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392 COMMON ELECTRONIC COMPONENTS FOR ROBOTICS

G In older books and magazines on electronics you may see microfarad shortened to mfd.
Example: 10 mfd is 10 microfarads (10 F). Mfd isn’t used as much today, but it’s good to
know what it means in case you want to try out an older circuit you find at the library.

HOW CAPACITORS ARE MARKED
Capacitors are routinely marked with at least their capacitance value; many capacitors are
also marked with value tolerance notation and a breakdown voltage. Additionally, capacitors
that are polarized— they have a + and a lead— also carry a polarization marking.

Capacitance Value
The capacitance values for some capacitors are printed directly on the component. This is
true of larger capacitors with values of 1 F or higher, if for no other reason than that their
larger physical size allows the manufacturer to directly print the value on the component.
But for other capacitors, things aren’t always so simple. Smaller capacitors often use a
common three- digit decade marking system to denote capacitance. The numbering system is
easy to use if you remember it’s based on picofarads, not microfarads.
A number such as 104 means 10, followed by four zeros, as in

100,000

or 100,000 picofarads. To make the conversion, move the decimal point to the left six
spaces: 100,000 becomes 0.1. Therefore, that 104 capacitor is 0.1 F, or 100 nF. Note that
values under 1000 picofarads do not use this numbering system. Instead, the actual value, in
picofarads, is listed, such as 10 (for 10 pF).Table 31- 2 provides a quick glance at how several
common capacitor number markings convert to their F (microfarad) equivalents.

Table 31- 2 Capacitor Value Reference

Marking Value ( F) Marking Value ( F)

xx (number from xx pF
01 to 99)
101 0.0001 331 0.00033
102 0.001 332 0.0033
103 0.01 333 0.033
104 0.1 334 0.33
221 0.00022 471 0.00047
222 0.0022 472 0.0047
223 0.022 473 0.047
224 0.22 474 0.47

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