADB-15-20N77 ANTENNA TUNER HAM. $75.00. $9.50 shipping ; Jennings UCS-500 Variable Vacuum Capacitor 15KV 500pf. $199.00.
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— Jennings® Vacuum devices – ABB
Jennings variable vacuum capacitor. Two sets of concentric cylinder plates, one adjustable and the other fixed, are enclosed in an evacuated ceramic.
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201 to 500 pf Max – Vacuum Variable – Capacitors – RF Parts
201 to 500 pf Max ; CV1C-500UIHN/15 Vacuum Variable Capacitor, 12-500pf, 15kv Peak / 9KV, Comet (NOS). $899.95 ; UCS300-10KV Jennings Vacuum …
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Vacuum Capacitors: 101 – 500pF – Surplus & Sales of Nebraska
Jennings vacuum variable capacitor. 75 amps. 1/2″ shaft. Front head is tapped and has sol copper block attached (removable). Rear (fixed end) has a …
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US9472347B2 – Variable vacuum capacitor – Google Patents
A variable vacuum capacitor includes two pairs of electrodes ganged together in series such that no moving parts are required to connect electrically to any …
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- Author: Brighton Beach
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- Date Published: 2021. 12. 25.
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What does a vacuum variable capacitor do?
A vacuum variable capacitor is a variable capacitor which uses a high vacuum as the dielectric instead of air or other insulating material. This allows for a higher voltage rating than an air dielectric using a smaller total volume.
What is the difference between capacitor and variable capacitor?
The variable capacitors are the ones whose capacitance value can altered either electrically or mechanically. The variable capacitors consist of sets of stationary and movable plates. A shaft is attached with the movable plates and by rotating the shaft, the capacitance value can be altered.
What are the two types of variable capacitor?
There are many uses of these variable resistors such as for tuning in LC circuits of radio receivers, for impedance matching in antennas etc. The main types of variable capacitors are Tuning capacitors and Trimmer capacitors.
Where is a variable capacitor used?
Variable air capacitors are used in circumstances where the capacitance needs to be varied. They are sometimes used in resonant circuits, such as radio tuners, frequency mixers or antenna impedance matching applications. Another use for variable capacitors is while prototyping an electronic circuit design.
How does a variable capacitor work?
Unlike standard fixed capacitors, variable capacitors are configured to allow changing capacitance levels. In most cases, variable capacitance is accomplished by altering the distance between the parallel plates in a capacitor or by shifting the cross-sectional area at which the plates face one another.
How many types of variable capacitors are there?
What are the two types of variable capacitors? They are tuning capacitors and trimming capacitors.
How do I choose the right capacitor?
The capacitor physical size is directly proportional to the voltage rating in most cases. For instance, in the sample circuit above, the maximum level of the voltage across the capacitor is the peak level of the 120Vrms that is around 170V (1.41 X 120V). So, the capacitor voltage rating should be 226.67V (170/0.75).
What is the working voltage of a variable capacitor?
Voltage rating, capacitance range, polarity
Trimmer capacitors can be rated for voltages up to 300 volts, although voltage ratings of up to 100 volts are much more common. Since trim caps are variable capacitors, they come in a capacitance range rather than a single capacitance value.
How do you identify capacitor types?
Generally the first two digits indicate the capacitors value and the third digit indicates the number of zero’s to be added. For example, a ceramic disc capacitor with the markings 103 would indicate 10 and 3 zero’s in pico-farads which is equivalent to 10,000 pF or 10nF.
Does the type of capacitor matter?
Yes, the type of capacitor can matter. Different types of capacitor have different properties. Some of the properties that vary between capacitor types: Polarised vs unpolarised.
What is the symbol of a variable capacitor?
The arrow symbol indicates a variable capacitor (adjustable by the equipment user, and the T shaped diagonal indicates a preset capacitor, for technician adjustment only. The dotted line connecting a pair of variable capacitors indicates that they are ganged.
What are plastic capacitors used for?
Film capacitors are also known as plastic film capacitors or film dielectric capacitors. Plastic film capacitors are mainly used in circuits where low loss and high insulation resistance is required.
What is the use of non polarized capacitor?
A non-polarized capacitor is a type of capacitor that has no implicit polarity – it can be connected either way in a circuit. They are mainly used in circuits of coupling, decoupling, feedback, compensation, and oscillation.
Which is variable capacitor?
A variable capacitor is a capacitor whose capacitance may be intentionally and repeatedly changed mechanically or electronically.
Which one is a variable capacitor?
A variable capacitor is a capacitor whose capacitance can be adjusted within a certain range. When the relative effective area between the pole metal plate or the distance between the plates is changed, its capacitance changes accordingly. It is usually used as a tuning capacitor in a radio receiving circuit.
What is the symbol of a variable capacitor?
The arrow symbol indicates a variable capacitor (adjustable by the equipment user, and the T shaped diagonal indicates a preset capacitor, for technician adjustment only. The dotted line connecting a pair of variable capacitors indicates that they are ganged.
What is a fixed capacitor?
A fixed capacitor is a capacitor that stores a fixed amount of electric charge (capacitance) and this is not adjustable at any instance. Their values are mostly fixed while manufacturing. A fixed capacitor helps maintain a constant charge and energy output in electric appliances or devices.
201 to 500 pf Max
$299.95
Out of stock
CVDE-200-5 Jennings 15-250pF 5Kv Variable Vacuum Capacitor
Used, Great Condition * No longer available for export
Made in the USA by Jennings
SKU: CVDE-200-5
Please see our Warranty page regarding our warranty.
Made in the USA
Vacuum variable capacitor
A vacuum variable capacitor
A vacuum variable capacitor is a variable capacitor which uses a high vacuum as the dielectric instead of air or other insulating material. This allows for a higher voltage rating than an air dielectric[1] using a smaller total volume. However, many dielectrics have higher breakdown field strengths than vacuum: 60-170 MV/m for teflon, 470-670 MV/m for fused silica and 2000 MV/m for diamond, compared with 20-40 MV/m for vacuum. There are several different designs in vacuum variables. The most common form is inter-meshed concentric cylinders, which are contained within a glass or ceramic vacuum envelope, similar to an electron tube. A metal bellows is used to maintain a vacuum seal while allowing positional control for the moving parts of the capacitor.[2]
Invention [ edit ]
Nikola Tesla filed a patent in 1896 for a vacuum capacitor. The original use was to enhance the quality of the electrical components for handling “currents of high frequency and potential”. These components were necessary for the DC impulse research which Tesla was studying. Commercial products have been available since 1942.[1]
Applications [ edit ]
Vacuum variable capacitors are commonly used in high-voltage applications: 5000 volts (5 kV) and above. They are used in equipment such as high-powered broadcast transmitters, amateur radio RF amplifiers and large antenna tuners. Industrially they are used in plasma generating equipment, for dielectric heating, and in semiconductor manufacturing.[1] The main applications today are RF plasmas of 2 to 160 MHz where the vacuum capacitor is used as the impedance variation part in an automatic matching network in the fabrication of chips and flat panel displays.
A 12 pF 20 kV fixed vacuum capacitor
Other variations of vacuum capacitors include fixed-value capacitors, which are designed very much like the variable versions with the exception that the adjustment mechanism is omitted.
Comparison [ edit ]
When compared to other variable capacitors, vacuum variables tend to be more precise and more stable. This is due to the vacuum itself. Because of the sealed chamber, the dielectric constant remains the same over a wider range of operating conditions. With air variable capacitors, the air moving around the plates may change the value slightly; often it is not much but in some applications it is enough to cause undesirable effects.[citation needed]
Vacuum variable capacitors are generally more expensive than air variable capacitors. This is primarily due to their design and the materials used. Although most use copper and glass, some may use other materials such as ceramics and metals such as gold and silver. Vacuum variables also vary in adjustment mechanisms.
Capacitor Types: Fixed & Variable Capacitors
Capacitor Types: Fixed & Variable Capacitors
Capacitors can be classified depending upon their fixed or variable capacitance as follows −
Fixed Capacitors
Those capacitors whose value of capacitance is fixed during the manufacturing and cannot be changed later are known as fixed capacitors. The symbol of the fixed capacitor is shown in figure.
The fixed capacitors are classified into two categories as −
Polarized Capacitors
Non-Polarized Capacitors
Polarized Capacitors
Those capacitors which are having the specified positive and negative polarities, are called as polarized capacitors. When these capacitors are used in the circuits, they should be connected in perfect polarities.
Polarized capacitors are further classified as −
Electrolytic Capacitors
Those capacitors in which some electrolyte is used as a dielectric medium are called as electrolytic capacitors. These are the polarised capacitors i.e. marked with specific polarities as anode (+) and cathode (-). There are mainly three types of electrolytic capacitors −
Aluminium Electrolytic Capacitor
In these capacitors, the anode (+) terminal is made of a pure aluminium foil with an etched surface. The aluminium forms a thin insulating layer of aluminium oxide that acts as the dielectric of the capacitor. A non-solid electrolyte covers the rough surface of the oxide layer and acts as the cathode (-) terminal of the capacitor.
Tantalum Electrolytic Capacitor
It consists of a pellet of porous tantalum metal that acts as the anode of the capacitor. The tantalum metal is covered by an insulating oxide layer that forms the dielectric and surrounded by a solid or liquid electrolyte that acts as cathode terminal.
Niobium / Niobium Oxide Electrolytic Capacitor
In a niobium capacitor, the anode terminal is made of passivated niobium metal on which an insulating niobium pent-oxide layer acts as the dielectric. A solid electrolyte on the surface of the oxide layer acts as the cathode of the capacitor.
Super Capacitors
These are the types of capacitors whose capacitance value is much greater and they can store and deliver charge much faster than the other types of capacitors. As these capacitors are also polarized capacitors, therefore they are also having specific positive and negative polarities.
The types of super capacitors are as follows:
Double Layer Capacitor
It is an electrostatic capacitor. The principle of this capacitor is based on the double-layer capacitance. In an electrical double layer which appears at the interface between a conductive electrode and a liquid electrolyte. Two layers of charge with opposite polarity form at this interface, one at the surface of electrode and one in the electrolyte. These two layers are separated by a single layer of solvent molecules that stick to the surface of electrode and act as dielectric in the capacitor.
Pseudo Capacitor
The charge in the pseudo capacitor is stored faradically by the transfer of charge between electrode and electrolyte. The pseudo capacitor is a part of an electrochemical capacitor.
Hybrid Capacitor
These capacitors are the combination of double layer capacitor and pseudo capacitor. In these super capacitors, the anode is made of pre doped carbon and the cathode is of activated carbon. The lithium-ion capacitor is an example of hybrid capacitor.
Non-Polarized Capacitors
The non-polarised capacitors are the ones that does not have specific positive and negative polarities i.e. they can be connected in the circuits without considering that which lead is connected to the positive and which one to the negative. There are various types of nonpolarized capacitors as follows −
Ceramic Capacitors
When the ceramic material is used as a dielectric medium in the capacitor, the capacitor is called as ceramic capacitor.
Film Capacitors
These types of capacitors have a film substance as a dielectric medium. They are of following types −
Paper Capacitor
The dielectric medium used in paper capacitors is a waxed or oiled paper. The paper is sandwiched in between two thin tin foils sheets and these sheets are rolled into a cylindrical shape and encapsulated in a plastic enclosure.
Metal Film Capacitor
In these capacitors, a paper coated with metallic film is used as a dielectric medium. The metal (aluminium) coated sheets are rolled in the form of cylinder and encapsulated in a plastic enclosure.
Miscellaneous Capacitors
There are some more capacitors which are named according to dielectric material used. Some of them are −
Mica Capacitor
These capacitors consist of a thin mica sheet as dielectric. In these capacitors, a mica sheet is sandwiched in between thin metal sheets, leads are taken out and this whole assembly is enclosed in a plastic enclosure.
Glass Capacitor
In these capacitors, the glass is used as the dielectric medium. These are noise free capacitors with the low temperature coefficient.
Air Capacitor
When air is used as the dielectric medium in the capacitor, the capacitor is known as an air capacitor.
Vacuum Capacitor
In these capacitors, vacuum is used as a dielectric medium.
Variable Capacitors
The variable capacitors are the ones whose capacitance value can altered either electrically or mechanically. The variable capacitors consist of sets of stationary and movable plates. A shaft is attached with the movable plates and by rotating the shaft, the capacitance value can be altered.
There are mainly two types of variable capacitors −
Tuning Capacitors
The tuning capacitors are type of variable capacitor consisting of a set of semi-circular stationary (stator) and movable (rotor) plates, a shaft is attached to the movable plates, and this whole assembly is supported by a frame. The movable plates when moved into the space between the stator plates, they come close to form plates a capacitor. When the movable plates sit completely in between the stator plates, the capacitance value being maximum and when the movable plates are completely out of stator, the capacitance value is minimum.
Trimmer Capacitors
The capacitance of a trimmer capacitor is varied by using a screwdriver. These capacitors consist of two plates: one is stationary and the other is movable and these plates are arranged parallel to each other with a dielectric material in middle.
These capacitors have three terminal leads: one is connected to stationary plate; second is connected to movable plate and the third lead is common. The variation of capacitance value can be observed with the movement of semi-circular shaped movable disc. Trimmer capacitors are frequently arranged on the printed circuit boards so that the user does not have the right of entry to change them.
Depending upon the type of dielectric material used, these types of capacitors are classified into two types −
Air trimmer capacitor
Ceramic trimmer capacitor
Basic Electronics – Variable Capacitors
Basic Electronics – Variable Capacitors
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There are many types of capacitors depending upon their function, the dielectric material used, their shape etc. The main classification is done according to fixed and variable capacitors.
Types of Capacitors
The classification is as shown in the following figure.
The main classification is just like the above one. The fixed capacitors are the ones whose value is fixed at the time of manufacturing itself and the variable ones provide us with an option to vary the value of capacitance.
Variable Capacitors
Let us know something about the variable capacitors whose value alters when you vary, either electrically or mechanically. Variable capacitors in general consists of interwoven sets of metallic plates in which one is fixed and the other is variable. These capacitors provide the capacitance values so as to vary between 10 to 500pF.
The ganged capacitor shown here is a combination of two capacitors connected together. A single shaft is used to rotate the variable ends of these capacitors which are combined as one. The dotted line indicates that they are connected internally.
There are many uses of these variable resistors such as for tuning in LC circuits of radio receivers, for impedance matching in antennas etc. The main types of variable capacitors are Tuning capacitors and Trimmer capacitors.
Tuning Capacitors
Tuning capacitors are popular type of variable capacitors. They contain a stator, a rotor, a frame to support the stator and a mica capacitor. The constructional details of a tuning capacitor are shown in the following figure.
The stator is a stationary part and rotor rotates by the movement of a movable shaft. The rotor plates when moved into the slots of stator, they come close to form plates of a capacitor. When the rotor plates sit completely in the slots of the stator then the capacitance value is maximum and when they don’t, the capacitance value is minimum.
The above figure shows a ganged tuning capacitor having two tuning capacitors connected in a gang. This is how a tuning capacitor works. These capacitors generally have capacitance values from few Pico Farads to few tens of Pico Farads. These are mostly used in LC circuits in radio receivers. These are also called as Tuning Condensers.
Trimmer Capacitors
Trimmer capacitors are varied using a screwdriver. Trimmer capacitors are usually fixed in such a place where there is no need to change the value of capacitance, once fixed.
There are three leads of a trimmer capacitor, one connected to stationary plate, one to rotary and the other one is common. The movable disc is a semi-circular shaped one. A trimmer capacitor would look like the ones in the following figure.
There are two parallel conducting plates present with a dielectric in the middle. Depending upon this dielectric used, there are air trimmer capacitors and ceramic trimmer capacitors. The constructional details of a trimmer capacitor are as shown below.
One of the two plates is movable, while the other is fixed. The dielectric material is fixed. When the movable plate is moved, opposite to the area between movable and fixed electrode, then the capacitance can be changed. The capacitance will be higher if the opposite area gets bigger, as both the electrodes act as two plates of a capacitor.
The Trimmer Capacitors are easily fixed on a PCB (Printed Circuit Board) and they are mostly used for calibration of equipment.
Jennings Vacuum Capacitors
Jennings Vacuum Capacitors
A vacuum capacitor is a capacitor which uses vacuum as dielectric instead of air or other insulating materials. The vacuum dielectric allows a higher voltage rating that an air dielectric.
Jennings Vacuum capacitors
A typical Jennings vacuum capacitor consists of two sets of concentric cylinder plates, one adjustable and the other fixed, are enclosed in an evacuated ceramic envelope with OFHC copper seals at both ends. A flexible metal bellows, attached to a sleeve-type bearing, maintains vacuum while allowing capacitance to vary.
The linear sliding motion required to vary capacitance is converted to rotary tuning via an adjustment screw; in many capacitors, direct pull tuning is an alternative. Internal breakdown voltage is primarily determined by the spacing of the opposing plates and a high vacuum level.
The following are general specifications pertaining to Jennings vacuum capacitors. Current ratings are for normal convection cooling in ambient temperature of 25 °C unless otherwise specified.
Maximum allowable operating temperature — 125 °C (257 °F) for ceramic capacitor
Cooling — natural convection unless otherwise specified
Mounting position — any
Rotation to increase capacity — counterclockwise
If none of our standard catalog models meet your needs, our engineers will work with you to design a custom solution to meet your specific needs.
Features
US9472347B2 – Variable vacuum capacitor – Google Patents
BACKGROUND AND SUMMARY
The present invention relates to the field of variable vacuum capacitors and in particular, but not exclusively, to motorized variable vacuum capacitors.
Vacuum capacitors typically consist of or comprise a vacuum-tight enclosure and a capacitance generating arrangement of conductive surfaces (electrodes) inside the vacuum-tight enclosure. The inner volume is pumped down to a very low pressure (typically lower than 10-6 mbar) and kept low over the entire lifetime of the device (typically years) by the vacuum-tight enclosure. The vacuum ensures rood electrical insulation between the electrodes and very low dielectric losses of the device.
The vacuum-tight enclosure is typically made of two conductive collars (which also serve as the electrical terminals of the device), attached in a vacuum-tight manner to an insulating piece (often a cylindrical-shaped ceramic piece). A vacuum capacitor can be fixed (ie no adjustment of the capacitance value is possible after manufacturing), or it can be made into a variable vacuum capacitor in which the capacitance value can be varied, which is typically achieved by moving one electrode with respect to the other by means of an expansion joint (a bellows, for example). The expansion joint is typically driven by a drive system which also includes a motor and some form of control mechanism. The motor is often constructed as a separate addition to the variable vacuum capacitor. However, a variable vacuum capacitor cannot function without such a means of driving and controlling the variable electrode (and hence the capacitance value).
Most common applications of variable vacuum capacitors include broadcasting (in an oscillation circuit of a high power transmission), as well as plasma controlling processes in the semiconductor, solar and flat panel manufacturing equipment (in so-called impedance matching networks). The adjustment of the capacitance value of a variable vacuum capacitor allows modifying and matching a power supply’s output impedance to the application’s impedance value.
Any part of an electrical circuit responds to the amplitude and phase of an alternative (AC) current. That response (i.e. how it changes the amplitude and/or phase of the current) is described by the impedance which is (in mathematical terms) a complex number made out of a real part and an imaginary part.
High frequency power supplies are manufactured to have standardized impedance values. The standard impedance is 50 Ohms.
High frequency applications (such as plasma processes) called the “loads” of the circuit, can have any impedance value (a+bj) where a and b can be any real numbers and j is defined as the mathematical number whose square equals −1. Typical semiconductor, solar, or flat panel manufacturing require a succession of various plasma processes, which translates into varying load impedances that must be continuously and dynamically matched to the fixed impedance of the power supply.
In impedance matching networks, the function of the variable vacuum capacitor is therefore to equate the following relations at all times (for all loads generated by the applications):
Zpower supply=Zmatching network(C, . . . )+Zload,for any (time-varying) load
50+0j=Zmatching network(C, . . . )+a+jb,for any a,b values of a time-varying load
Where Z designates the complex impedance values of the high-frequency circuit part (the part is indicated as an index).
The impedance of the matching network Zmatching network(C, . . . ) is a function of the capacitance value C of the variable vacuum capacitor, and can also be a function of other components of the matching network, such as inductive, or resistive, or other capacitive components.
If the load is not properly matched at all tunes, the electrical power from the supply is not well transmitted into the load. Unwanted consequences include energy dissipation or energy reflected back into the power supply which can lead to its destruction. By appropriately adjusting the value of the variable vacuum capacitor, the impedance of the matching network can be tuned for optimum power transfer from the power supply to the load.
The means of moving the movable electrode (sometimes also called the “variable electrode”) can be a separate addition to the device or can be integrated into the device. When integrated, the variable vacuum capacitor is sometimes explicitly referred to as a “motorized variable vacuum capacitor” In any case when comparing the size or speed or other characteristic of the variable vacuum capacitor device, one should always consider the entire system made of “motor ±variable capacitor device”, as both are required in applications.
Known variable vacuum capacitors typically have a bellows which must serve three functions: it must provide a reliable vacuum seal, it must be capable of extending and contracting to allow movement of the movable electrodes, and it must also carry the electrical high-frequency current from the terminal to the movable electrode. This limits the choice of material for the bellows to very few options, as it must be optimized simultaneously for electrical characteristics and for mechanical characteristics. Even with a good choice of material, the long path of the electrical current along the bellows (high-frequency currents are forced to flow along the surface of conductors, a phenomenon known as “skin effect”) can result in considerable electrical losses inside a very critical part of the device, therefore generating undesired heat and an additional parasitic electrical resistance to the capacitive device. Such elevated temperatures and thermal cycling will reduce the total number of duty cycles of the expansion joint, thereby reducing the operating lifetime of the variable vacuum capacitor.
Japanese patent application JP10284347A proposed a variable vacuum capacitor which makes use of two bellows to mitigate the aforementioned inconvenience. Patent document U.S. Pat. No. 6,473,289 (B1), on the other hand, proposed to eliminate the bellows completely and substitute its fictions with other parts and a different layout of electrodes inside the vacuum enclosure.
Patent application US2005052820A, from the present applicant, proposed the use of two series-connected sets of electrodes arranged adjacent to each other in the radial direction. This arrangement results in a rather large diameter device, because a large space in needed in the plane perpendicular to the movement of the variable electrode (to achieve a reasonably high capacitance value). Such a design is discussed in more detail below, with reference to FIG. 2 .
A variable vacuum capacitor described in patent application U.S. Pat. No. 3,611,075 A suffers from the same disadvantage, namely that the two fixed electrodes and the two variable electrodes are positioned next to one another in the radial direction. For a given diameter of the device, the capacitance that can be achieved is thus inferior in those prior designs which do not use series-connected electrode sets. Another inconvenience of these devices disclosed in US2005052820A and U.S. Pat. No. 3,611,075 is that, because the electrode radii of the inner set of electrodes are substantially different from the radii of the outer set of electrodes, it is difficult to manufacture the outer and inner electrode sets to have equal capacitance. One must for example adapt the number of turns and/or the length of the inner electrodes as compared to those of the outer electrode.
A further inconvenience of many prior art variable vacuum capacitors is that the motor must be well insulated from the movable electrodes, because the motor is mounted on or near a high voltage terminal of the device. To avoid high voltage discharges from that terminal on to the motor, and to avoid other electrical, interference between the high voltage terminal and the much lower voltage of the motor it is necessary to use a long insulating part, which adds significantly to the overall size of the device.
The variable vacuum capacitor of an aspect of the invention aims to address these and other problems with prior art devices. It is desirable to provide a variable vacuum capacitor having:
an increased serviceable lifetime,
improved voltage and current handling characteristics as compared to those obtained with prior art devices having similar size and capacitance, and/or
a smaller diameter and/or length (eg having capacitative electrodes which can fit into a smaller cylindrical volume with small cylindrical diameter).
In particular, an aspect of the invention foresees a variable vacuum capacitor comprising:
a vacuum enclosure,
a first variable electrode assembly comprising one or more first static electrodes and one or more first mobile electrodes,
a second variable electrode assembly comprising one or more second static electrodes and one or more second mobile electrodes,
a first electrical connection terminal for providing an electrical connection to the one or more first static capacitor electrodes,
a second electrical connection terminal for providing an electrical connection to the one or more second static capacitor electrodes,
displacement means for displacing the first and/or second mobile electrodes relative to the first and/or second static electrodes respectively, along an axis of the vacuum capacitor,
the variable vacuum capacitor being characterized in that
the first and second electrode assemblies are ganged along the axis such that the first mobile electrode assembly is offset along the axis by a gang offset distance from the second electrode assembly, and
the variable vacuum capacitor comprises mobile electrode linkage means for providing a kinematic linkage between the one or more first mobile electrodes at a first position along the axis and the one or more second mobile electrodes at a second position along the axis, such that a first displacement of the one or more first mobile electrodes along the axis results in a second displacement of the one more second mobile electrodes along the axis.
By arranging the first and second electrode assemblies in to linearly ganged configuration, the diameter of the device can be significantly reduced. It is also possible to avoid the need for any electrical connection to any moving parts such as the mobile electrodes, which means that the bellows are not required to act as electrical conductors and can be made of a material which is more suited to the mechanical function. This in turn can significantly extend the working life of the device.
According to a variant of the variable vacuum capacitor of an aspect of the invention, the mobile electrode linkage means is arranged such that the magnitude of the second displacement is the same as the magnitude of the first displacement. The mobile electrode linkage means can for example be a simple, rigid structure which provides a direct mechanical link between the two sets of mobile electrodes, thus enabling a simple and robust construction and reducing the possibility of stray capacitance due to the linkage geometry.
According to another variant of the variable vacuum capacitor of an aspect of the invention, the mobile electrode linkage means comprises electrical connection means for electrically connecting the one or more first mobile electrodes to the one or more second mobile electrodes. Combining the two functions of mechanically and electrically connecting the mobile electrodes further reduces the complexity of the device.
According to another variant of the variable vacuum capacitor of an aspect of the invention, the displacement means comprises a motor outside the vacuum enclosure, and drive transmission means for transmitting a drive force of the motor through a wall of the vacuum enclosure to the on or more first mobile electrodes inside the vacuum enclosure. Since the bellows and the outer surface of the device is insulated from the electrodes, the motor can be mounted much closer to the device (eg on the outer surface of the wall of the vacuum enclosure), which can significantly reduce the overall size of the device.
According to another variant of the variable vacuum capacitor of the an aspect of invention, motor protection insulation can be included to electrically insulate the motor against a high voltage on the one or more first mobile electrodes.
According to another variant of the variable vacuum capacitor of the an aspect of invention, the motor protection insulation is arranged between the drive transmission means and the one or more first mobile electrodes.
According to another variant of the variable vacuum capacitor of the an aspect of invention, the one or more first mobile electrodes and the one or more first static electrodes are substantially cylindrical and coaxial with the axis, such that the one or more first mobile, electrodes are at least partially interleaved with the one or more first static electrodes, and/or
the second mobile electrodes and the one or more second static electrodes are substantially cylindrical and coaxial with the axis, such that the one or more second mobile electrodes are at least partially interleaved with the one or more second static electrodes.
According to another variant of the variable vacuum capacitor of an aspect of the invention, the one or more first mobile electrodes and the one or more first static electrodes are configured as spiral electrodes, and/or wherein the one or more second mobile electrodes and the one or more second static electrodes are configured as spiral electrodes.
According to another variant of the variable vacuum capacitor of an aspect of the invention, the mobile electrode linkage means comprises a substantially cylindrical element arranged around the outside of the first electrode assembly and arranged coaxially with the one or more first mobile and one or more first static electrodes.
The substantially cylindrical element may be at least partially constructed from an electrode material and arranged sufficiently close to an outer one of the one or more first static electrodes to function at least partially as one of the one or more first mobile electrodes. This refinement offers a simple, robust structure which also contributes to an increase in the maximum variable capacitance of the device.
According to another variant of the variable vacuum capacitor of an aspect of the invention, the substantially cylindrical element comprises open regions, and wherein one or more static electrode support elements extend from the first static electrodes, through the openings, to the wall of the vacuum enclosure.
According to another variant of the variable vacuum capacitor of an aspect of the invention, its insulating parts are made at least partially of a ceramic material.
According to another variant of the variable vacuum capacitor of an aspect of the invention, extensible vacuum sealing means (eg bellows) extend between the first electrode assembly and the wall of the vacuum enclosure, the extensible vacuum sealing means being constructed with such a shape and of such materials that it behaves as an electrical insulator, at least when the variable vacuum capacitor is operating at a high voltage and/or at a high frequency.
According to another variant of the variable vacuum capacitor of an aspect of the invention, the one or more first static and the one or more first mobile electrodes have substantially the same dimensions and spatial configuration as the one or more second static and the one or more second mobile electrodes respectively. This variant has two principal benefits: firstly, that the manufacture of the device can be significantly simplified by only requiring tooling for one electrode configuration, and, secondly, that using identical or similar first and second electrode assemblies results in an even distribution of capacitance between the two assemblies, thereby minimising the voltage on the mobile electrodes, which means that the device can operate at a higher applied voltage.
BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in detail, with reference to the accompanying drawings, in which: FIG. 1 shows in schematic, sectional view, a simple prior art variable vacuum capacitor having a single pair of electrodes. FIG. 2 shows in schematic, sectional view, a prior art variable vacuum capacitor have two sets of electrodes arranged electrically in series, and mechanically in parallel. FIG. 3 shows in schematic, sectional view, an example of a variable vacuum capacitor according to an aspect of the invention, having two sets of electrodes arranged electrically and mechanically in series.
The figures are provided for illustrative purposes only, and should not be construed as limiting the scope of the claimed patent protection. Where the same references have been used in different drawings, they are intended to refer to similar or corresponding features. However, the use of different references does not necessarily indicate that the features to which they refer are different.
DETAILED DESCRIPTION
FIG. 1 illustrates the configuration of a simple variable vacuum capacitor as known in the prior art. Such a vacuum capacitor typically consists of or comprises two conducting high voltage terminals, 24 and 9, attached to an insulating cylindrical vacuum enclosure wall, 26, in a vacuum-tight manner. Increasing the overlap area of electrodes, 7 and 8, and/or decreasing their separation, increases the capacitance value of the device. The electrodes 7 and 8 are conductively attached to the terminals 24 and 9 respectively. In order to vary the capacitance of the variable vacuum capacitor device, one electrode, 7, is moved with respect to the other. This is typically achieved by means of an expansion joint (bellows, 5) and a drive system, 16, 12 whose motion is controlled by an electrical motor, 1, such as a stepper motor.
As mentioned above, the bellows 5 have a triple function: while transmitting the movement to the movable electrode, 7, they must also carry the electrical high-frequency current from the terminal, 24, to the movable electrode, 7, while also separating the vacuum from the chive system, which is at atmospheric pressure. This limits the choice of material for the bellows, 5, to very few options, as it must be optimized simultaneously for electrical characteristics and for mechanical characteristics. Even with a good choice of material, the long path of the electrical current along the bellows, 5, (high-frequency currents are forced to flow along the surface of conductors, a phenomenon known as “skin effect”) can result in considerable electrical losses inside a very critical part of the device, thereby generating undesired heat and an additional parasitic electrical resistance to the capacitive device. Such elevated temperatures and thermal cycling will reduce the total number of cycles the expansion joint, 5, will work, thereby reducing the operating lifetime of the variable vacuum capacitor.
FIG. 2 shows a schematic representation of a series electrode arrangement known in the prior art (eg US2005052820 A1).
Two concentric electrode sets, 7, 8 and 17, 18 are arranged, one outside the other, in the same plane, with a common support element 22 supporting all the mobile electrodes 7, 17. To increase the capacitance, the height and number of the electrode surfaces must be increased, which means increasing the dimensions of the device. Alternatively, the spacing between the electrodes can be decreased, which leads to a lower maximum operating voltage of the device.
Connections to the variable vacuum capacitor are made at the end surfaces 13 and 14, which are connected internally to the static and mobile electrodes 18 and 17 respectively. The bellows, 5, are at least partially made of an insulating material such that no current can flow between the mobile electrodes 22, 17 and the upper terminal 14.
FIG. 3 shows an example of a variable vacuum capacitor according to an aspect of the invention. The required capacitance is generated by means of two electrode assemblies, 17, 18, 21, 23 and 7, 8, 11, 13. Each electrode assembly comprises one or more movable 7, 17 and one or more fixed 8, 18 electrodes. Each set of electrodes may be for example be constructed as one or more concentric cylinders or as a spiral having one or more turns.
One set of static electrodes, 18, is shown supported by a support element, 23, secured to the wall 4 of the vacuum enclosure. The other set of static electrodes, 8, is shown supported by the end cap 13 of the vacuum capacitor and the end terminal 9.
One mobile sets of electrodes 17 is shown supported by electrode support 21, which is in turn supported by insulator 2 and insulating, bellows 5 and motor drive 12, 16. Electrode support 21 is mechanically and electrically connected by a connecting means, 10, denoted by dashed line, to the electrode support 11 of the lower mobile electrodes 7. In the simple case, the connecting means may be a simple, rigid element such as a cylinder of copper. In this case, the wall of the cylinder is provided with openings so as to allow the cylinder 10 to move up and down parallel to the longitudinal axis A of the device without interfering with the electrode support 23, which has one or more arms or other support structures for securing to the wall 4 of the vacuum enclosure.
The series connection of the two electrode assemblies means that the current which flows to and from the terminals is obliged to follow a path which does not include any moving parts such as bellows. Moreover, instead of being at opposite ends of the variable vacuum capacitor, the two high voltage terminals of the device can be placed at or towards one end of the device, for example in a region at a mid-point along the length of the device at the lateral cylinder periphery.
Siting the terminal 4 at a mid-way point on the length of the vacuum enclosure also means that the current path from the terminal to the static electrodes 18 is short and direct, which in turn minimises unwanted EMC emissions and thermal dissipation.
In this way, the variable vacuum capacitor has an end portion 14 to which the motor assembly 1 can be mounted, at least a portion which is essentially free of the influence of the high voltages present at either end of a conventional variable vacuum capacitor.
FIG. 3 shows the motor mounting terminal 14 separated from the high voltage terminals 4 by an insulating vacuum enclosure part, 6. Because the bellows do not carry current, they also do not need to be electrically conducting, and therefore motor mounting terminal 14 is also insulated from the electrodes 7. Alternatively if one still uses a conducting bellows 5, then an insulating part 2 at either end of the bellows 5 would insulate the motor terminal 14 and motor 1 from the electrodes 7. Because this insulating part is in vacuum, it does not need to be as large as the motor-insulating part 19 used outside the vacuum in prior art (see FIGS. 1 and 2 ).
The advantage provided by being able to mount the motor directly on the vacuum capacitor enclosure makes the motorized variable vacuum capacitor of the present invention more compact and/or frees space to be filled with electrodes inside the vacuum. This is turn results in higher achievable capacitance values and higher achievable maximum operating voltages.
In FIG. 2 , electrode pairs are shown mounted in series, co-axially, each electrode of each pair mounted one above the other along a single axis corresponding to the movement axis, A (there are no “inner” or “outer” electrodes, as there are in the device shown in FIG. 2 ), resulting in a small diameter (perpendicular the movement axis) similar to the devices of prior art not using a serial geometry (such as those of FIG. 1 ) and resulting in a smaller diameter as the devices of prior art using a serial geometry (such as those of FIG. 2 ).
At the same time, the voltage capability of a serial geometry is increased between the two high voltage terminals, 4 and 9, because the total voltage splits between the different pairs of electrodes in series. For example, in the example embodiment shown in FIG. 3 , the voltage between the conducting surfaces 4 and 17 and the voltage difference between the conductive surfaces 7 and 9 are half the voltage difference applied across the terminals 4 and 9 of the variable vacuum capacitor. This voltage splitting, which is a consequence of mounting electrodes in series, is advantageous because it permits smaller electrode separation without risking voltage breakdowns in the vacuum; and thanks to the smaller electrode separation achievable, the capacitance value can be significantly increased.
In the example shown in FIG. 3 , both movable electrodes 7 and 17 are shown connected by a conducting piece (10), preferably made of a good electrical conductor and preferably structured as a rigid tube-shaped part having a diameter similar but bigger than the outermost surface of the fixed electrode, therefore generating an additional capacitative contribution.
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