Variable Vacuum Capacitors

30 to 4,000 pF; 1.8 to 36 kV

Vacuum capacitors for high voltage and high frequency applications offer long, maintenance-free service life and the ability to withstand transients that destroy other types of capacitors. Vacuum assures oxidation-free surfaces and a dielectric that is self-healing when subject to transient over-voltage conditions.

This series of variable vacuum capacitors offers capacitances of 30 to 4,000 pF, withstanding working voltages at 50/60 Hz in the range of 1.8 to 36 kV. In addition to this working voltage, a value for AC test voltage is quoted in this series’ product specifications. The maximum operating current for vacuum capacitors is limited by temperature rise and working voltage. A current vs. frequency chart is provided for each capacitor.

If none of our standard catalog models meet your needs, our supplier`s engineers are happy to work with you to design a custom solution that meets your specific requirements.

Capacitance Tolerance: For this series of variable capacitors, the low-end capacity will be equal to or less than minimum rating. The capacitance change is substantially uniform with rotation, and there are no capacitance reversals. Capacitance is within ±10% of the nominal value of the curves shown in the data sheet (capacity vs. turns), in the linear portion of this curve.

Torque/Direct Pull: In variable capacitors, the linear sliding motion of the moving electrode assembly is converted to rotary tuning via a threaded shaft. The torque values given in the tables are the maximum torque needed to reach minimum capacitance when rotated with a standard lead screw; the torque required to tune away from minimum may be less than half this value. For most variable capacitors, direct pull tuning is an available option to rotary tuning. Maximum required direct pull force values are also given in the tables. Capacitance range end-stops are built into every variable capacitor. It is recommended that the user install their own external stops to prevent damage from gear-reduction drives.

Mechanical Life: The mechanical life of variable capacitors is related to length of stroke, speed of operation, bellows material and total number of cycles. Extensive mechanical life tests have been run, operating units for complete cycles from maximum to minimum and back to maximum capacity covering 95% of the full stroke of the movable plates. Capacitors with a large bellows and a short stroke will have the greatest life expectancy under cycling operation. Our most recent variable capacitor models are rated for >2 million cycles, ideal for the semiconductor processing industry.

Testing Standards: All capacitors are factory tested for dielectric strength on a 100% basis prior to shipment, using a low current, high potential source at 60 Hz voltage. Upon customer request, certified test reports will be made available.

Key Features:

• High Voltage Rating
• High RF Current Ratings for normal convection cooling in ambient temperature of +25 °C (unless otherwise specified)
• Maximum Allowable Temperature: +125 °C
• Low Losses
• Self-healing
• High Altitude Operation
• Wide Tuning Ranges
• Mounting Position: Any
• Rotation to Increase Capacity: Counterclockwise

Typical Applications: Broadcast Radio Transmitters; Semiconductor Manufacturing Equipment; Plasma Generating Equipment; Industrial Dielectric Heating Equipment; Power Switching and Interrupting; Avionic and Mobile Radio Systems; Radar Antenna Switching; MRI and NMR; High Voltage Capacitor Banks