Each capacitor is characterized by a marking which groups together the electrical operating characteristics expressed in the form of an alphanumeric code or in colors such as that of the resistors.
According to international standards, more or less followed by the manufacturers of electronic components, each capacitor must have the following marking :
Nominal capacity in pF, nF or µF (the unit can be omitted), Nominal operating voltage in volts, Tolerance on the value of the capacity in %, Acronym of the type of capacitor, Acronym of the manufacturer, Date of manufacture.
The first two data (capacity and nominal operating voltage) are always specified while the others are not clearly or not always indicated.
On the electrolytic capacitors, in addition to the acronyms of polarity, is reported the range of temperatures allowed for their use while the very wide tolerance is absent.
Here are some examples that can be found on the body of the components :
Clearly : 470 pF - 160 V - 5% ; 22 nF - 630 V - 10% ... In alphanumeric code : 470 J ; 022 K 630 ... In color code : yellow, purple, brown, green ; red, red, orange, white, blue ... In mixed code (alphanumeric and colors) : 470 J with red stripe ; 0.022 K with black stripe ...
The trend today is to eliminate all marking that is not essential from the marking and to keep the most important data of the capacitors. Many manufacturers therefore eliminate from the marking the symbols of the units of measurement (pF, nF, µF, V, %) as well as the zero which precedes the decimal point. In this case, however, the capacity value is always implied in microfarads.
For example, a 0.047 µF - 630 V - 10% capacitor can be marked as follows :
When the tolerance of the capacitor is ± 20%, it is generally not indicated ; therefore a capacitor of 0.1 µF 400 V. 20% can be marked simply.
Marking in alphanumeric code is very widespread, but it is more difficult to interpret because it uses acronyms to indicate the data of the capacitor:tolerance and for ceramic capacitors: the temperature coefficient.
In Figure 20, a table represents the marking code for ceramic, tubular and disc capacitors according to I.E.C. (International Electrotechnical Commission) which deals with the international standardization of components produced by several industries.
Let us now see with a few examples how it is possible to read this table below.
first example :
Capacitor marked :2K7
PG
We start first with the capacity value, which according to the multiplier K = 1 000 which constitutes the decimal point, will be 2.7 x 1 000 = 2 700.
This value between 1 000 and 10 000 will be expressed in pF, so the capacitance of the capacitor will be 2 700 pF.
The two letters P and G indicate the tolerances and the temperature coefficient respectively.
The letter P, located in the first column of the table, corresponds to a tolerance of ± 100% - 0% in the third column while the letter G (first column) defines the temperature coefficient -150 x 10-6 / °C (fourth column) which can also be expressed by the code N150
100 obviously indicates the capacity value expressed in pF (100 pF).
The letter J (first column) indicates the tolerance which is here ± 5% because the value of the capacity is greater than 10 pF.
The letter N (first column) finally indicates the temperature coefficient (fourth column) here equal to - 750 x 10-6 / °C (N750).
We will therefore have :
100 JN = 100 pF ± 5 % ; - 750 x 10-6 /°C
(N750)
Third example:
Capacitor marked 4.7 BC.
4,7 is the value of the capacity in pF4,7 pF.
The letter B (first column) indicates the tolerance of the capacitor : here ± 0.1 pF (second column) because the value of the capacitor is less than 10 pF.
The letter C indicates the temperature coefficient (fourth column) equal to 0. In this case, the capacitor does not show any variation in capacity as a function of that of the temperature.
We will therefore have :
4.7 BC = 4,7 pF ± 0,1 pF ; (NP0)
In the table in Figure 21 is given the code provided by the EIA (Electronic Industries Association) standards for ceramic disc capacitors.
Some examples are reported below for a correct interpretation of the EIA code.
First example:
Capacitor marked .1 MUIG
The inscription .1 indicates the capacity value in µF because according to what has been said previously, the acronym .1 represents the value 0.1 µF.
The capital letter M (first column) indicates the tolerance which should be read in the third column, as long as the value of the capacity is greater than 10 pF ; it will therefore correspond to ± 20%.
The acronym UIG (seventh column) finally corresponds to the temperature coefficient - 80 x 10-6 / °C, read in the eighth column.
The inscription 6p8, where the letter "p" replaces the decimal point, indicates the capacitance of the capacitor expressed in pF, which is therefore 6.8 pF.
The letter D (first column) indicates the tolerance that should be read in the second column because the capacitor has a capacity less than 10 pF : ± 0.5 pF.
Finally, the acronym COG (seventh column) indicates a zero temperature coefficient (eighth column). In this case too, the temperature variation does not determine any change in the capacitive value.
We will therefore have :
6p8 D COG = 6,8 pF ± 0,5 pF ; (COG = 0)
In the table in Figure 22 is indicated a marking code widely used by Japanese manufacturers and which relates not only to ceramic capacitors but also to polyester capacitors. Reading it does not present any particular difficulty, because it suffices to remember that the third digit indicates the number of zeros to be added to the first two digits to reconstitute the value of the capacity while the letter indicates the tolerance.
The examples given in the table above are sufficient to explain the marking.
The table in Figure 23 at the bottom of this page refers to another code, used to mark ceramic and polyester capacitors ; as we can see, it is a code entirely made up of colored bands. To be able to use it, it is first necessary to define the shape of the capacitor available.
It is marked on the drawings reported above the table to determine the color band which corresponds to the column in question.
Let us now see some examples of the application of this code, knowing that the second column concerns only ceramic disc and tubular capacitors and the seventh column only those of polyester.
First example :
Polyester capacitor marked with the colors red - purple - orange - black - yellow.
4th band : black
(1st column) = ± 20 % (6th column) because C = 27 000 pF (> 10 pF). The graphic symbol ">"
means "greater than ..." while the symbol "≤"
indicates "less than or equal to ...".
5th band : yellow
(1st column) = 400 V
(7th column).
We will therefore have :
27 000 pF (27 nF) ± 20 % - 400 V
Second example:
Ceramic condenser "tubing" marked with the colors : brown - orange - white - black - green.
1st band :brown
(1st column) = - 33 x 10-6 /°C(2nd column),
2nd band :orange
(1st column) = 3 (3rd column),
3rd band :white
(1st column) = 9 (4th column),
4th bande :black
(1st column) = x 1 (5th column).
So we get :
39 x 1 = 39 pF
5th bande : green
(1st column) = ±5 % (6th column ; C > 10 pF).
We will therefore have :
39 pF ± 5 % ; - 33 x 10-6 /°C
third example:
Ceramic disc capacitor, marked with the colors : black - blue - gray - white - brown.
4th band : white
(1st column) = x 0,1 (5th column).
The value will therefore be :
68 x 0,1 = 6,8 pF
5th band : brown (1st column) = ± 0,1 pF (6th column ;C ≤ 10 pF).
We will therefore have :
6,8 pF ± 0,1 pF ; (zero temperature coefficient).
For the polystyrene capacitors, the color code and literal used in the table in Figure 24 are used.
The interpretation of this code does not present any particular difficulty because the value of the capacitance is expressed in pF, the tolerance and the insulation voltage (only for 1 000 Vncc capacitors) are indicated in clear.
The letters which appear in the first column refer to the tolerance of the component when it is not indicated in clear, while the possible strip of color (2nd column) relates to the operating voltage when it is different from 1 000 Vncc.
The examples given in the table are sufficiently explicit for the interpretation of the code.
Let us now see how one should consider the data reported in the table of Figure 25 used by certain manufacturers to mark the ceramic type capacitors.
These capacitors have a colored band on the upper body indicating the temperature coefficient (3rd and 4th column). The value of the capacity is written in clear on the body of the component, the letter "p" or "n" replaces the decimal point to indicate respectively the pF or the nF.
Let's see some examples :
P68 = 0,68 pF,
4p7 = 4,7 pF,
33p = 33 pF,
n15 = 0,15 nF = 150 pF,
2n2 = 2,2 nF = 2 200 pF,
39n = 39 nF.
To better understand the method adopted for the correct interpretation of the code, we can see the examples given in the table in Figure 25.
In Figure 26, the code used for marking the electrolytic capacitors with tantalum has been indicated.
To properly interpret the code, it is necessary to orient the capacitor correctly by referring to the colored dot which provides information on the polarity of the component (7th column).
This point indicates the multiplier (4th column) which must be used to establish the correct value of the capacity designated by the colored bands corresponding to the first, second and third column.
The examples given in the table are self-explanatory, but it should be pointed out that some manufacturers of this type of capacitor adopt plain labeling.
Like resistors, capacitors do not exist in all values and manufacturers, for reasons of economy and convenience, produce these components in series of values that should be known.
The values of the current production capacitors are called standard values or normalized values.
In trade, we find these component values easily and at moderate cost. Each manufacturer chooses his own series of standardized values according to production possibilities and demand. However, we are trying to eliminate this trend by standardizing, on a national and international scale, series of values to facilitate the maintenance of devices of all brands and make production more economical.
In the past, the decimal series was widely used to express the value of resistors or capacitors : 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 or 1 000, 2 000, 3 000 ... ( in ohms for resistors, in picofarads for capacitors). This series of values however had a drawback, especially with regard to the overlap between one value and the next for a precise tolerance.
Currently, there is a tendency to manufacture resistors and capacitors with other series of values as shown in the table in Figure 27.
These series are called (according to the I.E.C. standard) E6, E12, E24, E48 because the values included in a decade (between 10 and 100) are respectively 6, 12, 24, 48 ; in reality, the values are given by a geometric (mathematical) sequence of reason :
Note that depending on the percentage of tolerance, more or less nominal values are obtained : the narrower the tolerance, the greater the choice of values existing in the series.
There are other series of values reserved for a more specific (professional) use : the E96 series (tolerance ± 1%) and the E192 series (tolerance ± 0.5%) which include 96 and 192 nominal values per decade.
When replacing a capacitor, it is imperative to take into account not only the value of the capacitance but also the operating voltage. Indeed, one can replace a capacitor by another having a higher operating voltage with the same capacity value but not the reverse. For example, a 100 nF / 25 V capacitor can be replaced by a 100 nF / 50 V capacitor if space permits.
The electrolytic capacitors must be stored in a dry and cool room (t° ≤ 25°) to prevent them from drying out (loss of the electrolyte). If the storage period has been particularly long, it is advisable to reform them before use. This treatment consists in subjecting the capacitors, for a few minutes, to a DC voltage lower than that of service marked on the component case (about half).
As with the resistors, it is possible to use the serial or parallel links of several capacitors to obtain determined values of capacity and operating voltages.
In a series arrangement of capacitors, you should know that the operating voltage of each capacitor adds up.
So for example, if we have three capacitors of the same value 3.3 nF / 250 V connected in series, the overall voltage that can be supported by the group is 250 V x 3 = 750 V with an equivalent capacity of 1.1 nF (3.3 nF / 3).
But it must be remembered that by making a series connection of capacitors of the same nominal value with wide tolerances and different leakage resistances (example : electrolytic capacitors), the voltage applied to the series grouping is not divided into equal parts across each capacitor. It is therefore desirable to stick to a maximum voltage equal to the lowest operating voltage. It is advisable for this to always connect in parallel on each capacitor in series (especially electrolytic), a resistance of high value so as to ensure an equal distribution of the voltage across the terminals of the two capacitors (Figure 28).
Variable capacitors differ from fixed by the fact that their capacitive value can be changed by means of a mechanical movement (in general, by rotation) provided by a control axis.
A variable capacitor is formed by a fixed part, called the stator, and by a mobile part called the rotor ; these two parts are electrically isolated from each other by a dielectric.
By turning the moving part, the capacitor capacity is varied from the maximum value to the minimum value or vice versa. When the moving blades which constitute the rotor are inserted between those which are fixed to it and which constitute the stator, the maximum capacity of the variable capacitor is obtained. Conversely, when the movable blades have left the stator, a residual capacity is obtained which depends on the mechanical system.
The shape of the blades is particularly important because it greatly influences the characteristics of the capacitor.
The Figure 29 illustrates the different laws of possible variation (capacity, wavelength, frequency) of the variable capacitors as a function of the position of the movable blades relative to those which are fixed.
The Figure 30 below shows a variable air capacitor with a single cage. It consists of a group of mobile metal blades integral with a control shaft which constitute the rotor. Thereof is electrically connected to the frame while the stator is insulated by a ceramic support. The value of the capacitance varies between 10 pF and 500 pF and in current radio receivers, the variable capacitor is with two cages (or double). The ability of the two cages can be identical or different from each other depending on the requirements that vary from one receiver to another.
On the Figure 31-a, is represented the type of condenser which has two equal sections with a variable capacity of 15 pF with 450 pF.
For the capacitors of current type, the angle of rotation of the control axis is approximately 180° whereas others have a reduction gear (Figure 31-b) which makes it possible to carry out an angle of rotation of the control axis greater than 500°, greater accuracy of the capacitive value is thus obtained.
Some variable capacitors sometimes have adjustment screws which allow the minimum capacity to be varied within certain limits. These adjustment screws are small variable capacitors called "trimmers".
The trimmers are only adjusted during the development phase of a device and this procedure is called taring.
There are also "butterfly" capacitors (Figure 32-a) which are generally not used in the current receivers and which have maximum capacities of 6 pF, 10 pF and 20 pF.
For particular circuits, one sometimes needs condensers with three cages (Figure 32-b) with equal or different capacities according to the needs.
In portable and transistorized radio receivers, miniature variable capacitors are widely used ; they are also called mixed dielectric capacitors, because between the reinforcements and the solid insulating material (generally made of polythene), there are always air spaces ; therefore, the dielectric consists of polythene and air.
On the Figure 33-a is illustrated a miniature variable air condenser with a capacity going from 4 pF to 124 pF ; for the two sections (cages), the dielectric used is polyethylene. The variable solid dielectric capacitor reported on the Figure 33-b is of larger dimensions and has a section (cage) whose capacitive value is between 8 pF and 130 pF while the other has a capacity lying between 7,5 pF and 39 pF.
The trimmers are adjustable capacitors used separately or in parallel with the variable capacitors for the adjustment (setting) of the devices.
They are made with air, mica or ceramic dielectrics.
On the Figure 34-a, is represented an air trimmer from 1.5 to 30 pF with adjustment by screw, on the Figure 34-b, are illustrated on the other hand two leather trimmers of identical value 1.5 to 30 pF assembled on a suitable support by mechanical fixing.
The trimmer with mica represented on the Figure 34-c, has a variation of greater capacity, ranging between 10 pF and 150 pF.
In the Figures 34-d, 34-e and 34-f, three types of ceramic trimmers are illustrated, characterized by reduced dimensions and by a small variation in capacity (2 to 8 pF) ; they are used in high frequency circuits. These trimmers are adjusted using a screw which is actuated with a small screwdriver (Figures 34-d and 34-f) or by sliding a sleeve along the body of the capacitor (Figure 34-e).
Normalization of values
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