delnaz_4242
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سلام من یک پروژه درباره ی digital multimeter دارم لطفا اگه link یا اطلاعاتی دارید بذارید
اطلاعاتی درباره ی digital multimeter میخوام
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electronwizard
عضو جدید
سلام
آی سی ICL7106 یک مدار مجتمع شامل مبدل آنالوگ به دیجیتال، مدار ولتاژ مرجع و درایور LCD هستش (3.5 Digit ) ، اگر datasheet این آی سی رو بگیرید(از datasheetarchive میتونید بگیرید) ، با ده تا قطعه پسیو ،ساخت ولتمتر دیجیتال با lcd رو توضیح داده ، برای اضافه کردن اهم متر ،احتیاج به یک منبع جریان دقیق با آپ امپ دارید که جریان ثابتی را از داخل مقاومت تحت تست عبور بده و از روی ولتاژ دو سرش ، مقدار مقاومت مشخص بشه ، برای آمپرمتر هم ،یک مقاومت سری کوچک میخواید با مقدار دقیق ، که با عبور جریان تحت تست از اون ، ولتاژ دو سرش رو تقسیم بر مقدار مقاومت کنید و جریان به دست بیاد.(مثلا 0.1 اهم که روی جریان اثر نگذاره)
اصلش ساخت اون ولتمتره ، بقیه اش رو میتونید با درنظر گرفتن مقادیر رند درست کنید ، مثلا منبع جریانتون رو 1 میلی امپر بگیرید ، بنابراین هر مقاومتی به دو سرش وصل بشه ولتاژ دو سر مقاومت از نظر عددی برابر خود مقاومته ، فقط باید ممیزها رو تنظیم کنید( مثلا مقاومت 237 اهم ، مقدار ولتاژ 0.237 ولت میده که شما باید ممیز رو بعد از237 بیارید)
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elaheh_1363
عضو جدید
Digital Multimeters (DMMs) and LCR Meters
[+] Enlarge Picture
[+] Enlarge Picture
- Measure up to 1000 VDC/700 Vrms
- 5½, 6½, and 7½-digit digital multimeter/voltmeters and LCR meters
- 1.8 million samples/s isolated waveform acquisition
- NIST-traceable calibration certificates available
- Measure inductance and capacitance up to 5 H and 10,000 µF
- Seamless integration with PXI and SCXI switches
elaheh_1363
عضو جدید
A multimeter or a multitester is an electronic measuring instrument that combines several functions in one unit. The most basic instruments include an ammeter, voltmeter, and ohmmeter. Analog multimeters are sometimes referred to as "volt-ohm-meters", abbreviated VOM. Digital multimeters are usually referred to as "digital-multi-meters", abbreviated DMM.
A multimeter can be a handheld device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. Such an instrument will commonly be found in a calibration lab and can be used to characterise resistance and voltage standards or adjust and verify the performance of multi-function calibrators.
Current, voltage, and resistance measurements are considered standard features for multimeters. AVO multimeters, a manufacturer of early multimeters, derived their name from amperes, volts, and ohms, the units used for the measurement of current, voltage, and resistance.
Multimeters are available in a wide ranges of features and prices (in the United States, inexpensive multimeters can be purchased for less than US$20). They are extremely handy devices to have around the house as they can be used to troubleshoot electrical problems in a wide array of household devices such as possibly dead batteries, washing and drying machines, kitchen appliances, and even automobile electronics and electrical systems.
A multimeter can be a handheld device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. Such an instrument will commonly be found in a calibration lab and can be used to characterise resistance and voltage standards or adjust and verify the performance of multi-function calibrators.
Current, voltage, and resistance measurements are considered standard features for multimeters. AVO multimeters, a manufacturer of early multimeters, derived their name from amperes, volts, and ohms, the units used for the measurement of current, voltage, and resistance.
Multimeters are available in a wide ranges of features and prices (in the United States, inexpensive multimeters can be purchased for less than US$20). They are extremely handy devices to have around the house as they can be used to troubleshoot electrical problems in a wide array of household devices such as possibly dead batteries, washing and drying machines, kitchen appliances, and even automobile electronics and electrical systems.
elaheh_1363
عضو جدید
[edit] Resolution
The resolution of a multimeter is often specified in "digits" of resolution. The use of a digit count dates back to the 1970s when multimeter vendors were very proud of how many digits their products could display (this was important, because readout displays were costly). The vendors started to specify the maximum resolution of the multimeter based on the digital display. For example, the term 5½ digits refers to the number of digits displayed on the readout of a multimeter.
By convention, a half digit can display either a zero or a one, while a three-quarters digit can display a numeral higher than a one but not nine. Commonly, a three-quarters digit refers to a maximum count of 3 or 5. The fractional digit is always the most significant digit in the displayed value. A 5½ digit multimeter would have five full digits that display values from 0 to 9 and one half digit that could only display 0 or 1. Such a meter could show positive or negative values from 0 to 199,999. A 3¾ digit meter can display a quantity from 0 to 3,999 or 5,999, depending on the manufacturer.
[edit] Accuracy
Similarly, better circuitry and electronics have improved meter accuracy. Older analog meters might have basic accuracies of three to five percent. Modern portable DMMs may have accuracies as good as ±0.01%, and high-end bench-top instruments can have accuracies in the hundredths of parts per million figures.[2] At the other end of the spectrum, meters with ±1% basic accuracy are available for less than US$20.
Manufacturers may provide calibration services so that a new meter may be purchased with a certificate of calibration indicating the meter has been adjusted to standards traceable to the National Institute of Standards and Technology. Such manufacturers usually provide calibration services after sales, as well, so that older equipment may be recertified.
[edit] Common features
A benchtop multimeter from Hewlett-Packard.
Modern multimeters are most commonly digital, and identified by the term DMM or digital multimeter. In such an instrument, the signal under test is converted to a voltage and an amplifier with an electronically controlled gain preconditions the signal. Since the digital display directly indicates a quantity as a number, there is no risk of parallax causing an error when viewing a reading. A few analog units are available, however, and are sometimes considered better for detecting the rate of change of a reading; electronics expert Forrest Mims suggests keeping both analog and digital meters in one's toolbox, and the 2003 ARRL handbook suggests that analog multimeters are often less susceptible to radio frequency interference.
The inclusion of solid state electronics, from a control circuit to small embedded computers, has provided a wealth of convenience features in modern digital meters. Commonly available measurement enhancements include:
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 or for the instrument to upload a series of results to the computer.[8]
As modern appliances and systems become more complicated, the multimeter is becoming less common in the technician's toolkit. More complicated and specialized equipment replaces it. Where a service man might have used an ohmmeter to measure resistance while testing an antenna, a modern technician may use a hand-held analyzer to test several parameters in order to determine the integrity of a network cable
The resolution of a multimeter is often specified in "digits" of resolution. The use of a digit count dates back to the 1970s when multimeter vendors were very proud of how many digits their products could display (this was important, because readout displays were costly). The vendors started to specify the maximum resolution of the multimeter based on the digital display. For example, the term 5½ digits refers to the number of digits displayed on the readout of a multimeter.
By convention, a half digit can display either a zero or a one, while a three-quarters digit can display a numeral higher than a one but not nine. Commonly, a three-quarters digit refers to a maximum count of 3 or 5. The fractional digit is always the most significant digit in the displayed value. A 5½ digit multimeter would have five full digits that display values from 0 to 9 and one half digit that could only display 0 or 1. Such a meter could show positive or negative values from 0 to 199,999. A 3¾ digit meter can display a quantity from 0 to 3,999 or 5,999, depending on the manufacturer.
[edit] Accuracy
Similarly, better circuitry and electronics have improved meter accuracy. Older analog meters might have basic accuracies of three to five percent. Modern portable DMMs may have accuracies as good as ±0.01%, and high-end bench-top instruments can have accuracies in the hundredths of parts per million figures.[2] At the other end of the spectrum, meters with ±1% basic accuracy are available for less than US$20.
Manufacturers may provide calibration services so that a new meter may be purchased with a certificate of calibration indicating the meter has been adjusted to standards traceable to the National Institute of Standards and Technology. Such manufacturers usually provide calibration services after sales, as well, so that older equipment may be recertified.
[edit] Common features
A benchtop multimeter from Hewlett-Packard.
Modern multimeters are most commonly digital, and identified by the term DMM or digital multimeter. In such an instrument, the signal under test is converted to a voltage and an amplifier with an electronically controlled gain preconditions the signal. Since the digital display directly indicates a quantity as a number, there is no risk of parallax causing an error when viewing a reading. A few analog units are available, however, and are sometimes considered better for detecting the rate of change of a reading; electronics expert Forrest Mims suggests keeping both analog and digital meters in one's toolbox, and the 2003 ARRL handbook suggests that analog multimeters are often less susceptible to radio frequency interference.
The inclusion of solid state electronics, from a control circuit to small embedded computers, has provided a wealth of convenience features in modern digital meters. Commonly available measurement enhancements include:
- Autoranging, 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 1.234 instead of 0.012, or overloading. Autoranging meters usually include a facility to 'freeze' the meter to a particular range, because a measurement that causes frequent range changes is distracting to the user.
- Sample and hold, which will latch the most recent reading for examination after the instrument is removed from the circuit under test.
- Current-limited tests for voltage drop across semiconductor junctions. While not a replacement for a transistor tester, this facilitates testing diodes and a variety of transistor types.[3][4]
- 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.
- A continuity tester that beeps when a circuit conducts.
- A low-bandwidth oscilloscope.[5]
- Automotive circuit testers, including tests for automotive timing and dwell signals.[6]
- Simple data acquisition features to record maximum and minimum readings over a given period, or to take a number of samples at fixed intervals.[7]
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 or for the instrument to upload a series of results to the computer.[8]
As modern appliances and systems become more complicated, the multimeter is becoming less common in the technician's toolkit. More complicated and specialized equipment replaces it. Where a service man might have used an ohmmeter to measure resistance while testing an antenna, a modern technician may use a hand-held analyzer to test several parameters in order to determine the integrity of a network cable
elaheh_1363
عضو جدید
Digital multimeters
Multimeters are designed and mass produced for electronics engineers. Even the simplest and cheapest types may include features which you are not likely to use. Digital meters give an output in numbers, usually on a liquid crystal display.
The diagram below shows a switched range multimeter:
Switched range multimeter
The central knob has lots of positions and you must choose which one is appropriate for the measurement you want to make. If the meter is switched to 20 V DC, for example, then 20 V is the maximum voltage which can be measured, This is sometimes called 20 V fsd, where fsd is short for full scale deflection.
For circuits with power supplies of up to 20 V, which includes all the circuits you are likely to build, the 20 V DCvoltage range is the most useful. DC ranges are indicated by
on the meter. Sometimes, you will want to measure smaller voltages, and in this case, the 2 V or 200 mV ranges are used.
What does DC mean? DC means direct current. In any circuit which operates from a steady voltage source, such as a battery, current flow is always in the same direction. Every constructional project descirbed in Design Electronics works in this way.
AC means alternating current. In an electric lamp connected to the domestic mains electricity, current flows first one way, then the other. That is, the current reverses, or alternates, in direction. With UK mains, the current reverses 50 times per second.
For safety reasons, you must NEVER connect a multimeter to the mains supply.
You are not at all likely to use the AC ranges, indicated by
, on your multimeter.
An alternative style of multimeter is the autoranging multimeter:
Autoranging multimeter
The central knob has fewer positions and all you need to do is to switch it to the quantity you want to measure. Once switched to V, the meter automatically adjusts its range to give a meaningful reading, and the display includes the unit of measurement, V or mV. This type of meter is more expensive, but obviously much easier to use.
Where are the two meter probes connected? The black lead is always connected into the socket marked COM, short for COMMON. The red lead is connected into the socket labelled V
mA. The10Asocket is very rarely used.
Multimeters are designed and mass produced for electronics engineers. Even the simplest and cheapest types may include features which you are not likely to use. Digital meters give an output in numbers, usually on a liquid crystal display.
The diagram below shows a switched range multimeter:
The central knob has lots of positions and you must choose which one is appropriate for the measurement you want to make. If the meter is switched to 20 V DC, for example, then 20 V is the maximum voltage which can be measured, This is sometimes called 20 V fsd, where fsd is short for full scale deflection.
For circuits with power supplies of up to 20 V, which includes all the circuits you are likely to build, the 20 V DCvoltage range is the most useful. DC ranges are indicated by
What does DC mean? DC means direct current. In any circuit which operates from a steady voltage source, such as a battery, current flow is always in the same direction. Every constructional project descirbed in Design Electronics works in this way.
AC means alternating current. In an electric lamp connected to the domestic mains electricity, current flows first one way, then the other. That is, the current reverses, or alternates, in direction. With UK mains, the current reverses 50 times per second.
For safety reasons, you must NEVER connect a multimeter to the mains supply.
You are not at all likely to use the AC ranges, indicated by
An alternative style of multimeter is the autoranging multimeter:
The central knob has fewer positions and all you need to do is to switch it to the quantity you want to measure. Once switched to V, the meter automatically adjusts its range to give a meaningful reading, and the display includes the unit of measurement, V or mV. This type of meter is more expensive, but obviously much easier to use.
Where are the two meter probes connected? The black lead is always connected into the socket marked COM, short for COMMON. The red lead is connected into the socket labelled V
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