# Digital voltmeter pdf

DVM is essentially an Analog to digital converter (A/D) with a digital display. Digital voltmeter. Attenuator. Amplifier. Analog to Digital. Converter. Digital display. The circuit works like many other digital measurement circuits in that it converts the suitable conversion and a display, this makes a digital voltmeter (DVM). operates as a peak voltmeter, calibrated to read rms values of a sine wave or of the peak value of a complex wave. On distorted waveforms the percentage.

 Author: MARILU KENNEALY Language: English, Spanish, Dutch Country: Bolivia Genre: Art Pages: 351 Published (Last): 05.10.2015 ISBN: 736-4-63517-409-8 Distribution: Free* [*Register to download] Uploaded by: YAJAIRA The Basics of Digital Multimeters. A guide to help you understand the basic. Features and Functions of a Digital Multimeter. Author: Patrick C Elliott. Field Sales. Wireless Digital Voltmeter. A Major Qualifying Project Report. Submitted to the faculty. Of the. Worcester Polytechnic Institute. Worcester, MA. In partial fulfillment . Electronic counters are extensively used for measuring the frequency (number of occurrence .. Simplified block diagram of a single-ramp type digital voltmeter.

While the other is a digital meter which shows a series of digits in the screen, indicating the magnitude of the variable that measures. Figure 2 shows the symbols of the voltmeters and ammeters that are used in the electrical circuit diagrams. Figure 1. Symbol of each meter 2 Practice 1: use of ohmmeter, ammeter and voltmeter To measure the current in the branch of a circuit, you must open this branch and the ammeter should be inserted so that it is connected in series with the element from which you want to know their current. It is said that two elements are in "series" if one end of one joins with one end of the other, and there is no conductor connected to that union. The current flowing through that path, necessarily pass through the current meter ammeter. To measure the voltage between two points, the voltmeter connects in parallel with the electronic device from which you want to know the voltage drop. Two elements of two terminals are connected in parallel if the terminals are connected one to the other terminals. It doesn't matter if in these unions or not there is another connection. The essential characteristic of a parallel connection, which, through the elements there is the same voltage. Development of the practice Use of the ohmmeter. Without energize any circuit element, measure the resistance value that presents each resistor, as shown in figure 3 and fill in the table 1. Ohmmeter Figure 3. Connection of the Ohmmeter. Measure of resistive values.

If you're measuring DC voltage such as a battery or a sensor hooked up to an Arduino you want to set the knob where the V has a straight line. AC voltage like what comes out of the wall can be dangerous, so we rarely need to use the AC voltage setting the V with a wavy line next to it.

If you're messing with AC, we recommend you get a non-contact tester rather than use a digital multimeter. The reading on the multimeter is simply negative. Nothing bad happens! The multimeter measures voltage in relation to the common probe. Now let's construct a simple circuit to demonstrate how to measure voltage in a real world scenario. To begin, let's make sure the circuit you are working on is powered up correctly.

If your project should be at 5V but is less than 4. Measuring the voltage coming off of a Power Supply Stick. Multimeters are generally not autoranging. You have to set the multimeter to a range that it can measure. For example, 2V measures voltages up to 2 volts, and 20V measures voltages up to 20 volts. So if you've measuring a 12V battery, use the 20V setting. Use the 20V setting. If you set it incorrectly, you will probably see the meter screen change and then read '1'.

With some force imagine poking a fork into a piece of cooked meat , push the probes onto two exposed pieces of metal. One probe should contact a GND connection. One probe to the VCC or 5V connection. We can test different parts of the circuit as well.

This practice is called nodal analysis , and it is a basic building block in circuit analysis. By measuring the voltage across the circuit we can see how much voltage each component requires.

Let's measure the whole circuit first.

## Digital Multimeter working principle

Measuring from where the voltage is going in to the resistor and then where ground is on the LED, we should see the full voltage of the circuit, expected to be around 5V. We can then see how much voltage the LED is using.

This is what is referred to as the voltage drop across the LED. If that doesn't make sense now, fear not. It will as you explore the world of electronics more. The important thing to take away is that different parts of a circuit can be measured to analyze the circuit as a whole.

This LED is using 2. This is lower than the forward voltage stated in the datasheet on account of the circuit only having small amount of current running though it, but more on that in a bit. Overload What happens if you select a voltage setting that is too low for the voltage you're trying to measure? Nothing bad. The meter will simply display a 1. This is the meter trying to tell you that it is overloaded or out-of-range. Whatever you're trying to read is too much for that particular setting.

Try changing the multimeter knob to a the next highest setting. Reading the 5V across this circuit is too much for the 2V setting on the multimeter. Selection Knob Why does the meter knob read 20V and not 10V? If you're looking to measure a voltage less than 20V, you turn to the 20V setting. This will allow you to read from 2. The first digit on many multimeters is only able to display a '1' so the ranges are limited to Hence the 20V max range instead of 99V max range.

In general, stick to DC circuits the settings on the multimeter with straight lines, not curvy lines. Most multimeters can measure AC alternating current systems, but AC circuits can be dangerous. A wall outlet with AC or 'main voltage' is the stuff that can zap you pretty good.

If you need to check to see if an outlet is 'on' then use a AC tester. Really the only times we've needed to measure AC are when we've got an outlet that is acting funny is it really at V? Go slow and double check everything before you test an AC circuit. Measuring Resistance Normal resistors have color codes on them. If you don't know what they mean, that's ok!

There are plenty of online calculators that are easy to use. However, if you ever find yourself without internet access, a multimeter is very handy at measuring resistance. Then hold the probes against the resistor legs with the same amount of pressure you when pressing a key on a keyboard.

The meter will read one of three things, 0. In this case, the meter reads 0. If the multimeter reads 1 or displays OL, it's overloaded. There is no harm if this happen, it simply means the range knob needs to be adjusted.

If the multimeter reads 0. Don't worry, it'll work just fine as a pull-up or general resistor. What happens? Not a whole lot changed. However, you'll notice that there is one more digit after the decimal point giving us a slightly higher resolution in our reading. What about the next lowest setting? As a rule of thumb, it's rare to see a resistor less than 1 Ohm. Remember that measuring resistance is not perfect. Temperature can affect the reading a lot.

Also, measuring resistance of a device while it is physically installed in a circuit can be very tricky. The surrounding components on a circuit board can greatly affect the reading. Measuring Current Reading current is one of the trickiest and most insightful readings in the world of embedded electronics. It's tricky because you have to measure current in series. Where voltage is measure by poking at VCC and GND in parallel , to measure current you have to physically interrupt the flow of current and put the meter in-line. To demonstrate this, we'll use the same circuit we used in the measuring voltage section.

The first thing we'll need is an extra piece of wire. As mentioned, we'll need to physically interrupt the circuit to measure the current. Said another way, pull out the VCC wire going to the resistor, add a wire where that wire was connected, and then probe from the power pin on the power supply to the resistor.

This effectively "breaks" power to the circuit. We then insert the multimeter in-line so that it can measure the current as it "flows" through to the multimeter into the bread board. For these pictures, we cheated and used alligator clips.

## Digital Voltmeters Working Principle of Digital Voltmeter

When measuring current, it's often good to watch what your system does over time, for a few seconds or minutes. While you might want to stand there and hold the probes to the system, sometimes it's easier to free up your hands.

These alligator clip probes can come in handy.

Note that almost all multimeters have the same sized jacks they're called "banana plugs" so if you're in a pinch, you can use your friend's probes. With the multimeter connected, we can now set the dial to the proper setting and measure some current.

Measuring current works the same as voltage and resistance -- you have to get the correct range. Set the multimeter to mA, and work from there. The current consumption for many breadboard projects is usually under mA. Make sure the red probe is plugged into the mA fused port. This means you can keep the red probe in the same port to measure current, voltage, or resistance.

However, if you suspect that your circuit will be using close to or more than mA, switch your probe to the 10A side, just to be safe. Overloading the current can result in a blown fuse rather than just an overload display.

More on that in a bit. This circuit was only pulling 1. The average reading was closer to 2. Realize that the multimeter is acting as a piece of wire -- you've now completed the circuit, and the circuit will power on.

This is important because as time goes on the LED, microcontroller, sensor, or whatever device being measured may change its power consumption such as turning on an LED can resulting in a 20mA increase for a second, then decrease for a second when it turns off.

On the multimeter display you should see the instantaneous current reading. All multimeters take readings over time and then give you the average, so expect the reading to fluctuate.

In general, cheaper meters will average more harshly and respond more slowly, so take each reading with a grain of salt. In your head, take an average range such as 7 to 8mA under normal 5V conditions not 7. Similar to the other measurements, when measuring current, the color of the probes does not matter.

What happens if we switch probes? It simply causes the current reading to become negative: Current is still flowing through the system, you've just changed your perspective and now the meter reads negative. When you're done using the meter, always return the meter to read voltage return the probes to the voltage port, set the meter to read the DC voltage range if necessary.

It's common to grab a meter and begin to quickly measure the voltage between two pins. If you have left your meter in 'current' mode, you won't see the voltage on the display. Instead you'll see '0.

So before you put the meter down for the night, remember to leave your meter in a friendly state. This is achieved by using a sensitive galvanometer in series with a high resistance, and then the entire instrument is connected in parallel with the circuit examined. The sensitivity of such a meter can be expressed as "ohms per volt", the number of ohms resistance in the meter circuit divided by the full scale measured value.

For multi-range instruments, the input resistance varies as the instrument is switched to different ranges. Moving-coil instruments with a permanent-magnet field respond only to direct current.

Measurement of AC voltage requires a rectifier in the circuit so that the coil deflects in only one direction. Some moving-coil instruments are also made with the zero position in the middle of the scale instead of at one end; these are useful if the voltage reverses its polarity.

## - modular digital voltmeter iVLT - V - V | Schneider Electric

Voltmeters operating on the electrostatic principle use the mutual repulsion between two charged plates to deflect a pointer attached to a spring. Meters of this type draw negligible current but are sensitive to voltages over about volts and work with either alternating or direct current.

The sensitivity and input resistance of a voltmeter can be increased if the current required to deflect the meter pointer is supplied by an amplifier and power supply instead of by the circuit under test. The electronic amplifier between input and meter gives two benefits; a rugged moving coil instrument can be used, since its sensitivity need not be high, and the input resistance can be made high, reducing the current drawn from the circuit under test.

Amplified voltmeters often have an input resistance of 1, 10, or 20 megohms which is independent of the range selected. A once-popular form of this instrument used a vacuum tube in the amplifier circuit and so was called the vacuum tube voltmeter, or VTVM.

These were almost always powered by the local AC line current and so were not particularly portable. Today these circuits use a solid-state amplifier using field-effect transistors , hence FET-VM, and appear in handheld digital multimeters as well as in bench and laboratory instruments. These are now so ubiquitous that they have largely replaced non-amplified multimeters except in the least expensive price ranges.

These instruments are optimized for measuring AC voltage. They have much wider bandwidth and better sensitivity than a typical multifunction device. A digital voltmeter DVM measures an unknown input voltage by converting the voltage to a digital value and then displays the voltage in numeric form. DVMs are usually designed around a special type of analog-to-digital converter called an integrating converter. DVM measurement accuracy is affected by many factors, including temperature, input impedance, and DVM power supply voltage variations.