What is ceramics? In everyday life, this is the name for products made by firing a mass, mainly clay. In technology, ceramic materials mean materials with a similar structure, although there is no clay in them at all, or it is present in small quantities. These include capacitor ceramics used as a dielectric in capacitors.
Ceramic capacitors
These products are characterized by high electrical performance, small size and low cost. Ceramic capacitors are widely used in the circuits of radio equipment. They come with fixed capacity and trimmers.
Types of fixed capacitors
Thermostable ceramic capacitors are used in high stability oscillator and local oscillator circuits. Thermal compensating elements are used to restore the temperature. A special group consists of ferro-ceramic capacitors, in which ferro-ceramic is used as a dielectric - a material with a very high dielectric constant (up to several thousand) incertain temperature range. The mentioned products differ from high-frequency ceramics in their higher capacitance at the same dimensions.
Ceramic tubular condenser (CT-1, CT-2) is a thin-walled tube, the outer and inner surfaces of which are coated with a layer of silver.
Ceramic disk capacitor (KD1, KD2) and disk ferro-ceramic models (KDS1, KDS2, KDS3) are a round ceramic plate with a lining in the form of thin layers of silver.
Ceramic molded plastic barrel element (KOB1, KOB2, KOB3) is a ceramic cylinder, on the base of which linings are also applied.
Color scale and its meaning
Different colors in which products of KT, KDS, KD, etc. are painted, indicate the stability of their capacity when the temperature changes. Blue, blue and gray paint is used if the capacitance of the capacitor reacts insignificantly to temperature changes. Such elements are called thermostable. Red and green colors mean that as the temperature rises, the capacity of the products will noticeably decrease - these are thermocompensating capacitors. The orange color indicates that in the event of a change in temperature over a wide range, the capacity of the product will change quite strongly (however, at room temperature, the capacity remains stable).
Types of ceramic trimmer capacitors
These items are designed to fit (fit)parameters of oscillatory circuits, they are also called semi-variables. Let's look at each one briefly.
The ceramic tuning capacitor (CPC) consists of a ceramic base (stator) and a ceramic movable disk (rotor). The disk on the axle is attached to the stator and can be rotated with a screwdriver. Sector-shaped silver plates are applied on the planes of both components. The rotor material is a dielectric. During rotation, the relative position of the plates changes, respectively, and the capacitance between them.
Tubular ceramic tuning capacitor (KPT) - the name itself indicates that the product in question has the form of a tube. Its inner surface is also coated with a thin silver fixed lining - a metal rod with a screw thread. When rotated (achieved with a screwdriver), the capacitance is changed by inserting or withdrawing the rod from the tube.
Capacity of ceramic capacitors
Even 10-20 years ago, due to the difficulties associated with the production of the mentioned capacitors, the products were classified as small-capacity devices. More recently, a 1 uF ceramic capacitor would not surprise anyone, but a 10 uF element was perceived as exotic.
But today, the development of technology has allowed some manufacturers of radio components to declare that they have reached the capacitance limit in such capacitors up to 100 microfarads, but, as they assure, this is not the limit yet.
