What is a digital multimeter?
Digital multimeters long ago replaced needle-based analog meters due to their ability to measure with greater accuracy, reliability and increased impedance. Fluke introduced its first digital multimeter in 1977.
A digital multimeter is a test tool used to measure two or more electrical values—principally voltage (volts), current (amps) and resistance (ohms). It is a standard diagnostic tool for technicians in the electrical/electronic industries.
Digital multimeters long ago replaced needle-based analog meters due to their ability to measure with greater accuracy, reliability and increased impedance. Fluke introduced its first digital multimeter in 1977.
To better understand digital multimeters, it’s helpful to become clear on the basics of electricity.
After all, digital multimeter always measure some aspect of electricity. In the case of electricity, that force might be a generator, battery, solar panel or some other power supply. The pressure created by that power supply is called voltage. Voltage is the pressure applied to the circuit. Current is the Flow of the electricity in the conductor. Resistance is any restriction to the flow of the current in a conductor. Voltage, current and resistance are the three most fundamental components of electricity. Voltage is measured in volts, current in amps and resistance in ohms.
The primary difference between the two is the display, an analog multimeter uses a needle to show the value, while a digital multimeter will show the results as numbers on a screen.
The advantages of using an analog multimeter is when checking a diode the analog is usually more accurate.
The most important debugging tool in any E.E.'s toolbox is a trusty multimeter. A multimeter can measure continuity, resistance, voltage and sometimes even current, capacitance, temperature, etc. It's a swiss army knife for geeks!
What can we measure by multimeter?
(1) Continuity
What is Continuity?
You might be asking, "What is continuity?" But don't worry, it's quite simple! Continuity means, are two things electrically connected. So if two electronic parts are connected with a wire, they are continuous. If they are connected with cotton string, they are not: while they are connected, the cotton string is not conductive.
You can always use a resistance-tester (ohmmeter) to figure out if something is connected because the resistance of wires is very small, less than 100 ohms, usually. However, continuity testers usually have a piezo buzzer which beeps. This makes them very useful when you want to poke at a circuit and need to focus on where the probes are instead of staring at the meter display.
(2) Resistance
Resistance is just what it sounds like, its the characteristic that makes a component fight current flow. The bigger the resistance value (in ohms Ω) the more it fights. Most resistors (https://adafru.it/aIo) you'll see range between 1 ohm and 1 megaohm (1.0 MΩ) they often have 5% tolerance but you can buy 1% or even 0.1% accuracy resistors. In general, resistence testing is best for measuring resistors, but you may find yourself measuring the resistance of other things, such as sensors and speakers.
What is resistance testing good for?
Resistance-testing is very useful
If you don't have a continuity tester,
it can double as one Check resistors whose values are not clear,
if you aren't good at reading color codes or if the marking has come off
Measure input and output resistance of circuits
Test and characterize sensors and potentiometers
Remember
You can only test resistance when the device you're testing is not powered.
You can only test a resistor before it has been soldered/inserted into a circuit.
You can make sure your meter is working well by having a 'reference resistor'.
Resistance is non-directional, you can switch probes and the reading will be the same.
(3) Current
Why Measure Current?
If there is not enough current, your circuit may not be able to do the work it was designed to do. Logic circuits may not function reliably, displays may be dim, motors may stall.
On the other hand, if there is too much current, things will heat up and components may be damaged. In extreme cases there may even be smoke or flames.
Reasons for measuring current in a circuit include:
Determining circuit power requirements.
Verifying correct circuit operation.
Testing power supply performance.
Verify that batteries are charging or discharging at a safe rate.
Estimating battery life or recharge time Diagnosing circuit problems.
(4) Voltage
To start, let's measure voltage on a AA battery: Plug the black probe into COM and the red probe into mAVΩ.
Voltage is the pressure that is applied to a conductor. There are two common types of power sources, Alternating Current (AC) and Direct Current (DC). Alternating Voltage is the most common form of electricity. It is the power supplied by the utility or generators, which flows through our electrical circuits. The symbol for AC voltage is V ~ .
DC Voltage is a constant level of stored energy. It is stored in batteries or converted from alternating voltage through the use of electronic rectifiers. Electronic products like TVs, VCRs and computer equipment run on DC power. The symbol for DC voltage is V---.
(5) capacitance
(6) Diode
Types of Multimeters
There are two common types of Multimeters, Analog and Digital. Digital Multimeters (DMMs) are the most common. They use a liquid crystal display (LCD) technology to give more accurate readings. Other advantages include higher input impedances, which will not load down sensitive circuits, and input protection.
Analog meters use a needle movement and calibrated scale to indicate values. These were popular for years, but recently their numbers have declined. Every voltmeter has an internal resistance or impedance. The input impedance of an analog meter is expressed in ―Ohms per Volt‖
Technical note: Analog Meters The internal impedance of the meter is in parallel to the measured circuit. You want this impedance to have as little effect on the measurement as possible so the higher the impedance the better. For most electrical measurements this effect is minimal, but for sensitive electronics of today the effect of the added resistance could be significant. This is just one of the disadvantages of an Analog meter. There are however a few useful applications for analog meters, so they aren’t going away tomorrow.
The Digital Multimeter (DMMs) feature a digital or liquid crystal display (LCD). Measurement readings are displayed as numerical values on the LCD Display. The display also alerts you to any pertinent symbols and warnings.
Technical Note: Digital Multimeters and ClampMeters use different techniques internally, to measure AC, DC voltage, Resistance and Amperes. An advantage of a digital multimeter is their accuracy and input protection. Their input resistance or impedance is very high, in the range of 1,000,000 to 10,000,000 ohms, so there is little effect on the measurement. On good quality meters, their inputs are also protected from faults and misuse. Test instruments today devote a good deal of architecture to overload protection. Most digital meters meet some safety standard such as UL601010 or IEC (International Electrotechnical Commission).
I did an online check of this for sale multimeter in the Philippines. I think I will get one.
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