## Wiring diagram compressor, star-triangle (star-delta) switching system

In most cases compressor driven by the large power motor, above 10 KW. That used to generate the huge air pressure anyway.

Example of compressor with power 30 KW (40 HP) as shown in the picture below.

To reduce inrush current (electric current of early motion) that can reach 200% to 300% of normal current when the motor will rotate, the system needs to be made such a wiring diagram star-triangle (star-delta) switching, as shown by the picture below.

Click to enlarge
Electric parts needed for the wiring above:
1. Breaker 100 A 1 pc
2. Transformer step down 380 V / 220 V 3 A 1 pc
3. Magnetic contactor 3P 55 KW coil 220 V 3 pcs
4. Power on delay (Timer) 220 V 1 pc
5. Thermal over load relay 65 A 1 pc
6. Fuse glass 2 A dan 3 A @ 1 pc
7. Start button 1 pc
8. Stop button 1 pc
9. Motor 37 KW 380 V 3 φ 1 unit

## Multiplication and division method of a complex numbers

When the addition and subtraction method of a complex numbers must be in rectangular form, the multiplication and division method of a complex numbers, should be in polar form. Where has the rule: absolute value multiplied (or divided) with absolute value. For angle value have rules: if multiplication, angle value added with angle value and if division, angle value subtracted with angle value.

Sample question 1: (36 ∠ 22°) × (5 ∠ 45°) = ?

Completion:

r (abs) = 36 × 5 = 180

φ (angle) = 22 + 45 = 67

Result:

(36 ∠ 22°) × (5 ∠ 45°) = 180 ∠ 67°

If there is a question multiplication (or division) of rectangular and polar, then the rectangular form must be converted into polar form.

Sample question 2: (14 + j63) ÷ (25 ∠ 37°) = ?

Completion:

Conversion rectangular form (14 + j63) into polar form

14 + j63 = 64.53681 ∠ 77.47119°

we have

r (abs) = 64.53681 ÷ 25 = 2.58147

φ (angle) = 77.47119 - 37 = 40.47119

Result:

(14 + j63) ÷ (25 ∠ 37°) = 2.58147 ∠ 40.47119°

## Addition and subtraction method of a complex numbers

Addition and subtraction method of a complex numbers given by the problem, solved in rectangular form. Where has the rule: real part added (or subtracted) with real part, and imaginary part added (or subtracted) with imaginary part of a complex numbers.

Sample question 1: (30 + j25) + (13 − j5) = ?

Completion:

x (real) = 30 + 13 = 43

y (imaginary) = 25 − 5 = 20

Result:

(30 + j25) + (13 − j5) = 43 + j20

If there is a question addition (or subtraction) of polar and rectangular, then the polar form must be converted into rectangular form.

Sample question 2: (53 + j17) + (21 ∠ 22°) = ?

Completion:

Conversion polar form (21 ∠ 22°) into rectangular form

21 ∠ 22° = 21 (cos 22 + jsin 22) = 19.47086 + j7.86674

we have

x (real) = 53 + 19.47086 = 72.47086

y (imaginary) = 17 + 7.86674 = 24.86674

Result:

(53 + j17) + (21 ∠ 22°) = 72.47086 + j24.86674

## How to operation of a scientific calculator for conversion complex numbers

To solve the problems of a complex numbers (manual method), you should have a scientific calculator. An example Casio S-V.P.A.M fx-570w as I use to my scientific calculator, that looks like the picture below.

Operating a scientific calculator you notice calculator buttons present in a [ ] that will be described below, this applies to brands and types of scientific calculator in general.

1. Conversion the complex numbers rectangular form into polar form

Example: 30 + j25 = ?

r (abs) = [ SHIFT ] [ Pol( ] [ 30 ] [ , ] [ 25 ] [ ) ] [ = ] 39.05125

φ (angle) = [ RCL ] [ F ] [ = ] 39.80557

Becomes: 30 + j25 = 39.05125 39.80557°

2. Conversion the complex numbers polar form into rectangular form

Example: 40 ∟ 65° = ?

x (real) = [ SHIFT ] [ Rec( ] [ 40 ] [ , ] [ 65 ] [ ) ] [ = ] 16.90473

y (imaginary) = [ RCL ] [ F ] [ = ] 36.25231

Becomes: 40 65° = 16.90473 + j36.25231

Notes:
• Mode position calculator in D or Deg (degree)
• RCL-E and RCL-F is use to switch the value shown.

## Calculation polar form into rectangular form of a complex numbers

After understanding the manual calculation method to convert complex numbers rectangular form into polar form, this time we'll learn the manual calculation method to convert complex numbers polar form into rectangular form, or the otherwise.

The complex numbers conversion's software, I have given it for free, click Converting complex numbers. It's how to compare the results of manual calculation with the execution of software's program.

Here I will give an example of the manual calculation method to convert complex numbers polar form into rectangular form, with sample questions 40 ∟ 65°

Given the polar form:
40 ∟ 65°
r (abs) = 40
φ (angle) = 65

Completion:
x (real) = r (cos φ) = 40 (cos 65) = 16,90473
y (imaginary) = r (sin φ) = 40 (sin 65) = 36,25231

Then the rectangular form becomes:
x + jy = 16,90473 + j36,25231

See a picture below, the calculation above Polar form into rectangular form

## Calculation rectangular form into polar form of a complex numbers

After learning the complex numbers conversion software (I have given it for free, click Converting complex numbers), then how to compare the results of execution software's program with the manual calculation?

Here I will give an example of the manual calculation method to convert complex numbers rectangular form into polar form, with sample questions 30 + j25

Given the rectangular form:
30 + j25
x (real) = 30
y (imaginary) = 25

Completion:
r (abs) = √(x2 + y2) = √(302 + 252)= 39.05125
φ (angle) = tan-1 (y/x) = tan-1 (25/30) = 39.80557

Then the polar form becomes:
r ∟ φ° = 39.05125 ∟ 39.80557°

See a picture below, the calculation above Rectangular form into polar form

As someone who studied electricity, you will be confused with the imaginary calculations such as: (30 + j25) × (40 ∟ 65°). Two models number in parentheses is a complex numbers, where 30 + j25 is call rectangular form and 40 ∟ 65° is call polar form.

Rectangular form is a number that can be put in the form x + jy, where x and y are real numbers and j is called the imaginary unit. In this expression, x is called the real part and y the imaginary part of the complex number.

Polar form is a number that can be put in the form r ∟ φ°, where r is absolute value and φ is angle value. Together, r and φ give another way of representing complex numbers.

To solve the above calculations problem, you should have a scientific calculator, and you should know how to operate it. Can you do it? And to make it easier I will give complex numbers conversion software, free for you.

## Magnetic relay, TPDT switch and QPDT switch

Magnetic relay or just called relay is a type of switch that is controlled by an electric current. The main part of relay consists of a coil and contacts. Relay coil wrapped around the core. There is an iron armature will be attracted to the core when a current flows through the coil. Armature is mounted on a spring-loaded lever. When the armature attracted to the core, relay contact will change its position from normally closed contacts to the normally open contacts.

A relay can be activated in about 10 ms. Most relay placed in packaging that fully closed, as shown below.

Most among the relay has contacts type of SPDT switch, but there are also several types of DPDT switch, TPDT switch (Triple Pole Double Throw) and QPDT switch (Quadruple Pole Double Throw, as shown above right).

The important thing to note on a relay that will be used is the coil voltage and the maximum, current and voltage contacts.

Larger relays can be connected to the currents up to 10 A at a voltage of 250 VAC. The DC maximum voltage for switching is always lower than AC maximum voltage, sometimes even just half of the AC maximum voltage.

Symbol relay with QPDT contact switch

## Micro switch

Micro term on the micro switch, doesn't mean that the size of micro switch is small. This name indicates that the keys used to operate micro switch, only shifted by a very small distance.

Micro switch is type of very sensitive switch, just a little pressure on a lever may cause the switch move from one position to another. Most micro switches have contacts SPDT type, so that the switch can be used to connect or disconnect, or both simultaneously.

SPDT contacts in the micro switch is generally composed of three terminal tag, such a Common line, NO (Normally Open) contact and NC (Normally Closed) contact. Contacts are equipped with spring-loaded, on normal condition, Common line will be connected to NC contact.

There are various types of micro switch, which can be used according to the applications where the switch should be operated mechanically. Image below shows the various types of micro switches.

For example, a micro switch can be mounted in such a way in a refrigerator. Common line and NC contact connected to a lamp. When the door closed, contacts will open and the light will turn off. When the doors opened, the contacts will close and light will turn on.

## Schematics power supply 12 VDC 5 A

Circuit power supply 12 VDC 5 A usually used for audio amplifier. With the characteristics of its pure DC output voltage, big power, and very stable, to avoid hum or noise on the speakers.

Power supply audio amplifier
Schematics power supply 12 VDC 5 A as shown below

Components are required:
1. C1 = Elco 6800 uF/25 V
2. C2 = Elco 100 uF/16 V
3. C3 = Elco 2200 uF/25 V
4. D1, D2 = Diodes IN 5402
5. Q1 = Transistor 2N 3055
6. IC1 = Regulator 7812
7. T1 = Transformer step down 220 V/15 V 5 A CT

## Table data of high power transistors

Table data of high power transistors below, provide information about the type of (BD131, BD132, BD139, BD140, BD437, BD438, BD679, BD680, 2N3055, MJ2955, TIP31, TIP32, TIP33, TIP34, TIP35, TIP36, TIP41, TIP42, TIP2955, and TIP3055), type (PNP or NPN), supply voltage, current, and maximum power, HFE, HFE bias, the opponent (if the PNP type replaced with NPN type, or reverse), and packaged transistor (click here to view the package).

High power transistors or large signal transistors used for general purpose, amplifier circuit, the output power circuit, or a large current circuit switch.

## Table data of low power transistors

Table data of low power transistors below, provide information about the type of (BC107, BC108, BC109, BC140, BC141, BC160, BC161, BC177, BC178, BC179, BC327, BC328, BC337, BC338, BC546, BC547, BC548, BC556, BC557, BC558, BC639, and BC640), type (PNP or NPN), supply voltage, current, and maximum power, HFE, HFE bias, the opponent (if the PNP type replaced with NPN type, or reverse), and packaged transistor (click here to view the package).

Low power transistors or small signal transistors used for general purpose, small-signal amplifier, or the circuit switch.

## Transistors package - TO (Transistor Outline)

Packaged transistors are varied, low power transistor package will be different with the packaging of high power transistor. Low-power transistors made with the packaging from plastic or metal. Low power transistor packaging made of plastic material having a characteristic surface is flat, while those made of metal having a protrusion (tag) on the plate underneath.

Transistors with a higher power, usually made of plastic packaging, metal, or a mixture of plastic and metal. Metals in the body transistor, generally signifies a collector terminal, and specialized in high power transistor, the metal tag is useful for attaching a heat sink or appliance exhaust heat dissipation that occurs during the process.

Packaging features are intended to identify the terminal legs of the transistor. Most of the packaged transistor is grouped with the term TO (Transistor Outline).

Picture below is a transistor package which we use in the electronics world, including TO-92a, TO-92B, TO92C, TO-126, TO-220, TO-18, TO-39, TO-3, and TO-3P (N), following the legs or the terminal base, emitter, and collector.

## Key switch and DPDT switch

Key switch
Key switch is a type of switch that can only be turned on and turned off by using a key. Only a key partner and the right locking device which can be used to operate the switch. Key switch can be used in applications that require high levels of security, such as electrical control circuit in the industry.

Examples of key switch as shown in the picture below

DPDT switch
Toggle switch, rocker switch, and slide switch, can also be made ​​in a Double Pole Double Throw version, which is abbreviated with DPDT switch. Form of this switch combine two separate switches in one unit, but they operated together.

DPDT switch can be used to connect two circuits at the same time. These switches can also be connected to the neutral wire line and the line wire voltage of the source at once. When a switch is in off state, the electrical equipment connected to the switch is totally isolated from the source voltage.

Symbol of DPDT switch as shown in the picture below

## Rocker switch and Slide switch

Rocker switch
Rocker switch works the same way as a toggle switch, where there is a lever that can be pressed up and down. Lever of the rocker switches are usually called to rocker lever, shaped like an electric bell button.

Generally there are two numbers on the rocker lever, numbers 1 and 0. When the lever is pressed on number 1, indicating that the switch in the On position, and when the lever is pressed on number 0, indicating a switch in the Off position.

Examples of rocker switch as shown below

Slide switch
Slide switches are used for similar purposes to the use of toggle switches, but the slide switch is operated by using a sliding knob.

Examples of slide switches as shown in the picture below

## Rotary switch

Rotary switch is a switch type which is operated by way of played. These switches are used to connect one line to one other line, among several lines that already exist. Often, several pieces of rotary switch is used in the same unit.

Examples of common use rotary switch is serves to select a range of measurements on an AVO meter or a multimeter, or to choose a power supply voltage. This type of switch has one or more contacts are surrounded by a ring with 12 stationary contacts. Such switches are made with the composition different contacts. These arrangements can be either 1 pole of 12 lines, 2 poles 6 lines, 3 poles 4 lines or 4 poles 3 lines.

The symbol of rotary switch with 2 poles 6 lines shown bellow

## Press switch, PTM switch and PTB switch

Press switch is a type of switch that is operated by pressing a button. There are two types of press switch, ie push to make (PTM) switch and push to break (PTB) switch.

Most of the press switch is a kind of the PTM switch. By pressing a button PTM switch, the contacts will be depressed until the switch is closed and touch each other. While by pressing a button switch type of PTB switch, the contacts are normally closed contact, but will be forced open when the button is pressed.

Each type of PTM switch and PTB switch, can work to connect or disconnect during a moment or locking (latching). A switch work during a moment, will close (connect) or open (disconnect) as long as the button is pressed. When the button is released the switch will return to its original position.

Connection on the switch that locks, the button will remain in a depressed position after the first time pressed. Switch contacts will remain closed or open, depending on the type of switch is concerned. You must press the button again to unlock and return the buttons to its normal position.

Press switches are widely used in various industrial applications, the motor control circuit, and can also be used to connect power to the lights, radio devices, and other electrical equipment.

Symbol press switch such us PTM switch and PTB switch as shown below

## Toggle switch, SPST switch and SPDT switch

Toggle switch is the simplest form of switch, operated by a toggle lever that can be pressed up and down. According to the convention, position of the lever downwards to indicate OFF conditions or switch contacts is disconnected, and position of the lever upwards to indicate ON conditions or switch contacts are connected.

Toggle switch have two terminal tag, which indicates that switch have a contact type single pole single throw or single pole single direction, which is usually referred to as SPST switch.

Toggle switch that are smaller have three terminals tag, which indicates that switch have a contact type single pole double throw or single pole two direction, normally abbreviated with the SPDT switch. Terminal tag at the center is the line common current flow and can establish contact with either of these two other tag. Such contacts are called changeover contacts switch.

Symbol for SPST switch and SPDT switch as shown below

## The Switch, On condition and Off condition

The switch is a device used to control the flow of electrical current into the circuit. In the previous discussion about electric current, the electrical current will only flow in a closed circuit. So as to create a current to flow or not, we can use the switch.

Current flows when the switch contacts touch each other. In this state, the switch is said to be closed or made ​​contact.

Current can not flow into the circuit when the contacts are not touching. In this state the switch is said to be opened or lost contact.

Other terms of the condition of the switch is On and Off. On condition occurs when the contacts is made​​, and the Off condition occurs when the contact is lost.

There are various types of switches are used for many different purposes. Figure above shows the general symbols of switch, Off the conditions shown in Figure A, and On conditions are shown in Figure B.

## Reflections, Diffusion and Refraction

Reflection
Whenever light falls onto surface, some of it is absorbed and the remainder is either reflected or transmitted. If the surface is opaque and smoothly polished, the specularly reflected light leaves the surface at the same angle as is arrived (as a billiard ball striking a cushion), and by suitably shaping the surface it is possible to redirect the light in any desired direction (e.g. a motor car headlight, with lamp placed at the focal point of a polished parabolic mirror directing most of the light forward).

Diffuse reflection occurs from matt surfaces. The light is reflected most strongly at right angles to the surface (whatever the direction from which the light arrives) and progressively more weakly at other angles. Matt surface show no highlights. Most painted and many other surfaces are partly specular and partly diffuse reflectors of a light and are classified according to which type or reflection predominates.

Diffusion
Light passes straight through a transparent material, but it scattered or diffused to a greater or lesser extent in a translucent material. Flashed opal glass or its plastics equivalent scatters it completely so that it emerges in all directions, and complete concealment of lamps behind a panel of this material is easy achieved. Frosted glass diffuses the light less perfectly, so that it emerges mainly in the same general direction as when it entered the glass; in effect, it is usually possible to see vaguely the positions of lighted lamps behind frosted panels. Hammered and rolled glasses and clear plastics with a similar finish generally have less diffusing and concealing power than frosted glass but have a sparkle that may be preferred in many cases.

Refraction
If light passes through a transparent material which does not have parallel side, it will be bent away from its original direction by a process known as refraction. Ribbed glass or plastic fittings in which each rib is a carefully designed prism can therefore be made to control light very accurately in a required direction, and this principle is very widely used in electric street lighting fittings.

## Lighting and common terms used in lighting design

Virtually all buildings have electric lighting which serves two purpose. It help us to recognise objects quickly and in sufficient detail to learn all we need to know about them, and it contributes to making buildings safe and pleasant place in which to work or take part in other activities.

There must always be enough light to make object visible but other factors are no less important. The directions from which light come, the brightness and color contrasts created between details of interest and their background, the presence or absence of bright reflections in the part of the object being looked at, and changes in color resulting from the type of lamp used can all effect ease of recognition.

Some of the more common terms used in lighting design and the associated units are given below
Luminous flux. The light emitted by a source, or received by a surface. It is expressed in lumens. Symbol: Ø
Lumen. This is the SI (Standard International) unit of luminous flux. An ordinary 100W lamp for example emits about 1200 lumen. One lumen is the luminous flux emitted within solid angle (one steradian) by a point source having intensity of one candela. Symbol: lm
Luminous intensity. The quantity which describes the power of a source or illuminated surface to emit light in a given direction. It is the luminous flux emitted in very narrow cone containing the given direction divided by the solid angle of the cone. The result is expressed in candelas. Symbol: I
Candela. The SI unit of intensity. It is lumen per steradian. Symbol: cd
Illuminance. The luminous flux density at a surface, i.e. the luminous flux incident per unit area. The quantity was formerly know as the illumination value or illumination level. It is expressed in lux (lumens/m2 or lm/m2). Symbol: E
Lux. SI unit of illuminance. It is equal to one lumen per square meter.
Room index. An index related to the dimensions of a room, and used when calculating the utilization factor and the characteristics of a lighting installation. It is given bellow
lw / hm (l + w)
where l is the length and w the width of the room and hm the height of luminaires above the working plane.

## Application for Thyristor: Excitation of synchronous motor

In the past the overload torque requirement has been met by using a large frame size than necessary to meet full load torque requirements, the torque being proportional to the product of the AC supply voltage and the DC field produced by the excitation current.

With thyristor control of excitation current it is possible to use a smaller frame size for a given horse power rating and arrange to boost the excitation by means of a controller to avoid loss synchronism under torque overload conditions.

The excitation current of a synchronous motor may be controlled by supplying the motor field winding from a static thyristor bridge, using the motor supply current to control the firing angle, figure below. A pulse generator varies the firing angle of the thyristors in proportion to a DC control signal from a diode function generator. Variable elements in the function generator enable a reasonable approximation to be made to any of a wide range of compensating characteristics.

Simple compensated excitation circuit
When the motor operates a synchronously, i.e. during starting, a high emf is induced in the field winding, and the resulting voltage appearing across the bridge must be limited to prevent the destruction of the bridge elements. This may be done by using a shunt resistor connected as shown.

Where more exacting requirements have to be met, current feed back can be applied to eliminate effects of non-linearity in the pulse generator and rectifier bridge and it will also improve the response of the system to sudden changes of load. Automatic synchronizing is possible without relays by incorporating a slip frequency sensing circuit to control the gate which supplies the control signal to the pulse generator.

## Passive components and active components

Electronic components are divided into two types, namely passive components and active components. Passive component is a component that can not lead to increase in the electric power circuit, examples of passive components are resistors, capacitors, and inductors.

While the active component is a component that can lead to increase in the electric power circuit, examples of active component is tansistor.

Resistor has the ability to convert electrical energy into heat. Inductor has the ability to convert electrical energy into magnetic force. However, neither of the two components that can lead to the addition of power in the circuit, it is called passive components.

Instead of a transistor receives the low power input (small current) and converts it into a high power output (large current), the transistor is called the active component.

## Gain transistor

Gain transistor or the acquisition of the current generated by the transistor, commonly referred to as the small signal current gain, while the magnitude of the gain is written with symbols HFE. This gain value is determined when the transistor is made, and with a very diverse range. For example, type BC548 NPN transistor has a range between 110 and 800.

Under conditions of saturation, the gain is the ratio of collector current to base current, or by the equation

HFE = IC / IB

Example question:
Calculate the gain transistor in the circuit below

completion:
Known value of IC = 60 mA, IB currents obtained by Ohm's law
IB = VBB - VBE / RB
IB = (6 - 0.7) V / 10 kΩ
IB = 5.3 V / 10 kΩ
IB = 0.00053 A
IB = 0.53 mA
The amount of gain or HFE = IC / IB = 60 mA / 0.53 mA = 113

## Cut off condition and saturated condition of transistors

In the switch circuit, transistor sometimes be in the inactive state, where there is no any current flows through it. These conditions is called transistor's cut off condition.

Figure A shows the state of the transistor in a cut off condition

At other times when the transistor is in the fully active state, where there are only a relatively small potential difference between the emitter and collector terminals. These conditions is called transistor's saturated condition.

Figure B shows the state of the transistor in saturated condition.

## Thyristors or SCR (Silicon Controlled Rectifier)

The Thyristors is a semiconductor switch either of the pnpn or npnp type, whose bi-stable action depends on regenerative internal feedback. Figure at the left is symbol of thyristor, where A is anoda terminal, C is cathode terminal and G is gate terminal.

The four layer device is usually silicon although germanium has been used. Devices with the two endmost layers only connected to external terminals (anode and cathode) are called four layer diode, those with three layers accessible (anode, cathode, and p gate) are called thyristors. SCR (Silicon Controlled Rectifier) is other name of thyristors.

The structure is best visualized as consisting of two transistors, a pnp and an npn interconnected to form a regenerative feedback pair as shown in figure bellow.

Current gain around the internal feedback loop G (Gate) is hfe1 x hfe2, where hfe1 and hfe2 are the common emitter current gains of the individual sections. If Ico1 is the collector to base leakage current of the npn section and Ico2 is the collector to base leakage of the pnp section, then:
for the pnp section: Ic1 = hfe1 (Ic2 + Ico1) + Ico1
for the npn section: Ic2 = hfe2 (Ic1 + Ico2) + Ico2
and the total anode to cathode current Ia = (Ic1 + Ic2)

from which Ia = [(1 + hfe1) (1 + hfe2) (Ico1 + Ico2)] / [1 – (hfe1) (hfe2)]

With a proper bias applied, ie positive anode to cathode voltage, the structure is said to be in the forward blocking or high impedance 'off ' state. The switch to the low impedance 'on' state is initiated simply by raising the loop gain G to unity. As this occurs the circuit starts to regenerate, each transistor driving its mate to saturation. Once in saturation all junctions assume a forward bias, and the total potential drop across the device approximates to that of a single junction. Anode current is then only limited by the external circuit.

To turn off thyristor in a minimum time it is necessary to apply a reverse voltage and under this condition the holes and electrons in the vicinity of the two end junctions will diffuse in these junction and result in a reverse current in the external circuit. The voltage across the thyristor will remain at about 0.7 V positive as long as an appreciable reverse current flows.

After the been removed, the reverse current will cease and the junction assume a blocking state. The turn-off time is usually of the order of 10-15 μs. The fundamental difference between the transistor and thyristor is that with the former conduction can be stopped at any point in the cycle because the current gain is less than unity. This is not so far the thyristor, conduction only stopping at a current zero.

## Photo Electric Devices

There's a lot of photo electric devices, such as photo-cell relays, photoelectric switch units, silicon photo-electric cells and silicon blue cell.

Photo-cell relays. Basic component of photo-cell relay is an integral light activated switch. It combines a silicon planar photo diode with integrated circuit on a single substrate to provide a highly sensitive photo electric device. Operation is such that when light of a selected intensity falls upon it, the device switches on and supplies current to an external load. When the light intensity falls below the critical level the load current is turned off. This critical level can be adjusted within wide limits.

The equipment comprises a projector containing a light emitting diode and optical system projecting a beam of light either directly or by reflection onto a photo-cell mounted in a receiver unit. The relay coil is energized when the light beam is made and de-energized when it is broken. Thus the relay contacts can provide a change over operation which can be used to perform some external control function. The control unit can contain additional circuitry such as time delays or LED failure circuits to meet a wide variety of application requirement. System are available for operating over distances from 10-15 mm up to 50 m or more.

Applications include conveyor control, paper breakage alarm, carton sorting and counting, automatic spraying, machinery guarding, door opening, level controls, burglar alarms, edge alignment control and punched card reading.

Photoelectric switch units. Light sensitive switches are used for the economical control of lighting. They consist of a photo-cell which monitors the intensity of the light and automatically switches the lighting on or off. Construction of s typical unit is shown in figure 4.10 and this will switch a resistive load of 3 A at 250 VAC. The unit is based on a cadmium-sulphide cell and it incorporates a 2 minute time delay to prevent 'hunting'. Larger units are available with resistive switching capacities up to 10 A.

Silicon photo-electric cells. These cells are designed to provide large output current even under low illumination intensities. Currents of several milliamperes are obtainable. Structure of a photo-electric cell will be seen to consist of a thin p type layer on n type silicon. Due to its linear photo-voltaic effect there is no need for a bias power source. A linear output can be obtained by selecting a suitable load resistance for a wide range of illuminance. Like the silicon blue cell, described below, it has no directivity of receiving light, so there is no need to adjust the optical axis as is the case with photo-transistors.

Silicon blue cell. The sharps silicon blue cell manufactured by photain controls is claimed to be the world's first photo-electric diode possessing high sensitivity over the entire visible light spectrum. It is more reliable than the selenium or cadmium-sulphide photo-cells and has superior time response. No bias power is required, it has a lower noise level than the other two type and it is non-directional.

Application include illumination meters, exposure meters, optical readouts of film sound tracks, colorimetry, flame spectrometry, photo spectrometry and color or pattern recognition equipment.

## Resistivity of any material

The resistivity of any material is the resistance of a piece of material having unit lenght and unit sectional area. The symbol is ρ and the unit is the Ohm meter. The resistivity of a material is not usually constant but depends on the temperature.

Table below shows the resistivity (with its reciprocal, conductivity) of the more usual metals and alloys
Table Resistivity of any material at 20 °C
 Material Resistivity (Ohm meter) Conductivity (Siemens per meter) Silver 1.64 x 10-8 6.10 x 107 Copper (annealed) 1.27 x 10-8 5.8 x 107 Gold 2.4 x 10-8 4.17 x 107 Aluminium (hard) 2.82 x 10-8 3.55 x 107 Tungsten 5.0 x 10-8 2.0 x 107 Zinc 5.95 x 10-8 1.68 x 107 Brass 6.6 x 10-8 1.52 x 107 Nickel 6.9 x 10-8 1.45 x 107 Platinum 11.0 x 10-8 9.09 x 106 Tin 11.15 x 10-8 8.7 x 106 Iron 10.15 x 10-8 9.85 x 106 Steel 19.9 x 10-8 5.03 x 106 German silver 16-40 x 10-8 6.3-2.5 x 106 Platinoid 34.4 x 10-8 2.91 x 106 Manganin 44.0 x 10-8 2.27 x 106 Gas carbon 0.0005 200 Silicon 0.06 16.7 Gutta-percha 2 x 107 5 x 10-8 Glass (soda-lime) 5 x 109 2 x 10-10 Ebonite 2 x 1013 5 x 10-14 Porcelain 2 x 1013 5 x 10-14 Sulphur 4 x 1013 2.5 x 10-14 Mica 9 x 1013 1.1 x 10-14 Paraffin-wax 3 x 1016 3.3 x 10-17

## Power supply circuit with variable voltage

By using a transformer without ct, a bridge rectifier circuit system, and rotary switch, we can create a power supply for electronic equipment with voltage range from 3 V, 4.5 V, 6 V, 7.5 V, 9 V, to 12 V.

Add component such a rocker switch or a slide switch as the main switch, and put one LED as an indicator tool.

Power supply circuit with variable voltage as shown below

Click to enlarge

Components are required:
1. S1 = Rocker switch
2. S2 = Rotary switch (2 pole 6 lanes)
3. T1 = Step-down transformer without ct (220V/12V 500mA)
4. D1, D2, D3, D4 = Diodes IN4002
5. D5 = LED
6. R1 = Resistor 220 Ω
7. C1 = Elco (electrolytic capacitor) 2200 μF/16V

## Diode bridge rectifier circuit

Diode bridge rectifier's circuit is a full-wave rectifier circuit that uses four diodes, and connected as a bridge. Unlike the full-wave rectifier discussion in previous article, where the circuit uses two diodes, this time is full-wave rectifier circuit with four diodes.

Beside different from amounts of diodes, other difference lies in use of a transformer, which transformer used in the bridge rectifier circuit system is not a transformer which has ct (center tap) or using a conventional transformer without ct.

Diode bridge rectifier's circuit as shown below

which:
• AC = AC voltage source
• D1, D2, D3, D4 = diode rectifier
• C = electrolyte capacitor

## Transistor as a switch

One function of transistor most commonly used in the electronics world is as a switch. To find out how transistor as a switch, we do experiments on the following circuit.

Switch (S1) condition in Off state or open, there is no voltage source attached to the base terminal of transistor, so that there will be no current flowing in the circuit, in other words, the lamp will not light.

Switch (S1) condition in On state or closed, voltage source is attached to the base terminal of transistor, so that there will be currents flowing in the circuit, in other words, the lamp will turn on.

## How transistors work

If there is no external voltage is connected to transistor, then there is no current flowing in a circuit, in other words all the electrical current equal to zero. So to use a transistor, we need to link in such a way, to obtain a current flow that we want.

Circuit below is an example of how the NPN transistors work

where:
1. Emitter terminal is a negative polarity
2. Collector terminal has a few volts more positive than emitter terminal
3. Base terminal is 0.7 Volt more positive (see break down voltage) or greater.

With these conditions, we can see that:
• A relatively small current flows through the base (IB)
• Currents with a much greater value flow through the collector (IC)
• Base current and collector current flowing out of transistor through the emitter.

## Determine terminals and type of transistor using analog multimeter

Almost all of analogue multimeter or AVO meter (Ampere, Volt and Ohm meter, as shown in the figure below), can use to determine terminals (base, emitter, and collector) and type of transistor (PNP or NPN). On this configuration, turn the knob multimeter's position on Ohm meter test or at symbol Ω.

We take an example to be measured is transistor BJT type FCS9015, which is quite widely use. We learned to determine terminals and type of transistor FCS9015, and the following steps:
1. Measuring and create tables of measurement
• Set analogue multitester and adjust position of rotary knob on Ohm meter, a measurement scale at x10
• Imagine or describe the position of terminals transistor with sequence numbers 1, 2, and 3
• Create a table with 6 units of measurement measuring point, ie 1-2, 1-3, 2-3, 2-1, 3-1, and 3-2
• Specify black probe or negative test probe for the first number, and red probe or positive test probe for the second number, ie the measuring point 1-2, the black probe at point 1, and the red probe at point 2
• Record the results of each measurements, indicated by Ohm meter's needle movement

2. Determine base terminal and type of transistor
On the measurements table, there are two measurement points that get results, that is point 1-2 and point 3-2 (see figure above). It is time for us to determine the terminals and type of transistor, by the way:
• Base is the same number found on the two measuring points
• Type NPN or type PNP, we can set it to see what probe is connected to the base. If base point connected to black probe, then NPN type transistor, and when base point connected to red probe, then PNP type transistor
There is different probe usage between analog multimeter and digital multimeter. In the analog multimeter, red probe is connected to negative battery Ohm meter, and black probe is connected to positive battery Ohm meter

3. Determine emitter and collector terminals of transistor
Needle's moves at measurements points 1-2 and 3-2, almost have equal value, so it will be difficult to determine terminals collector and emitter using analogue meter. So we use a manual way, ie with visual or sight. There are several characteristics that indicate the collector's terminal, among others:
• The letter C is printed larger
• There is a little hole
• Generally connected to the metal on packaging or transistor's body, especially at high power transistor body

We've been able to determine base and collector of terminals transistor, then last is emitter terminal.

So we get the conclusion:
1. At point 2 terminal base of transistor FCS9015
2. FCS9015 is a PNP transistor, the base on red probe
3. At point 3 terminal collector FCS9015, see! there is letter C is printed larger
4. At point 1 terminal emitter of transistor FCS9015
5. Terminals and type of transistor FCS9015 as shown in the picture below

How to determine terminals base, emitter and collector of transistor using digital multimeter? just click that link.

## How to determine terminals and type of transistor using digital multimeter?

Requirement to determine terminals (base, emitter, and collector) and type (PNP or NPN) transistor using an AVO meter or multimeter or digital multitester, is multitester must have a diode test feature. Diode test feature is usually denoted by symbol of a diode, as shown in multitester's picture below.

We take an example to be measured is transistor type C945, which is quite widely use. We learned to determine terminals and type of transistor C945, and the following steps:

1. Measuring and create tables of measurement
• Set Multitester the rotary knob of multitester on diode test feature
• Imagine or describe the position of terminals transistor with sequence numbers 1, 2, and 3
• Create a table with 6 units of measurement measuring point, ie 1-2, 1-3, 2-3, 2-1, 3-1, and 3-2
• Specify black probe or negative test probe for the first number, and red probe or positive test probe for the second number, ie the measuring point 1-2, the black probe at point 1, and the red probe at point 2
• Record the results of each measurements

2. Determine terminals and type of transistor
On the measurements table, there are two measurement points that get results, that is point 1-3 at 0.720 VDC, and point 2-3 at 0.716 VDC (see figure above). It is time for us to determine the terminals and type of transistor, by the way:
• Base is the same number found on the two measuring points
• Type NPN or type PNP, we can set it to see what probe is connected to the base. If base point connected to black probe, then PNP type transistor, and when base point connected to red probe, then NPN type transistor
• Emitter-Base forward bias greater than Collector-Base, or EB > CB, that is PNP type transistor. Base-emitter forward bias greater than Base-Collector, or BE > BC, that is NPN type transistor

So we get the conclusion:
1. At point 3 the transistor base C945
2. C945 is a NPN transistor, the base on red probe
3. At point 1 terminal emitter and at point 2 terminal collector C945, because the point 1-3 > 2-3
4. Terminals and type of transistor C945 as shown in the picture below

## Transistor, bipolar and unipolar

Transistor is an electronic component semiconductor, has ability to control the effective resistance by controlling the main signal (voltage and amperage) from a distance.

There are two types of transistors, namely a bipolar junction transistor or abbreviated by BJT, such as PNP and NPN, and unipolar transistor junction transistor or abbreviated by UJT, such as FET and MOSFET.

Transistors made from crystalline silicon or germanium, where a layer of N type silicon layer sandwiched by two types of P. Conversely it could also be made transistor consisting of two N-type silicon layers sandwiching a layer of type P. Both transistors are kind of BJT transistor, or PNP and NPN type.

In general, BJT transistor has three terminals, ie base (abbreviated with the letter B), collector (abbreviated with the letter C), and emitter (abbreviated with the letter E).

Below is a symbol of PNP and NPN transistor

## Produce a pure wave DC from rectifier circuit

DC output generated by a rectifier circuit, not a wave of pure DC, but the waveform up and down or pulsing. These waves can not be used to distribute electronic circuits.

Process of flattening the pulsing waves of rectifier circuit, it can be done by connecting in parallel a large value of filter capacitor to output DC, as in the circuit below

The capacitor used is usually electrolytic capacitors (elco) and has a capacitance value of 1000 μF or more. DC pulses from rectifier circuit are generated continuously and will fill capacitor immediately, until the voltage reaches maximum value.

When the load draw current of the circuit, the voltage on capacitor bit by bit away from maximum value, but the voltage will be immediately returned to maximum value by the next pulse. The result is a DC waveform with a little wave ripple.

DC waveform with a little wave ripple like picture above, can use to supply or distribute electronic circuit. It's almost a wave of pure DC.

## Full-wave rectifier circuit

Current output generated by half-wave rectifier circuit, is only worth half input cycle. This means that half of the input power is wasted.

Rectifier would be better, when using two diodes in series. Consider the circuit below

On positive cycle and negative cycle of the AC waveform, given a forward bias diode. Current flows through two diodes to the load and returned to the transformer through the ct (center tap). So that the circuit can be considered to consist of two half-wave rectifier circuit that works in turn.

Waveform at the output of which is at the end of RL load is shown in the picture below

Rectifier circuit is still generating output during the second half-wave cycles (cycles of positive and negative). So this series 100% efficient, because there is no input power is wasted. The circuit is called a full wave rectifier circuit.