dc voltage and current meter with lcd display free sample

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This ultra-compact, low current consumption panel meter features a 3½ digit LED voltmeter with 8mm (0.31") digit height.  With 200mV d.c. full scale reading, 3 decimal points, auto-polarity, auto-zero, this meter is connected via two rows of pins.The OEM 1B-LED is a low cost, popular part, normally stocked in high quantity and suitable for new designs.

It is a Digital Meter Multimeter 4in1 Voltmeter/Ammeter/Power Meter/Energy Meter, 6.5 ~ 100VDC, Rated Power: 5000W, Measuring Current Range: 0~50A,  It has small size, high efficiency, long term stable and reliable quality,easy installation and use . Applications:Suitable for industrial equipment,electronic equipment measurement or other products voltage/current /Power /Energy measurement.

A multimeter is a measuring instrument that can measure multiple electrical properties. A typical multimeter can measure voltage, resistance, and current, in which case it is also known as a volt-ohm-milliammeter (VOM), as the unit is equipped with voltmeter, ammeter, and ohmmeter functionality, or volt-ohmmeter for short. Some feature the measurement of additional properties such as temperature and capacitance.

Analog multimeters use a microammeter with a moving pointer to display readings. Digital multimeters (DMM, DVOM) have numeric displays and have made analog multimeters virtually obsolete as they are cheaper, more precise, and more physically robust than analog multimeters.

Multimeters vary in size, features, and price. They can be portable handheld devices or highly-precise bench instruments. Cheap multimeters can cost under calibration can cost over US$5,000.

The first moving-pointer current-detecting device was the galvanometer in 1820. These were used to measure resistance and voltage by using a Wheatstone bridge, and comparing the unknown quantity to a reference voltage or resistance. While useful in the lab, the devices were very slow and impractical in the field. These galvanometers were bulky and delicate.

The D"Arsonval–Weston meter movement uses a moving coil which carries a pointer and rotates on pivots or a taut band ligament. The coil rotates in a permanent magnetic field and is restrained by fine spiral springs which also serve to carry current into the moving coil. It gives proportional measurement rather than just detection, and deflection is independent of the orientation of the meter. Instead of balancing a bridge, values could be directly read off the instrument"s scale, which made measurement quick and easy.

The basic moving coil meter is suitable only for direct current measurements, usually in the range of 10 μA to 100 mA. It is easily adapted to read heavier currents by using shunts (resistances in parallel with the basic movement) or to read voltage using series resistances known as multipliers. To read alternating currents or voltages, a rectifier is needed. One of the earliest suitable rectifiers was the copper oxide rectifier developed and manufactured by Union Switch & Signal Company, Swissvale, Pennsylvania, later part of Westinghouse Brake and Signal Company, from 1927.

The invention of the first multimeter is attributed to British Post Office engineer, Donald Macadie, who became dissatisfied with the need to carry many separate instruments required for maintenance of telecommunications circuits.amperes (amps), volts and ohms, so the multifunctional meter was then named Avometer.

The Automatic Coil Winder and Electrical Equipment Company (ACWEECO), founded in 1923, was set up to manufacture the Avometer and a coil winding machine also designed and patented by MacAdie. Although a shareholder of ACWEECO, Mr MacAdie continued to work for the Post Office until his retirement in 1933. His son, Hugh S. MacAdie, joined ACWEECO in 1927 and became Technical Director.

Any meter will load the circuit under test to some extent. For example, a multimeter using a moving coil movement with full-scale deflection current of 50 microamps (μA), the highest sensitivity commonly available, must draw at least 50 μA from the circuit under test for the meter to reach the top end of its scale. This may load a high-impedance circuit so much as to affect the circuit, thereby giving a low reading. The full-scale deflection current may also be expressed in terms of "ohms per volt" (Ω/V). The ohms per volt figure is often called the "sensitivity" of the instrument. Thus a meter with a 50 μA movement will have a "sensitivity" of 20,000 Ω/V. "Per volt" refers to the fact that the impedance the meter presents to the circuit under test will be 20,000 Ω multiplied by the full-scale voltage to which the meter is set. For example, if the meter is set to a range of 300 V full scale, the meter"s impedance will be 6 MΩ. 20,000 Ω/V is the best (highest) sensitivity available for typical analog multimeters that lack internal amplifiers. For meters that do have internal amplifiers (VTVMs, FETVMs, etc.), the input impedance is fixed by the amplifier circuit.

The first Avometer had a sensitivity of 60 Ω/V, three direct current ranges (12 mA, 1.2 A, and 12 A), three direct voltage ranges (12, 120, and 600 V or optionally 1,200 V), and a 10,000 Ω resistance range. An improved version of 1927 increased this to 13 ranges and 166.6 Ω/V (6 mA) movement. A "Universal" version having additional alternating current and alternating voltage ranges was offered from 1933 and in 1936 the dual-sensitivity Avometer Model 7 offered 500 and 100 Ω/V.

High-quality analog (analogue) multimeters continue to be made by several manufacturers, including Chauvin Arnoux (France), Gossen Metrawatt (Germany), and Simpson and Triplett (USA).

Pocket-watch-style meters were in widespread use in the 1920s. The metal case was typically connected to the negative connection, an arrangement that caused numerous electric shocks. The technical specifications of these devices were often crude, for example the one illustrated has a resistance of just 25 Ω/V, a non-linear scale and no zero adjustment on both ranges.

Vacuum tube voltmeters or valve voltmeters (VTVM, VVM) were used for voltage measurements in electronic circuits where high input impedance was necessary. The VTVM had a fixed input impedance of typically 1 MΩ or more, usually through use of a cathode follower input circuit, and thus did not significantly load the circuit being tested. VTVMs were used before the introduction of electronic high-impedance analog transistor and field effect transistor voltmeters (FETVOMs). Modern digital meters (DVMs) and some modern analog meters also use electronic input circuitry to achieve high input impedance—their voltage ranges are functionally equivalent to VTVMs. The input impedance of some poorly designed DVMs (especially some early designs) would vary over the course of a sample-and-hold internal measurement cycle, causing disturbances to some sensitive circuits under test.

Additional scales such as decibels, and measurement functions such as capacitance, transistor gain, frequency, duty cycle, display hold, and continuity which sounds a buzzer when the measured resistance is small have been included on many multimeters. While multimeters may be supplemented by more specialized equipment in a technician"s toolkit, some multimeters include additional functions for specialized applications (temperature with a thermocouple probe, inductance, connectivity to a computer, speaking measured value, etc.).

A multimeter is the combination of a DC voltmeter, AC voltmeter, ammeter, and ohmmeter. An un-amplified analog multimeter combines a meter movement, range resistors and switches; VTVMs are amplified analog meters and contain active circuitry.

For an analog meter movement, DC voltage is measured with a series resistor connected between the meter movement and the circuit under test. A switch (usually rotary) allows greater resistance to be inserted in series with the meter movement to read higher voltages. The product of the basic full-scale deflection current of the movement, and the sum of the series resistance and the movement"s own resistance, gives the full-scale voltage of the range.

As an example, a meter movement that required 1 mA for full-scale deflection, with an internal resistance of 500 Ω, would, on a 10 V range of the multimeter, have 9,500 Ω of series resistance.

For analog current ranges, matched low-resistance shunts are connected in parallel with the meter movement to divert most of the current around the coil. Again for the case of a hypothetical 1 mA, 500 Ω movement on a 1 A range, the shunt resistance would be just over 0.5 Ω.

Moving coil instruments can respond only to the average value of the current through them. To measure alternating current, which changes up and down repeatedly, a rectifier is inserted in the circuit so that each negative half cycle is inverted; the result is a varying and nonzero DC voltage whose maximum value will be half the AC peak to peak voltage, assuming a symmetrical waveform. Since the rectified average value and the root mean square (RMS) value of a waveform are only the same for a square wave, simple rectifier-type circuits can only be calibrated for sinusoidal waveforms. Other wave shapes require a different calibration factor to relate RMS and average value. This type of circuit usually has fairly limited frequency range. Since practical rectifiers have non-zero voltage drop, accuracy and sensitivity is poor at low AC voltage values.

To measure resistance, switches arrange for a small battery within the instrument to pass a current through the device under test and the meter coil. Since the current available depends on the state of charge of the battery which changes over time, a multimeter usually has an adjustment for the ohm scale to zero it. In the usual circuits found in analog multimeters, the meter deflection is inversely proportional to the resistance, so full-scale will be 0 Ω, and higher resistance will correspond to smaller deflections. The ohms scale is compressed, so resolution is better at lower resistance values.

Amplified instruments simplify the design of the series and shunt resistor networks. The internal resistance of the coil is decoupled from the selection of the series and shunt range resistors; the series network thus becomes a voltage divider. Where AC measurements are required, the rectifier can be placed after the amplifier stage, improving precision at low range.

Digital instruments, which necessarily incorporate amplifiers, use the same principles as analog instruments for resistance readings. For resistance measurements, usually a small constant current is passed through the device under test and the digital multimeter reads the resultant voltage drop; this eliminates the scale compression found in analog meters, but requires a source of precise current. An autoranging digital multimeter can automatically adjust the scaling network so the measurement circuits use the full precision of the A/D converter.

In all types of multimeters, the quality of the switching elements is critical to stable and accurate measurements. The best DMMs use gold plated contacts in their switches; less expensive meters use nickel plating or none at all, relying on printed circuit board solder traces for the contacts. Accuracy and stability (e.g., temperature variation, or aging, or voltage/current history) of a meter"s internal resistors (and other components) is a limiting factor in long-term accuracy and precision of the instrument.

The frequency range for which AC measurements are accurate is important, depends on the circuitry design and construction, and should be specified, so users can evaluate the readings they take. Some meters measure currents as low as milliamps or even microamps. All meters have a burden voltage (caused by the combination of the shunt used and the meter"s circuit design), and some (even expensive ones) have sufficiently high burden voltages that low current readings are seriously impaired. Meter specifications should include the burden voltage of the meter.

Capacitance in farads, but usually the limitations of the range are between a few hundred or thousand micro farads and a few pico farads. Very few general purpose multimeters can measure other important aspects of capacitor status such as ESR, dissipation factor, or leakage.

Continuity tester; a buzzer sounds when a circuit"s resistance is low enough (just how low is enough varies from meter to meter), so the test must be treated as inexact.

Battery checking for simple 1.5 V and 9 V batteries. This is a current-loaded measurement, which simulates in-use battery loads; normal voltage ranges draw very little current from the battery.

large currents – adapters are available which use inductance (AC current only) or Hall effect sensors (both AC and DC current), usually through insulated clamp jaws to avoid direct contact with high current capacity circuits which can be dangerous, to the meter and to the operator

very high voltages – adapters are available which form a voltage divider with the meter"s internal resistance, allowing measurement into the thousands of volts. However, very high voltages often have surprising behavior, aside from effects on the operator (perhaps fatal); high voltages which actually reach a meter"s internal circuitry may internal damage parts, perhaps destroying the meter or permanently ruining its performance.

The resolution of a multimeter is the smallest part of the scale which can be shown, which is scale dependent. On some digital multimeters it can be configured, with higher resolution measurements taking longer to complete. For example, a multimeter that has a 1 mV resolution on a 10 V scale can show changes in measurements in 1 mV increments.

Absolute accuracy is the error of the measurement compared to a perfect measurement. Relative accuracy is the error of the measurement compared to the device used to calibrate the multimeter. Most multimeter datasheets provide relative accuracy. To compute the absolute accuracy from the relative accuracy of a multimeter add the absolute accuracy of the device used to calibrate the multimeter to the relative accuracy of the multimeter.

The resolution of a multimeter is often specified in the number of decimal digits resolved and displayed. If the most significant digit cannot take all values from 0 to 9 it is generally, and confusingly, termed a fractional digit. For example, a multimeter which can read up to 19999 (plus an embedded decimal point) is said to read 4+1⁄2 digits.

By convention, if the most significant digit can be either 0 or 1, it is termed a half-digit; if it can take higher values without reaching 9 (often 3 or 5), it may be called three-quarters of a digit. A 5+1⁄2-digit multimeter would display one "half digit" that could only display 0 or 1, followed by five digits taking all values from 0 to 9.3+3⁄4-digit meter can display a quantity from 0 to 3999 or 5999, depending on the manufacturer.

While a digital display can easily be extended in resolution, the extra digits are of no value if not accompanied by care in the design and calibration of the analog portions of the multimeter. Meaningful (i.e., high-accuracy) measurements require a good understanding of the instrument specifications, good control of the measurement conditions, and traceability of the calibration of the instrument. However, even if its resolution exceeds the accuracy, a meter can be useful for comparing measurements. For example, a meter reading 5+1⁄2 stable digits may indicate that one nominally 100 kΩ resistor is about 7 Ω greater than another, although the error of each measurement is 0.2% of reading plus 0.05% of full-scale value.

Specifying "display counts" is another way to specify the resolution. Display counts give the largest number, or the largest number plus one (to include the display of all zeros) the multimeter"s display can show, ignoring the decimal separator. For example, a 5+1⁄2-digit multimeter can also be specified as a 199999 display count or 200000 display count multimeter. Often the display count is just called the "count" in multimeter specifications.

The accuracy of a digital multimeter may be stated in a two-term form, such as "±1% of reading +2 counts", reflecting the different sources of error in the instrument.

Resistance measurements on an analog meter, in particular, can be of low precision due to the typical resistance measurement circuit which compresses the scale heavily at the higher resistance values. Inexpensive analog meters may have only a single resistance scale, seriously restricting the range of precise measurements. Typically, an analog meter will have a panel adjustment to set the zero-ohms calibration of the meter, to compensate for the varying voltage of the meter battery, and the resistance of the meter"s test leads.

Digital multimeters generally take measurements with accuracy superior to their analog counterparts. Standard analog multimeters measure with typically ±3% accuracy,parts per million.

Accuracy figures need to be interpreted with care. The accuracy of an analog instrument usually refers to full-scale deflection; a measurement of 30 V on the 100 V scale of a 3% meter is subject to an error of 3 V, 10% of the reading. Digital meters usually specify accuracy as a percentage of reading plus a percentage of full-scale value, sometimes expressed in counts rather than percentage terms.

Quoted accuracy is specified as being that of the lower millivolt (mV) DC range, and is known as the "basic DC volts accuracy" figure. Higher DC voltage ranges, current, resistance, AC and other ranges will usually have a lower accuracy than the basic DC volts figure. AC measurements only meet specified accuracy within a specified range of frequencies.

Manufacturers can provide calibration services so that new meters may be purchased with a certificate of calibration indicating the meter has been adjusted to standards traceable to, for example, the US National Institute of Standards and Technology (NIST), or other national standards organization.

Test equipment tends to drift out of calibration over time, and the specified accuracy cannot be relied upon indefinitely. For more expensive equipment, manufacturers and third parties provide calibration services so that older equipment may be recalibrated and recertified. The cost of such services is disproportionate for inexpensive equipment; however extreme accuracy is not required for most routine testing. Multimeters used for critical measurements may be part of a metrology program to assure calibration.

A multimeter can be assumed to be "average responding" to AC waveforms unless stated as being a "true RMS" type. An average responding multimeter will only meet its specified accuracy on AC volts and amps for purely sinusoidal waveforms. A True RMS responding multimeter on the other hand will meet its specified accuracy on AC volts and current with any waveform type up to a specified crest factor; RMS performance is sometimes claimed for meters which report accurate RMS readings only at certain frequencies (usually low) and with certain waveforms (essentially always sine waves).

When used for measuring voltage, the input impedance of the multimeter must be very high compared to the impedance of the circuit being measured; otherwise circuit operation may be affected and the reading will be inaccurate.

Meters with electronic amplifiers (all digital multimeters and some analog meters) have a fixed input impedance that is high enough not to disturb most circuits. This is often either one or ten megohms; the standardization of the input resistance allows the use of external high-resistance probes which form a voltage divider with the input resistance to extend voltage range up to tens of thousands of volts. High-end multimeters generally provide an input impedance greater than 10 GΩ for ranges less than or equal to 10 V. Some high-end multimeters provide >10 Gigaohms of impedance to ranges greater than 10 V.

Most analog multimeters of the moving-pointer type are unbuffered, and draw current from the circuit under test to deflect the meter pointer. The impedance of the meter varies depending on the basic sensitivity of the meter movement and the range which is selected. For example, a meter with a typical 20,000 Ω/V sensitivity will have an input resistance of 2 MΩ on the 100 V range (100 V × 20,000 Ω/V = 2,000,000 Ω). On every range, at full-scale voltage of the range, the full current required to deflect the meter movement is taken from the circuit under test. Lower sensitivity meter movements are acceptable for testing in circuits where source impedances are low compared to the meter impedance, for example, power circuits; these meters are more rugged mechanically. Some measurements in signal circuits require higher sensitivity movements so as not to load the circuit under test with the meter impedance.

Sensitivity should not be confused with resolution of a meter, which is defined as the lowest signal change (voltage, current, resistance and so on) 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 microamperes, although instruments with greater current sensitivity are available. Multimeters designed for (mains) "electrical" use instead of general electronics engineering use will typically forego the microamps current ranges.

Measurement of low resistance requires lead resistance (measured by touching the test probes together) to be subtracted for best accuracy. This can be done with the "delta", "zero", or "null" feature of many digital multimeters. Contact pressure to the device under test and cleanliness of the surfaces can affect measurements of very low resistances. Some meters offer a four wire test where two probes supply the source voltage and the others take measurement. Using a very high impedance allows for very low voltage drop in the probes and resistance of the source probes is ignored resulting in very accurate results.

The upper end of multimeter measurement ranges varies considerably; measurements over perhaps 600 volts, 10 amperes, or 100 megohms may require a specialized test instrument.

Every inline series-connected 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 sets, since different ranges usually use different shunt resistors.

The burden voltage can be significant in very low-voltage circuit areas. 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. RMS sensing is necessary for measurements on non-sinusoidal periodic waveforms, such as found in audio signals and variable-frequency drives.

Modern multimeters are often digital due to their accuracy, durability and extra features. In a digital multimeter the signal under test is converted to a voltage and an amplifier with electronically controlled gain preconditions the signal. A digital multimeter displays the quantity measured as a number, which eliminates parallax errors.

Modern digital multimeters may have an embedded computer, which provides a wealth of convenience features. Measurement enhancements available include:

Auto-ranging, which selects the correct range for the quantity under test so that the most significant digits are shown. For example, a four-digit multimeter would automatically select an appropriate range to display 12.34 mV instead of 0.012 V, or overloading. Auto-ranging meters usually include a facility to hold the meter to a particular range, because a measurement that causes frequent range changes can be distracting to the user.

Auto-polarity for direct-current readings, shows if the electric polarity of applied voltage is positive (agrees with meter lead labels) or negative (opposite polarity to meter leads).

Current-limited tests for voltage drop across semi conductor junctions. While not a replacement for a proper transistor tester, and most certainly not for a swept curve tracer type, this facilitates testing diodes and a variety of transistor types.

A graphic representation of the quantity under test, as a bar graph. This makes go/no-go testing easy, and also allows spotting of fast-moving trends.

Automotive circuit testers, including tests for automotive timing and dwell signals (dwell and engine rpm testing is usually available as an option and is not included in the basic automotive DMMs).

Modern meters may be interfaced with a personal computer by IrDA links, RS-232 connections, USB, or an instrument bus such as IEEE-488. The interface allows the computer to record measurements as they are made. Some DMMs can store measurements and upload them to a computer.

The first digital multimeter was manufactured in 1955 by Non Linear Systems.handheld digital multimeter was developed by Frank Bishop of Intron Electronics in 1977,

A multimeter may be implemented with a galvanometer meter movement, or less often with a bargraph or simulated pointer such as a liquid-crystal display (LCD) or vacuum fluorescent display.

Analog meters were intuitive where the trend of a measurement was more important than an exact value obtained at a particular moment. A change in angle or in a proportion was easier to interpret than a change in the value of a digital readout. For this reason, some digital multimeters additionally have a bar graph as a second display, typically with a more rapid sampling rate than used for the primary readout. These fast sampling rate bar graphs have a superior response than the physical pointer of analog meters, obsoleting the older technology. With rapidly fluctuating DC, AC or a combination of both, advanced digital meters were able to track and display fluctuations better than analog meters whilst also having the ability to separate and simultaneously display DC and AC components.

Analog meter movements are inherently more fragile physically and electrically than digital meters. Many analog multimeters feature a range switch position marked "off" to protect the meter movement during transportation which places a low resistance across the meter movement, resulting in dynamic braking. Meter movements as separate components may be protected in the same manner by connecting a shorting or jumper wire between the terminals when not in use. Meters which feature a shunt across the winding such as an ammeter may not require further resistance to arrest uncontrolled movements of the meter needle because of the low resistance of the shunt.

The meter movement in a moving pointer analog multimeter is practically always a moving-coil galvanometer of the d"Arsonval type, using either jeweled pivots or taut bands to support the moving coil. In a basic analog multimeter the current to deflect the coil and pointer is drawn from the circuit being measured; it is usually an advantage to minimize the current drawn from the circuit, which implies delicate mechanisms. The sensitivity of an analog multimeter is given in units of ohms per volt. For example, a very low-cost multimeter with a sensitivity of 1,000 Ω/V would draw 1 mA from a circuit at full-scale deflection.

To avoid the loading of the measured circuit by the current drawn by the meter movement, some analog multimeters use an amplifier inserted between the measured circuit and the meter movement. While this increases the expense and complexity of the meter, by use of vacuum tubes or field effect transistors the input resistance can be made very high and independent of the current required to operate the meter movement coil. Such amplified multimeters are called VTVMs (vacuum tube voltmeters),

Because of the absence of amplification, ordinary analog multimeter are typically less susceptible to radio frequency interference, and so continue to have a prominent place in some fields even in a world of more accurate and flexible electronic multimeters.

A multimeter can use many different test probes to connect to the circuit or device under test. Crocodile clips, retractable hook clips, and pointed probes are the three most common types. Tweezer probes are used for closely spaced test points, as for instance surface-mount devices. The connectors are attached to flexible, well insulated leads terminated with connectors appropriate for the meter. Probes are connected to portable meters typically by shrouded or recessed banana jacks, while benchtop meters may use banana jacks or BNC connectors. 2 mm plugs and binding posts have also been used at times, but are less commonly used today. Indeed, safety ratings now require shrouded banana jacks.

The banana jacks are typically placed with a standardized center-to-center distance of 3⁄4 in (19 mm), to allow standard adapters or devices such as voltage multiplier or thermocouple probes to be plugged in.

Clamp meters clamp around a conductor carrying a current to measure without the need to connect the meter in series with the circuit, or make metallic contact at all. Those for AC measurement use the transformer principle; clamp-on meters to measure small current or direct current require more exotic sensors, such as; hall effect based systems that measure the nonchanging magnetic field to determine the current.

Most multimeters include a fuse, or two fuses, which will sometimes prevent damage to the multimeter from a current overload on the highest current range. (For added safety, test leads with fuses built in are available.) A common error when operating a multimeter is to set the meter to measure resistance or current, and then connect it directly to a low-impedance voltage source. Unfused meters are often quickly destroyed by such errors; fused meters often survive. Fuses used in meters must carry the maximum measuring current of the instrument, but are intended to disconnect if operator error exposes the meter to a low-impedance fault. Meters with inadequate or unsafe fusing were not uncommon; this situation has led to the creation of the IEC61010 categories to rate the safety and robustness of meters.

Category IV: used on locations where fault current levels can be very high, such as supply service entrances, main panels, supply meters, and primary over-voltage protection equipment

Each Category rating also specifies maximum safe transient voltages for selected measuring ranges in the meter.optical isolation may be used to protect attached equipment against high voltage in the measured circuit.

Good quality multimeters designed to meet Category II and above standards include high rupture capacity (HRC) ceramic fuses typically rated at more than 20 A capacity; these are much less likely to fail explosively than more common glass fuses. They will also include high energy overvoltage MOV (Metal Oxide Varistor) protection, and circuit over-current protection in the form of a Polyswitch.

Meters intended for testing in hazardous locations or for use on blasting circuits may require use of a manufacturer-specified battery to maintain their safety rating.

A quality general-purpose electronics DMM is generally considered adequate for measurements at signal levels greater than 1 mV or 1 μA, or below about 100 MΩ; these values are far from the theoretical limits of sensitivity, and are of considerable interest in some circuit design situations. Other instruments—essentially similar, but with higher sensitivity—are used for accurate measurements of very small or very large quantities. These include nanovoltmeters, electrometers (for very low currents, and voltages with very high source resistance, such as 1 TΩ) and picoammeters. Accessories for more typical multimeters permit some of these measurements, as well. Such measurements are limited by available technology, and ultimately by inherent thermal noise.

Analog meters can measure voltage and current by using power from the test circuit, but require a supplementary internal voltage source for resistance testing, while electronic meters always require an internal power supply to run their internal circuitry. Hand-held meters use batteries, while bench meters usually use mains power; either arrangement allows the meter to test devices. Testing often requires that the component under test be isolated from the circuit in which they are mounted, as otherwise stray or leakage current paths may distort measurements. In some cases, the voltage from the multimeter may turn active devices on, distorting a measurement, or in extreme cases even damage an element in the circuit being investigated.

Keysight Technologies. "Keysight 3458A Digital Multimeter Data Sheet" (PDF). Keysight Technologies. Archived (PDF) from the original on 9 October 2022. Retrieved 31 July 2014.

Advance Devices Inc. "Smart Tweezers Digital Multimeter/LCR Meter" (PDF). Archived from the original (PDF) on 9 January 2007. Retrieved 20 January 2009.

Fluke Manufacturing. "Logging and analyzing events with FlukeView Forms Software" (PDF). Archived (PDF) from the original on 9 October 2022. Retrieved 28 January 2007.

Frank Spitzer and Barry Horwath Principles of Modern Instrumentation, Holt, Rinehart and Winston Inc., New York 1972, no ISBN, Library of Congress 72-77731, p. 39

A maximum of three modules may be attached to the meter at the same time. If a communication module is used (e.g. AXM-WEB-PUSH), it must be installed on the back of the meter FIRST before other modules are attached.

No more than two, identical I/O modules may be attached to the meter. Additionally, the two I/O modules must have a different component number. For example, two AXM-IO2 will be designated AXM-IO2-1 and AXM-IO2-2.

The meter supports single phase systems. Single phase 2-wire and single phase 3-wire are supported. The wiring configuration should be set to 1LN, 1CT for single phase 2-wire and 1LL, 2CT for single phase 3-wire systems.

Yes, you can use a jumper to power the meter as long as the voltage input is within the meter"s control power limit of 100-415Vac for P1 meters and 20-60Vdc for P2 meters. V1 on the voltage input can be jumped to "L" on the meter"s power supply terminal and V2 of the voltage input can be jumped to "N." NOTE: If there is a neutral in the system you can jump the neutral from the voltage input to the ‘N’ terminal of the meters power supply, and use one of the voltage inputs to connect to "L".

Yes, the Acuvim II meter supports SunSpec. The SunSpec registers can be found in the download section of the website as well as in the meter"s user manual.

Yes, the Acuvim II can be used to monitor 400Hz systems. In addition, the meter can automatically detect and adapt to the frequency of the electrical system.

Acuview software can be downloaded by using the link below and scrolling down to the "Acuvim II" Section. www.accuenergy.com/support/product-support-documents/

Yes, the meter may be powered up using only one voltage wire (V1) and the neutral wire (Vn). This may be accomplished by jumping the voltage phase wires.

Let’s start by getting your multimeter ready to measure voltage. To measure voltage, you will need to plug your leads into the correct ports on your multimeter.

For measuring voltage, your red lead plugs into the port marked with the "V” symbol. This is the symbol for voltage. Our black lead will be plugged into the port marked with “COM”.

Recall that there are two types of current: direct current (DC) and alternating current (AC). With DC, the current flows in one direction. With AC, the current will periodically alternate the direction it flows in.

AC and DC current also produce a unique voltage. Voltage coming from an AC system is called AC voltage. Voltage coming from a DC system is called DC voltage.

Before taking any measurements, you need to set your multimeter dial to AC or DC voltage. Your multimeter will have two voltage symbols around the dial. One “V” symbol is for AC voltage. The other “V” symbol is for DC voltage.

The AC voltage symbol will be a “V” with a “∿” over the V. The DC voltage symbol will be a “V” with a solid and dashed line over the V. Rotate your dial until it points to the correct symbol.

Recall each dial position on a multimeter can have multiple measurements. It is common for AC and DC voltage to be on the same dial position. If they are on the same dial position, you will need to use the “function” key to switch between AC or DC voltage.

For example, you want to measure AC voltage. You would rotate the dial on your meter until it points to the “V” sign. See the picture to the right for an example. Then, you would press the function key until “AC” and “V” are displayed on the screen.

Start by confirming that your black lead is plugged into the “COM” port and your red lead is plugged into the port marked “V”. Determine if the system runs on AC or DC power. Usually, you can find this information on the schematic. Set your multimeter dial to measure AC or DC voltage.

When measuring voltage, you will place your leads in parallel with the component. Recall that in parallel means that there are multiple paths for current to flow through a circuit. Parallel components will have reduced current, but the same voltage as each other.

To place your leads in parallel, you do not need to disconnect the circuit. You will place the tip of one lead on the entrance and the exit of the component. This places your meter in parallel with the component.

When you are measuring DC voltage, the placement of your leads effects the measurement. Since current flows in one direction in a DC circuit, each component has a positive and a negative end. For some components, the positive end will be marked in red. The negative end will be marked in black.

Place your leads on the positive and negative terminals of the component you are measuring. The red lead should be touching the positive end. The black lead should be touching the negative end.

If your multimeter reads a negative voltage, it means that your leads are in the wrong position. To fix this, reverse the order of your leads. Your black lead should go where your red lead is. Your red lead should go where your black lead is.

For example, let"s say that you wanted to measure the voltage across a 12V DC battery. You would place your red lead onto the terminal marked with a “+” sign. The black lead will go on the terminal with a “-” sign. The voltage will appear on the multimeter display. For example, 12V.

Recall that AC current alternates direction. Because the current changes direction, there is no positive or negative side of components like in DC voltage. Your multimeter will not display a negative voltage while reading AC voltage.

Just like DC voltage, you need to place your leads in parallel with the component. Since there is no positive or negative terminals, you can place your leads on either terminal of the component. The voltage and units will appear on your multimeter display. For example, 5V.

Recall that some multimeters require you to manually set the range of your measurement. If your multimeter is not auto ranging, you will need to change the range to get a more accurate measurement. Slowly turn the dial to lower ranges until you get an accurate measurement.

In this section, you learned how to use your multimeter to measure AC and DC voltage. In the next section, we will teach you how to measure temperature.

True, the current only flows in one direction with DC current. Since the current flows in one direction, each component has a positive and negative end.

To start, let"s measure voltage on a AA battery: Plug the black probe into COM and the red probe into mAVΩ. Set the multimeter to "2V" in the DC (direct current) range. Almost all portable electronics use direct current), not alternating current. Connect the black probe to the battery"s ground or "-" and the red probe to power or "+". Squeeze the probes with a little pressure against the positive and negative terminals of the AA battery. If you"ve got a fresh battery, you should see around 1.5V on the display (this battery is brand new, so its voltage is slightly higher than 1.5V).

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.

What happens if you switch the red and black probes? The reading on the multimeter is simply negative. Nothing bad happens! The multimeter measures voltage in relation to the common probe. How much voltage is there on the ‘+’ of the battery compared to common or the negative pin? 1.5V. If we switch the probes, we define ‘+’ as the common or zero point. How much voltage is there on the ‘-’ of the battery compared to our new zero? -1.5V!

Now let"s construct a simple circuit to demonstrate how to measure voltage in a real world scenario. The circuit is simply a 1kΩ and a Blue super bright LED powered with a SparkFun Breadboard Power Supply Stick. 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 4.5V or greater than 5.5V, this would quickly give you an indication that something is wrong and you may need to check your power connections or the wiring of your circuit.

Set the knob to "20V" in the DC range (the DC Voltage range has a V with a straight line next to it). 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. 5V system? 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. 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 2.66V of the available 5V supply to illuminate. 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.

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.

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 2.00 to 19.99.

The first digit on many multimeters is only able to display a "1" so the ranges are limited to 19.99 instead of 99.99. Hence the 20V max range instead of 99V max range.

Warning! 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. VERY carefully respect AC. 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 110V?), or if we"re trying to control a heater (such as a hot plate). Go slow and double check everything before you test an AC circuit.

This device is a panel mount or flush mount power meter with a 96mm by 96mm bezel size having backlit LCD display of 128 by 128 pixels. The meter measures active energy as per accuracy class Class 0.5S complying to IEC 62053-22 standard with sampling rate of 64 samples per cycle. Able to measures all three vectors of power and energy such as Active, Apparent & Reactive beside Voltages, Current, Frequency and Power Factor. Plus the total Harmonic Distortion and Individual harmonics up to 31st Harmonic order. The meter will function in either 50Hz or 60Hz network frequency and accepts universal control power voltages ranging from 80 to 300 V Line to Neutral AC or DC voltages. Rated current for this meter is either 1A or 5A input. it supports up to 13 different types of wiring schemes under Single Phase, Two Phase or Three Phase configuration types. The range of measurement voltage between Phases is 35 to 480 V Line to Line AC at 45 to 65 Hz while it is 20 to 277 V between Line and Neutral. It is having RS485 communication port over Modbus RTU protocol. The meter can be upgraded with optional add on IO modules for WAGES monitoring. These module comes with either two channels each of digital inputs and outputs or analog inputs and outputs. This version can be configured for 23 different types of alarms stored in 40 registers. Product dimensions are as follows: width 3.78 in (96 mm), depth 2.16 in (54 mm), height 3.78 in (96 mm) and product weight 10.58 oz (300 g).

The Keysight 3458A digital multimeter (8.5 digits) has been the industry’s benchmark for its remarkable DC accuracy and stability. It is the tool for making precision measurements with the highest degree of accuracy, transfer standard for instrument calibration, or high throughput digital multimeter measurements in manufacturing.

Learn how to use the 3458A to perform automated or manual ratio measurements to determine the value and measurement uncertainty of an unknown voltage compared to a known reference voltage. In addition, learn how to minimize measurement errors by eliminating instrument-contributed errors or using metrology-grade transfer measurement procedures.

Not sure what a multimeter is or what you can do with one? Then you"re in the right place! Below is an overview of what multimeters are and what they are useful for. To learn how to use a multimeter, to find multimeter usage ideas, or to find labeled photographs of assorted multimeter models, click on the other tabs (above) in this multimeter tutorial.

A multimeter is a handy tool that you use to measure electricity, just like you would use a ruler to measure distance, a stopwatch to measure time, or a scale to measure weight. The neat thing about a multimeter is that unlike a ruler, watch, or scale, it can measure different things — kind of like a multi-tool. Most multimeters have a knob on the front that lets you select what you want to measure. Below is a picture of a typical multimeter. There are many different multimeter models; visit the multimeter gallery for labeled pictures of additional models.

Almost all multimeters can measure voltage, current, and resistance. See the next section for an explanation of what these terms mean, and click on the Using a Multimeter tab, above, for instructions on how to make these measurements.

Some multimeters have a continuity check, resulting in a loud beep if two things are electrically connected. This is helpful if, for instance, you are building a circuit and connecting wires or soldering; the beep indicates everything is connected and nothing has come loose. You can also use it to make sure two things are not connected, to help prevent short circuits.

Some multimeters also have a diode check function. A diode is like a one-way valve that only lets electricity flow in one direction. The exact function of the diode check can vary from multimeter to multimeter. If you"re working with a diode and can"t tell which way it goes in the circuit, or if you"re not sure the diode is working properly, the check feature can be quite handy. If your multimeter has a diode check function, read the manual to find out exactly how it works.

Advanced multimeters might have other functions, such as the ability to measure and identify other electrical components, like transistors or capacitors. Since not all multimeters have these features, we will not cover them in this tutorial. You can read your multimeter"s manual if you need to use these features.

If you haven"t heard of these terms before, we"ll give a very simple introductory explanation here. You can read more about voltage, current, and resistance in the References tab, above. Remember that voltage, current, and resistance are measurable quantities that are each measured in a unit that has a symbol, just like distance is a quantity that can be measured in meters, and the symbol for meters is m.

Voltage is how hard electricity is being "pushed" through a circuit. A higher voltage means the electricity is being pushed harder. Voltage is measured in volts. The symbol for volts is V.

Current is how much electricity is flowing through the circuit. A higher current means more electricity is flowing. Current is measured in amperes. The symbol for amperes is A.

The symbol that is used for a unit is usually different than the symbol for a variable in an equation. For example, voltage, current, and resistance are related by Ohm"s law (see the References tab to learn more about Ohm"s law):

In this equation, V represents voltage, I represents current, and R represents resistance. When referring to the units volts, amps, and ohms, we use the symbols V, A, and Ω, as explained above. So, "V" is used for both voltage and volts, but current and resistance have different symbols for their variables and units. Don"t worry if this seems confusing; this table will help you keep track:

This is very common in physics. For example, in many equations, "position" and "distance" are represented by the variables "x" or "d," but they are measured in the unit meters, and the symbol for meters is m.

A simple analogy to better understand voltage, current, and resistance: imagine water flowing through a pipe. The amount of water flowing through the pipe is like current. More water flow means more current. The amount of pressure making the water flow is like voltage; a higher pressure will "push" the water harder, increasing the flow. Resistance is like an obstruction in the pipe. For instance, a pipe that is clogged with debris or objects will be harder for water to flow through, and will have a higher resistance than a pipe that is free of obstruction.

Direct current (abbreviated DC) is current that always flows in one direction. Direct current is supplied by everyday batteries—like AA and AAA batteries—or the one in your cell phone. Most of the Science Buddies projects you do will probably involve measuring direct current. Different multimeters have different symbols for measuring direct current (and the corresponding voltage), usually "DCA" and "DCV," or "A" and "V" with a straight bar above or next to them. See

Alternating current (abbreviated AC) is current that changes direction, usually many times in one second. The wall outlets in your house provide alternating current that switches directions 60 times per second (in the U.S., but 50 times per second in other countries). (Warning: Do not use a multimeter to measure the wall outlets in your home. This is very dangerous.) If you need to measure alternating current in a circuit, different multimeters have different symbols to measure it (and the corresponding voltage), usually "ACA" and "ACV," or "A" and "V" with a squiggly line (~) next to or above them.

When you take measurements with a multimeter, you will need to decide whether to attach it to your circuit in series or in parallel, depending on what you want to measure. In a series circuit, each circuit element has the same current. So, to measure current in a circuit, you must attach the multimeter in series. In a parallel circuit, each circuit measurement has the same voltage. So, to measure voltage in a circuit, you must attach your multimeter in parallel. To learn how to take these measurements, see the Using a Multimeter tab.

Figure 2 shows basic series and parallel circuits, without a multimeter connected. To learn more about voltage, current, and resistance in series and parallel circuits, check out the References tab.

Figure 2. In a basic series circuit (left), each element has the same current (but not necessarily the same voltage; that will only happen if their resistances are all the same). In a basic parallel circuit (right), each element has the same voltage (but not necessarily the same current; that will only happen if their resistances are all the same).

You might be confused by all the symbols on the front of your multimeter, especially if you don"t actually see words like "voltage," "current," and "resistance" spelled out anywhere. Don"t worry! Remember from the "What are voltage, current, and resistance?" section that voltage, current, and resistance have units of volts, amps, and ohms, which are represented by V, A, and Ω respectively. Most multimeters use these abbreviations instead of spelling out words. Your multimeter might have some other symbols, which we will discuss below.

Most multimeters also use metric prefixes. Metric prefixes work the same way with units of electricity as they do with other units you might be more familiar with, like distance and mass. For example, you probably know that a meter is a unit of distance, a kilometer is one thousand meters, and a millimeter is one thousandth of a meter. The same applies to milligrams, grams, and kilograms for mass. Here are the common metric prefixes you will find on most multimeters (for a complete list, see the References tab):

These metric prefixes are used in the same way for volts, amps, and ohms. For example, 200kΩ is pronounced "two hundred kilo-ohms," and means two hundred thousand (200,000) ohms.

Some multimeters are "auto-ranging," whereas others require you to manually select the range for your measurement. If you need to manually select the range, you should always pick a value that is slightly higher than the value you expect to measure. Think about it like using a ruler and a yardstick. If you need to measure something that is 18 inches long, a 12-inch ruler will be too short; you need to use the yardstick. The same applies to using a multimeter. Say you are going to measure the voltage of a AA battery, which you expect to be 1.5V. The multimeter on the left in Figure 3 has options for 200mV, 2V, 20V, 200V, and 600V (for direct current). 200mV is too small, so you would pick the next highest value that works: 2V. All of the other options are unnecessarily large, and would result in a loss in accuracy (it would be like using a 50-foot tape measure that only has markings every foot, and no inch markings; it isn"t as accurate as using a yardstick with 1-inch markings).

Figure 3. The multimeter on the left is manual-ranging, with many different options (indicated by metric prefixes) for measuring different amounts of voltage, current, and resistance. The multimeter on the right is auto-ranging (note how it has fewer options for the selection knob), meaning it will automatically select the appropriate range.

You might have noticed some other symbols besides V, A, Ω, and metric prefixes on the front of your multimeter. We"ll explain some of those symbols here, but remember, all multimeters are different, so we cannot cover every possible option in this tutorial. Check your multimeter"s manual if you still can"t figure out what one of the symbols means. You can also browse our multimeter gallery to see labeled pictures of different multimeters.

~ (squiggly line): You might see a squiggly line next to or above a V or A on the front of your multimeter, in addition to metric prefixes. This stands for alternating current (AC). Note that the voltage in an AC circuit is usually referred to as "AC voltage" (even though it sounds strange to say "alternating current voltage"). You use these settings when you are measuring a circuit with alternating current (or voltage).

—, - - - (solid line or dashed line): Like the squiggly line, you might see this next to or above a V or an A. The straight lines stand for direct current. You use these settings when you are measuring a circuit with direct current (e.g., most circuits that are powered by a battery).

DCV, ACV, ACA, DCA, VAC, or VDC: Sometimes, instead of (or in addition to) using squiggly or dashed lines, multimeters will use the abbreviations AC and DC, which stand for alternating current and direct current, respectively. Note that some multimeters might have AC and DC after the V and A, instead of before.

Continuity check (series of parallel arcs): This is a setting used to check if two things are electrically connected. The multimeter will beep if there is a conductive path between the two probe tips (meaning, if the resistance is very close to zero), and will not make any noise if there is no conductive path. Note that sometimes the continuity check can be combined with other functions on a single setting.

Your multimeter probably came with red and black wires that look something like the ones in Figure 4. These wires are called probes or leads (pronounced "leeds"). One end of the lead is called a banana jack; this end plugs into your multimeter (Note: some multimeters have pin jacks, which are smaller than banana jacks; if you need to buy replacement probes, be sure to check your multimeter"s manual to find out which kind you need). The other end is called the probe tip; this is the end you use to test your circuit. Following standard electronics convention, the red probe is used for positive, and the black probe is used for negative.

Although they come with two probes, many multimeters have more than two places in which to plug the probes, which can cause some confusion. Exactly where you plug the probes in will depend on what you want to measure (voltage, current, resistance, continuity test, or diode test) and the type of multimeter you have. We have provided one example in the images below—and you can check our gallery for a multimeter similar to yours—but since all multimeters are slightly different, you might need to consult the manual for your multimeter.

Most multimeters (except for very inexpensive ones) have fuses to protect them from too much current. Fuses "burn out" if too much current flows through them; this stops electricity from flowing, and prevents damage to the rest of the multimeter. Some multimeters have different fuses, depending on whether you will be measuring high or low current, which determines where you plug the probes in. For example, the multimeter shown in Figure 5 has one fuse for 10 amps (10A) and one fuse for 200 milliamps (200mA).

The left image is a multimeter with no probes inserted. The center image is a multimeter that has a black probe inserted into the center port and a red probe inserted into the right-most port. This setup is rated to measure current under 200 milliamps. The right image shows a multimeter that has a black probe inserted into the center port and a red probe inserted into the left-most port. This setup is rated to measure current up to 10 amps.

Figure 5. This multimeter has three different ports labeled 10A, COM (which stands for "common"), and mAVΩ. The fuse between mAVΩ and COM is rated for 200mA, which is a relatively "low" current. So, in order to measure small currents-or voltage or resistance (very little current flows through the multimeter when measuring voltage or resistance)—you plug the black probe into COM and the red probe into the port labeled mA