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--- tutorials:learn:multimeter:continuity.html [2010/10/18 20:02]
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+++ tutorials:learn:multimeter:continuity.html [2016/01/28 18:05] (current)
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-==== Introduction  ====
+==== What is continuity?  ====
-The most important debugging tool in any E.E.'s toolbox is a trusty multimeter. A multimeter can measure continuity, resistance, voltage and sometimes even current, capacitance, temperature, etc. It's a swiss army knife for geeks!
-==== What you will learn!  ====
-You should go through all of these sections in order, as they build on each other.
-  *[[http://www.ladyada.net/learn/multimeter/continuity.html|Continuity measurements]]  \\ How to tell if two points are electrically connected
-  *[[http://www.ladyada.net/learn/multimeter/resistance.html|Resistance measurements]]  \\ How to measure resistance - resistors, potentiometers and sensors
-  *[[http://www.ladyada.net/learn/multimeter/voltage.html|Voltage measurements]]  \\ How to measure voltage - battery testing, wall-wart adaptor testing, and the terror of mixed AC/DC measurements.
-==== What to look for?  ====
-Everyone always asks **What multimeter should I get?**
+You might be asking, "What is continuity?" But don't worry, it's quite simple! Continuity means, are two things electrically connected. So if two electronic parts are connected with a wire, they are continuous. If they are connected with cotton string, they are not: while they are connected, the cotton string is not conductive.
-Well, since they're rather commodified (there are dozens of manufacturers) it is hard to make everyone use the same model, even though it would make things easier.
+You can always use a resistance-tester (ohmmeter) to figure out if something is connected because the resistance of wires is very small, less than 100 ohms, usually. However, continuity testers usually have a piezo buzzer which beeps. This makes them very useful when you want to poke at a circuit and need to focus on where the probes are instead of staring at the meter display.
-These are the necessities:
+For some basic circuits you can just look to see where the wires go to determine continuity but it's always wise to use a multimeter. Sometimes wires break or you're tired and can't easily follow all the PCB traces. I use continuity check all the time!
-  *Continuity testing with piezo buzzer
+==== What is it good for?  ====
-  *Resistance test down to 10 ohm (or lower) and up to 1 Megaohm (or higher)
-  *DC voltage test down to 100mV (or lower) and up to 50V
-  *AC voltage test down to 1V and up to 400V (or 200V in the US/Canada/Japan)
-  *Diode testing
-Here are nice things to have in your meter
+Continuity is one of the most important tests. Here are some things it is good for
-  *Auto-off - to keep from draining the batteries
-  *AC and DC current test, from 10mA to maybe 200mA and then also a 10A one as well
-  *Stand - a thing that flips out and keeps it upright on your table
-  *Auto-ranging - note: some people don't like auto-ranging because its slower and not as precise
-  *Hold - keep the maximum value on the screen so you can probe without looking at the meter.
-  *Common battery - such as 9V or AA's, pocket meters use hard-to-replace coin cells
-These are things that I rarely (if ever) use, in decending order
+  *Determine if your soldering is good. If your solder joint it is a //cold solder connection// it will appear connected but in actually it is not! This can be really frustrating if you are not experienced in visually detecting cold solder joints
+  *Determine if a wire is broken in the middle. Power cords and headphone cables are notorious for breaking inside the shielding, it appears as if the cable is fine but inside the wires have been bent so much they eventually broke.
+  *Making sure something **isn't** connected. Sometimes a solder joint will //short// two connections. [[http://s3.amazonaws.com/ladyadanet/make/x0xb0x/shorts_t.jpg|Or maybe your PCB has mistakes on it and some traces were shorted by accident. ]]
+  *Reverse-engineering or verifying a design back to a schematic
+==== Remember!  ====
-  *Frequency counter - before I had a scope this was surprisingly useful!
+**You can only test continuity when the device you're testing is** **not powered**. Continuity works by poking a little voltage into the circuit and seeing how much current flows, its perfectly safe for your device but if its powered there is already voltage in the circuit, and you will get incorrect readings
-  * Capacitance testing - usually to check random SMT caps
-  *Inductance testing - how often do you really use an inductor?
-  *Duty cycle - never used this
-  *Transistor beta meter - people don't really work with transistors anymore
-  *Temperature probe - I use the "Pease temperature test": a finger
-==== Where to get one?  ====
-I have a selection of [[http://www.ladyada.net/learn/../library/equipt/kits.html|suggested meters on this page]], I strongly suggest the "[[http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=220759|better]]" (At $15 its a great value) or "[[http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=645626|best]]" ($50, autoranging, has a temp probe, all sorts of other junk) ones as the "good" one is really kinda bad. If you already have a multimeter then just use that one. I'll only be covering digital multimeters here so if you have an analog one, it may be a little different and you'll have to experiment to figure out what's up
+**Always** test to make sure your meter is working before starting the test by brushing the two tips together, and verifying you hear the beep. Maybe the battery is low or its not in the right mode.
-A good multimeter will cost about $25. I suggest getting a ranging one , with current testing, and a wide range as well as easy-to-replace battery. You don't need to spend [[http://us.fluke.com/usen/products/Fluke+73+77.htm?catalog_name=FlukeUnitedStates|$200 on a Fluke 73]]! A $50 meter will be excellent. Auto-ranging meters may keep you from tripping up on ranges at first, but they're slower and often flakier.
+**Continuity is non-directional**, you can switch probes and it will be the same.
-I have had a [[http://www.inotek.com/Catalog/wavetek1et.html|Wavetek Meterman 27XT]] for half a dozen years and its been really good to me, but it was also about $80.
+If you are testing two points in a circuit and there is a (big) capacitor between those points **you may hear a quick beep and then quiet**. That's because the voltage the meter is applying to the circuit is charging up the capacitor and during that time the meter 'thinks' its continuous (essentially)
-==== More links  ====
-Here are many other links for learning how to use a multimeter
+**Small resistors (under 100 ohms or so) and also all inductors will seem like short circuits** to a multimeter because they are very much like wires.
+**Likewise, continuity doesn't mean "short"** it just means very very low resistance. For example, if you have a circuit that draws an Amp from a 5V supply, it will appear to be a 5Ω resistor. If you measure that with your meter it will think its a short circuit, but really its just a high-drain circuit.
+==== Get into the mode  ====
+First step is to get your multimeter into the correct mode. Look for the icon that looks sort of like a 'sound wave'
+Here are three examples. Note that sometimes the mode is "dual" (or possibly more) usage,
+{{  http://www.ladyada.net/images/metertutorial/conticon2.jpg?nolink&258x227  |}} \\  \\ {{ http://www.ladyada.net/images/metertutorial/conticon1.jpg?nolink&258x290 |}}  \\  \\ {{ http://www.ladyada.net/images/metertutorial/conticon3.jpg?nolink&348x239 |}}
+Turn the multimeter knob so that it points to this symbol
+==== Touch and go  ====
+For a majority of multimeters, you're ready to go, just touch the tips of the probes together so that they make a beeping sound!
+Here's a video demonstration
+{{bliptv>332691}}
+If you can't view embedded videos, [[http://blip.tv/file/get/Ladyada-multimeterTest124.mp4|click here to download an mp4]]
+Here are some examples covering a couple of different multimeters
+==== Example 1  ====
+This meter is very simple. When the probes are not touching, the display shows "1"
+[[http://www.ladyada.net/images/metertutorial/mastechopen.jpg|{{  http://www.ladyada.net/images/metertutorial/mastechopen-500.jpg?nolink&500x375  |}}]]
+When you touch the tips together, the display changes to a three digit mode (it's displaying resistance, which we will cover later) It also emits a beep
+[[http://www.ladyada.net/images/metertutorial/mastechcont.jpg|{{  http://www.ladyada.net/images/metertutorial/mastechcont-500.jpg?nolink&500x375  |}}]]
+==== Example 2  ====
+This meter is dual-mode but still very easy to use. Turn the dial to the symbol. When the probes are not touching the display shows "OL" which stands for Open Loop. (Open loop is another way of saying there is no continuity)
+[[http://www.ladyada.net/images/metertutorial/wavetekopen.jpg|{{ http://www.ladyada.net/images/metertutorial/wavetekopen-500.jpg?nolink&481x500 |}}]]
+When you touch the probes, the soundwave icon shows up in the display (upper right) and it also shows a number. The number is not the resistance, actually...its the voltage (look for the V in the right hand side for Volts). This is because this mode is also a **Diode Test** (which will be discussed later)
+[[http://www.ladyada.net/images/metertutorial/wavetekcont.jpg|{{ http://www.ladyada.net/images/metertutorial/wavetekcont-500.jpg?nolink&494x500 |}}]]
+==== Example 3  ====
+This meter is triple-mode and requires an extra step to get to the continuity function. Click on the image to get a closer view of the triple-mode. After you dial to this mode you must press the **Mode** button, the wave icon will then appear in the display.
+[[http://www.ladyada.net/images/metertutorial/extechmode.jpg|{{ http://www.ladyada.net/images/metertutorial/extechmode-500.jpg?nolink&500x390 |}}]]
+You can see the wave icon in the top right as expected. This meter also displays OL (I've noticed that nicer meters do this)
+[[http://www.ladyada.net/images/metertutorial/extechopen.jpg|{{ http://www.ladyada.net/images/metertutorial/extechopen-500.jpg?nolink&500x375 |}}]]
+Unlike the other meter, this one displays Ohms (see the symbol on the right of the display). The resistance is low (4.7Ohms) but not 0 (the ideal value) because the probes and wires act as resistors. Usually with these sorts of meters they will beep whenever resistance is under 100 ohms or so.
+[[http://www.ladyada.net/images/metertutorial/extechcont.jpg|{{ http://www.ladyada.net/images/metertutorial/extechcont-500.jpg?nolink&500x375 |}}]]
+==== Probing a PCB  ====
+Here is an example of testing a PCB for continuity.The first test shows that the two points are not connected.[[http://www.ladyada.net/images/metertutorial/pcbcheckopen.jpg|{{  http://www.ladyada.net/images/metertutorial/pcbcheckopen-500.jpg?nolink&500x329  |}}]]
+The second test shows that these two points are connected
+[[http://www.ladyada.net/images/metertutorial/pcbcheckcont.jpg|{{ http://www.ladyada.net/images/metertutorial/pcbcheckcont-500.jpg?nolink&500x386 |}}]]
-  *[[http://tangentsoft.net/elec/movies/tt06.html|TangentSoft's half-hour video tutorial]]
-  *[[http://www.makezine.com/blog/archive/2007/01/multimeter_tuto.html|Make Magazine's Bre & Joey Grand on how to use a multimeter ]]

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