Although there are numerous types of diodes—zener, light-emitting, photoconductive, varactor, and tunnel—each has its own unique characteristics. For example, zener diodes are special diodes that can operate in reverse bias. In reverse bias the zener diode does not conduct until the voltage threshold, or breakdown voltage, is reached, and then it conducts at a relatively constant voltage.
This operation allows the zener diode to act as a voltage regulator that can be used for regulated voltage power supplies. The transistor is actually made up of two diodes back to back. The first section is called the emitter. The middle section is called the base. The last section is called the collector. A troubleshooter should understand the reason why a transistor amplifies.
Also, the collector base has high resistance to current flow, or is reverse-biased. The negative potential of the battery forces the electrons in the emitter to flow into the base region. Very few of these electrons bond with positive holes, since most electrons continue on through to the collector region.
This is due to the strong positive attraction of the battery. The electrons complete the circuit by returning to the battery supply. Keep in mind that new positive holes are being pulled into the base region from the battery when electrons fill the holes. Since the collector region has a higher value of resistance than the emitter region, any current change in the emitter will cause proportionally a greater change in the collector.
A signal passing through its transistor will be amplified. The amount of signal amplification can be controlled by regulating the amount of electron flow into the base region. The amount of electrons supplied to the base region determines the amount of electrons available to the collector region. The regulation of electrons into the base region is called biasing. In a transistor, the forward bias or emitter-to-base bias determines the amplification of the transistor.
The forward biasing of a transistor can be controlled by increasing or decreasing the voltage or resistance at the emitter-base region see Fig.
The basic operation of current flow in the pnp transistor is very similar to that of the npn except that instead of current flow by electrons, the current flow in the pnp transistor is completed by holes. The positive force from the battery forces the positive holes from the emitter through the base- collector region and back to the negative side of the battery.
Here again, as with electrons in the npn transistor, a small number of holes bond with electrons in the base region, but the majority of these holes continue on into the collector region. Conduction takes place by hole current from emitter to collector. Electron flow is opposite to hole flow conventional theory. Therefore, electron flow in this circuit is considered to travel in the opposite direction, or from collector to emitter.
Do not let this explanation of hole current confuse you; basically, the main function of both transistors in the circuit is the same. Both transistors amplify Fig. The three basic circuit configurations of transistors are the common base, common emitter, and common collector. Each circuit configuration has its own unique characteristics.
TABLE 1. Transistors are usually tested either by a transistor checker or by an ohmmeter. Keep in mind that a transistor is actually two diodes back to back and, therefore, can be checked accordingly. Now the transistor is forward-biased, and a low resistance reading should be read. Reversing the leads will reverse-bias the emitter-base regions, and the ohmmeter will show a high-resistance reading.
The base-collector regions are checked in the same way. Two highs indicate an open transistor; two lows indicate a shorted transistor out-of-circuit test. Transistors can be checked while in or out of the circuit in this manner. It is recommended that a transistor that has checked out defective in the circuit be taken out of the circuit and checked again before being replaced.
Some kind of reading should result on the ohmmeter scale. Now short-circuit the base lead to the emitter; the resistance on the meter scale should increase. When the base lead is shorted to the collector, the resistance on the meter scale should decrease Fig. The field-effect transistor FET is a special transistor used frequently in electronic circuitry. Although its outward appearance is similar to the bipolar transistor npn and pnp , the construction is different.
The FET consists of three terminals—source, gate, and drain—which correspond to the emitter, base, and collector of the bipolar transistor Fig. The gate is a diode junction that is reverse-biased rather than forward- biased as in the bipolar transistor. Therefore, the gate has very high resistance, allowing for a very high input impedance desired in many circuits.
Two high readings indicate an open transistor, and two low readings indicate a short circuit. The ohmmeter reading between the source and drain shows a low resistance in either polarity in a good transistor. Two highs indicate an open circuit Fig. The current flow in a p-channel is reduced by applying a positive voltage and increased by applying a negative voltage.
The depletion type conducts at zero bias and is reduced with reverse bias. With enough reverse bias, it can be cutoff. The depletion-enhancement type has some conduction with zero bias. Current is reduced with negative bias and increased with positive bias.
They are also sensitive to static electricity and must be carefully handled. For this reason, the gate is kept short-circuited to the source by twisting their leads together during shipping and handling or by a spiral short-circuiting spring. There should be zero resistance between the gate and source or drain. A reading on the ohmmeter indicates a short circuit. To check the drain-source condition, place a kW resistor from the gate to drain. Note, however, the best test is by substitution or by use of test instruments Fig.
There are several different testing techniques. Many of these can be used to directly or indirectly test the performance of a transistor.
Transistor cutoff Voltage readings can be very useful in determining transistor circuit action. For example, the transistor in Fig. If the transistor is open, or not conducting, the transistor will not draw current; and the voltage at the collector will not be 6 V but the full, source voltage of 10 V. If the transistor is short-circuited, the transistor will draw excessive current.
This will load down the circuit. Often, transistors can be checked by simply applying a combination of heat and cold. First, apply heat by using a hot blower on the suspected transistor. If the transistor is restored to normal operation, the transistor can be diagnosed as defective. Thermally intermittent transistors are defective transistors that usually break down after lengthy operation. A rise in temperature increases the current in the transistor; this increased current conduction in turn produces more heat that causes the transistor to draw even more current.
Eventually the transistor destroys itself. This sequence is called thermal runaway. Remember, do not be too eager or determined to disable the transistor.
This technique is used only for suspected thermally intermittent transistors. Never apply too much heat to a transistor, especially specialized or sensitive ones, or else needless damage will result. Signal tracing can also be used to isolate a particular defective transistor. For example, if a signal is injected into each stage of a malfunctioning transistor receiver, starting at the speaker and working backward, the defective open transistor will prevent the signal from reaching the speaker.
The transistor substitution technique can be effective in determining a defective transistor. Keep in mind that when you substitute a transistor, be sure to use a similar transistor. This can save the troubleshooter valuable time.
Another technique to determine whether a transistor is operating is to short-circuit the base to the emitter, which cuts off the transistor Fig. A noticeable difference in the overall operation of the equipment should result if the transistor is working.
If no noticeable difference is indicated, the transistor is most likely defective. Use caution when you do this test, and make sure you do not short- circuit the base to the collector, since this will cause the transistor to draw excessive current and destroy itself.
Also, this method is only useful for certain circuit operations, such as amplifiers or oscillators. The transistor cutoff technique can be compared to locating a bad spark plug wire on a car. While the automobile is idling, each plug wire is lifted off for a second and the idling operation of the engine is noticed.
If the removed spark plug wire causes the engine to idle more roughly, the plug is good; but if the performance of the engine is unchanged, the plug wire is probably defective. Never overheat transistors. Use a heat sink. Use a W, or lower, solder iron. Use an exact or recommended replacement type. Identify E, B, and C positions. The silicon-controlled rectifier SCR is formed when three diodes are arranged back to back Fig.
The SCR acts as a rectifier, except that conduction in the forward direction can only take place when sufficient voltage triggers the gate, at which time the SCR conducts as long as sufficient holding current is maintained. The SCR is a popular device used in burglar alarms and automatic control circuits. It can best be checked by substitution or use of an ohmmeter. Zero ohm indicates a short-circuited SCR. Integrated Circuits Although the actual construction of an integrated circuit IC is complicated, the process of checking ICs is much easier to understand.
The three basic types of ICs are dual-in-line type, round type, and flat type. The IC basically consists of many micro-size components. One small IC may consist of several resistors, capacitors, diodes, and transistors, all connected into a micro circuit. They are hermetically sealed in a ceramic or plastic package. The two basic methods of IC construction are called monolithic and hybrid. The hybrid, however, is custom-made, and this involves manufacturing the different circuits of the IC separately and then assembling them on the substrate.
The approach to testing either IC type is the same. Courtesy Sylvania, Inc. Logic pulse probe The first step in troubleshooting an IC is to use your senses. Look for obvious problems such as corroded, defective, or damaged pins, sockets, or solder connections. Make sure the IC is completely inserted in its socket. Check the component identification number of the IC with those of the manufacturer to make sure the correct IC is in the circuit and is correctly positioned.
Touch is one technique that many service troubleshooters use. A hot IC is a good indication of a defective or short-circuited component. Most IC components should feel cool to warm when touched. As stated before, a suspected thermally intermittent component can be checked by first heating the component with a hot blower—noting the performance of the circuit—and then cooling or freezing the component. The defective thermally intermittent IC should break down when heated but operate again when cooled off.
Voltage checks can be performed easily with a voltmeter or an oscilloscope. An incorrect voltage reading probably indicates a faulty IC or surrounding component. The capacitor bypasses the signal around the IC Fig. If the signal increases when the IC is jumped with the capacitor, the IC is probably defective.
Courtesy Motorola, Inc. Any suspected IC should be replaced by a similar known good IC. This technique of substitution saves valuable time for the service technician. Realistically speaking, troubleshooters do not rely solely on this technique because it would require having a large inventory of ICs on hand, which would be costly.
Also keep in mind that if the root of the problem is not a bad IC, replacing a bad IC with a good one could destroy the good one. Many ICs are mounted on circuit boards, and it is often more practical to simply replace the entire board. IC testers and kits are available to test ICs; however, they may require the IC to be checked while out of the circuit. Also, special multipin clips can be used with a comparator box.
These testers and kits can be very handy but are often expensive. The logic digital IC probe is probably one of the most important test instruments used by troubleshooters. This small, handheld probe is generally used to test logic pulses and levels. The probe contains a complex circuit that identifies, through use of light-emitting diodes LEDs high or low , operating logic-level responses.
Like the voltmeter, the logic probe is applied to each IC pin or test point. Courtesy Hewlett-Packard. If you know what the input and output values of the IC are supposed to be, you can measure these values and generally conclude whether the IC is good. This way of thinking about the IC often eliminates the need to understand the complex internal structure of the IC.
Digital logic circuits usually have two logic levels: 0 or 1. Connecting negative or positive voltages can determine whether switching occurs. A signal-tracing method using an oscilloscope is generally preferred to voltage-resistance checks, since true IC operation is dependent on the dynamic operating characteristics of the circuits. The signal-tracing method will be explained in greater detail in later chapters. Order the exact replacement. Insert or position the IC exactly as the original IC.
It is extremely easy to insert an IC backward! When you insert a dual-in-line pin IC into the socket, it is easy to miss and smash at least one of the 16 pins. Make sure all 16 pins are aligned properly before you press the IC fully down into the socket. Never overheat an IC. Do not overuse solder; prevent overflow of solder onto the board. This overflow can cause bridging among adjacent pins and components. Always use desoldering wick or IC suction bulbs to remove excess solder.
Electron Tubes Since electron tubes are rarely used today, little mention of their theory will be made. Electron tubes are found in some industrial and military applications and in a few guitar amplifiers.
Some guitar players prefer the more hollow sound that electron tube amplifiers tend to produce as compared to semiconductor amplifiers.
Basically, besides the CRT, the troubleshooter might occasionally run into other tubes such as the diode, triode, tetrode, pentode, gas-filled, and multielement tubes. The diode tube consists of a negative cathode and a positive plate. The negative cathode, when heated, gives off electrons; and conduction takes place. The process of giving off electrons from the cathode is called thermionic emission.
When the polarity is reversed, no thermionic emission takes place and no current flows. This valve-like action serves as a one-way gate and is, therefore, used as a rectifier. The number of electrons that reach the plate from the cathode in the triode tube is controlled by placing a fine-mesh wire called a grid. This control grid is made negative in relation to the cathode. The more negative the grid, the less the current flows; the less negative the grid, the more the current flows.
Cutoff is the point where the grid is made too negative and current flow stops. Saturation is the point where the grid is at the least negative point and current flow is at a maximum between grid and cathode. In order to prevent interelectrode capacitance, an undesired effect in the triode, a second grid, called a screen grid, is added in the tetrode tube.
When increased performance under certain applications is desired, a third grid is added. It is called a suppressor grid. The pentode that contains this grid eliminates secondary emission uncontrolled acceleration electrons near the plate by controlling these accelerated electrons. Power tubes are basically for high-power amplification. Gas tubes are often filled with nitrogen or mercury vapor and are used in high-current applications. The thyratron tube is a common example of a gas tube.
Multielement tubes are tubes consisting of two or more tubes enclosed in the same glass envelope. The pentagrid converter is a common example of a multielement tube. It consists of both the local oscillator and mixer stages in a receiver. Substitution Even though electron tubes are rarely used today, you may still encounter them, especially in servicing old hybrid televisions, computer monitor CRTs, and old industrial and communications equipment.
To examine the quality of a tube while the circuit is operating, use the plastic end of a screwdriver. Gently tap the top of each tube while listening or watching the performance of the circuit such as in a radio or television. Keep in mind that a loose connection or poor soldering connection in the same area could cause the same problem.
Another way to quickly examine the quality of some tubes is to visually see if the heater is lighted. If the heater is open, no glow will be produced and the tube will not operate. An ohmmeter can also be used to check the heater.
Although the tube tester can be a helpful instrument for the troubleshooter, it can also be a handicap. Undoubtedly, the tube tester will indicate that many of the tubes need to be replaced but will often fail to pinpoint the one tube that is causing the problem. Valuable time and money can be saved by understanding the function of each tube in a circuit and how to properly use a tube tester.
For example, tube testers cannot match the operating conditions of the circuit. They cannot adequately measure interelectrode capacitance. Also, oscillators, limiters, and high-voltage tubes where characteristic curves are critical are difficult to test on the tube tester. Remember, if the tube failed because of a circuit problem, the substitution of another new tube will only ruin the new tube. For example, when you are servicing an electronic device, if a rectifier tube is found short-circuited, also look for a short-circuited filter capacitor.
Perhaps the filter capacitor caused the rectifier tube to short-circuit. Also, before you replace any tube, it is a good idea to visually inspect the area for charred resistors or any other problem that could have caused the tube to fail. Unlike the transistor, which could theoretically last forever, the life of an electron tube is limited because the cathode simply wears down and, with time, emits fewer and fewer electrons. Also, mechanical vibrations, excessive heat, and current all contribute to tube breakdowns.
When you are replacing a tube, be sure to use the exact replacement or recommended substitute and make sure the tube socket is clean and free of corrosion. Also, be careful not to bend the tube pins. Ultracapacitors Ultracapacitors, also called double-layer capacitors DLCs , are very powerful capacitors that can store over times more electrical energy than conventional capacitors.
They operate by using nonreactive, porous plates with an extremely high surface area in an electrolytic solution through the movement of charged ions. Electrical energy is charged electrostatically. Ultracapacitors offer many benefits over conventional capacitors and batteries, such as quick charging, high energy, low weight, high reliability, long life, and low maintenance.
Maxwell Technologies. One of the more popular applications of ultracapacitors is in the automotive industry. Ultracapacitors are being used in regenerative braking systems, diesel-electric buses, and in conjunction with electrolytic batteries for hybrid vehicles. Ultracapacitors can operate more efficiently and longer than batteries in wide temperature ranges. An ultracapacitor also can operate at any voltage within its voltage rating, and unlike the battery, it can be stored without any charge and quickly recharged.
The use of ultracapacitors in conjunction with batteries can provide excellent power and energy for hybrid vehicle applications. They can extend conventional lead-acid battery life by adding power during peak loads and help provide quick acceleration and regenerative braking. It also has low weight, low current leakage, and excellent cycling reliability, making it suitable for other nonautomotive applications, such as backup power supplies during power outages for industrial and medical facilities.
Like other electrical components, ultracapacitors can experience faults such as internal shorts, open circuits, cell leakage, and material breakdowns, often due to internal stresses from excessive vibration, thermal expansions, damage, or abuse. Common tests for ultracapacitors consist of charge- discharge and measuring equivalent series resistance ESR.
Parameters such as initial working voltage, discharge current, minimum voltage under loads, voltage after load removal, and the time to discharge from initial charge to a minimum voltage can be measured to test the quality of ultracapacitors. Appendix L gives detailed test procedures from Maxwell Technologies for checking ultracapacitors. Inductors An inductor is basically an electromagnet that is used in many applications, such as transformers, up and down voltage steppers, filters, oscillators, phase shifters, integrators, and differentiators.
The inductor basically opposes any current changes, and this is often referred to as inductance. The inductor creates a magnetic field that induces a counter electromotive force EMF.
Inductance L is measured by the unit henry H. Types of inductors include air core, iron core, ferrite core, fixed, and variable. One common application of the inductor is in filtering circuits. At a basic level, inductors pass low frequencies and block high frequencies.
Capacitors, on the other hand, often pass high frequencies and block low frequencies. Therefore, when both inductors and capacitors are used in conjunction, they can act as a filter. For example, in a sound system, an inductor could be used to block high-frequency music to the woofer speaker, and the capacitor could be used to block low- frequency music to the tweeter speaker.
A combination of the inductor and capacitor can be used to provide proper midrange frequency music to the midrange speaker. Many inductors can be tested using an ohmmeter. While the windings of an inductor are often shorted, open circuits tend to account for the majority of defects.
When you use the ohmmeter, an inductor, depending on the size and number of windings, should have resistance from about zero to a few hundred ohms.
Larger inductors with many turns of wire generally measure some resistance. A shorted inductor would measure zero resistance. An open inductor would measure infinite resistance.
Therefore, it may be necessary to use an inductor analyzer to check the inductance. Which of the following is not an example of a source of breakdown? Heat B. Moisture C. Poor installation D. Animals and rodents E. Which of the following is not one of the senses commonly used by service troubleshooters? Sight B. Hearing C.
Touch D. Taste E. A hot, smoky product or device is often a sign of A. A short circuit B. A ground C. An open circuit D. All the above E. A circuit that has infinite resistance is called A. Voltage measurements are often taken by using a voltmeter or A. An ammeter B. An oscilloscope C. An ohmmeter D. A wattmeter E. Signal injection or tracing is a method commonly used in troubleshooting A. Electric motors B. Residential wiring C. Industrial wiring D.
Radio E. Bypassing B. Substitution C. Bridging D. A cold solder connection can best be repaired by A. Substitution B. Bridging C. Resoldering D. Cooling E. Discussion of defect with customer B. Acquisition of service information C. Selection of troubleshooting technique D. Repairing of the problem E. All the above The type of diagram that illustrates the component parts of a product or device is called a A.
Line drawing B. Schematic diagram C. Blueprint D. Pictorial diagram E. Schematic print A component having no continuity would have A. Zero resistance B.
Infinite resistance C. Both A and B D. None of the above A good fuse will have A. Small resistance D. Both A and B E. The physical size of a resistor, which determines the ability of the resistor to absorb heat, is rated in A.
Ohms B. Volts C. Watts D. Farads E. The new fully charged lead acid storage battery should measure A. Over 12 V B. Capacitors can be tested by A.
An ohmmeter B. A spark test C. Only B and C E. In order to make a p-type crystal, A. A pentavalent of gallium is added B. A trivalent of indium is added C. A pentavalent of antimony is added D. A trivalent of arsenic is added E. The term acceptor is referred to in the A. Addition of pentavalent to the crystal B. Actually a transistor is A. One diode B. Two diodes back to back C. Three diodes back to back D. Four diodes back to back E. High-voltage gain and low-current gain are characteristics of the A.
Common base circuit B. Common emitter circuit C. Common collector circuit D. Both A and C E. If the operating voltage at the collector of the transistor were much lower than normal, one could suspect A.
A defective filter B. An open resistor C. An open transistor D. A short-circuited transistor E. To cutoff a transistor for troubleshooting purposes A. Short E and B B. Short B and C C. Short gate to anode D. Either A or B E. Two, plate B. Three, gate C.
Four, base D. Two, emitter E. Three, plate Voltage B. Resistance C. Current E. Bridging The tube that contains three grids is the A.
Triode B. Tetrode C. Pentode D. Multielement E. Power tube Which of the following techniques is not common in troubleshooting electron tubes? Tapping B. Tube checker C. Substitution E. Both A and C The gate in the field-effect transistor FET is generally A. Reverse-biased B. Forward-biased C. Zero-biased D. An FET B. A bipolar transistor C. An SCR Forward bias B. Reverse bias C. Zero bias D. Positive bias B. Another name for an ultracapacitor is a: A. Double-layer capacitor B. Dielectric capacitor C.
Power-cache condenser D. List and explain seven causes of breakdowns. List and explain four senses commonly used in troubleshooting. What are the four causes of circuit faults? Also list how each one differs from the others. What are the characteristics of a short circuit? What are the characteristics of an open circuit?
What are the characteristics of a grounded circuit? What are the characteristics of a mechanical problem in a circuit? Explain the difference between the terms bridging and substitution.
Explain the technique of signal tracing. List and explain different types of service diagrams. Explain the techniques in troubleshooting capacitors. Name several different types of capacitors.
Explain the structure of a diode. Explain how to test a diode. What is a diode crystal detector? Explain the structure of a transistor. Explain how to test a transistor. Explain how to test an SCR. Explain the various techniques used to troubleshoot transistors. Explain the various techniques used to troubleshoot ICs. Explain the differences between several types of electron tubes. Explain the few basic ways to check an electron tube. Why should tube testers be used with caution in testing tubes?
What is a CRT? What is a thyratron tube? Explain how to check the FET. Chapter 2 Electronic Test Instruments A s electronic products and equipment become more sophisticated, the need for test instruments becomes increasingly important. There are hundreds of different types of test instruments used today.
Most electrical and electronic products and devices could not be effectively serviced without proper selection and use of test instruments. In this chapter, some of the most popular types of test instruments used by troubleshooters are presented. It may not be practical to invest in an instrument that has limited use. However, many troubleshooters have wasted valuable time, obtained inaccurate readings, experienced hours of frustration, and lost business opportunities, all because of ineffective or unavailable test equipment.
When you select test instruments, consideration must be given to instrument reliability, traceability, material and international standardization, calibration services, reliability, durability, readout and display features, and overall accuracy and performance. Always thoroughly read the operating manual before using the test instrument.
Many troubleshooters, upon acquisition of a test instrument, fail to take the time to fully understand all the functions and details of the instrument, which results in a surprisingly high incidence of inaccurate reading, misuse, and underutilization.
This analog meter is ideal for measuring fluctuating trends and rates, a task which is difficult for digital meters. Many troubleshooters, especially those who work in industrial electrical applications, have favored the observation of needle movement over digital readings.
Newer VOMs incorporate a combination of high-energy fusing and a diode network for meter movement protection. Courtesy Simpson Electric Co. Therefore, it is not uncommon for the voltage measurement to sometimes be inaccurate.
Small, inaccurate measurements of voltage do not usually present a problem for industrial electricians.
They do, however, present a problem for the electronic engineer. Small inaccuracies in measuring voltage may greatly affect the electronic diagnosis. The solid-state field-effect transistor FET multimeter overcomes this problem of loading down a circuit by its high input impedance and precision-regulated internal power supply.
This meter is a highly versatile, portable meter typically used for field and factory servicing and design testing. The digital multimeter DMM Fig. This meter uses circuits that produce numerical readouts using light-emitting diodes LEDs , and newer ones have LED graphic screens that function similarly to an oscilloscope.
Courtesy John Fluke Mfg. High-performance DMMs feature a five-digit multifunction vacuum fluorescent dual display with selectable reading rates and resolutions. For example, the troubleshooter is able to view two signal parameters from one test point by taking measurements sequentially and simultaneously.
This allows the troubleshooter increased versatility in applications requiring two separate examinations of the same signal.
DMMs are generally portable and use standard disposable batteries. Some DMMs have the capability of interfacing with a personal computer for automated recording of measurements.
All these advantages of the DMM, along with very accurate readings, make this test instrument very popular for digital equipment bench testing. Oscilloscope In the most simplistic sense, the oscilloscope is essentially a visual voltmeter. However, to the novice, this meter, with all its controls and visual screen, induces both fascination and intimidation.
The oscilloscope can be one of the most valuable types of equipment in troubleshooting. The basic advantage of the oscilloscope is that it provides a visible display of the waveform being measured. Most oscilloscopes use electrostatic deflection. The beam sent from the electron gun is deflected vertically or horizontally by pairs of vertical and horizontal plates.
Although the oscilloscope is largely used to measure peak-to-peak voltage, other measurements that can be taken are the frequency, time periods, wave slopes, phase angles, and frequency response. Figure 2. Courtesy Leader Instruments Corp. Z axis—varies the intensity of modulation of the trace Turn intensity, focus gain, and sync amplitude to minimum.
Turn vertical and horizontal controls to midrange. Turn on scope and adjust the intensity control to minimum brightness. Allow 1 to 2 minutes min for the scope to warm up and then adjust the focus control for a sharp trace. Center the trace signal by adjusting the vertical and horizontal controls. Connect a 6. Because 6. Adjust the sync control until a stationary pattern displaying three sine waves appears.
Each division will now equal 10 V peak. The vertical attenuator can be used to multiply the divisions by 0. When you calibrate an oscilloscope with an internal calibrator, the scope can be calibrated by adjusting a fixed pattern of 1 V peak to peak. More sophisticated oscilloscopes have features such as built-in calibrators for calibration checks, separate and independent comprehensive triggering facilities, and beam finders.
Voltage-divider probe The low-capacitance probe is generally used to measure high-frequency or high-impedance circuits. The demodulation probe or rf probe is often used to measure rf signals where the signal must be detected before being displayed on the scope.
The usual voltage division ratio is or When you select an oscilloscope, it is important to consider the bandwidth or rise time, triggering, and other specialized requirements. Bandwidths can vary from 10 megahertz MHz to more than MHz. For example, personal computers used to utilize 5-MHz clocks but are now often seen at 20 MHz. There can be dramatic differences in measurements of the actual waveforms between two different oscilloscopes, especially with digital pulses.
An oscilloscope with 10 MHz may be sufficient for automotive requirements but insufficient for video equipment and industrial programming circuitry. The selection of an analog versus a digital oscilloscope is also important depending on the application.
Analog oscilloscopes generally are less costly and are best for measuring analog and high-frequency signals, whereas digital oscilloscopes are used for special digital and storage applications. Also, recent technology now offers analog-digital combinations incorporating digital recording and control with analog familiarity. Other specialized applications require waveform recording capabilities. The EMG unit uses a built-in oscilloscope to measure the electrical impulses and the nerve conduction velocity that stimulate muscles and allow sensation.
In simplistic terms, electrodes record both the electrical activity that travels from one point of the body to another and the muscle or nerve activity at a fixed point.
It is important for the practitioner to be able to view more than one signal, freeze a signal, produce an instant hardcopy from a printer, or file a waveform for multiple comparisons. Special triggering requirements, such as delayed sweeps or expansion of full rise time, of a pulse are also available for troubleshooters.
In addition to bench oscilloscopes, there are several types of portable oscilloscopes. These instruments provide sufficient power and high-performance capabilities needed to troubleshoot devices on the job site. For example, some oscilloscopes combine high safety ratings and performance equivalent to many bench oscilloscopes with the extra protection of durable portability.
These instruments are useful for plant maintenance engineers and technicians who need a durable test instrument, especially in harsh and hazardous conditions. They are exceptionally good instruments for three-phase testing in diagnosing industrial systems, power inverters, and converters.
Other features include circuit voltage and amperage overloading, signal timing measurements, signal fluctuation, harmonic testing and transience loads, and three-phase power input. One of the more useful functions of portable oscilloscopes includes the paperless recording. This function can be convenient for collecting data by allowing the plotting of values over an extended period of time.
In addition, voltages, amperages, temperature, and frequency measurements can be recorded and stored in the unit. The more advanced bench oscilloscopes provide an extensive range of capabilities. For example, the phosphor oscilloscopes contain advanced triggering and protocol decode and search capabilities with bandwidths from MHz to 3. Other features include rapid capture of signal anomalies, serial triggering and analysis options, and software analysis packages.
Specialized Test Instruments There are hundreds of specialized test instruments used today for many different applications. Test lamp Digital logic probe Growler Optical time-domain reflectometer OTDR Field strength meter Network analyzer Logic troubleshooting kit Transistor testers are fairly accurate checkers of diodes and transistors.
They also have the capability of checking the performance of these components while in or out of circuit. They are able to measure transistor leakage and beta, and can automatically identify emitter, base, and collector leads Fig.
Transistor checkers are often multipurpose instruments with audible and visual test indications. Leakage currents can be made with transistors when they are out of the circuit. The probes of these meters contain flexible, spring-loaded pointed tips that allow for convenient and quick measurements.
Connections to transistors mounted as printed-circuit boards can also be easily checked. Capacitor testers not only check the quality of the capacitor but also determine the value of unknown capacitors. Many capacitor testers have the ability to check most capacitors in or out of the circuit, which can speed up the servicing time.
Also, the capacitor tester can identify power factor values, leakage, and open circuits, all problems common to capacitors. Keep in mind that the actual capacitance value of the capacitor can only be accurately measured when the capacitor is out of the circuit.
Capacitor checkers are very sensitive and can detect even small amounts of leakage. Also, when you check electrolytic capacitors, unlike other types, it is important to measure their power factor. Remember, never touch the terminals of the capacitor tester when the voltage is turned up!
Severe shocks can result. Frequency counters are used to measure the frequency, in hertz Hz , of an electronic product, and are often used to adjust the frequency of radio receivers and transmitters. They are also very valuable instruments used in research and experimentation. They generally offer automatic triggering, high- stability time base, multiple measuring functions, input voltage protection, and portability. Some counters include a variety of accessories such as compensated crystal oscillators for stability and memory options Fig.
There are various types of signal generators. The audio-frequency af generator provides signals in the audio range, whereas the rf generator provides signals in the rf range. Both meters provide sine wave or square wave outputs, contain built-in attenuators, and provide low-distortion outputs. They have the ability to create complex waveforms with stable high fidelity signals. A noise generator is a small handheld signal probe that is handy in signal tracing of radio receivers.
This small generator sends out a broadband signal from af to rf. This typical frequency range is from 1 kilohertz kHz to 30 MHz. The marker generator provides an unmodulated frequency and is used to identify frequencies on a response curve used in television alignment. The sweep generator is also used in television alignment.
It provides a frequency modulation FM signal at a desired range of frequencies. Equipment may operate in a manner far different than it was designed to, or not at all. Typically, when equipment fails there is a sense of urgency to get it fixed and working again. If the defective equipment is part of an assembly line, the whole assembly line could be down causing unexpected 'time off' and lost revenue. If you are at a customer site to repair equipment, the customer may watch you, knowing that they are paying for every minute you spend troubleshooting and repairing their equipment.
Either one of these scenarios, and there are more, can put a lot of pressure on you to solve the problem quickly. So What is troubleshooting? It is the process of analyzing the behavior or operation of a faulty circuit to determine what is wrong with the circuit.
It then involves identifying the defective component s and repairing the circuit. Depending on the type of equipment, troubleshooting can be a very challenging task. Sometimes problems are easily diagnosed and the problem component easily visible. Other times the symptoms as well as the faulty component can be difficult to diagnose. A defective relay with visual signs of burning should be easy to spot, whereas an intermittent problem caused by a high resistance connection can be much more difficult to find.
What makes an expert Troubleshooter? One trait of expert troubleshooters is that they are able to find virtually any fault in a reasonable amount of time. Easy faults, complicated faults, they find them all. Another trait is that they typically replace only the components that are defective. They seem to have a knack for finding out exactly what is wrong. No trial and error here. So what is their secret? You might think that a person who has a very good understanding of how the equipment works, should be able to troubleshoot it effectively.
Being a good at troubleshooting requires more than this. Expert troubleshooters have a good understanding of the operation of electrical components that are used in circuits they are familiar with, and even ones they are not. They use a system or approach that allows them to logically and systematically analyze a circuit and determine exactly what is wrong.
They also understand and effectively use tools such as prints, diagrams and test instruments to identify defective components. Finally, they have had the opportunity to develop and refine their troubleshooting skills. If you want to troubleshoot like the pros you will need to develop your skills in each of these areas.
Let's look at them in more detail. See A Systematic Approach to Troubleshooting for more details on this approach. Various types of test instruments are available for testing electrical circuits. The ones you choose depends on the type of circuit and its components.
A common test instrument which is invaluable to a troubleshooter is a Multimeter. It is capable of measuring voltage and resistance with some meters capable of other measurements such as current and capacitance. You must be able to determine what type of test instrument to use, when and where to use it, and how to safely take readings with it.
Review your own skills in each of these areas. Improving any one of them, along with a good dose of practice, will improve your troubleshooting skills.
An e-learning company that develops computer based training simulations for electrical troubleshooting. Warren has an electrical background and has taught troubleshooting for several years at a prominent electrical utility. Simutech Multimedia developed a series of award winning simulations for learning electrical troubleshooting skills. They no longer sell to individuals, but you may want to check if your company or college can afford their great electrical troubleshooting software.
This article is copyright protected by Simutech Multimedia Inc. Fieldbus Course. Top-Gun Maintenance Planner Scheduler. Distancle Learning Using Simulators. Types of Air Compressors and their use. Avoid Lean Six Sigma Failures.
Industry 4. PLC Management. Training Cost Justification.
0コメント