Electronics for HVACR Technicians

Transcription

1 Electronics for HVACR Technicians

2 SAFETY and HAZARD PREVENTION

3 CIRCUIT PROTECTION Fuses and circuit breakers are used to protect a circuit against over current. The amperage rating of a fuse must not be greater than the ampacity of the wires being protected. Fuses and breakers are used to protect wires, not people.

4 ELECTRICAL SHOCK Current is the killing factor in electrical shock. Currents between 100 and 200 ma generally cause the heart to fibrillate. A 110 volt power circuit will generally cause between 100 and 200 ma current flow through the bodies of most people.

5 LOCKOUT TAGOUT PROCEDURES Whenever a piece of equipment is being worked on, it should be disconnected from the power source and locked. The person working on the equipment should carry the only key to prevent accidental activation.

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9 Meter Problems High-Voltage spike or transients Input noise Meter 30% or more off true reading AC and DC not read at same time Response time to slow Not Analog Not designed for high speed switching

10 Measurements System requirements Complex wave forms Voltage within 2% Current within 5% Impedance of meter at least 10 MΩ +/- 2% meter accuracy True RMS With low and high band filtering Sampling minimum of 3 a second Speed 2X the speed of measurement

11 KIS Keep It Simple Look for the most obvious problems first. Systematically work back toward the electrical source. Check power quality Understand basics of troubleshooting Don t just replace parts.

12 What is a digital meter?

13 DVOM - Digital Volt-Ohm Meter A digital volt-ohm meter (DVOM) should be the standard hand held tester for testing electrical voltage, amperes, and resistance in all automotive shops. A DVOM is different from older testers in that the input impedance is high and it will not drain off any significant current to activate the meter. Many computer control circuits are very sensitive to any load created by testing equipment and will give improper readings if measured with an older low impedance analog (sweep hand) meter.

14 Why True-RMS? Electrical professionals today need current clamps that are up to the challenge of accurately measuring harmonic currents caused by non-linear loads. Virtually all electronic equipment falls into this category PCs, printers, HID lighting, adjustable speed drives, etc. Average-sensing meters can't do the job. They can produce readings that are 30%-50% low. Why? Harmonics cause distorted waveforms, and averagesensing meters can only accurately measure pure sine waves. One measure of waveform distortion is Crest Factor, the ratio of the peak to the rms value of the wave. CF for a pure sine wave is 1.4. Higher CF indicates harmonic currents.

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16 GENERAL TERMS AND THEORY In order for electricity to work, it needs a complete circuit. It has to be able to not only leave the battery, it has to have a path back to it! Normally, the last part of that path is through the metal of the body and this is called "ground". All references to a voltage are in relationship to this ground. Volts; This is the force behind the electricity. Or the "pressure" at the faucet. Amps; This is how much electricity flows. Or gallons per minute of water through the hose. Ohms; This is the resistance of the wire to flow of electricity. Or thinking of the difference between a small diameter hose and a large diameter hose. The range of ohms goes from zero to infinity. Zero ohms is when it's real easy for the electricity to flow. A reading of infinity is when there is no path for the electricity to go through (a closed valve).

17 GENERAL TERMS AND THEORY Cont. Watts; This is power and is a function of amps and volts. DC; Direct current. Other than within the alternator, all of the voltages in your car is "direct" current. AC; Alternating current. This is what you would see in the wiring in your house. 110 volts is in reality a wave that goes from a positive value to a negative value. Don't play with the house wiring!! Primary voltage; This is the input voltage to the coil and is around 12 volts (I'm trying to keep it simple!). Secondary voltage; This is the output from the coil and is MAJOR voltage. This is what ends up going to the spark plugs and will cause personal damage if you grab it!

18 XYZ s of Oscilloscopes

19 Basic Wave Forms

20 Types of Waves Sine Waves Square and rectangular waves Triangle and saw-tooth waves Step and pulse shapes Periodic and non-periodic signals Synchronous and asynchronous signals Complex waves

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37 What is Electricity Everything is made of atoms There are 118 elements, an atom is a single part of an element Atom consists of electrons, protons, and neutrons

38 Waterfalls and Circuits: More in common than you think Electrical Circuits can be thought of as a waterfall Voltage (V) Height of Waterfall Measured in volts Amperage or Current (I) Amount of water falling at one point at any moment Measured in amperes Resistance (R) Constriction of water Measured in ohms

39 Voltage A battery positive terminal (+) and a negative terminal (-). The difference in charge between each terminal is the potential energy the battery can provide. This is labeled in units of volts. Water Analogy

40 Electrons (- charge) are attracted to protons (+ charge), this holds the atom together Some materials have strong attraction and refuse to loss electrons, these are called insulators (air, glass, rubber, most plastics) Some materials have weak attractions and allow electrons to be lost, these are called conductors (copper, silver, gold, aluminum) Electrons can be made to move from one atom to another, this is called a current of electricity.

41 Surplus of electrons is called a negative charge (-). A shortage of electrons is called a positive charge (+). A battery provides a surplus of electrons by chemical reaction. By connecting a conductor from the positive terminal to negative terminal electrons will flow.

42 Voltage is like differential pressure, always measure between two points. Measure voltage between two points or across a component in a circuit. When measuring DC voltage make sure polarity of meter is correct, positive (+) red, negative (-) black.

43 Voltage Sources:

44 Exercise Measure DC voltage from power supply using multimeter Measure DC voltage from power supply using oscilloscope Measure DC voltage from battery using multimeter Measure AC voltage from wall outlet using a multimeter Measure AC voltage from wall outlet using an oscilloscope Effective or Root Mean Square Voltage (Measured with multimeter) E ERMS=0.707xEA

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46 Current Uniform flow of electrons thru a circuit is called current. WILL USE CONVENTIONAL FLOW NOTATION ON ALL SCHEMATICS

47 To measure current, must break circuit and install meter in line. Measurement is imperfect because of voltage drop created by meter.

48 Simple Electric Circuit Electrons flow from NEGATIVE to POSITIVE Voltage (V) Battery of the system Measured in volts Amperage (I) Component using Electricity Measured in amperes Resistance (R) Device inhibiting the flow of electrons Measured in ohms

49 DC power supplies Little or no AC on DC AC on DC causes failures DC can run on AC link Often AC neutral is us used for DC DC can be combined with other DC power supplies Use batteries or other DC is non discriminatory except for polarity

50 A/C Power

51 AC AC is discriminatory Phase sensitive Level sensitive Polarity sensitive Sensitive to DC Noise sensitive Carrier of noise Noise carried throughout system

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56 Inputs and Outputs Binary Input Output Analog Input Output

57 Inputs Externally Powered Binary Inputs Opto-Inputs (AC or DC) Internally Powered (On board controller) (AC or DC) Virtual Two States

58 Binary Outputs Contact Open/Closed AC or DC Two state

59 LOADS AND SWITCHES Manufacturers design devices with the correct amount of resistance for the device to perform the desired amount of energy conversion. Electrical energy flows through the device and is converted to another form of energy ( light, heat, motion, etc.). A load cannot operate unless the circuit provides a complete path for electrons to flow. Switches are used to control and / or provide safety protection. Switches are wired in series with the load.

60 LOADS AND SWITCHES When more than one load is connected to a power source, switches are connected in series with each load and each load is connected in parallel with the power source.

61 OVERLOAD PROTECTORS Many motors have an overload protection device in addition to any device that may be found in the power circuit. These are usually a bimetal disc that will deflect and open the circuit if an overload occurs.

62 Analog Input 0-10 VDC 4-20 ma DC Resistance Current Voltage Output 0-10 VDC 4-20 ma DC Resistance Current Voltage

63 Analog voltage & current time Voltage Current

64 Analogue Input AC or DC 0 - ~

65 RTD =Resistance Temperature detection. Pure metals material (PTC) Extended sensor range Thermistor = Temperature sensitive resistors. Ceramic or polymer material (NTC). Limited range.

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68 Analog Inputs

69 AC or DC 0 - ~ Analogue Output

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72 Components

73 Summary of schematic symbols + Battery Resistor Potentiometer AC voltage source Capacitor Potentiometer 2-inputs plus center tap Ground Inductor Diode External connection Non-connecting wires - + Op amp

74 Circuit Component classification Resistance Inductor Capacitor

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76 Electrical & Electronics

77 Ohm s Law I = E R Where: I = current (amperes, A) E = voltage (volts, V) R = resistance (ohms, Ω) If two of the values are known, you can solve the equation to find the other.

78 Simple Electric Circuit Electrons flow from NEGATIVE to POSITIVE Voltage (V) Battery of the system Measured in volts Amperage (I) Component using Electricity Measured in amperes Resistance (R) Device inhibiting the flow of electrons Measured in ohms

79 Ohm s Law Pie Chart Using the pie chart, cover the value that you want to find. By covering the I, you see that the formula is E divided by R. By covering the R, you see that the formula is E divided by I. By covering the E, you find that the formula is I times R. NEXT

80 OHM S LAW

81 TYPES OF RESISTANCE Pure Resistance Inductive Reactance Capacitive Reactance Pure resistance remains constant, such as in a heating element or a light bulb. Inductive reactance is caused by the magnetic field that develops around a conductor, especially in coils or motors. Capacitors store and discharge electrons that create an opposition to current flow. The total of pure resistance, inductive reactance, and capacitive reactance is called Impedance. NEXT

82 RESISTANCE Electron flow is energy in motion and must be controlled. Resistance refers to anything offering opposition to current flow. There are several types of resistance that will be discussed, but a basic understanding of Ohm s Law is is necessary before that discussion. NEXT

83 MEASURING RESISTANCE An ohmmeter is used to measure pure resistance. Batteries inside the meter provide a power supply to measure electron movement. NEVER connect an ohmmeter to a circuit with the power on or damage to the meter may occur. Also, be sure that the component you are measuring is electrically disconnected to prevent a feedback circuit and false readings. Resistance can be calculated on live circuits by measuring voltage and amperage, then using Ohm s Law, voltage divided by amperage equals resistance. NEXT

84 Resistance All materials have a resistance that is dependent on cross-sectional area, material type and temperature. A resistor dissipates power in the form of heat

85 Various resistors types

86 When measuring resistance, remove component from the circuit.

87 Resistor Color Code

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89 Ohm s Law

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94 RESISTANCE VS IMPEDANCE Until this time, we only discussed resistance. I said that resistance is the opposition to the flow of current. While this is true, it would be more precise to say that resistance is the opposition to the flow of direct current. Impedance is the opposition to the flow of alternating current. AC causes some devices to act differently than they do with DC. This is true with speakers. If you use a voltmeter to measure the resistance of a speaker's voice coil, you may read something like 3.2 ohms (resistance) even if the speaker is rated at 4 ohms (impedance). To measure the impedance of a speaker you need an instrument called an impedance bridge. The impedance of a speaker is not a constant. It's actual impedance changes with frequency and can vary greatly. Manufacturers give you a nominal impedance, which is generally the average impedance that the speaker will present to the amplifier when driven within the audio spectrum.

95 Resistors Can be rated by Resistance (Ohms, ) Tolerance (% of nominal value) Power Rating (Watts) Schematic Symbol

96 Components Resistor Types

97 Series Circuits One current path, therefore the current is the same everywhere Total resistance is the sum of the individual resistances RT = R R

98 Parallel Circuits More than one current path Total current is the sum of the individual currents IT = I I

99 SERIES CIRCUITS A series circuit has one single path for current flow. If the connection is broken or if one of the components fail, current flow stops in the entire circuit.

100 TOTAL RESISTANCE IN A SERIES CIRCUIT A series circuit has only one path for current flow. Therefore, the total resistance is the sum of all of the resistances in the circuit. R total = R 1 + R 2 + R 3.

101 PARALLEL CIRCUITS A parallel circuit has more than one path for current flow. Current flows through each load independent of the others. The current flow through each load is not necessarily equal, but the voltage supplied across the load is always equal.

102 TOTAL RESISTANCE IN A PARALLEL CIRCUIT Since a parallel circuit has more than one path for current flow, adding additional paths (loads) will decrease the total resistance in the circuit. The formula to calculate the total resistance in a parallel circuit is: Check your math! The total resistance in a parallel circuit will always be less than the smallest resistance in the circuit!

103 TOTAL RESISTANCE IN A PARALLEL CIRCUIT

104 TOTAL RESISTANCE IN A PARALLEL CIRCUIT R Total = (R1 X R2) / (R1 +R2)

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106 Inductors (Chokes) Inductors are simple coils of wire Stores energy in the form of magnetic fields Unit of measure is Henries Used to delay and reshape alternating currents

107 Inductor in use

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111 INDUCTOR An inductor is an electronic device which consists of a coil of wire which may have a metallic or ferrite core. If it appears to have no core, it is considered to have an air core. The core material will greatly affect the value of the inductor. The unit of measure is the 'henry', but since that is such a large value of inductance, the value is usually stated in millihenries. One henry is equal to one thousand millihenries. If everything else stays constant, increasing the number of turns of wire around the core, will increase the value of the inductor.

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116 SINGLE PHASE TRANSFORMERS Transformers have two windings, a primary (incoming voltage), and a secondary (outgoing voltage). Voltage at the secondary (step-up or step-down) is determined by the number of coils in the secondary versus the number of coils in the primary. Single phase transformers are rated by VA (volts x amps) at the secondary.

117 THREE PHASE TRANSFORMERS Three phase transformers are wound in wye or delta configurations. Combinations of wye and / or delta primary and secondary coils provide a variety of voltage and current outputs.

118 HIGH LEG SYSTEM In a high leg system, voltage from two of the hot legs to neutral will read 115 volts. However, one of the hot legs to neutral will register 208 volts. This is sometimes called the high leg, stinger leg, or crazy leg, and cannot be used for 115 volt circuits.

119 SOLENOID VALVE When current flows through the coil of a solenoid valve, the electromagnetism lifts the plunger, opening the valve. (Some valves are designed to close when energized.)

120 RELAYS A relay uses electromagnetism to operate a switch (or contacts). The electrical circuit to the relay coil is entirely separate from the circuit through the contacts. A relay allows high current loads to be controlled using low current control switches and safeties.

121 A contactor is basically a large rely. The contacts are much larger and capable of carrying more current. Contactor components (contacts, coil, etc.) are replaceable, whereas a relay is generally replaced as a complete unit. CONTACTORS Any number of switches may be located in the contactor coil control circuit.

122 MOTORS

123 INDUCTION MOTORS There are two main parts of a motor, the rotor (the part that rotates) and the stator (stationary electromagnetic coils arranged in a circular pattern). The rotor is placed inside the the stator. End bells with bearings are used on each end of the motor and the assembly is bolted together.

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125 Stepper motor Rotor has permanent magnet Constant power motors As speed increases motor torque decreases Motors vibrate more than standard motor The more phase the motor has the less vibration is experienced Bipolar motors have a single winding per phase Unipolar motors have two windings per phase

126 AMPERAGE Ampere, amperage, amps, and current are terms commonly used to describe the quantity and intensity of electrons moving through a conductor. When current flows through a conductor, a magnetic field is created. The clamp-on ammeter is most commonly used on AC circuits. NEXT

127 WATTAGE Electrical power is the rate at which electricity is used to perform useful work.the work performed is measured in units called watts. Watts are calculated by multiplying amperage x voltage. W = I x E 746 Watts is equal to 1 horsepower. NEXT

128 Power Power is an indication of how much work (the conversion of energy from one form to another) can be done in a specific amount of time; that is, a rate of doing work P = W t 1 Watt (W) = 1 joule / second

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130 Capacitance A capacitor is used to store charge for a short amount of time 90 Deg lag in signal Unit of Measure Farad

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133 CAPACITOR A capacitor is an electronic device which consists of two plates separated by some type of insulator. A capacitor's value is commonly referred to in microfarads, one millionth of a farad. It is expressed in micro farads because the farad is such a large value of capacitance. When a DC voltage source is applied to the capacitor there is an initial surge of current, then the current stops. When the current stops flowing, the capacitor is in a charged state. If the DC source is removed from the capacitor, the capacitor will retain a voltage across its terminals. This charge can be discharged by connecting the plates together. Generally, if an AC voltage source is connected across the capacitor, the current will flow through the capacitor until the source is removed. The exceptions to the situation, where an AC voltage is applied to a capacitor, are going to be explained later.

134 Capacitance A capacitor is used to store charge for a short amount of time Capacitor Battery Unit = Farad Pico Farad - pf = F Micro Farad - uf = 10-6 F

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136 Capacitor Charging

137 Capacitor Discharge

138 Capacitors How much is it??? Parallel Circuit Ct=C1+C2 Series Circuits For 2 Capacitors Ct=(C1xC2)/(C1+C2) For more than 2 capacitors in series Ct=(1)/((1/C1)+(1/C2)+(1/C3))etc.

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143 DIODES In general a diode will pass current in only one direction. There are a few exceptions like zener and current regulator diodes. When the voltage on the anode is more positive than the voltage on the cathode, current will flow through the diode. If the voltage is reversed, making the cathode more positive, then current will not flow through the diode.

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146 DIODES In general a diode will pass current in only one direction. There are a few exceptions like zener and current regulator diodes. When the voltage on the anode is more positive than the voltage on the cathode, current will flow through the diode. If the voltage is reversed, making the cathode more positive, then current will not flow through the diode.

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151 The bipolar junction transistor consists of three layers of highly purified silicon (or germanium) to which small amounts of boron (p-type) or phosphorus (n-type) have been added. The boundary between each layer forms a junction, which only allows current to flow from p to n. Connections to each layer are made by evaporating aluminum on the surface; the silicon dioxide coating protects the nonmetalized areas. A small current through the base-emitter junction causes a current 10 to 1000 times larger to flow between the collector and emitter. (The arrows show a positive current; the names of layers should not be taken literally.) The many uses of the junction transistor, from sensitive electronic detectors to powerful hifi amplifiers, all depend on this current amplification. Microsoft Corporation. All Rights Reserved. "Bipolar Junction Transistors," Microsoft Encarta Encyclopedia Microsoft Corporation. All rights reserved.

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154 The S.C.R.

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156 Wow the SCR works A pulse of control current applied to the gate will switch the SCR into conduction. Dropping cathode to anode current below the holding current turns the SCR off. The SCR is a switch. The SCR only conducts in one direction.

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158 TRIACS Triacs are like SCRs but they conduct in Both directions and switch either polarity of an applied voltage.

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162 Binary: How does K1 get energized?

163 The Transistor

164 Shockley s sandwitch transistor

165 BJT Transistors: NPN Transistor Sandwiching a P-type layer between two n- type layers. PNP Transistor Sandwiching a N-type layer between two p- type layers.

166 How a NPN Transistor works? The base-emitter diode (forward) acts as a switch. when v1>0.7 it lets the electrons flow toward collector. so we can control our output current (Ic) with the input current (Ib) by using transistors. C B E backward Forward

167 Transistors have three terminals: Base Collector Emitter Active: Always on Ic=BIb Transistors work in 3 regions Saturation :Ic=Isaturation On as a switch Off :Ic=0 Off as a switch

168 Transistor as a Switch Transistors can be used as switches. 1 Transistor Switch Transistors can either conduct or not conduct current. 2 ie, transistors can either be on or off. 2

169 Transistor Switching Example 15 X 12V Variable Voltage Supply When V BE is less than 0.7V the transistor is off and the lamp does not light. When V BE is greater than 0.7V the transistor is on and the lamp lights.

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171 PNP Transistor Negative Negative Positive

172 NPN Transistor Positive Positive Negative

173 Transistor operation Gate or Base is the switch input to turn on the transistor The Emitter and collector act as the path for current to flow. Can be used as switch, regulator or amplifier

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175 What does Onto-input do?

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180 WHAT IS THE OPTO? The phototransistor uses a transparent dielectric channel to isolate and insulate a LED from the phototransistor. The LED portion of the opto sensor connects to the input supply it puts out the signal to the phototransistor which sends the input signal to perform the proper action.

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182 EPROM [erasable programmable read-only memory] First appeared 1977 : a programmable read-only memory that can be erased by exposure to ultraviolet radiation

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184 EEPROM Electrically erasable programmable ROM With normal ROMs you have to replace the chip (or chips) when new BIOS instructions are introduced. With EEPROMs, a program tells the chip's controller to give it electronic amnesia and then downloads the new BIOS code into it. This means a manufacturer can easily distribute BIOS updates on floppy, for instance. This feature is also called flash BIOS, and you might also come across it in devices like modems and graphics/video cards.

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194 Combination

195 Permissions