How to calculate the value of a ceramic capacitor

You might have come across situations were you needed to calculate the value of a ceramic capacitor. Today a large variety of such capacitors are available in the market but the value calculation of all remains the same. All these capacitors are marked with a three digit number code, say, 104. There are two key points to remember in the value calculation. First point is that in the marked number code the first two digits are the significant digits and the third digit is the multiplier. The second point is that the final value is in the 'pico Farad' unit (without conversion).

For example, a value 104 on the capacitor indicates that the value of the capacitor is 10 x 10⁴ pF or 100 nano Farads (μF) or 0.1 micro Farads (μF). Some other codes and their corresponding values are given below:

Capacitor Code	Value in pF	Value in μF
101	100	0.0001
102	1000	0.001
103	10000	0.01
104	100000	0.1
105	1000000	1

For some capacitors there will be an additional alphabet code at the end of the number marking say 104J. This alphabet code indicates the capacitor tolerance. The tolerance values are calculated as given in the table below

Code	Tolerance
C	±0.25pF
J	±5%
K	±10%
M	±20%
D	±0.5pF
Z	+80% / -20%

For example, 104J coded capacitor has the value 0.1 ± 5% μF. 
For a 104C coded capacitor, the value is 0.1 μF ± 0.25pF

How to Design an Air Core Inductor

An air core coil inductor is made by winding several turns of enameled wire around a none ferromagnetic material core (like plastic, ceramic, or other non-magnetic forms, as well as only with air inside the windings).

These coils have lower inductance compared to the ferromagnetic core coils. Despite of this characteristic, air core coil inductors are often used at high frequencies because they are free from energy losses called core losses that occur in ferromagnetic cores (which increase with frequency).

In air core coils with winding not rigidly supported on a form (core), a side effect called 'microphony' may occur. 'Microphony' refers to the mechanical vibration of the windings which in-turn causes variation in the coil inductance.

The major advantages of air core coils are:

1. The inductance is independent of the electrical current through the coil since there is no ferromagnetic core to get saturated as the current increases.

2. There is no iron loss as in case of ferromagnetic cores, thus giving a better Q Factor and low distortion with increased frequency.

3. They can be operated at high frequencies (upto 1 Ghz).

The inductance of an air core coil inductor can be calculated using the equation shown in the above figure.

here,

    L = Inductance (in uH)
    a = Diameter of the coil (in Inches)
    b = Length of the coil (in Inches)
    c = Diameter of the winding wire (in Inches)
    n = Total turns of wire

Note: The formula is valid only if the value of b is greater than 0.4a.