digital voltmeter and ammeter pdf

Digital Voltmeter And Ammeter Pdf

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A voltmeter is an instrument used for measuring electric potential difference between two points in an electric circuit.

Voltmeters measure voltage, whereas ammeters measure current. Some of the meters in automobile dashboards, digital cameras, cell phones, and tuner-amplifiers are voltmeters or ammeters.

Package deliveries are being slightly delayed in transit but are still arriving. Orders are shipped the next business day after they are received. Contact Us for any questions. This compact panel meter measures currents from Display range for the voltmeter is 0.

DC Voltmeters

Voltmeters measure voltage, whereas ammeters measure current. Some of the meters in automobile dashboards, digital cameras, cell phones, and tuner-amplifiers are voltmeters or ammeters. See Figure. The internal construction of the simplest of these meters and how they are connected to the system they monitor give further insight into applications of series and parallel connections. A parallel connection is used because objects in parallel experience the same potential difference.

See Figure , where the voltmeter is represented by the symbol V. A series connection is used because objects in series have the same current passing through them.

See Figure , where the ammeter is represented by the symbol A. Analog meters have a needle that swivels to point at numbers on a scale, as opposed to digital meters , which have numerical readouts similar to a hand-held calculator.

The heart of most analog meters is a device called a galvanometer , denoted by G. This deflection is due to the force of a magnetic field upon a current-carrying wire. The two crucial characteristics of a given galvanometer are its resistance and current sensitivity. By connecting resistors to this galvanometer in different ways, you can use it as either a voltmeter or ammeter that can measure a broad range of voltages or currents.

This voltmeter would not be useful for voltages less than about half a volt, because the meter deflection would be small and difficult to read accurately. For other voltage ranges, other resistances are placed in series with the galvanometer.

Many meters have a choice of scales. That choice involves switching an appropriate resistance into series with the galvanometer. Since the shunt resistance is small, most of the current passes through it, allowing an ammeter to measure currents much greater than those producing a full-scale deflection of the galvanometer.

Suppose, for example, an ammeter is needed that gives a full-scale deflection for 1. When you use a voltmeter or ammeter, you are connecting another resistor to an existing circuit and, thus, altering the circuit. Ideally, voltmeters and ammeters do not appreciably affect the circuit, but it is instructive to examine the circumstances under which they do or do not interfere.

First, consider the voltmeter, which is always placed in parallel with the device being measured. Very little current flows through the voltmeter if its resistance is a few orders of magnitude greater than the device, and so the circuit is not appreciably affected. See Figure a. A large resistance in parallel with a small one has a combined resistance essentially equal to the small one. See Figure b. The voltage across the device is not the same as when the voltmeter is out of the circuit.

An ammeter is placed in series in the branch of the circuit being measured, so that its resistance adds to that branch. However, if very small load resistances are involved, or if the ammeter is not as low in resistance as it should be, then the total series resistance is significantly greater, and the current in the branch being measured is reduced. A practical problem can occur if the ammeter is connected incorrectly.

If it was put in parallel with the resistor to measure the current in it, you could possibly damage the meter; the low resistance of the ammeter would allow most of the current in the circuit to go through the galvanometer, and this current would be larger since the effective resistance is smaller. One solution to the problem of voltmeters and ammeters interfering with the circuits being measured is to use galvanometers with greater sensitivity.

This allows construction of voltmeters with greater resistance and ammeters with smaller resistance than when less sensitive galvanometers are used.

There are practical limits to galvanometer sensitivity, but it is possible to get analog meters that make measurements accurate to a few percent.

Note that the inaccuracy comes from altering the circuit, not from a fault in the meter. Making a measurement alters the system being measured in a manner that produces uncertainty in the measurement.

For macroscopic systems, such as the circuits discussed in this module, the alteration can usually be made negligibly small, but it cannot be eliminated entirely. For submicroscopic systems, such as atoms, nuclei, and smaller particles, measurement alters the system in a manner that cannot be made arbitrarily small.

This actually limits knowledge of the system—even limiting what nature can know about itself. We shall see profound implications of this when the Heisenberg uncertainty principle is discussed in the modules on quantum mechanics. There is another measurement technique based on drawing no current at all and, hence, not altering the circuit at all. These are called null measurements and are the topic of Null Measurements. Digital meters are able to detect smaller currents than analog meters employing galvanometers.

How does this explain their ability to measure voltage and current more accurately than analog meters? Since digital meters require less current than analog meters, they alter the circuit less than analog meters. Their resistance as a voltmeter can be far greater than an analog meter, and their resistance as an ammeter can be far less than an analog meter.

Consult Figure and Figure and their discussion in the text. Stimulate a neuron and monitor what happens. Pause, rewind, and move forward in time in order to observe the ions as they move across the neuron membrane.

Analog Meters: Galvanometers Analog meters have a needle that swivels to point at numbers on a scale, as opposed to digital meters , which have numerical readouts similar to a hand-held calculator.

Ammeters may also have multiple scales for greater flexibility in application. The various scales are achieved by switching various shunt resistances in parallel with the galvanometer—the greater the maximum current to be measured, the smaller the shunt resistance must be.

Taking Measurements Alters the Circuit When you use a voltmeter or ammeter, you are connecting another resistor to an existing circuit and, thus, altering the circuit. This is an example of a significant alteration of the circuit and is to be avoided. The circuit is essentially unaltered compared with when the ammeter is absent. This significant alteration of the circuit is to be avoided. Answer Since digital meters require less current than analog meters, they alter the circuit less than analog meters.

Summary Voltmeters measure voltage, and ammeters measure current. A voltmeter is placed in parallel with the voltage source to receive full voltage and must have a large resistance to limit its effect on the circuit. An ammeter is placed in series to get the full current flowing through a branch and must have a small resistance to limit its effect on the circuit. Both can be based on the combination of a resistor and a galvanometer, a device that gives an analog reading of current.

Standard voltmeters and ammeters alter the circuit being measured and are thus limited in accuracy.

How to Use an Ammeter to Measure Current

Definition: The instrument which measures the voltage or potential difference in volts is known as the voltmeter. It works on the principle that the torque is generated by the current which induces because of measurand voltage and this torque deflects the pointer of the instrument. The deflection of the pointer is directly proportional to the potential difference between the points. The voltmeter is always connected in parallel with the circuit. The voltmeter constructs in such a manner that their internal resistance always remains high.

Do you have a requirement to measure DC voltage and current in the Ham Shack, on the test bench, in your motorhome or boat or for monitoring a solar panel array? The compact panel meter contains dual LED displays. The top display in Red LEDs shows voltage measurements from 0 to Periodic adjustment of the meter is possible. With the meter turned off power removed , apply a short jumper between test points A and B. With the jumper in place, apply power to the meter which will be automatically calibrated to zero. Remove the jumper placed between A and B.


Compact panel meters designed to fit standard 17⁄32" switch knock-outs. The range offers high accuracy AC and DC ammeters and voltmeters, elapsed time.


DVAM-02 (0-99.9v and 0-50A)

Package deliveries are being slightly delayed in transit but are still arriving. Orders are shipped the next business day after they are received. Contact Us for any questions.

All the diagrams were somehow too technical for me. The original article included only one variant of these digital volt- and ammeters. I will cover wiring for all of them in this post.

3 comments

Isabelle F.

DC Analog Voltmeters and Ammeters. AC Analog Voltmeters and Ammeters. True rms Analog Voltmeters. 3. Digital Meters. Dual-Slope DVMs.

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Daitrapenob

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Mavise A.

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