trimmer capacitor[′tim·ər kə‚pas·əd·ər]
in radio engineering, a capacitor with a low variable capacitance that can be set at a certain value. Trimmer capacitors are used mainly to effect the alignment of resonant oscillatory circuits. As a rule, the capacitance of a trimmer capacitor is set during the fabrication of a radio-electronic device. After such setting, the movable parts of the trimmer capacitor are locked in place and remain in their fixed positions while the device is operating. A trimmer capacitor is generally a simplified parallel-plate variable capacitor with one stator plate and one rotor plate; less frequently, it may be, for example, a system consisting of two or more concentric ceramic cylinders or metal plates with an air gap or a system consisting of a rod and a metal-plated ceramic tube. The capacitance of a trimmer capacitor and the range in which the capacitance may be varied usually amount to several picofarads or several tens of picofarads.