Product Announcement from Oren Elliott Products, Inc.
Standing 4.5" high by 4.5" wide, with typical lengths of over one foot, the M90 is Oren Elliott Products' largest standard configuration of air-dielectric variable capacitor in terms of physical size, and can withstand voltages of up to 11000Vrms.
The latest revision of the M90 incorporates many of the improvements included in the M73A: Non-magnetic construction, ABEC-5 instrument bearings, clean-room assembly, a high-amperage rotor contact, and so on. This is a high-quality unit meant to give design engineers an alternative to vacuum variables in applications that involve high voltage (on the order of 10kV) and relatively small maximum capacitance.
The M90 configuration can be fitted with three types of high-amperage wiping contacts: the strap contact, the high-current (silver brush) contact, and the high-current (beryllium copper) contact. In some cases, capacitors can be fitted with two high-amperage contacts, one at each end, doubling the amperage rating of the capacitor. The choice of wiping contact depends upon the anticipated current load and desired life cycle.
Limitations of the design (and more often limited space in the customer's device) limit the length, and thus the number of blades and the maximum capacitance, that can be achieved with a given air gap. For an air gap capable of withstanding 10kV, for example, the highest maximum capacitance that would be practical would be around 100pF.