Handbook for Sound Engineers

Resistors, Capacitors, and Inductors 255

or picofarads (pF or 10^12 farads) with a stated accuracy
or tolerance. Tolerance is expressed as plus or minus a
certain percentage of the nominal or nameplate value.
Another tolerance rating is GMV (guaranteed minimum
value), sometimes referred to as MRV (minimum rated
value). The capacitance will never be less than the
marked value when used under specified operating
conditions but the capacitance could be more than the
named value.

Equivalent Series Resistance (ESR). All capacitors
have an equivalent series resistance expressed in ohms
or milliohms. This loss comes from lead resistance,
termination losses, and dissipation in the dielectric
material.

Equivalent Series Inductance (ESL). The equivalent
series inductance can be useful or detrimental. It does
reduce the high-frequency performance of the capacitor.
However, it can be used in conjunction with the capaci-
tors capacitance to form a resonant circuit.

Dielectric Absorption (DA). Dielectric absorption is
a reluctance on the part of the dielectric to give up
stored electrons when the capacitor is discharged. If a
capacitor is discharged through a resistance, and the
resistance is removed, the electrons that remained in the
dielectric will reconvene on the electrode, causing a
voltage to appear across the capacitor. This is also
called memory.
When an ac signal, such as sound, with its high rate
of attack is impressed across the capacitor, time is
required for the capacitor to follow the signal because
the free electrons in the dielectric move slowly. The
result is compressed signal. The procedure for testing
DA calls for a 5 min capacitor charging time, a 5 s
discharge, then a 1 min open circuit, after which the
recovery voltage is read. The percentage of DA is
defined as the ratio of recovery to charging voltage
times 100.

Insulation Resistance. Insulation resistance is basi-
cally the resistance of the dielectric material, and deter-
mines the period of time a capacitor, once charged with
a dc voltage, will hold its charge by a specified
percentage. The insulation resistance is generally very
high. In electrolytic capacitors, the leakage current
should not exceed

(10-22)

where,
IL is the leakage current in microamperes,
C is the capacitance in microfarads.

Maximum Working Voltage. All capacitors have a

maximum working voltage that should not be exceeded.

The capacitors working voltage is a combination of the

dc value plus the peak ac value that may be applied

during operation. For instance, if a capacitor has 10 Vdc

applied to it, and an ac voltage of 10 Vrms or 17 Vpeak is

applied, the capacitor will have to be capable of with-

standing 27 V.

Quality Factor (Q). The quality factor of a capacitor is

the ratio of the capacitors reactance to its resistance at a

specified frequency. Q is found by the equation

(10-23)

where,

f is the frequency in hertz,

C is the value of capacitance in farads,

R is the internal resistance in ohms.

Dissipation Factor (DF). The dissipation factor is the

ratio of the effective series resistance of a capacitor to

its reactance at a specified frequency and is given in

percent. It is also the reciprocal of Q. It is, therefore, a

similar indication of power loss within the capacitor

and, in general, should be as low as possible.

Power Factor (PF). The power factor represents the

fraction of input volt-amperes or power dissipated in the

capacitor dielectric and is virtually independent of the

capacitance, applied voltage, and frequency. PF is the

preferred measurement in describing capacitive losses

in ac circuits.

10.2.4 Types of Capacitors

The uses made of capacitors become more varied and

more specialized each year. They are used to filter, tune,

couple, block dc, pass ac, shift phase, bypass, feed

through, compensate, store energy, isolate, suppress

noise, and start motors, among other things. While

doing this, they frequently have to withstand adverse

conditions such as shock, vibration, salt spray, extreme

temperatures, high altitude, high humidity, and radia-

tion. They must also be small, lightweight, and reliable.

Capacitors are grouped according to their dielectric

material and mechanical configuration. Because they

may be hardwired or mounted on circuit boards, capaci-

tors come with leads on one end, two ends, or they may

be mounted in a dual-in-line (DIP) or single in-line

(SIP) package. Figs. 10-16 and 10-17 show the various

types of capacitors, their characteristics, and their color

codes.

IL 0.04C+= 0.30

Q^1

2 SfCR

-----------------=