How Do I ID Disc Capacitors?

Because disc capacitors are small, the value code on their casing is abbreviated.

Disc capacitors are thin, tan-colored, disc-shaped electronic components that are a few millimeters in diameter and possess two wire leads. Inside a disc capacitor are two metal films sandwiching a thin ceramic plate that serves as a dielectric between the two charged metal films. A plastic or epoxy coating encases the metal and ceramic components. Printed on the casing is a capacitor's capacitance value, usually rated between 1 picofarad to 0.1 microfarad. In comparison to larger-sized capacitors with capacitance values clearly indicated on the casing, a disc capacitor's value is cryptic and requires a simple decoding of the printed values.

Things You'll Need

• Magnifying glass

Instructions

1. Using a magnifying glass, find the number/letter code on a ceramic disk capacitor. Typically, it is a three-digit number followed by the letter K or M.

2. Write down the first two digits of the three-digit code. The third digit of the code is the number of zeroes to write following the first two digits. For example, a code that reads 103 would be the numbers one and zero followed by three zeroes. Disc capacitor values are expressed in picofarads. Therefore, using this system, if the code reads 103, then the value is 10,000 picofarads (pf). If the code reads 100, then the value is 10 pf because the third digit is zero, meaning that no zeroes follow the first two digits of the code.

3. The letter following the three-digit number code is either a K or an M. K and M represent a variance of plus or minus 10 percent and 20 percent, respectively. Therefore, a disc capacitor with 103K printed on it has a value within the range of 9,000 pf to 1,100 pf.

References

• "Basic Electricity and Electronics"; Charles Schuler, Richard Fowler; 1988