The concept used within the analogue to digital conversion is called a successive approximation register. As the name implies, the successive approximation register ADC operates by successively homing in on the value of the incoming voltage. The interfaces on the front of a digital multimeter are normally very straightforward.
The basic digital multimeter will typically have a switch, display, and the connections for the test probes. The main connection on a typical digital multimeter are given in the image and description below, but obviously the exact layout and capabilities will be dependent upon the particular test instrument in use.
The switches and controls are normally set out with the main range switch occupying the central position within the multimeter panel. The display typically occupies a position at the top of the instrument so that it is easy to see and it is free from being obscured by leads and also it can still be seen if the switch is being operated. Any additional switches are typically located around the main switch where they can be reached very easily.
The connections for the test leads are normally located at the bottom of the front panel of the meter. In this way that can be reached easily, but the leads do not obstruct the operation and view of the switches and the display. The operation of a DMM itself is normally very straightforward. Continuity and large capacitors: During normal troubleshooting. This is a good sanity check before powering up a prototype to make sure there is not a short on the power system.
But don't be surprised if you hear a short 'beep! This is because there is often significant amounts of capacitance on the power system. The multimeter is looking for very low resistance to see if two points are connected.
Capacitors will act like a short for a split second until they fill up with energy, and then act like an open connection. Therefore, you will hear a short beep and then nothing. That's ok, it's just the caps charging up. One of the most common mistakes with a new multimeter is to measure current on a bread board by probing from VCC to GND bad! This will immediately short power to ground through the multimeter causing the bread board power supply to brown out.
As the current rushes through the multimeter, the internal fuse will heat up and then burn out as mA flows through it. It will happen in a split second and without any real audible or physical indication that something is wrong. Wow, that was neat. Now what? Well first, remember that measuring current is done in series interrupt the VCC line to the breadboard or microcontroller to measure current.
If you try to measure the current with a blown fuse, you'll probably notice that the meter reads '0. This is because the internal fuse is broken and acts as a broken wire or open. To change the fuse, find your handy dandy mini screw driver , and start taking out screws. Start by removing the battery plate and the battery. Now notice the hooks on the bottom edge of the face.
You will need to slide the face sideways with a little force to disengage these hooks. Make sure to replace the correct fuse with the correct type. In other words, replace the mA fuse with a mA fuse. The components and PCB traces inside the multimeter are designed to take different amounts of current. You will damage and possibly ruin your multimeter if you accidentally push 5A through the mA port.
There are times where you need to measure high current devices like a motor or heating element. Do you see the two places to put the red probe on the front of the multimeter? But if you use the 10A port to measure current, you run a much lower risk of blowing the fuse. The trade-off is sensitivity. As we talked about above, by using the 10A port and knob setting, you will only be able to read down to 0. Most of my systems use more than 10mA so the 10A setting and port works well enough.
If you're trying to measure very low power micro or nano amps the mA port with the 2mA, uA, or 20uA could be what you need.
Remember: If your system has the potential to use more than mA you should start with the red probe plugged into the 10A port and 10A knob setting. If you really need to see how the IC uses current or voltage over time, use an Agilent or other high quality bench unit.
These units have higher precision and offer a wide range of fancy functions some include Tetris! Bunnie Huang , hardware designer behind Chumby , uses high-precision current readings to trouble shoot boards during the final testing procedures of a Chumby. By looking at the current consumption of different boards that have failed for example a given failed board uses mA over the normal , he could identify what was wrong with the board when the RAM fails, it generally uses mA over normal.
By pinpointing what may be potentially wrong, the rework and repair of boards is made much easier. Everyone has his or her preference, but in general multimeters that have continuity are preferred. Every other feature is just icing on the cake. There are fancy multimeters that are autoranging , meaning they automatically change their internal range to attempt to find the correct voltage, resistance, or current of the thing you're poking at. Auto-ranging can be very helpful if you know how to use it.
Generally speaking, autoranging multimeters are higher quality and generally have more features. So if someone gives you a multimeter with auto-range, put it to use! Just know how to get it into manual mode. A circuit's voltage or current can fluctuate quite quickly. With some of the systems, the current or voltage is so sporadic that the auto-range can't keep up sensibly. A back-lit LCD is fancy, but when was the last time you measured your circuit in the dark? We generally steer clear of scary forests and situations that require us to test stuff in the middle of the night, but some people may want or need a dark-friendly multimeter.
A good click on the range selector is actually a major plus in our book. A soft knob is usually indicative of a shoddy meter. Decent probes are a plus.
Over time the leads will tend to break down at the flex point. We've seen wires come completely out of probes - and it's always at the moment you need the probes to work! If you do break a probe, they are reasonably cheap to replace. Auto-off is a great feature that is rarely seen on cheaper multimeters. This is a feature that can benefit beginners and advanced users alike, as it's easy to forget to turn the meter off at 2AM.
The SparkFun digital multimeter doesn't have this feature, but luckily the meter is very low-power. We've left the multimeter for two days straight before the 9V battery began to get low. That said, don't forget to turn your meter off! You're now ready to use your digital multimeter to start measuring the world around you.
Feel free to start using it to answer many questions. I believe my LED is getting 20mA, is it really? How much voltage does a lemon have?
Is a glass of water conductive? Can I use aluminum foil to replace these wires? A digital multimeter will answer these and many more questions about electronics. A digital multimeter is an essential tool in every electronic enthusiasts arsenal.
Here are a few multimeters and kits with multimeters to suit the needs of beginners and experienced hobbyists alike. This assortment of tools is great for those of you who have experience with tools but need a fresh set of new parts for your …. The Mooshimeter is a multi-channel circuit testing multimeter that uses your smartphone or tablet, through Bluetooth 4.
A digital multimeter or DMM is one of the most useful items of test equipment to diagnose electrical or electronic problems. Of course, this all depends on the type of digital multimeter you have.
At a minimum, you should be able to measure voltage , resistance , and current with any digital multimeter. Testing a circuit or source of power for voltage is the most common use of a digital multimeter. You should now see a reading on the display. The display is now showing the voltage of the source battery or circuit.
Some measurements in signal circuits require higher sensitivity movements so as not to load the circuit under test with the meter impedance. Sometimes sensitivity is confused with resolution of a meter, which is defined as the lowest voltage, current or resistance change that can change the observed reading.
For general-purpose digital multimeters, the lowest voltage range is typically several hundred millivolts AC or DC, but the lowest current range may be several hundred milliamperes, although instruments with greater current sensitivity are available. Measurement of low resistance requires lead resistance measured by touching the test probes together to be subtracted for best accuracy.
The upper end of multimeter measurement ranges varies considerably; measurements over perhaps volts, 10 amperes, or megohms may require a specialized test instrument. Any ammeter, including a multimeter in a current range, has a certain resistance. Most multimeters inherently measure voltage, and pass a current to be measured through a shunt resistance , measuring the voltage developed across it. The voltage drop is known as the burden voltage, specified in volts per ampere.
The value can change depending on the range the meter selects, since different ranges usually use different shunt resistors. The burden voltage can be significant in low-voltage circuits. To check for its effect on accuracy and on external circuit operation the meter can be switched to different ranges; the current reading should be the same and circuit operation should not be affected if burden voltage is not a problem.
If this voltage is significant it can be reduced also reducing the inherent accuracy and precision of the measurement by using a higher current range. Since the basic indicator system in either an analog or digital meter responds to DC only, a multimeter includes an AC to DC conversion circuit for making alternating current measurements. Basic meters utilize a rectifier circuit to measure the average or peak absolute value of the voltage, but are calibrated to show the calculated root mean square RMS value for a sinusoidal waveform ; this will give correct readings for alternating current as used in power distribution.
User guides for some such meters give correction factors for some simple non- sinusoidal waveforms , to allow the correct root mean square RMS equivalent value to be calculated. More expensive multimeters include an AC to DC converter that measures the true RMS value of the waveform within certain limits; the user manual for the meter may indicate the limits of the crest factor and frequency for which the meter calibration is valid.
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