Trimmers

There are two types of Trimmer capacitors: air trimmers and ceramic trimmers. These two types use different materials as the dielectric. Both types use a rotating action to change the capacitance value. The construction of trimmer capacitors is similar to the construction of their larger variant, the variable capacitor. 

Trimmer capacitors are constructed in two ways. One is they are made with overlapping semi-circular metal plates. One is fixed, while the other can be rotated. The user can change the capacitance by rotating the shaft and increasing or reducing the amount of overlap between the two plates. 

The other way to make a trimmer capacitor is to place a metallic screw in a non-conductive threaded cylinder. The screw represents one electrode, while the other is located at the base of the cylinder. By rotating the screw, the distance between the two plates is varied which results in a change of capacitance. This construction is used in RF and microwave applications.