Reading schematics pdf

In the example below you can see an operational amplifier op-amp. The symbol shows only three pins. That means the designer has named this wire. This means that all other wires with the same name are actually connected.

And it also says something about its purpose. It is probably where you connect your input to the amplifier ;. Return from Reading Schematics to Electronic Schematics. I wanted to see and touch ele- tronics. Yes, they do no see and touch and you came on the way.

I AM in a small village in India. One request: do nat ask me money bu I shall give you. I can help you with your electronic classes and guide you how to train your students free of cost. I would like to help students from any village. Hey michael, I can also help your students. A small five-sided box, which has the shape of the home plate on a baseball field, shows where one page of a flowchart connects to the next, if the entire flowchart has more than one page.

The inter- mediate junction and off-page connection points are labeled with numbers and letters to let readers know that all like symbols with the same character inside are meant to be connected together. Arrows indicate the direction of the flow. Process paths Returning to the flowchart for duplicating punched cards Fig.

Figure shows the result. Process paths 23 Start A Read a card Card blank? Example of a flowchart that includes a decision block the diamond. The circles labeled A all represent a single junction point through which data flows in the directions shown by the arrows.

Follow the flow Except for the decision block, Fig. Most pro- grams and flowcharts involve more complicated processes. The field of microcomputers uses many different types of diagrams that deal mostly with software the operating systems and programs rather than hardware the physical components. From a purely elec- tronic standpoint, functional diagrams abound and are usually more numerous than the schematic diagrams in the computer world.

From an understanding standpoint, block diagrams can serve to display machine functions in general, but hardware maintenance and repair procedures require well-defined schematic drawings.

Computers take advantage of the latest state-of-the-art developments in electronic components and are relatively simple from this standpoint, especially when you consider all they can do.

However, from a pure electronics standpoint and as far as schematic diagrams are concerned, comput- ers are highly complex; it would take many pages of schematics to represent even the most rudimentary computer. Summary Block diagramming can help you understand the general functioning of electronic circuits. Block diagrams are easy to draw, usually requir- ing only a marking instrument, some paper, and a straightedge or a vector graphics computer program and a little bit of training on it.

Schematic diagrams, in contrast, need more tools and can, in some cases, take many hours to render in a form that people can easily read and interpret. The same rule applies to schematic drawings; symbols indicate conduc- tors, resistors, capacitors, solid-state components, and other electronic parts.

Every time a new component comes out, a new schematic sym- bol is derived for it. Often, a new type of component is a modification of one that already exists, so the new schematic symbol ends up as a modification of the symbol for the preexisting component.

Appendix A contains a more complete listing in alphabetic, tabular form. Resistors Resistors are among the most simple electronic components. As the term implies, they resist the flow of electrical current. Standard schematic symbol for a fixed-value resistor. Regardless of the ohmic value, all fixed-value resistors are sche- matically indicated by the symbol shown in Fig.

This is the most universally accepted symbol for a resistor. The two horizontal lines indicate the leads or conductors that exit from both ends of the physi- cal component. Sometimes the resistor contacts are not wire leads but more substantial metal terminals.

Figure shows pictorial drawings of two other types of resistors. Any resistor of the sort shown pictorially in Fig. A variable resistor has the ability to change ohmic value by means of a slide or rotary tap that can be moved along the resistive element. The variable resistor is usually set to one value, and it remains at this point until manually changed. However, when a variable resistor is required for the proper functioning of a specific circuit, it is neces- sary to indicate to any person who might build it from a schematic drawing that the resistor is actually a variable type.

Figure shows the schematic symbol for a variable resistor with two leads. Other types of variable resistors exist, and they have three leads two end leads and a tap. Figure shows two examples of schematic sym- bols for a three-terminal variable resistor, known as a potentiometer or a rheostat depending on the method of construction.

Pictorial illustration showing the anatomy of a carbon-composition resistor. Pictorial illustrations showing the anatomy of a wirewound resistor at A and a film type resistor at B. Did you know? Rheostats are in effect the same as potentiometers, but mechani- cally they differ. A rheostat contains a wirewound resistance ele- ment, while a potentiometer is normally of the carbon-composi- tion type. Schematic symbol for a two-terminal variable resistor. Tip In schematic drawings, an arrow often indicates variable proper- ties of a component, but not always!

Transistors, diodes, and some other solid-state devices have arrows in their schematic symbols. Arrows can also sometimes indicate the direction of current or signal flow in complex circuits. Figure is a pictorial drawing of a variable resistor of the wire- wound type, manufactured so that the resistance wire is exposed. A sliding metallic collar, which goes around the body of the resistor, can be adjusted to intercept different points along the coil of resis- tance wire. The collar is attached by a flexible conductor to one of the two end leads.

The collar, therefore, shorts out more or less of the coil turns, depending on where it rests along the length of the coil. As the collar moves toward the opposite resistor lead, the ohmic value of the component decreases. Figure shows a functional drawing of a rotary potentiometer at A , along with the schematic symbol at B. Alternate symbols for variable resistors, also known as potentiometers or rheostats depending on the physical construction method. The device at A con- nects one end to the tap; and the device at B uses a three-terminal arrangement.

Pictorial drawing of a wirewound variable resistor. Using the potentiometer control, the portion of the circuit that comes off the arrow lead can be varied in resistance to two circuit points, each connected to the two remaining control leads.

Figure shows a pictorial drawing of a typical potentiometer. The variable resistor shown pictorially in Fig. Simplified functional drawing of a rotary potentiometer A and its schematic symbol with corresponding connections B. Pictorial drawing of a full-size potentiometer, suitable for mounting on the front panel of an electronic device such as a radio receiver. Now, the collar can be used as the third or variable contact. Likewise, a rheostat or potentiometer can be turned into a two-lead variable resistor by shorting out the variable contact point with the lead on either end.

The schematic symbol for a resistor, all by itself, tells us nothing about the ohmic value, or anything else about the component such as its power rating or physical construction, either.

Tip You can usually determine the ohmic value of a fixed resistor by looking at the colored bands or zones on it. Appendix B lists the resistor color codes that specify the ohmic values of fixed resistors. Capacitors Capacitors are electronic components that have the ability to block direct current DC , while passing alternating current AC. They also store electrical energy.

The basic unit of capacitance is the farad symbolized F. Standard symbol for a fixed capacitor. The curved line represents the plate or set of plates electrically closer to ground. Figure shows the common schematic symbol for a fixed capac- itor. On occasion, you might see alternative symbols, such as those in Fig. Many different types of capacitors exist. Others are polarized, having a positive and a negative terminal, and you must take care to connect them so that any DC voltage that happens to appear across them has the correct polarity.

The basic capacitor symbol consists of a vertical line followed by a space and then a parenthesis-like symbol. Horizontal lines connect to the centers of the vertical line and the parenthesis to indicate the com- ponent leads.

The parenthesis side of a capacitor indicates the lead that should go to electrical ground, or to the circuit point more nearly connected to electrical ground. Unless the symbol includes a polar- ity sign, it indicates a nonpolarized capacitor, which might be made from metal plates surrounding ceramic, mica, glass, paper, or other solid nonconducting material and, in some cases, air or a vacuum. The material designation indicates the insulation, technically known as a dielectric, that separates the two major parts of the component.

A B FIG. Alternate symbols for fixed capacitors. At A, air dielectric; at B, solid dielectric. Schematic symbol for a polarized capacitor. Physically, a typical fixed-value capacitor comprises two tiny sheets of conductive material close to each other but kept electrically separated by the dielectric layer.

Figure shows the schematic symbol for a polarized or electro- lytic capacitor. This sign indicates that the positive terminal of the component goes to the external circuitry. When you see the plus sign, you know that the component is polarized, and therefore, that you must connect it to the remainder of the circuit in observance of the proper polarity.

That means the positive capacitor electrode must go to the more positive DC voltage point in the circuit, and the other electrode must go to the more negative DC voltage point in the circuit.

Tip Polarized capacitors have external markings that tell you the polarity. Some have a plus sign, and some have a minus sign, and a few have both. In other words, the components specified have no provision for chang- ing the capacitance value, which is determined at the time of manu- facture. Some capacitors, however, do have the ability to change value. These components are generally called variable capacitors, although some specialized types are known as trimmer capacitors or padder capacitors.

Figure shows the most common symbol for a variable capaci- tor. An arrowed line reveals the variable property; it runs diagonally through a fixed capacitor symbol.

Standard symbol for a variable capacitor. The curved line represents the rotor, and the straight line represents the stator. Most of the time, the sym- bol shown in Fig. An air variable capacitor one with an air dielectric can tune many types of radio-frequency RF equipment including antenna matching networks, transmitter output circuits, and old-fashioned radios. A typical air variable has many interlaced plates, with the plates connected together alternately to form two distinct contact points.

The set of plates that you can rotate is called the rotor ; the set of plates that remains stationary is called the stator. Tip In most air variables, the rotor should go to electrical ground.

The rotor connects physically to the shaft that you turn. Alternate symbols for variable capacitors. At A, the stator is not distin- guished from the rotor; at B, the rotor appears as a curved line with an arrow.

Schematic symbol for two variable capacitors ganged together. Sometimes, two separate variable capacitors are connected together or ganged in a circuit. In a ganged arrangement, two or more units are used to control two or more electronic circuits, but both compo- nents are varied simultaneously by tying the rotors of the two units together.

Figure shows the schematic symbol for two variable capacitors ganged together. They will, however, always track together. In a ganged system, when one of the capacitors increases in value, the others all increase as well. As is the case with most electronic components, the schematic sym- bol for the capacitor serves only to identify it and to show whether it is fixed or variable, and if fixed, whether or not it is polarized.

The component value might be written alongside the schematic symbol, or the component might be given a letter and number designation for example, C1, C2, C3, and so on for reference to a components list or table that goes along with the diagram. Inductors and transformers A basic inductor comprises a length of wire that is coiled up in order to introduce inductance into a circuit. Inductance is the property that opposes change in existing current; it acts in practice only while cur- rent increases or decreases.

Standard symbol for an air-wound or air-core inductor. The basic unit of inductance is the henry symbolized H , a large electrical quantity. Figure shows the basic schematic symbol for an air-core inductor. The two leads are designated by straight lines that merge into the coiled part. An air-core coil has nothing inside the windings that can affect the inductance.

Some air-core coils are wound from stiff wire and support themselves mechanically, and their cores do, in fact, comprise nothing but air. In most cases, however, a noncon- ductive and noninductive form made out of plastic, mica, or ceramic material serves as a support for the coil turns, keeping them in place and enhancing the physical ruggedness of the component.

Figure shows the schematic symbol for a tapped air-core inductor; in this case, the coil has two tap points along its length. Schematic symbol for an air-core inductor with two taps. Schematic symbols for a variable air-core inductor. At A, arrow above coil symbol; at B, arrow passing through coil symbol.

Whereas the fixed coil had only two leads, a tapped coil has three or more. When a coil is tapped, separate conductors are attached to one or more of the turns for intermediate connection. Maximum inductance is obtained from connecting the end leads to the external circuitry. A tapped arrangement allows for the selection of an input or output point that offers lower inductance than the full coil does. As an alternative to taps, a coil might have a sliding contact that can be advanced along the entire length of the windings.

This sliding contact allows adjustment of the inductance value, rather than hav- ing a select fixed point with the tapping arrangement. A variable coil can be indicated by either of the symbols shown in Fig.

The arrow indicates that the component can be adjusted from a maximum inductance value to a minimum inductance value. Figure shows symbols for a fixed air-core coil at A , a tapped air-core coil at B , and an adjustable air-core coil at C. An inductor meant for low-frequency applications can consist of a coiled wire wound around a solid or laminated layered iron core.

Schematic symbols for fixed A , tapped B , and adjustable C air- core inductors. Inductors and transformers 37 FIG. Schematic symbol for an inductor with a solid or laminated iron core.

For example, a Hz choke, intended for use in power-supply filters, will usually contain a single coil wound around a circular iron form. The ferromagnetic material greatly increases the magnetic flux density inside the coil windings, thereby increasing the inductance by a factor of many hundreds, or even thousands, of times compared with the inductance of an air- core coil having the same physical dimensions.

Figure shows the schematic symbol for an iron-core inductor. Notice that it is the basic fixed coil discussed earlier, along with two close-spaced straight lines that run for its entire length.

Sometimes the iron-core inductor is drawn as shown in Fig. Some iron-core inductors contain taps for sampling dif- ferent inductance values, and some might even be adjustable. The equivalent schematic symbols for these types of components appear in Fig. Engineers would say that they have too much loss. At frequencies above a few kilohertz kHz , a special core is needed if you want to increase the inductance over what you can get with nonferromagnetic core materials, such as air, plastic, ceramic, or wood.

The most common substance for this purpose consists of iron material that has been shattered into myriad tiny fragments, each of which has a layer of insulation applied to it.

After the fragmentation and insulation process has been completed, the particles are compressed to form a physically solid sample called FIG. Alternate symbol for an inductor with a solid or laminated iron core.

Symbols for a tapped coil A and an adjustable coil B with solid- or laminated-iron cores. Figure shows schematic symbols for pow- dered-iron-core inductors.

Tip The symbols for powdered-iron-core inductors are nearly iden- tical to those for solid- or laminated-iron-core inductors, except that the straight lines are broken up instead of solid. These types of components, like all other types of inductors, can be tapped or continuously variable. A transformer is made up of multiple inductors with the coil turns interspersed or wound around different parts of a single core.

Figure shows the symbol for a basic air-core transformer. Schematic symbols for fixed A , tapped B , and adjustable C induc- tors with powdered-iron cores.

Switches 39 FIG. Schematic symbol for a transformer with an air core. A transformer has the ability to transfer AC energy from one circuit to another at the same fre- quency. Because transformers are made by combining inductors, the schematic symbols are similar. Figure shows some transformers that contain iron cores. The ones at A and B have solid or laminated cores; the ones at C and D have powdered cores. Switches A switch is a device, mechanical or electrical, that completes or breaks the path of current.

At A, a transformer with a solid- or laminated-iron core. At B, a transformer with a solid- or laminated-iron core and tapped windings. At C, a transformer with a powdered-iron core. At D, an adjustable transformer with a powdered-iron core. Schematic symbol for an SPST switch. Symbolically, the pole coin- cides with the point of contact at the base of the arrowed line.

A throw is the contact point to which the arrow can point. The SPDT switch contains one pole contact and two throw positions; the input to the pole can be switched to either the upper or lower circuit point. Some switches contain two or more poles.

Some switches have even more elements. The one shown in Fig. This last designation can actually be covered under the heading of multicontact switches. This category takes in most switches that have more than two poles or two throw positions. For example, a rotary switch has a single pole and several throw positions; Fig. The arrow still indicates the pole contact. In this case the switch has 10 throw positions.

Schematic symbol for an SPDT switch. Figure shows the schematic symbol for an arrangement that uses two rotary switches. The dashed line tells us that the two switches are ganged. So, for example, when the left-hand switch or pole number 1 rests at throw number 3 as is the case here , the right-hand switch or pole number 2 also rests at throw number 3.

Schematic symbol for a five-pole double-throw 5PDT switch. Schematic symbol for a rotary or wafer switch. This one has a single pole and 10 throws SP10T. In each case, every switch contact point pole or throw is repre- sented by a tiny circle.

The variable element or pole is indicated by an arrow. The symbols shown here are all standard. Some amateur radio operators use a special switch called a Morse code key. This old-fashioned device, also called a hand key or a straight key, makes or breaks a circuit for the purpose of send- ing Morse code manually.

Figure shows its schematic symbol. Schematic symbol for two rotary switches ganged together. This one has two poles and 10 throws 2P10T. Conductors and cables 43 FIG. Schematic symbol for a Morse code key hand key or straight key. Conductors and cables Throughout this discussion, a straight line has always indicated a conductor, but most circuits contain a large number of conductors. Figure shows two conductors that must cross each other in a diagram, but that are not connected to each other in the physical cir- cuit at least not at the point where they cross in the schematic.

This diagram geometry does not imply that when you build the circuit, the conductors must physically cross over each other at that exact place. It simply means that in order to make the schematic drawing, you have to draw one conductor across another to reach various circuit points without introducing a whole lot of confusion and clutter, or resorting to three dimensions to make your drawing. A real-world circuit exists in three-dimensional 3D space, but when you want to diagram it, you must do it on a two-dimensional 2D surface.

To carry off that feat, you must learn a few tricks to make sure that your readers see things right! Schematic symbol for conductors that cross paths but are not electrically connected. At A, preferred symbol for conductors that intersect and are electrically connected to each other.

At B, alternate symbol for the same situation. Figure shows two ways of portraying a point where two wires cross and they are electrically connected at that point. Black dots indicate electrical connection. In the drawing at B, the two conduc- tors cross at right angles in this example , and a single black dot is drawn at the junction. This dot tells us that the conductors connect at this point. The method shown at B might look better at first glance, but the neatness comes along with a problem: Some readers might overlook the black dot and think that the two conductors are not meant to connect.

The method at A makes that potential misinterpre- tation impossible. Just as a reader might miss a black dot at a crossing point, as in Fig. Then the reader will think the two wires con- nect when in fact they do not. This problem rarely occurs in well- engineered schematics where the draftsperson makes sure to use big black dots and good quality printing presses.

However, in some older schematics you will see nonconnecting, crossed wires shown as in Fig. One of the wires has a half loop that makes it look like it jumps over the other wire to avoid contact. That trick which should never have gone out of style, in my opinion gets rid of any doubt as to whether the wires electrically connect at the crossover point or not. A cable consists of two or more conductors inside a single insu- lating jacket. Archaic but clear representation of conductors that cross paths but are not electrically connected to each other.

Shielded cables require additional symbology along with the conductors. Figure shows examples of shielded wire, often used to indicate the use of coaxial cable in an electronic circuit. Coaxial cable contains a single wire called the center conductor surrounded by a cylindrical, conduit-like conductive shield. An insulating layer, called the dielectric, keeps the two conductive elements isolated from each other.

In most coaxial cables, the dielectric material consists of solid or foamed polyethylene. Tip Figure shows a symbol for coaxial cable when the shield con- nects to a chassis ground, such as the metal plate on which an electronic circuit is constructed.

At A, symbol for a coaxial cable with an ungrounded shield. At B, symbol for a coaxial cable with an earth-grounded shield. Symbol for a coaxial cable with a chassis-grounded shield. In some cables, a single shield surrounds two or more conduc- tors. Figure shows the schematic symbol for a two-conductor shielded cable.

This symbol is identical to the one for coaxial cable, except that an extra inner conductor exists. If more than two inner conductors exist, then the number of straight, parallel lines going through the elliptical part of the symbol should equal the number of conductors. For example, if the cable in Fig. Diodes and transistors Figure shows the basic symbol for a semiconductor diode. In this symbol, an arrow and a vertical line indicate parts of the diode, and the horizontal lines to the left and right indicate the leads.

The symbol in Fig. Under normal operat- ing conditions, a rectifier diode conducts when the electrons move FIG. Symbol for a shielded two-conductor cable, in this case with a chassis ground for the shield.

Diodes and transistors 47 FIG. Symbol for a general-purpose semiconductor diode or rectifier. Figure shows the symbols for some specialized diode types. At A, we see a varactor diode, which can act as a variable capacitor when we apply an adjustable DC voltage to it. At B, we see a Zener diode, which can serve as a voltage regulator in a power supply. At C, we see a Gunn diode, which can act as an oscillator or amplifier at microwave radio frequencies.

A silicon-controlled rectifier SCR is, in effect, a semiconductor diode with an extra element and corresponding terminal. Its sche- matic symbol appears in Fig. In the SCR representation, a circle often but not always surrounds the diode symbol, and the control element, called the gate, shows up as a diagonal line that runs out- ward from the tip of the arrow.

Figure shows the schematic symbols for bipolar transistors. The only distinction between the two is the direction of the arrow. In the PNP device, the arrow points into the straight line for the base electrode. In the NPN device, the arrow points outward from the base. Symbol for a silicon-controlled rectifier SCR. Besides the bipolar variety, many other types of transistors exist.

Tip Transistors can be made from various types of semiconductor materials and metal-oxide compounds, but the schematic symbol, all by itself, tells us nothing about the elemental semiconductor material used in manufacture. The symbol merely indicates com- ponent functionality. When you want to create the symbol for a vacuum tube, you should start by drawing a fairly large circle, and then you should add the necessary symbols inside the circle to symbolize the type of tube involved.

Figure shows the schematic symbols for the various types of tube elements commonly used in schematic drawings. Figure shows the schematic symbol for a diode vacuum tube. This two-element device contains an anode also called a plate and a cathode. Just as with the semiconductor diode, the anode is nor- mally positive with respect to the cathode when the device conducts current.

The cathode emits electrons that travel through the vacuum to the anode. A hot-wire filament, something like a miniature low- wattage light bulb, heats the cathode to help drive electrons from it. In Fig. Symbols for tube elements and characteristics. A: Filament or directly heated cathode. B: Indirectly heated cathode. C: Cold cathode. D: Photocathode.

E: Grid. F: Anode plate. G: Deflection plate. H: Beam-forming plates. I: Envelope for vacuum tube. J: Envelope for gas-filled tube. Tip All tube elements are surrounded by a circle, which represents the tube envelope. Figure shows two versions of a triode vacuum tube, which consists of the same elements as the diode previously discussed, with the addition of a dashed line to indicate the grid. Can you see it?

Look closely FIG. Schematic symbol for a diode vacuum tube with an indirectly heated cathode. Although a filament exists, it is often omitted to reduce clutter in symbols for tubes with indirectly heated cathodes. Symbols for a triode tube with a directly heated cathode A and an indirectly heated cathode B.

The tube at A has a directly heated cathode, in which the filament and the cathode are the very same physical object! We apply the negative cathode voltage directly to the filament wire; no separate cathode exists at all. In this symbol, the fila- ment is inside the cathode, which comprises a metal cylinder running along the central vertical axis of the tube.

Tetrode vacuum tubes have two grids. To represent one of them, we need an additional dashed line, as shown in the drawings of Fig. In the tetrode, the upper grid, closer to the anode, is called the screen.

Figure shows symbols for the so-called pentode tube, which has three grids and a total of five elements. In the pentode, the second grid going from the bottom up is the screen, and the third grid just underneath the plate is called the suppressor. In both Figs. Symbols for a tetrode tube with a directly heated cathode A and an indirectly heated cathode B. Symbols for a pentode tube with a directly heated cathode A and an indirectly heated cathode B. Follow the flow In all the vacuum tube symbols shown here, electrons normally flow from the bottom up.

They come off the cathode, travel through the grid or grids if any , and end up at the plate. In that sort of situation, you can simply remember that the electrons go from the cathode to the plate under normal operating conditions.

Some vacuum tubes consist of two separate, independent sets of electrodes housed in a single envelope. These components are called dual tubes. If the two sets of electrodes are identical, the entire compo- nent is called a dual diode, dual triode, dual tetrode, or dual pentode.

Figure shows the schematic symbol for a dual triode vacuum tube with indirectly heated cathodes. In some older radio and television receivers, tubes with four or five grids were sometimes used.

These tubes had six and seven elements, respectively, and were called hexodes and heptodes. These esoteric devices were used mainly for mixing, a process in which two RF signals having different frequencies are combined to get new signals at the sum and difference frequencies.

The schematic symbol for a hexode is shown in Fig. Schematic symbol for a dual triode tube. At A, symbol for a hexode tube.

At B, symbol for a heptode tube, also known as a pentagrid converter. Some engineers called the heptode tube a pentagrid converter. Both of these symbols show devices with indirectly heated cathodes. Cells and batteries A cell or battery is often used as a power source for electronic circuits. A single-cell com- ponent such as this usually has an output of approximately 1. Schematic symbol for a single electrochemical cell.

Schematic symbol for a self-contained multicell electrochemical battery. The multicell battery symbol is simply a number of single-cell symbols placed end-to-end without any intervening lines. If a circuit calls for the use of three individual, discrete single-cell batteries in a series connection, you might draw three cell symbols in series with wire conductor symbols between them Fig.

Standard practice calls for polarity signs to go with the symbols for cells or batteries. Unfortunately, some draftspeople neglect this detail. Logic gates All digital electronic devices employ switches that perform specific logical operations. These switches, called logic gates, can have any- where from one to several inputs and usually a single output. Logic devices have two states, represented by the digits 0 and 1.

It reverses, or inverts, the state of the input. If the input equals 1, then the output equals 0. If the input equals 0, then the output equals 1. Symbol for three single electrochemical cells connected in series to form a battery. Logic gates 55 output equals 0. If any of the inputs equals 1, then the output equals 1. If both, or all, of the inputs equal 1, then the output equals 1. If any of the inputs equals 0, then the output equals 0.

If both, or all, of the inputs equal 0, then the output equals 1. If any of the inputs equals 1, then the output equals 0. The start pushbutton, a nonnally open Reducing the potential difference from volts switch labeled 2PB, is shown in parallel with to volts for the control circuit is a recom- the normally open holding or seal contacts, mended practice.

The lower potential difference is labeled 1M safer for operating personnel. Connected to the start switch are the overload Control Circuit relay contacts normally closed in serieswith coil 1M, which is connected to the common 1. The left-hand solid vertical line on the schematic is the hot This circuit provides the means of starting and conductor.

The right-hand solid vertical line is stopping the motor with nonlatching contacts. Conductor number 3 is at fuse 6FU. This is circuit. Conductor number 4 is at fuse 7FU. Coil I M is energized, closing the motor-run contacts I M in the power circuit and the auxil-.

The hot conductor is number above con. The common conductor is number 2 above longer needsto be held in to keep I M energized. At the time coil 1Mis energized,light 1LTcomes Numbers 5 and 6 are common to the rest of the on to indicate that the motors are running. Control relay master CRM, is energized. Thesecon- matic in Fig. The wire going from 4FU to the tacts energizethe rest of the control circuit.

Whereverwires make a control devices from functioning when the machine common junction point, they all have the same is turned off, either intentionally or because of a identifying number. With contacts CRM closed, the machine is ready to 1. For manual junction labeled number 7. The wire between the operation, the operator must press switch 5PB.

Identifying Conductors 1. Consecutive numbering is preferred. Number 10 is between 2 OL and 1M. Then The identification number is used only once in the number 2 goes to fuse 5FU and the common line, electrical control system. Each conductor has the completing the motor-control circuit. All conductors connected to the same terminal 1.

All wires connected to the vertical line on the left side below contacts CRM havea number 5. The hot conductor below fuse 4FU is number. Likewise, all wires connected to the vertical. The common conductor below fuse SFU is line on the right side havethe number 6 below number 2.

Wheneverthe switches are used, they are 1. On a schematic,one symbol designatesall sizes. The symbol does not 1. On control relay or switch. This system provides cross- referencesto the different locations of the switches 1. Relay contacts have the same number as the control relay. All The Programed Exercises on the next page will tell 1CR contacts are marked 1CR, no matter where you how well you understand the material you they appear on the schematic. The sameis true of have just read.

Before starting the exercises, re- limit switchesand pushbutton switches. Read the instructions printed on the 1. Follow these instructions as you work switches actuated by the same arm. In Fig. The drawings include a layout of the operator's console 1.

Their contacts are used in different not shown. This layout may be combined on the parts of the control circuit, and it takes time to same drawing with the interconnection diagramor find them on a complex schematic. An example of a contro1-pane11ayout is shown in Fig. The diagram have a series of numbers listed horizontally. The includes every panel and chassisin the complete numbers appear only on lines that have a control electrical system. Each connection is identified or relay CR.

Blank spaces and spareterminals are also shown. The horizontal series of numbers at the right 1. The numbers of each device used.

For motors, it also lists the indicate the lines on which you will find the con- horsepower, frame size, type of enclosure, and tacts of relay SCR. Notice that the numbers 12 and speed. Any other information necessaryfor order- 14 are underlined, indicating that on theselines the ing replacement electrical and electronic parts is contacts of SCRare normally closed.

A portion of a typical stocklist is shown in Fig. Control-Panel Layouts Sequenceof Operation 1. Devices 1. On elementary diagram. Locating relay contacts ANTI. If the fuse is operation is givenas shown in Fig.