Air dielectric capacitors are used mainly as laboratory standards of capacitance for measurement purposes. The insulating material used in these capacitances is fused silica and the whole capacitor is shielded in the metal case. They are very accurate (0.01 to 0.02%) but their size is large. The construction is parallel plate or concentric cylinder type. Plates are circular, square or triangular in shape. These metallic plates are insulated from each other and separated by air.
Specifications
Range of values 50pf to 10000pf
Tolerance 0.01 to 0.05%
Temperature coefficient 10ppm/0C
Applications: As residual inductance and resistance is low, they can be used at high radio frequencies. Also can be used a high voltage laboratory standards.