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I had the pleasure of attending Sub-Zero Wolf (SZW) factory training last week in Madison, WI. Flew in on Monday, training was Tuesday thru Thursday, and then flew out on Friday. The class consisted of 15 techs from around the country but also included a tech from Puerto Rico and another from Barbados. The techs included a few students from Master Samurai Tech and some Appliantology members.
This session was all Wolf products: gas and induction cooktops, gas and dual fuel ranges, vent hoods, downdraft vents, coffee makers, and microwaves. We worked on 5 different wall ovens, 4 different ventilation systems (both hood and down draft), 4 different ranges, 4 different cooktops, 2 different microwave ovens, a steam oven (each lab group actually baked a batch of chocolate chip cookies!), and the coffee maker system.
The 3-day training session was held in Madison, WI, from October 11-13 (Tuesday thru Thursday). Everyone arrived on Monday and SZW took us all out that evening for a traditional Wisconsin dinner of locally brewed beer and real Wisconsin brats and sauerkraut, beef brisket, and mac n' cheese. It was fantastic! SZW provided all our food during the training and paid for our hotel rooms. Breakfast was at the hotel, lunch was catered at the training center, and they took us out to a different restaurant each night for dinner. A shuttle took us from the hotel to the training center and back each day.
The training format was a mix of classroom instruction and "lab" exercises. During the lab portion, we broke up into groups of 3 or 4 techs and rotated around working on different product stations as we solved specific problems on those products. Doing this required extensive use of Sub-Zero's servicer site, Service Central, that we accessed on our tablet computers to find and refer to service manuals, schematics, and bulletins for the model/serial we were working on. Numerous rolling tool chests and Fluke meters with the LoZ function were also provided. Instructors would roam around from group to group to answer questions and provide hints, tips, and instructions. This was a great format for getting familiar with the products.
Part of the training was a factory tour of the Wolf production facility including the new 4,000 sq. ft. manufacturing space to accommodate the production of their new dishwasher, Cove, which they'll start selling in 2017. The facility was immaculate, highly organized, with surprisingly few production personnel on the floor. What amazed me most about the manufacturing process was the amount and sophistication of robotics they're using for everything from fabrication to QC testing. Every finished product is connected to electricity and/or gas (as appropriate for the product) and 100% function tested using robots!
After the factory tour, we got to sit in with a tech line tech and were given a headset so we could listen in to both sides of the conversation as they took calls from techs in the field. It was dizzying seeing how fast these guys could fly around Service Central pulling up service manuals and bulletins to help the tech on the phone. Most of the guys who called in while I was there were authorized and had access to Service Central so could have probably answered the question for themselves if they had just spent a few minutes at Service Central and then RTFM. Getting authorized techs to effectively use Service Central is one of SZW's big training objectives. Even among SZW authorized techs, there's an over-reliance on tech line and flow charts instead of reading the service manuals, using the schematics, and applying gray matter.
By the way, SZW tech line will help any tech, authorized or not, who calls in working on one of their products. Non-authorized techs are treated exactly the same as authorized techs and they'll be talked through as much as they need to complete the diagnosis and repair, including step-by-step disassembly if needed. Their main concern is getting the customer's appliance fixed as quickly as possible, not protecting SZW service information.
Sitting with tech line, I also realized why SZW uses a select circle of parts distributors (Premier Partners). Here's a typical scenario: a tech calls in working on a SZW product and, working with tech line, determines he needs a kit described in a recent service bulletin to fix the problem. Tech line is tied directly into the inventory database of all their Premier Partners and can tell the tech if that kit is in stock there or not. If it is, he'll go ahead and have that part shipped right then and there. If not, he can check factory inventory and have it shipped to the partner right there during the call. There's no ambiguity about whether a part is in stock or where it is or when it will arrive like there is with so many other manufacturers.
In addition to a great technical training experience on Wolf products, I also got a good feel for the SZW corporate culture. Not surprisingly, it reflects the people who work there, mostly native midwesterners and particularly Wisconsin: not at all stuffy or pretentious but instead clean, organized, competent, down-to-earth, get things done. Real people making really excellent, 100% US-made appliances. If any of you guys are SZW authorized and haven't been to the factory training yet, you really should go. I think you'll be impressed and learn one helluva lot.
In this video, I use an old skool Whirlpool electric dryer to demonstrate electric circuit troubleshooting and analysis techniques. This is the ancient art of Circuit Fu. Although this is a simple circuit by today's standards, the principles and techniques can be used on any circuit because electricity works the same way. When you know basic electricity and circuits, you can decipher these diagrams and become a troubleshooting master...
Learn Circuit Fu and how to kick appliance butt at the Master Samurai Tech Academy. The training is distilled down to the fundamental essentials that every appliance tech should know (but, alas, many do not). The training covers the classic skills, like those shown above, yet is up to to date with the current technologies used in modern appliances. Our training is affordable for anyone, self paced, on demand, and comprehensive.
Enroll at the Master Samurai Tech Academy and start learning today: http://MasterSamuraiTech.com
Had some good questions at the webinar on the Bi-Directional PSC drive motor system used in Whirlpool VM washers. Professional Appliantologist members can grab some popcorn and watch the webinar recording here: Bi-directional PSC Drive Motor Systems in Whirlpool VM Washers
During the webinar, Joe asked how triacs are turned off. I wanted to give a more complete and accurate answer in this post.
To understand how triacs are turned off once they're turned on (and conducting) we need to have a little understanding about how triacs work. So that's what I'm going to do here. Before we light this candle, I'll start with the three take-away points that we need to know about triacs:
1. Triacs are used to control AC power supplies
2. You can think of them as solid state relays
3. Triacs are current controlled devices. This means that you need electrons bustin' down the Gate to turn it on AND you need load current flowing through them in order to stay on.
Okay, here we go...
The word "Triac" is an acronym that stands for Triode for Alternating Current. "Triode" is the old Skool word for a three-terminal (or electrode) vacuum tube used to amplify a signal.
Triacs are used to control a AC power supply. In appliances, they are used to turn the AC power supply off or on.
Here's what a typical triac looks like, such as what you might find on an appliance control board:
Here is the schematic symbol:
The leads labelled A1 and A2 stand for “Anode 1” and “Anode 2.” You will also see them referred to as “MT1” and “MT2” where MT stands for Main Terminal. Same thing. This is the business end of the triac where the main working current passes. This part of triac can complete the circuit for lots of different AC loads, from light bulbs to motors.
The other important thing to point out is the “G” terminal. This is the Gate and it has the power to turn the triac on with just a little DC voltage, usually a 5 VDC digital pulse generated by a microprocessor. So this little Gate voltage and tiny current can make a triac turn on and pass a heap big mondo working current.
Triacs are like solid state relays and, in the appliance world anyway, serve the purpose of the relays with a coil and set of contacts. The difference is that triacs don't have metal contacts that can arc and burn out and don't have a coil. (And, of course, triacs are made of semiconductors and PN junctions. More on that in a bit.)
Relays are electromechanical devices whereas triacs are solid state devices.
Inside a Triac
Triacs have two sets of three PN junctions. Look at the diagram below:
As with any semiconductor device, it requires current flowing through it, or more properly stated, electrons being forced through it by a voltage source, in order to collapse the PN junctions and cause it to start conducting. Refer to the webinar recording on “Semiconductors and PN Junctions” in the Professional Appliantologists forum and at Master Samurai Tech for more details on this.
The triac is constructed in such a way that a little tiny gate current is all that's needed to “forward bias” the triac and make it turn on and conduct a large AC current that can drive a load like a motor. This Gate current is typically driven by a small DC voltage like 5VDC.
Turning a Triac On and Off
Triacs require a minimum current through the Gate in order to turn on. In order to stay on, they also need a minimum load current flowing through them from MT1 to MT2. This is called the “holding current.” This is why we say that triacs are current controlled devices.
When the AC voltage crosses the zero line (the x-axis), the current then goes to zero and the triac “turns off.” So the triac naturally turns off at every half cycle of the AC sine wave. The Gate voltage, which produces the Gate current, must then be reapplied in order to the turn the triac on for the next half cycle.
Let's look at this:
In the diagram above, the sine wave is the current passing through the triac from MT1 to MT2 (or A1 to A2, same thing). The notches represent the triggering points where Gate current has to be supplied in order to keep the triac turned on for the next half cycle. Also notice the holding current dashed lines. This is the minimum current that needs to be passing through the triac in order to stay on.
AC voltage goes to zero every half cycle (120 times a second in a 60 Hz power supply). No voltage means there's no current because current, electrons, cannot move unless there is a voltage difference between two points as you learned in the Basic Electricity module of the Fundamentals course.
Since there is no current flowing through the triac at this point forcing the PN junctions to stay collapsed (current drops below the minimum holding current required to keep the triac conducting), the triac turns off and stops conducting.
To get the triac to turn on and start conducting again, you have apply a Gate trigger voltage (which drives the gate current) to the Gate terminal. If you to want to have the triac conduct through several AC cycles, you have to re-apply the Gate trigger voltage each and every time the AC voltage sine wave goes to zero (i.e., when it crosses the x-axis).
Here's another diagram showing the gate current triggering pulses:
A couple things to notice about the graph above:
1. Look at the timing of the Gate current pulse. It occurs right around the time the AC load current through the triac goes to zero.
2. You don't need to keep supplying Gate current the entire cycle to keep the triac turned on, just when the load current goes to zero. So you can supply Gate current in specifically-timed pulses. We're talking accurate timing down to the microsecond. Mind boggling for us; piece of cake for a microprocessor-- they do this kind of stuff all day long.
If you were to connect an oscilloscope to both the gate voltage and the voltage output at one of the the triac main terminals, it would look something like this:
The Gate pulses in the oscilloscope photo above are wider than the ones in the preceding diagram but the idea is exactly the same. Channel 1 is the Gate voltage and Channel 2 is the AC voltage output of the triac.
I'm talking about voltage now. That's perfectly fine because in non-reactive devices, like triacs, there is no phase shift between current and voltage. So whatever voltage does, current also does at the exact same time. It's just easier to show voltage on an oscilloscope.
Notice that the gate pulse on Channel 1 goes from zero to 5.5 VDC each and every time the AC voltage sine wave on Channel 2 crosses the x-axis (at which point the AC voltage is zero). So while the frequency of the AC line voltage is 60 Hz, the frequency of the Gate pulses is 120 Hz. You can see this in the lower right hand corner of the photo above.
Since the AC voltage (and hence current) goes to zero 120 times a second, all you need to do to stop the triac from conducting is remove the Gate voltage. Done!
The Two Golden Rules for Gating Triacs
1. To turn a triac ON, a gate current greater than the minimum required for that particular triac model must be applied until the load current is passing through from MT1 to MT2 . Being a semiconductor, temperature affects this and is one of the design considerations the engineers have to consider.
2. To turn off a triac, the load current must go below the minimum holding current for that particular triac model long enough for the PN junctions to re-establish themselves. We're talking microseconds here. And, of course, remove the Gate current. With the Gate current removed when the load current (and hence voltage) goes to zero, the triac will not conduct, even if the load voltage later goes to something other than zero.
1. Triacs are used to control AC power supplies
2. You can think of them as solid state relays
3. Triacs are current controlled devices. This means that you need electrons bustin' down the Gate to turn it on AND you need load current flowing through them in order to stay on.
Beyond understanding how triacs operate, technicians need to be aware of configurations where a triac is controlling the power supply to a load because this affects how the supply voltage is tested and measured. We go into details on that in this webinar recording: Voltage Measurements, Meters, Ghost Voltages, and Triac-controlled Neutrals
No schematics on this one! I know that'll be a relief for some of you. Honestly, it was a nice break for me, too. I love these easy jobs where you can troubleshoot using only your eyeballs and fix it with something as simple as a paper clip.
In this short little video, I show you how to troubleshoot a problem with a surface burner on Bosch gas range. The burner was not lighting correctly and would sometimes flare up.
All gas range surface burners operate using the same principles so don't let the fact that this is a Bosch fool you. Gas fuel, just like electricity, works the same way in the US as it does in Germany, Korea, or anywhere else in the world. So the same principles and repair shown here apply to all gas surface burners regardless of brand.
Master Samurai Tech Academy students may access the webinar recordings here.
Mr. Appliance® Academy Bundle 1 students may access the webinar recordings here.
Professional Appliantologist members may access the webinar recordings here. The index page is continually updated with new webinar recordings but this is the index page as of this post:
Ultra Short Primer on Basic Electricity, Circuits, Ohm's Law, and Schematic Reading
Basic Refrigerator Troubleshooting
Schematic Reading Workshop, 10/2015
Troubleshooting Strategies for Computer-Controlled Appliances
Semiconductors and PN Junctions
Appliance Temperature Sensing Devices & Technology
Voltage Measurements, Meters, Ghost Voltages, and Triac-controlled Neutrals
Troubleshooting with Tech Sheets, Part 1, 4/2016
Troubleshooting with Tech Sheets, Part 2, 4/2016
Tech Sheet Review, 4/9/2016: Bosch Speed Cooker, Amana Refrigerator, GE Glass Cooktop Range
Pulse Width Modulated (PWM) Switches used in Samsung Switched Mode Power Supplies (SMPS)
PWM Computer Cooling Fan in a Whirlpool Refrigerator
Understanding AC Split-phase Household Power Supplies
Troubleshooting a Samsung Electric Dryer without Disassembly using Live Tests and the Schematic
Troubleshooting a Bosch Dishwasher No-Heat Problem using the Schematic and Live Tests
Linear Motors and Linear Compressors
In case you missed it or would like to review, Professional Appliantologist members here at Appliantology may watch the recording on Linear Motors and Linear Compressors webinar on August 15, 2016 here:
And just a reminder that Professional Appliantologist members have convenient access to all the webinar recordings on the Webinar Recordings Index page here:
Master Samurai Tech Academy students have access to all the webinar recordings here: http://mastersamuraitech.com/webinar-recordings/
This short little video shows you how to enter program mode in Bosch SHE SHU model dishwashers. You'll want to enter program mode to retrieve error codes, which can help inform your troubleshooting strategy. You can also run the test program, which is helpful in diagnosing individual loads in the dishwasher.
One of the many benefits of Professional Appliantologist membership at Appliantology is hi-speed, unlimited service manuals and tech sheet downloads at Appliantology.org. Included with your membership is access to exclusive webinars and webinar recordings where you get deep, specialized training in appliance technology and troubleshooting strategy with the Samurai.
Professional Appliantologist members should also watch the video where I who to troubleshoot a no-heat problem using live tests:
Learn more about Professional Appliantologist membership here:
Get state-of-the-art, cost-effective, online appliance repair training at the Master Samurai Tech Academy: http://mastersamuraitech.com
In this video for Professional Appliantologist members and Master Samurai Tech Academy students, I show you how to troubleshoot a Bosch dishwasher no-heat problem. No heat problems can manifest in a variety of ways: really long cycle times, a "1" shown on the display at the end of the cycle, or as an error code. Some models will show an error code readout, others may just show the error code as a flashing light. Whichever way, you need to troubleshoot the heating circuit.
As with all electrical problems, you need to use the schematic to pinpoint the open (bad) component. The problem could be the circuit board heating relay, the heater thermostat, the heating element itself, or the pressure switch. I show you how to use the schematic and live voltage tests to pinpoint the exact problem.
Professional Appliantologist members can watch the video at the link below:
Master Samurai Tech Academy students can watch the video here: http://mastersamuraitech.com/webinar-recording-troubleshooting-bosch-dishwasher-no-heat-problem-using-schematic-live-tests/
Here's the schematic used in the video:
Learn how to troubleshoot like a pro online at the Master Samurai Tech Academy: http://mastersamuraitech.com
Join the Samurai on this Samsung electric dryer service call and learn how to troubleshoot a no-heat complaint from the control board, without having to tear apart the whole dryer, by using the schematic and strategic electrical tests. Work smarter, not harder!
Learn how to troubleshoot appliances like a real technician at http://mastersamuraitech.com
Professional Appliantologist members here at Appliantology should watch my webinar recording on troubleshooting this same problem using live voltage tests for deeper understanding of troubleshooting techniques
Most appliances today use computers to control the various appliance functions. Computers talk in logical 1's and 0's which are actually pulses or square waves of voltage that you can see on an oscilloscope or measure with a meter. These pulses are arranged in a specific sequence to transmit and receive information inside the appliance. In this video, the Samurai uses a Samsung dryer to show you what these pulses look like and how to use this information for troubleshooting.
Come with me now on Journey of Total Appliance Enlightenment.
Learn how to troubleshoot appliances like a real technician at http://mastersamuraitech.com
This LG refrigerator was DOA- warm inside, no compressor operation, no lights, no nuttin'. Found a blown fuse on the main control board. What took out the fuse: bad board or just a spike on the power line? I show how to check for that.
The fuses on these LG boards are soldered in and not easily replaceable. But a new fuse can be installed and I show how to do that without even having to remove the board, while it's still installed in the refrigerator.
Learn appliance repair at http://mastersamuraitech.com
This short little screencast by @Son of Samurai shows you how to renew your Professional Appliantologist membership at Appliantology.org so you can continue to enjoy the many benefits the site provides to professional appliance repair technicians.
Introducing the mysterious Son of Samurai (yes, the actual spawn of Samurai), the man behind the scenes running Appliantology.org and MasterSamuraiTech.com. He's also a certified Master Samurai Tech and the Samurai's service call partner. In this episode we talked about:
- Son of Samurai, who he is and what he does to keep our websites running
- Behind the scenes at Appliantology
- Common user questions at Appliantology
- What it takes to be a professional appliance repair technician today
- Getting the most out of your Professional Appliantologist membership at Appliantology.org
Subscribe to this podcast at http://mstradio.com
Subscribe to our newsletter at http://mst.buzz
Special 4th of July episode:
- Industry News: Haeir buys GE Appliances; new Wolf induction cooktop; Italian appliance manufacturer, SMEG, gaining market share
- Firing your customer; identifying and harpooning "land sharks." Link to article discussed in the vodcast: https://www.groovehq.com/support/how-to-fire-a-bad-customer
- Current thinking on responding to negative reviews
- Dealing with unreasonable customers
- Master Samurai Tech news
Subscribe to the podcast on iTunes or Android and listen to past episodes at http://mstradio.com
Subscribe to our newsletter at http://mst.buzz
If you're contemplating doing work for someone who lives out of town (eg., rental property in your area) and whom you've never met, it's worth spending a few minutes looking them up online. Google is your friend! Choosing the wrong customer can cost you a bad online review, even though you've already refunded 100% of their money after you've provided services. There are people out there (mostly real estate types) who take a sadistic pleasure in screwing over service companies. Here's an example of such a guy: http://toddhwaller.com
This is an excerpt of the full split-phase household power supply webinar held on June 6, 2016. In this excerpt, I explain why antiphase sine waves (meaning 180 degrees out of phase with each other) cancel each other out in a sound mixer but not in a center tapped transformer. Just because an AC voltage can be represented or modeled as a sine wave does not mean all sine waves behave the same way everywhere regardless of the device-- you have to know what you're measuring!
Summing Amplifier Basics
How Sine Waves are Used to Model things in the Real World
Using an Oscilloscope to Understand 120 VAC Household Power Supplies
Can you believe there are techs out there who use an o-scope to look at the output from a sound mixer and conclude this is how Line voltage works? The output of a sound mixer is the output of a summing amplifier (Google it). It is an electronically modified signal. To look at this output and assume that Line voltage behaves this way is the height of stupidity. I call it "Idiot with an O-scope syndrome."
Household power supplies in North America use what's called a split-phase system. The transformer on the pole outside the house takes grid power and steps it down to 240 VAC from end to end on the secondary winding. The secondary winding has a center-tap in it which splits this 240 VAC into two 120 VAC voltages from either end to the center tap. This center tap is defined as Neutral and it is tied to Ground in the circuit breaker box inside the home. The two 120 VAC voltages are 180 degrees out of phase with each other and it is this very antiphase relationship that creates the voltage difference of 240 vac between L1 and L2.
There's a lot of disinformation and tech myths out there about 120/240 split-phase household power supplies. You may have even seen videos online claiming that the split phases are in-phase with each other. This is complete hogwash and I prove it to you in this video.
I show the proper phase relationship (180 degrees) between Line 1 to Neutral and Line 2 to Neutral right at the circuit breaker box using an oscilloscope.
I challenge anyone to show differently and to clearly show how you're measuring.
Had some great conversations in the Appliantology Chatroom today!
First, had a very interesting conversation with Brother smee about carbon monoxide, measurements, standards, production and health effects. We pulled up this excellent training presentation from GE, that demystified a lot of the confusion about CO, and looked at it together:
Might make a good topic for a future Office Hours.
Next, had a good conversation with Mr.Pro-- to be continued-- as we tracked down a DE1 error code on a Samsung washer he was working on. We thought we were looking at the same Fast Track but turns out not to be the case. The correct Fast Track for his model is this one:
Probably shoulda taken that one to a Join.me webinar to make sure we were on the same page. Anyway, we at least established that much! We'll nail the rest of it down in a later chat.
Okay, until next time-- drink beer, sleep well, get shit fixed (in that order).
Some people say that a technician is only as good as his test instruments. I strongly disagree! In fact, just the opposite is true: a test instrument is only as good as the technician using it.
You can have the best, most expensive, fanciest test instruments in the world, but if you don’t know how to interpret what that instrument is telling you, what good does it do you?
Some techs are using an oscilloscope in appliance repair. Now, I’m all into cool toys but I don’t think we’re at the point in appliance repair where an o-scope is needed just yet. But they are definitely fun to play with!
Properly understood, an oscilloscope can give a skilled tech great insight into what’s going on with a circuit or whatever else you’re measuring, such as sound waves. O-scopes are great for showing different types and shapes of waveforms, including sine waves, chasing signals through a circuit, comparing the timing of two different data trains in digital circuits and lots of other applications. Their real strength is in repairing electronic circuit boards and are often used with a signal generator where a generated signal is injected into a circuit and then inspected at various points in the circuit with an o-scope to troubleshoot a particular problem.
O-scopes can show other things besides voltages such as electronic representations of sound waves. But unless you understand some basics about both sine waves and the physics of what you're looking at with the o-scope, you could draw some blatantly incorrect conclusions. Let's start with sine waves, what they are and what they are not.
Sine Waves: Mathematical Models of the Real World
A sine wave is a mathematical curve that describes a smooth repetitive oscillation. It is named after the trigonometric sine function. You've probably seen a sine wave many times, it looks like this:
All sine waves have common properties such as amplitude, period, and frequency. These are used to quantify (put numbers on) the physical process being analyzed or studied.
The period is the amount of time it takes for the sine wave to complete one full cycle, its units are time, could be seconds (or some fraction thereof), days, hours, years... depends on what you're modeling. The frequency is the number of of complete cycles completed per unit time, such as 60 cycles per second, also called Hertz (Hz). The amplitude also depends on what you're measuring and the instrument you're using to measure it (more on this later)-- could be volts, decibels, pressure, force, etc.
Sine waves are useful because lots of different physical oscillation processes can be represented by them. Examples are an oscillating spring, AC voltages, ocean waves, planetary rotation, sound waves, light waves, and many others. But the important thing to keep in mind is that in every case, a sine wave is only a mathematical model of some physical reality but is NOT the physical thing itself!
The other thing to keep in mind is that a sine wave is not to be confused with wave physics.
Wave physics is a branch of classical mechanics physics that describes processes that exist as waves in the physical world. A wave is an oscillation (that means is moves back and forth, up and down, you get the idea) of a mass that transfers energy as it moves through some medium, such as air, water, or some other mass. Examples are sound, light, ripples on water, etc.
Although physical waves, such as sound waves, are always three dimensional, they can be mathematically represented as a two-dimensional x-y sine wave plot either on paper, a computer (like a spread sheet), or on an o-scope.
But keep in mind that, in every case, this sine wave representation is just that: a mathematical abstraction of a three-dimensional physical wave phenomena.
But there are lots of other phenomenon in the physical world that do NOT exist as waves-- so wave physics DOES NOT apply-- yet they can still be mathematically represented by sine waves! The most familiar example is AC voltage and current. Since these are not waves, wave physics does not apply. AC voltage and current are explained by the physics of electricity, not wave physics or any other branch of classical mechanics.
Let's look at some examples of the sine wave representations of sound (wave physics) and AC voltage (electrical physics) and compare them.
The Physics of Sound
Sound waves are mechanical vibrations of pressure. They exist in the real world as variations in pressure in a medium such as air. Waves of Increasing pressure are called compression waves; waves of decreasing pressure are called rarefaction waves. These pressure variations produced by the sound source cause movement of the human eardrum and this movement is interpreted by our brains as a sound.
Although sound waves are three dimensional-- they travel outward from the source in all directions-- they can also be represented as a sine wave and plotted on a standard x vs y graph or on a spectrum analyzer or even an o-scope because they have properties of frequency and amplitude. Modeling sound waves as sine waves lets us visualize, quantify, and analyze them.
Although we're using a sine wave to model a vibrating guitar string in the image above, the sound produced by that vibrating guitar string doesn't actually look that way-- the sine wave is only a mathematical model of the pressure variations produced by the sound of the vibrating guitar string.
The wavelength (an actual, physical distance measured in meters) determines the frequency-- the longer the wavelength, the lower the frequency because it takes longer for the sine wave to make a complete cycle. Frequency and wavelength are related by the speed of sound: wavelength = speed of sound / frequency.
The units of the amplitude of the sine wave representing a sound wave would be some units of pressure, such as decibels. The larger the amplitude, the louder the sound being represented by the sine wave.
But some instruments, such as o-scopes, only have the ability to show volts/division on the vertical (amplitude) axis so that's what will be shown on the screen. But knowing that you're actually looking at a sine wave representation of sound, you would interpret this as a relative index of loudness. This is analogous to the temperature controls on some refrigerators where they only give you a number, such as 1 through 9. The number on the dial, such as "7" doesn't correspond to any actual temperature (as many customers think), it's just an index so you can distinguish one setting from another. Although the sine wave produced by a sound mixer or signal generator actually does have a voltage amplitude, this is to be understood as a substitute for actual sound "loudness," which is measured in units of pressure (most commonly, decibels). For this very reason, some instruments used in sound analysis, such as spectrum analyzers, only show a relative index for amplitude:
The important take-away point here is that the image being shown on the sine wave graph, such as on an o-scope or spectrum analyzer, is just a model-- an abstraction-- of the actual physical phenomena being shown. So those sine wave models of a sound wave must be interpreted and understood in the context of the actual physics of the phenomena producing the image on the screen.
Note that the waveform graph is two-dimensional but in the real world sound waves are three-dimensional. This graph is exactly how a pure-frequency sound wave would be generated by a sound mixer board and depicted on an o-scope or spectrum analyzer.
The graph indicates a wave traveling along a path from left to right, but real sound waves travel in an expanding sphere from the source. However the 2-dimensional model works fairly well when thinking about how sound travels from one place to another. But, again, the o-scope is just showing you a model, or abstract representation, of the actual, physical sound propagation.
Alright, so we have an idea of some of the physics involved in sound propagation. Let’s explore the question of how sound waves can cancel each other out in the air.
Recall that sound is composed of mechanical compression waves moving through some medium, such as air. That means the wave first compresses to an amount greater than normal air pressure. A sine wave model of this sound would show this as the positive part of the sine wave curve. Then the air expands to a pressure less than normal air pressure. This is the negative part of the sine wave—the part below the zero centerline.
If you have two sounds waves of the exact same frequency and amplitude (volume) but 180 degrees out of phase (one of them is inverted) then one of the sound waves is compressing (higher pressure) at the exact same time the other sound wave is decompressing (lower pressure). Adding the positive pressure from one sound wave and negative pressure from the other sound wave will give you the normal air pressure. The two pressures are cancelling each other out because the air is being decompressed at the exact same time it is being compressed. Since there is no variation in air pressure, there is no sound. This process is called destructive interference and is a basic principle of wave physics.
On a sine wave model of the two sound waves, you would see them as two sine waves 180 degrees out if phase with each other, like this:
So how can sound waves be displayed on an o-scope? A common method is to use a sound mixer board. A sound mixer is a device that mixes sounds from different sources. Some mixers can also be used to generate sounds of various frequencies. Sound mixers electronically (digitally) reproduce the wave physics of sound. They do this using SUMMING amplifiers that ADD the voltages of the sound frequencies together. It is the electronically manipulated output of a specific type of circuit designed to mimic the physics of sound. This is why they are called sound mixers, not voltage mixers.
So when you use a sound mixer to produce two antiphase sine waves representing sound frequencies, as shown in the photo above, the resulting waveform is seen as a flat line on an o-scope or spectrum analyzer. The sound mixer is doing exactly what it was designed to do: mathematically and electronically produce what you would actually hear in the air (nothing) using good ol' wave physics calculations. Ain't science and technology cool?
From Sound to Voltage
But voltage is not sound! The electronically-manipulated signals from the output of a SUMMING amplifier in a sound mixer has nothing to do with the output of a center-tapped transformer. None of the mechanical wave physics in the foregoing discussion applies to voltage. So things like interference waves, destructive interference, compression, and rarefaction do not apply when you're talking about electricity.
Although sound waves that are 180 degrees out of phase cancel each other in a process called destructive interference, AC voltage is NOT a mechanical wave phenomenon and is not explained by the mechanical wave physics. Yet AC voltage can, and often is, modeled or represented by a sine wave.
To say that because inverted sound waves cancel other out through destructive interference so therefore AC voltage must also behave the same way simply because both can be represented as sine waves is absurd. This would be like saying that because ocean waves can be represented by sine waves, that voltage behaves the same as ocean waves. It's utter balderdash! While this makes for great comedy, it's completely wrong physics. Same sine wave model, different physics. Get it?
The Physics of Voltage
Let’s start by thinking about what voltage is. Voltage is the difference in electric potential energy, in joules, per unit charge, in coulombs, between two points. So a volt is joule/coulomb. There is no type of compression or rarefaction (decompression) happening in electricity.
We never talk about voltage at a single point, it is always relative to some other point, a "reference point", be it ground, Neutral, L2, whatever. For example, there is no absolute 100 volts “out there” somewhere. It is 100 volts relative to some reference point. By convention, we arbitrarily assign a voltage of 0 volts to the earth and all other voltage measurements on planet Earth are relative to this reference.
Electrons, the negatively charged subatomic particles that comprise current flow, are driven by the difference in voltage between two points. It doesn’t matter if one voltage is negative and one positive, both positive, or both negative as long as there is a voltage difference.
As an example, let’s suppose that point A had a steady voltage of +1,000,000 volts and point B also had a steady voltage of +1,000,000 volts. Since both voltages are the same scalar quantity (1,000,000) and polarity (both positive), there is no voltage difference between the two points so no electrons would flow between A and B (or vice versa). The simplified math looks like this:
+1,000,000 volts - (+1,000,000 volts) = 0 volts
Now let’s suppose the voltage at point B is reduced to +500,000 volts. The voltage difference between A and B becomes:
+1,000,000 volts - (+500,000 volts) = 500,000 volts
Since point A is more positive than point B (conversely, you could also say that point B is more negative than point A) the electron flow is from point B to point A.
Now let’s say that point A stays at +1,000,000 volts but point B goes to -1,000,000 volts, the exact same amount of voltage but opposite polarity. Since we’re talking about DC voltage here (i.e., the polarities are fixed over time) we can’t properly talk about phase yet but this would be a DC equivalent, if you will, of two AC voltages being 180 degrees out of phase. Let’s look at the voltage difference between A and B now:
+1,000,000 volts - (-1,000,000 volts) = 2,000,000 volts
The potential difference (or voltage difference, same thing) between A and B quadruples because you’re subtracting a negative voltage. Four times as many electrons are doing all they can to get from point B to point A in this case compared to the case where the voltage difference was only 500,000 volts.
When we deal with AC voltages, the polarities are constantly reversing 120 times a second, twice in each 1/60th of a second cycle. So the same principles we just looked at with the DC examples above would also apply to AC. But with AC, since the voltage polarities are reversing 120 times a second, we have to consider time in our calculations. This is done by referencing the phase of the voltages between two points which is done using either polar or rectangular notation.
Most people, including many techs, assume that single phase means that both 120vac legs in residential application are of the same phase. This is a complete misconception. If the two 120vac legs were in phase, the voltage difference between the two would never change, giving no voltage difference between each hot leg:
Note that as the vertical line between the sine waves moves from left to right (the horizontal axis represents the passage of time) on the graph, it's "length," representing the voltage difference, never varies so we have no potential difference between the two points (0vac). If this were the incoming power supply to a home, you could never have a 240vac outlet across L1 and L2.
Run the numbers yourself:
Start with the blue segment where each sine wave is at a maximum +120 vac. What's the voltage difference between these two points? +120 vac - (+120 vac) = 0 vac. The voltage difference (or potential difference, same thing) between the two waveforms is zero.
Now go to the red segment where each sine wave is at a maximum - 120 vac. What's the difference now? -120 vac - (120 vac) = 0 vac.
And so on for every point along the two curves, you get the idea. Here again, just a little bit of mathematical literacy let's you see how obvious this is.
Voltage difference is exactly like the name says: the mathematical difference in electrical potential between two points. That means subtracting. When you subtract a positive number from a positive number, the answer (called the difference) gets smaller. When you subtract a negative number from a positive number, the answer gets bigger. I hesitated to even explain this elementary school math but, sadly, it seems to elude many people, even techs, who should know better.
In the step-down transformers used to supply residential single-phase power in North America, the secondary winding of that transformer is center-tapped. The end-to-end voltage on the secondary is 240 VAC. The center-tap on the secondary is the definition of the Neutral wire in household AC power supply systems and it causes two voltages to develop from either end to the center tap, as shown in this diagram:
Since the secondary winding is center-tapped, two voltages are developed across each split from either L1 or L2 to Neutral (the center-tap) as shown above. Since the center-tapped Neutral is tied to Ground, the electrical polarity at Neutral never changes-- it is always at Ground potential. However, the electrical polarity at each end of the transformer is changing 120 times a second with reference to Neutral.
Now, let's take a closer look at those voltages being developed across the secondary of the transformer:
These two voltages are 180º out of phase as shown in this diagram:
This phase relationship between these two voltages can be expressed using phase notation as shown below:
An o-scope, properly configured, would show the two center-tapped voltages as sine waves 180 degrees out of phase with each other. The resultant wave from combining the two waveforms would have an amplitude that is double of either the voltage at A or B.
Watch me demonstrate this in action:
These two voltages can be mathematically combined using either polar or rectangular math. You can do this long-hand as shown below:
In the special case when voltage sine waves of the same frequency are antiphase (another way of saying "180 degrees out of phase with each other"), you can tell the voltage difference between them at any point by using simple arithmetic. But what about when two voltages are only 120 degrees out of phase with each other, such as in three-phase voltage? Again, you have to use polar or rectangular math to calculate the voltage difference between the two lines at any given point in time. Most engineering calculators will have polar and rectangular functions built into them to facilitate these calculations.
Why should math matter? Why isn't this all just a matter of opinion, preference, or "alternative views?" Because if electricity could not be 100% described by mathematics, none of these systems could be designed in the first place.
How do you think engineers design these systems? Do they guess and hope to get lucky? Do they go with how they're feeling that day? Is it all a matter of how they "believe" these systems work or their "opinion" about how they might work? I guarantee you that they have all this stuff completely nailed down with calculations and they know exactly how the system will behave before the first dollar is committed to building it. That's the essence of what engineers do.
Here again, the abstraction being shown on the o-scope has to be interpreted with an understanding of the physics of the phenomena being viewed, whether sound or voltage.
- Sine waves are a useful mathematical model used to abstractly represent a wide range of very different physical phenomenon. But the sine wave is not the thing itself-- it is just a mathematical model of the thing.
- By modeling various physical phenomenon as sine waves, scientists, engineers, and technicians can analyze how that physical process changes over time.
- Sound waves, spring compression, AC voltage and current are just a few examples of the widely different physical processes that can all be mathematically and conveniently modeled as a sine wave.
- An oscilloscope is an instrument used to measure the time-varying behavior of various oscillating physical functions and represents them as different types of waveforms, including sine waves.
- Sound waves and AC voltage can both be represented as sine waves with all the various properties of sine waves, such as frequency and amplitude, but this is where the similarity ends.
- Widespread mathematical illiteracy among the population today has resulted in a proliferation of gross misconceptions and "tech myths" about how electricity works.
- O-scopes are fun and, in the right hands, can be a powerful analytical tool. But if you don’t understand the underlying physics of what the sine waves (or other types of wave forms) on the scope are representing or even what a sine wave actually is, you won't know how to interpret what you’re seeing or you will just confuse yourself. Worst of all, you could delude yourself into believing something that just isn't true because you don't know what you don't know.
Professionals working in a skilled trade like appliance repair must have the math and science skills to understand the physical phenomena (electricity, mechanics) that they are measuring with their test instruments or even observing with their senses, or else they can easily get fooled by those observations or measurements and waste time and money in their repair work.
The abysmal public school system in Ameedica today may have let you down by not giving you this foundation, but the Samurai's got your back! Between the Master Samurai Tech Academy and pearls of wisdom such as this post here at Appliantology, I'll help get you up to speed. If I could learn this stuff as a punk-ass, snot-nosed 17-year old kid in the Navy, then anyone can with a little effort and someone to guide them along the way.
Learning never stops, even for the Samurai! Keep your mind open and keep studying so you can know what you don't know.
The internet has been a game-changer for the appliance repair industry. But it only works for you if you know how to work it!
Information is key. Professional appliance repair techs work on so many brands and models that access to manuals for disassembly info, schematics, and specifications is a big factor in the success of the repair.
And with the increase in computerization of appliances, war-gaming the service call ahead of time has become critical for increasing first-call completes, decreasing reliance on time-wasting and unpredictable tech lines, and increasing customer satisfaction - and yours! And you can’t war game without the info ahead of time.
Back in the old days, we had shelves overflowing with annoying paper copies of manuals, VHS videos to scrub through, and tech lines operators to wait on hold for. Thankfully, those days are over!
Now we have Appliantology: the web’s premier appliance repair tech support site.
Appliantology is rich and deep with resources for the professional tech: repair forums with world-class peer-to-peer tech support, live chat and tech help, service manual downloads for all makes and models, live training webinars, and exclusive tech training videos.
But like any powerful tool, it’s only as useful as your ability to avail yourself of its many treasures.
Some of our professional tech members sign up and only come around every now and then, and then wonder if the membership fee was worth it. It’s disappointing to invest in something and then not really know how to take advantage of it.
The Samurai sheds a tear for every Professional Appliantologist who barely scratches the surface of the site and never sees the power and beauty within!
Others learn how to use the site fully, unleashing Appliantology’s power to amp up their repair mojo, and then ask us how we can offer such an amazing resource at such a low annual fee.
A Professional Appliantologist membership is $149/year, that's less than $3 per week.
When you are well-prepared for your jobs, you will not only be more profitable, but you will have more fun doing it. Who doesn’t want that?
To take the free Appliantology 101 short course, all you need is a free registration at Master Samurai Tech which you can get here.
If you already have a student account just make sure you are logged in and you’ll see it in your course listings on your login/welcome page.
Take our FREE short course, Appliantology 101, and see how easy it is to get started with the awesome functionality of the site, and then dive deeper into how to really take your work to the next level!
Learn the troubleshooting skills you need to repair today's computer-controlled appliances. Increase your earnings with our empowering, comprehensive training. It's all done online, self-paced, and cost-effective. All our courses offer a terrific value with proven results. Use the coupon code MEMORIAL2016 for 10% off any course or course bundle through the end of May. See this page for a description of our course offerings and enroll today: http://mastr.tech/1TVQZkt
Wassmatta, Boopie-- got the Don't-know-my-ass-from-that-hole-called-the-Internet Blues? Well, unfurl thy brow and unbunch thy panties, my Internet-bungling friend for the Samurai shall shine the light of wisdom upon thee and make straight thy cyberpaths. And for FREE! Yes, my sweet-- the Internetology Course is our latest electronic offering to the Great Virtual Universe and we bequeath it unto all posterior unto the ages of ages. Amen.
[Read more about the Free Internetology course here]
Fantastic web meeting last night with many assembled Brethren! This was one of the weekly web meetings that we have every Monday evening for Professional Appliantologists and Mast Samurai Tech Academy students.
Personally, I think it was the best one yet-- lots of interactivity and discussion about all kinds of different appliance repair topics. It was a especially great because we had the audio under control so other people besides just me were able to talk. Mrs. Samurai even joined in the conversation and it was kinda-sorta like a live, interactive podcast!
We started off by looking at a schematic and wiring diagram for a GE Cafe duel fuel double oven. The complaint on this was that the warming drawer wasn't heating up at all and neither of the indicator lights for the warming drawer would come on. Using the schematic and wiring diagram, we developed some specific troubleshooting strategies for pinpointing the problem.
We also talked about all kinds of other things, all pertaining to running an appliance repair business and livin' the life of an appliance tech. Some of the other things we talked about are:
- Pricing your services, pros and cons of using the online Blue Book
- Dealing with Craig's List competition who advertise "no service call fee with repair" and otherwise appealing to bottom-feeder customers
- The Appliantology chatroom, it's currently an underused resource at the site and we talked about using it more, including our plans to use it for live tech help (as well as just chit chat and hoo-ha). I'm generally hanging out in the chatroom most mornings while I'm checking email, answering forum posts, and otherwise takin' care o' bidness. Pop on in and say hey. One of the brethren suggested an informal chat each evening where we would hang out while surfing the web or checking out other parts of the site. Sounds good to me! I'll try to be there when I can but if I'm not, go ahead and get the party started without me.
- Doing schematic markups-- How do I whip out all those schematic markups? Ahh, Grasshoppah, only the Chosen have received this Divine Wisdom.
- We talked about different types of tablet computers and PDF reading apps that people use to carry service manuals and tech sheets with them to service calls.
- PSA vs. USA - which is the better group to belong to? I am personally a member of USA and think it's a great group. I don't have any experience with PSA so couldn't offer anything on that.
- I also announced our latest and greatest offering at Master Samurai Tech: a new, fun, and FREE course on Internetology: Internet Basics for Everyone. Just register (for free) at Master Samurai Tech and take the course right away. It'll probably take you a half hour to do and you'll get a few laughs along the way. If you already have an account at MST, just log in and you'll see the Internetology course on your login/welcome page.
- Finally, we compared Appliantology and Master Samurai Techs. Two different sites with different missions. Appliantology is our tech support site while MST is our tech training site. Although Team Samurai runs both sites, they each use completely different software so membership at one does not transfer to membership at the other.
We talked about other things, too, that I'm probably forgetting. Maybe someone else will comment on tis post and remind us.
Good talk, good talk!