Thyristor

Thyristor is an NPNP four layer or three junction semiconductor device. Thyristor is used switch. Thyristor is big family having several devices performing different tasks. One of them is SCR. SCR stands for silicon controlled rectifier. An SCR has three terminals Anode, Cathode and gate. The anode is connected to the positive supply and normally load is taken in series of anode. Cathode is connected to the negative supply and gate is used to trigger the device. A small voltage short duration pulse at gate with respect to ground or cathode can switch on this device. On DC supply if SCR is once switched on, it cannot be off through gate. It will remain on even if the gate pulse is removed. The only way to switch off an SCR from on to off is to remove the anode voltage. But in AC supply the SCR remains on in corresponding half cycle the device is switched on. For AC two SCRs are connected back to back to work for both half cycles or one Triac is connected which is usually the combination of two SCRs.

Silicon control rectifier

SCRs are available in different current rating and sizes. Also PIV is another consideration to be taken into account. PIV is peak inverse voltage. Normally used scrs have a high piv rating of 1200v. The current rating is from one ampere to thousands of amperes. If a low PIV SCR is used at high voltage, it will breakdown and destroyed.

Thyristors are very commonly used in industrial control systems and motor controls. They are used in motors soft starters. In motor soft starters they start and stop the motors softly by controlling input energy to the motor. Meaning they controls the motor three phase power input and starting the motors from some low voltage of say 70V and bring the motor up to line voltage 380 or 480v in certain amount of time. This time is known as ramp up time. Also same is applied in reverse to stop the motor softly. The motor stopping is known as ramp down. This way motor starts and stops softly and it is not giving mechanical and electrical stress to the system.

SCR or silicon control rectifier is a sort of rectifier with control. It means you can control the energy passes through scr by triggering its gats at certain time. That time is angle of half cycle. This angle is known as alfa angle. The value of alfa angle can be from zero to 180 degrees. The less the angle, the more the power passes through the scr. The bigger the angle, less the power passes through the scr. This is a sort of inverse proportion.

Transistors

Transistor is the most important electronic device. Transistor had been invented in 1948 in bell laboratories but they had been used in 1960s. Before transistors thermionic tubes were used in electronics. Transistor is a three layer semiconductor device. Transistor has a very fast switching capability. The word transistor is the combination of transfer resistor. It means transistor is an electronic device which can change or transfer its resistance. Hence it controls the flow of current by changing its resistance from very high to very low resistance. A transistor can be used as an on an off switch as well as it can be used as a variable resistance to provide limitation to current flow electronically.

Transistors are made of N and P type semiconductor. The semiconductor could be germanium or silicon. In older days germanium was used and now a days silicon is used. Silicon is more stable than germanium at high temperature. There are two main types of injunction transistors. One is NPN and second one is PNP. There are three terminals of a transistor. They are Collector, Emitter and Base. The emitter is the out layer and is forward biased to base. The collector is also the outer layer and has a reverse bias with base. The collector has opposite polarity to the applied voltage and emitter has the same polarity to the applied voltage.

Transistor function and symbol schematics

There are two circuits in a transistor. One is base emitter circuit and the other the collector emitter circuit. When voltage is applied to the base emitter circuit and the voltage passes the value 0.7v in silicon diode and 0.3v in germanium diode, the transistor conducts and current passes between collector and emitter. A small current in the base emitter circuit can control large current in the collector emitter circuit. This is somewhat like a relay operation. But relay is electromagnetic or electromechanical switch whereas transistor is an electronic switch.

Transistor can be used as switch as well as amplifier. If it is used as switch the load is connected in the series of collector or emitter. If it is used as amplifier the load resistance is connected in series of collector or emitter and change in current would be taken as voltage drop on the load resistance.

 Transistors are made in different power ratings. They have different sizes. There are thousands of models designated with different numbers. They have many shapes. Some are small signal transistors and some are power transistors. Some are low frequency and some are high frequency transistors. Some have high gain and some have low gain. There characteristics are mentioned in data books. A single transistor cannot have all characteristics. That is the reason there are thousands of transistor models available for different application. While selecting a transistor for a specific job and application you should keep the requirements and parameters of operation in mind.

There are three biasing method of transistor. Common base, common collector and common emitter. All these three transistor circuit configurations provide different characteristics. All you should know these configuration characteristics and your requirements of operation.

Zener Diode

An ordinary of general purpose diode conducts in one direction. In the reverse direction the diode withstand up to certain limit and don’t conduct. But it we keep on increasing reverse voltage a point will reach at which the diode breaks down and it will conduct in the reverse direction as well. That point is known are zener voltage point. An ordinary diode reached to its zener voltage will breakdown and would be destroyed at that point. Whereas a special diode can be constructed which could withstand this zener voltage level in reverse bias and will not destroy itself at that certain level. These diodes are called zener diodes. They are doped with special materials to obtain zener property.

Zener diode is designed to work at zener voltage at reverse bias in the breakdown region. At breakdown or zener state the diode conducts in the reverse direction and heavy current flows in the reverse direction which is limited with series resistance. Zener diode always maintain a certain voltage drop on itself in the reverse direction due to its reverse conduction property. This property makes it suitable to work in voltage reference circuits and power supply circuits where regulated voltage is needed.

Zener diode has two types of ratings. One is its zener voltage and the second one is the power rating the zener diode can handle. Very common power rating is 400mw. Whereas the zener voltage rating is somewhere from 2v to 110v. Zener diode is made for certain zener voltage rating in the manufacturing process. This is done during its doping process. That voltage rating is normally written on the zener diode body.

Zener diode always maintains its zener voltage value on itself. For example a 6.2v zener diode will only conduct on above 6.2v in reverse. It will not conduct below 6.2v. The current would be limited with external series resistance. This way it will always maintain a 6.2v voltage on itself. The voltage will never cross 6.2v limit. This property of zener diode makes it a voltage reference.

Normally zener diodes are fixed diodes with a certain voltage rating. But some special zener diodes are there which are known as adjustable or programmable zener diodes. Those diodes can be adjusted externally by connected a few resistors to any value within a certain voltage range. Very common of them is TL431 which is very widely used in switching power supplies circuits.

In the figure below a zener diode is connected in parallel to the gauge which is fed by battery through a temperature sensor which acts like a series resistance. The gauge maximum voltage is 7v full scale. In such a case the zener diode must be of 7v voltage rating so that it will limit the voltage on the gauge at 7v and the gauge point would not step over the maximum and gauge would not be burned in due to overshoot at maximum. This way a steady and safe reading could be obtained from a gauge without damaging it in case if high voltage comes on its terminals.

Zener diode typical use in instrumentation gauge.

Resistor

Every circuit have a property of resistance at which they do operate. In a circuit if we have engineered resistance and it does its function properly then this resistance is called a load resistance or loading device. Resistance is used to limit the current and also to produce a voltage drop in electrical circuits. Also resistance is used to measure some quantities like pressure, temperature and current flow in computer systems of automotive. There are three types of resistors. Fixed resistance, variable resistance and stepper resistance. 

Fixed resistors:

Fixed resistors have fix value. They are coming in different ohmic values and power rating (wattage). They are made of carbon or metal oxide. They have fix value and they are used to create a voltage drop depends upon current flow and also they are limiting current through the circuit they are connected in. Fix resistors has value written on them if they are of big wattage rating. Otherwise they have a color code on them if they are of small wattage rating. They use four or five color bands to show their resistance value. If there are four bands on a resistor, the first two bands shows digits and the third band is multiplier band. Whereas the fourth band shows the tolerance of resistance value in that specific resistor. This tolerance is normally 5% to 10% in most resistors. Some very good quality resistors have tolerance as low as 1%.

Resistance color code table

Variable resistor:

As the name employee the variable resistors are not fixed resistance. The value of those resistances can be changed through a knob or a shaft provided on them. There are infinite values can be selected on the given range of a variable resistor. They are both rotating type and sliding type. Both have different used in electrical and electronic circuits. They are same like radio or stereo volume control. They have usually three pins or three terminals. The two terminals have fixed resistance in between them and the third terminal is wiper or the variable terminal of potentiometer and it provides the variable resistance value. They are also available in different values and power rating sizes. The very common purpose of the variable resistance is to make the voltage divider network. In such a case one end of the resistance is connected to the positive voltage supply and the far end is connected to the ground or return or negative of the supply. The third terminal is providing the divided voltage or the variable voltage in such a case. Such voltage dividers have many uses. They are used as throttle position sensor, tank fuel level sensors, cng tank level sensor and accelerator position sensor.

Variable resistance or potentiometer

Stepper Resistor:

Stepper resistor is a combination of fixed resistors arranges in steps. For stepping a switch is used to change the resistance value. This type of resistance have also three terminals same like variable resistor. But stepper resistor has limited and known number of resistance steps. This type of resistance is used in automotive fan speed control. As in most vehicles there are a few steps of speed control is provided on the dashboard as climate control. By changing the steps of switch we can vary speed of the fan motor hence air is controlled through the fan motor speed. The way is controls is we add resistance in the fan circuit due to which a voltage drop is produced on that resistance and fan motor is taking limited current and it spins at lower speed.

Stepper resistance. Car fan motor control system schematic

Buzzer

Buzzer is a sound generator or somewhat a bell you can say. It is to warn the person that something happened and you should give attention. The buzzers are used as door bells or sometimes they are uses with machines to give warning to the operator or in vehicles and they are providing warning to drivers about some action to be taken as something is going wrong. Like if a driver is not fastening his or her seat belt, a warning buzzer is sounding. If a driver is crossing the allowable speed limit for his or her vehicle, a buzzer is sounding and informing him or her to reduce the speed to the safe speed limit.

Typical buzzer arrangement and its function diagram

Most buzzers are very small and they are electromagnetic devices. Sometimes they are piezo electric devices. In autos they are located in dashboards or in the meter clusters to warn the driver about certain conditions. They are usually powered by ecu or engine control unit.

Buzzers have same like construction like a relay. But in buzzer the power applied to the buzzer electromagnetic coil is applied through its nc or normally closed contracts. At rest, no power is applied to the buzzer and its nc contacts are closed together. The current can pass through the contacts and can be applied to the buzzer coil. Then when power is applied to the coil, the armature or diaphragm is attracted towards the buzzer coil due to its electromagnetism. But the at that time the nc contacts opens and current path disconnects to the buzzer coil. At this moment the armature of the buzzer if retracted due to spring attached to it. The NC contacts close again and the same cycle repeated again. This all is happening very fast. The armature in this case is a diaphragm which produces a sound. That sound is warning the person.

Solenoids

What is solenoid

Solenoid is a package of insulated wire and a plunger inside the coil. A solenoid is working on electromagnetic effect of electricity. When power is provided to the solenoid coil, it attracts or repel the metal or magnet core inside the coil which is known as plunger. The plunger is normally spring loaded. When power is applied to the coil, the plunger is attracted inside the coil and it compresses the spring. The other end of the solenoid is attached to the mechanism to be attracted or actuated. Then when power is cut off from the solenoid, the electromagnet coil loses its magnetism and the energy stored in the spring pushes out the plunger. The principle of a solenoid is somewhat like a relay. But in relay there are contacts attached to the armature whereas in solenoid the plunger is attached to the mechanism to be actuated.

In automotive the solenoid is used in several circuits like in door locks, self-starter, trunk lock, egr system, evap control system, automatic transmission and many more. The solenoid is controlled through a relay or sometimes it is driven by a transistor somewhere in the body control unit or ecu. When a solenoid is powered up or driven by a transistor, its one end is connected to battery positive through a fuse and the other end of the solenoid is connected to the driver transistor collector or drain in case of a mosfet transistor. When signal is applied to the base or gate of the transistor, the transistor conducts which causes current to flow in the solenoid and makes it working.

All solenoids used in automotive are normally 12v. They have different current or power rating. The current consumption or the power rating of a solenoid depends upon the size of the solenoid and the thickness of the wire used in solenoid coil. The bigger is solenoid, the thicker the wire used in its coil. The smaller the solenoid, the thinner the wire used in its coil.

Sometimes a diode is connected across the solenoid terminals. This diode is functioning like a flywheel, free wheel or damper diode. It damps the back emf produced in the solenoid when the solenoid is switched off. This is normally used when the solenoid is driven through a transistor. If this diode is not used the back emf can easily destroy the driving transistor.

Relays

What is Relay

Relays are electromagnetic switches which are frequently used in electrical circuits. In a relay there is an electromagnetic coil and set of contacts. The coil is wound with thin copper wire so it has a high resistance due to which it takes or consumes very low current. Current taken by the electromagnetic coil is used to produce electromagnetic force which attracts the armature in the relay. The points or contacts are attached to the armature hence they state change when armature is attracted by the coil electromagnetic force. There are two types of contracts used in a relay. They are normally opened and normally closed. They are mentioned when the circuit is at rest and there is no power applied to the relay coil. When power is applied to the relay coil the contacts changes their state. Means the normally opened then becomes closed contact and normally close becomes opened. The armature is pivoted with a spring. When power is disconnected, the spring brings the armature back to its rest condition and the contacts also change their state accordingly. In a relay there are two circuits. One is the coil circuit and the other is the contacts circuit. The coil circuit controls the contacts circuit. Contacts are design to take heavy current. By applying small current to the relay coil could switch on heavy contacts which could pass large current. Relays are very frequently applied in automotive and cars electrical circuit application. They are used in horn circuit, fuel pump circuit, starter circuit, fan circuit, lights circuit, air conditioner circuit and many more.

A typical relay circuit diagram and working principle

In industry relays are used to translate status of machines to plc or dcs system and also for interlocking. Industrial relays are more robust and strong compared to other ordinary relay. In industry 24v, 110v and 220v coil relays are common. They could be 4 pin to 24 pin. 14 pin relays are very common which have four sets of normally open and closed contacts set.

Typical relay application in automotive horn circuit.

ISO Standards for relays:

ISO International Standards Organization had given specification for most common relays in automotive. They specify terminals as 30,87a, 87,86 and 85. Normally terminal 30 is connected to battery positive voltage or BT+. This applied voltage could come from some switch for control or they can directly come from battery through a suitable fuse. Terminal 30 and 87a forms normally closed and they are connected together when power is not applied to the relay coil. When power is applied to the coil terminal 30 and 87 are connected. So terminal 87 is NO or normally open terminal. Terminal 85 is connected to ground to provide ground or return path to the coil. Terminal 86 is connected to battery positive.

Automotive relay iso standard and pin configuration

Definition of Electricity

What is electricity

The moment and running of electrons in a specific direction is known as electricity. This moment and running of electrons is from one atom to another atom freely in a conductor or conducting material. Protons are attracting electrons. As we have plenty of electrons on the far end of conductor; many electrons are attracted by protons. This is how electricity flows. This push and pull of electrons and protons is creating a pressure. This pressure is known as voltage in electrical. The other name of the voltage is electro motive force or emf. All generators and batteries are producing emf. The emf forces electrons in the conductor resulting in current. The emf pushes and tending the electrons to flow from the outer orbit of electrons. On the outer orbit of electrons the nucleus has less force of attraction or bonding. These electrons in the outer orbit are known as free electrons. The less the number of electrons in the outer orbit, the more that material will be conductor. The more the number of electrons in the outer orbit of an atom the less that material will be conductor. When an electron is free from its outer orbit, the atom becomes more positive. That atom can take electron from another associated atom outer orbit. This way the flow of electrons stays all the time. The flow of electrons in a conductor is happening in the speed of light. Also we cannot see electricity. But we can feel its effect and also we can measure it using measuring instruments. There are different measuring instruments for different electrical quantities. A voltmeter for example is used to measure voltage. An ampere meter is used to measure current. A watt meter is used to measure electrical power. Electricity is used everywhere in our life. In household, in computer, in communication, in mobile phones, in automotive means everywhere there is a use of electricity. Without electricity one cannot think to live today.

Vibration Analysis

What is vibration analysis

Vibration analysis is the very important and essential technique used in industry for the last few decades to diagnose and troubleshoot rotating machinery.  The MCA and ESA are new technologies which are in concept since 1900; both of them have been practically available and in practice in the mid of 1980s.  Vibration analysis technique had been introduced in the industrial market somewhere in 1940 to 1950. A lot of research had been made to purify the knowledge and practices used to analyze the vibration and resonance related problems.  Vibration analysis had been used to detect machine health, rotating machines defects and it is useful to plan and schedule the maintenance routines for machines. Vibration analysis is basically the technology to diagnose and pin point mechanical problems in rotating machinery but it can also be implemented to see the electrical problems related to rotating magnetic flux through vibration spectrum in electrical machines.  

Newer vibration analysis uses accelerometers to collect vibration reading from bearing housings of rotating machines. Then this data is wirelessly shared on iCloud to use this data through ipads and iPhones for further analysis. Data is collected from motors, fans, generators and wind turbines.  

Industrial Motor Circuit Testing and Analysis

Induction motor testing and circuit analysis

Induction motor testing

Very common way to test motor in industry is to test its insulation resistance with a high voltage mega ohm meter or Mager. Mager testing is in practice for a long time in industry to test and analyze motor winding and its insulation condition. But problem with mager is it can destroy or runaway the “weak” spot in winding insulation. Mager testing can damage weak insulation in motor winding due to its aggressive testing behavior. Modern test equipment uses to test motor inductance and capacitance without stressing the winding to high voltage.  

There is another technology which is focusing on a 4 wire kelvin resistance, dissipation factor, insulation resistance, capacitance, impedance, inductance, phase angle or power factor, and change the applied frequency output to see the effect on inter -turn capacitance which is I/F current/frequency response of motor.  This type of testing tests all parameters of a motor like motor winding resistance, inductance, impedance as well as rotor and stater air gap.  All these tests are only be applied while the machine is disconnected from power but they can be done on motor disconnected from its circuit or even can be performed from the motor control center or mcc.  

MCA motor testing in practice

MCA Tester or MCA test equipment

The newest MCA devices; like the one shown in figure above, provides both the automated fault detection better/warning/defective as well as it collects data for further analyses on maintenance PC or work station.  Software shows and narrow down the potential problem as well as it provides the ability to load routes for data trending, for compression of data over time and more advanced trending. 

MCA all test pro equipment

MCA can also be used to detect cable problems, DC motors problems, Power transformer faults along with ac generators and motors faults. MCA is the most advanced technology of troubleshooting and diagnostic used in the modern era of industry. Industries aware themselves with the use and need of such new technologies for reliable machines operations and more productivity with reduced down time.

Transformer

What is transformer

Transformer is used in electrical to transform power from one circuit to another circuit.

Capacitance

What is capacitance

Capacitance is an electrical property. A capacitor is a device which stores electricity in the form of electric charge.

Resistance

What is resistance

Resistance is an electrical property.

Electricity

What is electricity

Electricity is flow of charges or flow of electrons.