digital voltmeter and ammeter pdf

Digital voltmeter and ammeter pdf

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Chapter 2 - Basic Concepts and Test Equipment

How to wire digital dual display volt- and ammeter

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A voltmeter is an instrument used for measuring electric potential difference between two points in an electric circuit. It is connected in parallel. It usually has a high resistance so that it takes negligible current from the circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage measured; digital voltmeters give a numerical display of voltage by use of an analog-to-digital converter. Voltmeters are made in a wide range of styles. Instruments permanently mounted in a panel are used to monitor generators or other fixed apparatus.

Portable instruments, usually equipped to also measure current and resistance in the form of a multimeter , are standard test instruments used in electrical and electronics work. Any measurement that can be converted to a voltage can be displayed on a meter that is suitably calibrated; for example, pressure, temperature, flow or level in a chemical process plant.

General-purpose analog voltmeters may have an accuracy of a few percent of full scale and are used with voltages from a fraction of a volt to several thousand volts. Specially calibrated test instruments have higher accuracies, with laboratory instruments capable of measuring to accuracies of a few parts per million. Meters using amplifiers can measure tiny voltages of microvolts or less. Part of the problem of making an accurate voltmeter is that of calibration to check its accuracy. In laboratories, the Weston cell is used as a standard voltage for precision work.

Precision voltage references are available based on electronic circuits. In circuit diagrams, a voltmeter is represented by the letter V in a circle, with two emerging lines representing the two points of measurement.

A moving coil galvanometer can be used as a voltmeter by inserting a resistor in series with the instrument. The galvanometer has a coil of fine wire suspended in a strong magnetic field. When an electric current is applied, the interaction of the magnetic field of the coil and of the stationary magnet creates a torque, tending to make the coil rotate. The torque is proportional to the current through the coil. The coil rotates, compressing a spring that opposes the rotation.

The deflection of the coil is thus proportional to the current, which in turn is proportional to the applied voltage, which is indicated by a pointer on a scale. One of the design objectives of the instrument is to disturb the circuit as little as possible and so the instrument should draw a minimum of current to operate.

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 example, a meter with a sensitivity of ohms per volt would draw 1 milliampere at full scale voltage; if the full scale was volts, the resistance at the instrument's terminals would be ohms and at full scale, the meter would draw 1 milliampere from the circuit under test.

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.

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. To ensure that a DVM's accuracy is within the manufacturer's specified tolerances, it must be periodically calibrated against a voltage standard such as the Weston cell. The first digital voltmeter was invented and produced by Andrew Kay of Non-Linear Systems and later founder of Kaypro in From Wikipedia, the free encyclopedia.

Instrument used for measuring voltage. This article is about Voltmeters. It is not to be confused with Voltameter. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.

The red wire carries the current to be measured. The restoring spring is shown in green. N and S are the north and south poles of the magnet. New York Times. Retrieved 7 September Electrical and electronic measuring equipment.

Arbitrary waveform generator Digital pattern generator Function generator Sweep generator Signal generator Video-signal generator. Categories : Electrical meters Measuring instruments Electronic test equipment Voltmeters.

Hidden categories: Articles with short description Short description is different from Wikidata Articles needing additional references from April All articles needing additional references Commons category link is on Wikidata Wikipedia articles with MA identifiers Wikipedia articles with NDL identifiers.

Namespaces Article Talk. Views Read Edit View history. Help Learn to edit Community portal Recent changes Upload file. Download as PDF Printable version. Wikimedia Commons. Wikimedia Commons has media related to Voltmeters.

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Chapter 2 - Basic Concepts and Test Equipment

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.

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

How to wire digital dual display volt- and ammeter

DC voltmeter is a measuring instrument, which is used to measure the DC voltage across any two points of electric circuit. The series resistance, which is used in DC voltmeter is also called series multiplier resistance or simply, multiplier. It basically limits the amount of current that flows through galvanometer in order to prevent the meter current from exceeding the full scale deflection value. The circuit diagram of DC voltmeter is shown in below figure. We have to place this DC voltmeter across the two points of an electric circuit, where the DC voltage is to be measured.

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.

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.

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

Voltmeters measure voltage, whereas ammeters measure current.


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