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Vacuum Capacitors

Technical information

Operational Precautions and Characteristic

Peak Test Voltage at 50/60 Hz

This refers to a limit value of dielectric breakdown voltage between electrodes. Before shipment, MEIDEN checks the vacuum capacitors to confirm that no dielectric breakdown occurs when the rated voltage is applied for the specified time.

Peak RF Working Voltage

This refers to the rated voltage value capable of being applied continuously. The peak RF working voltage is set at 60% of the peak test voltage.

Maximum Permissible Current

This is the maximum rated current capable of being carried continuously. At higher frequencies, the maximum permissible current decreases with a greater loss due to the skin effect. The maximum rated current is defined as follows:


Capacitance adjustment

Vacuum variable capacitors can be adjusted to any capacitance value within the specified range by the linear sliding motion of the moving electrode assembly, which is converted to the rotary tuning via the capacitance adjustment shaft. Capacitance decreases with rightward (clockwise) rotation of the shaft and can be adjusted to the minimum capacitance in the end-stop position. Likewise, capacitance increases with leftward (counterclockwise) rotation and can be adjusted to the maximum capacitance in the end-stop position. Although two capacitance range end-stops are incorporated into every variable capacitor, please note that the motor should not collide with the maximum capacitance end-stop. Otherwise, it may impair the screw.

The permissible collision torque value at the minimum capacitance end-stop is as follows:

VM Type…40N · cmVT Type…40N · cmVH Type…40N · cm


Life span

  1. For variable capacitors, the life span depends on the expendable bellows material and the capacitance adjustment mechanical part.
  2. Please use the variable capacitors within the range that does not exceed the total number of tuner turns. Exceeding any of the conditions below may result in an extreme decrease in the life span.

    - High acceleration (greater than 30min-1/ms)
    - Ultra-small motion (less than several degrees)
    - High speed (greater than 600 min-1)

  3. Re-greasing is recommended after every 200,000 cycles. (Definition of Re-greasing: spreading the uneven coating of grease uniformly over the entire screw surface) Please re-grease the whole operating range; otherwise, re-greasing may be less effective in performance. Re-greasing is recommended when giving the capacitors a prolonged rest or using them after storage.