Variable Vacuum Capacitor

Product overview

 

A variable vacuum capacitor changes capacitance by moving one electrode group relative to another inside a sealed vacuum body. It is installed in long-wave, medium-wave and short-wave transmitters, RF matching networks, high-frequency induction heating systems, medical RF equipment and other high-voltage tuning or neutralization circuits. Unlike a fixed model, it is used when capacitance must change during setup, frequency selection or load matching.

Tuning ranges extending to 400 or 500 pF

The two listed models tune from below 10 or 15 pF to 400 or 500 pF. In RF matching and induction-heating circuits, this span lets the same capacitor cover setup changes and load variation within the selected model range.

Up to 20 kV working voltage and 120 A RF current

The higher-rated model combines 20 kV high-frequency peak working voltage, 28 kV peak test voltage and 120 A at 13.56 MHz. This supports tuning positions where substantial RF voltage and current occur at the same operating point.

23 to 26 turns for controlled adjustment

Mechanical travel is distributed over 23 or 26 turns with maximum torque of 0.2 to 0.5 N·m. Near resonance, the multi-turn mechanism provides smaller capacitance changes per shaft movement than a short-travel adjustment.

The capacitor consists of a ceramic vacuum envelope, metal end fittings, concentric oxygen-free copper electrode groups and an external adjustment mechanism. One electrode group remains stationary. The other moves axially, changing electrode overlap and capacitance.

A metal bellows, or an equivalent motion seal, carries the mechanical movement through the enclosure without breaking the vacuum boundary. Shaft, bearings, terminals and mounting parts are selected for the required travel, tuning direction and installation method. Models carrying higher current may also have a dedicated cooling connection.

Capacitance range and tuning response

The custom specification can define minimum and maximum capacitance, adjustment ratio, mechanical travel and number of turns. The useful range is then checked against the equipment frequency band and circuit load.

Drive, cooling and installation interface

Shaft shape, tuning direction, mounting dimensions, terminal position and connection method can be adjusted for the equipment layout. The cooling arrangement is selected separately according to RF current and the amount of heat that must be removed.

Electrode alignment and sealing

Before sealing, the fixed electrodes, moving electrodes, bellows and drive parts are assembled to the confirmed model. Alignment and travel are checked through the intended movement so the electrodes do not touch, overlap unevenly or interfere with the ceramic body.

Electrical and mechanical checks across the range

Capacitance is measured at several positions across the range, including intermediate points. Insulation, voltage withstand, adjustment continuity and mechanical operation are also checked before the finished capacitor is assigned to its production batch.

A separate assembly route for variable structures

Variable capacitors are built on their own assembly route; they are not fixed capacitors with an adjustment part added later. Moving electrodes, bellows, drive components and the vacuum envelope follow a sequence developed for the approved tuning structure.

Sample and batch production in one facility

Wanping's in-house R&D team reviews the electrical rating, equipment fit and mechanical layout before a sample is built. Once the sample is approved, its drawing, model and configuration are used for batch production in the same facility.

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