As you already know, capacitors are essential circuit elements for storing and suppling charge on demand. For inductors and resistors, capacitors act as the building blocks of passive circuits and the supporting components for active circuits. While a wide range of fixed-value capacitors are used in most electrical circuits, it is sometimes preferable, or necessary, to use a component with a variable capacitance range.
These variable capacitors are known as trimmer capacitors because these capacitors can be used to trim the performance of both active and passive circuits. These components allow for variable tuning – think oscillator frequency values or rise and fall times. Additionally, if values drift over the life of a device, trimmer capacitors can be recalibrated as needed. For sensitive applications like magnetic resonance imaging (MRI), these components help optimize performance where any instability in time or temperature could impact the image output.