ac voltage and current meter with lcd display free sample

2. Monitors are not calibrated same, item color displayed in photos may be showing slightly different from the real object. Please take the real one as standard.

Just read Dale Klines review. DANGER!!! If youre going to run 18# wire, you need to fuse the hot, at the source, with a 250VAC or better fuse rated no higher than a couple Amps. The green wire should be used only as an Equipment Ground! You should use a twisted pair cable with at least 300 volt insulation to connect to the CT. current Transformer DO NOT ASSUME that you can connect a CT input in common with a power connection!

To answer the question regarding length of cable from the current transformer to the meter module: There is no hard limit. The main consideration is the resistance of the connecting cable. Since the resistance of the transformer itself is about 55 ohms, up to 20% of that, 10 ohms, should have no observable effect on current measurement accuracy. Voltage rating is not an issue because the transformer output is in the millivolt range. However the connecting cable WILL be sensitive to AC magnetic fields such as from a nearby current-carrying wire or cable. For this reason, the current transformer connecting cable should be kept away, an inch is plenty, from other current-carrying wiring. In particular the current transformer wires should not be in the same cable as the load current-carrying wires. Using a twisted pair cable is ideal. Ordinary doorbell wire, #22 or #24 conductor, should be good for up to 100 feet. This applies to all MPJA AC meters that use current transformers.

I have used several other of MPJA DC meters with great success. But I have a question on this AC V/A meter... How far away can the meter readout be from the LOAD under test? I have two electric heaters in the basement that I would like to monitor from the kitchen about 35 feet away. SInce there is very little power pulled by the meter itself, a simple 18GA extension will bring the 220VAC to the meter in the kitchen, and the third wire for the toroid. ---White & Black across the 220VAC, and the Green for the toroid--- Will that long wire for the toroid affect the accuracy of the current measurement?

In regards to Mr. Lopez comment; I have used 6 of these meters with no problem. PDF data clearly shows 1 of the load power leads going through the current ttransformer with the CT leads connected to Meter. My 33yr. Granddaughter a nurse connected 2 up at her house. you must be doing something wrong. I plan on us8ing 2 more in a solar demo. class

I mounted two of these in a pair of 4x4x2 metal Handy Boxes to monitor my 20KW backup diesel genny. I also did the same on a break out panel for 15KW diesel genny mounted on a trailer to assist with balancing loads on a temporary electrical service.

I have bought more than 10 of these meters and they work great. They are cheap and do a great and accurate job of telling me when my motors are in trouble. I will keep buying these and I recommend them as well.

I bought two of these meters and have not worked for me. The voltage measurement is correct, but the current is always maintained 26-29Amp. The diagram is in the data sheet does not say how and where to use the current transformer, only said that the load must be connected to the connector, but no output voltage. I bought other meters ME 31496 and work perfectly.

I chose to use mine as a portable AC voltage and current monitor. It mounts easily in a deep 1900 box with a duplex/GFCI cover.Almost! Its about 5mm too wide to fit in the GFCI opening without a little grinding. I havent had a chance to check it for accuracy yet but it sure looks good!

Depending on your plan, the price of electricity can fluctuate based on the demand – the average rate at which your home consumes electricity during a specific time.

A standard meter is a clock-like device that records the amount of electricity you use. It shows your home"s electricity consumption in kWh. Some are mechanical, while others have LCD displays.

To read your kW demand, wait for the meter LCD display to cycle to code 10. The code is displayed in area 3. Your maximum kW for the day will be displayed; this is the maximum average load over a 15- or 30-minute interval (depending on your price plan) for the day.

New: A brand-new, unused, unopened, undamaged item in its original packaging (where packaging is applicable). Packaging should be the same as what is found in a retail store, unless the item was packaged by the manufacturer in non-retail packaging, such as an unprinted box or plastic bag. See the seller"s listing for full details.See all condition definitionsopens in a new window or tab

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.

Multimeters are widely used by professionals in several fields including industrial maintenance and testing, research, appliance repair and electrical installation. However a digital multimeter or DMM is also an invaluable test instrument for home and DIY use. The instrument can used for measuring voltage, current and resistance and can check:Battery voltages

Before we learn how to use a multimeter, we need to become familiar with the quantities we are going to be measuring. The most basic circuit we"ll encounter is a voltage source, which could also be connected to a load. The voltage source might be a battery, DC power supply or a mains power supply. There are many types of loads, but typically they could be devices such as bulbs, motors or electronic components called resistors. The circuit can be represented by a diagram called a schematic.In the circuit below, the voltage source V creates an electrical pressure which forces a current I to flow in a loop around the circuit and through the load R. Ohm"s Law tells us that if we divide the voltage V by the resistance R, measured in ohms, it gives us a value for the current I in amps:

Parts of a MeterThe Display. This is usually a multidigit, 7 segment LCD display. Some laboratory instruments however have LED displays which are easier to read under certain lighting conditions.

Rotary Range Selector Dial. This allows you to select the function which you will be using on the meter. On a non-autoranging meter, it also selects the range.

Probes. These have a pointed tip on one end for touching against the point of measurement and a plug on the other end for insertion into a connection socket.

The arrangement is non-standard and depends on the brand/model of meter, so it"s important to understand the function of each socket to avoid damage to the meter:Com is the common socket into which the black probe lead is plugged. This is standard on all meters.VΩmAmarked on a socket indicates that the red probe lead is plugged into it for measuring voltage, resistance or low current ("mA" means "milliamps" for current measurement and the Greek letter Omega "Ω" is the symbol for ohms, the unit of resistance).

If there"s no mention of "mA" on the socket as explained above, there will be one or more separate sockets for connecting the red probe lead to measure current. These sockets will be marked "A" or "mA" with the max current range (e.g. 10A for high current readings and 400 mA for lower current readings).

Voltage, current and resistance ranges are usually set by turning a rotary range selection dial. This is set to the quantity being measured, e.g. AC volts, DC volts, Amps(current) or Ohms (resistance).

If the meter is non-autoranging, each function will have several ranges. So for example, the DC volts function range will have 1000V, 200V , 20V, 2V and 200mV ranges. Using the lowest range possible gives more significant figures in the reading.WARNING !!!

How to Measure VoltagePower off the circuity/wiring under test if there is a danger of shorting out closely spaced adjacent wires, terminals or other points which have differing voltages.

If the meter has has a manual range selection dial, turn this to select AC or DC volts and pick a range to give the required accuracy. So for instance measuring 12 volts on the 20 volt range will give more decimal places than on the 200 volt range.

A multimeter must be connected in parallel in a circuit (see diagram below) in order to measure voltage. So this means the two test probes should be connected in parallel with the voltage source, load or any other two points across which voltage needs to be measured.

Touch the other red probe against the second point of test. Ensure you don"t bridge the gap between the point being tested and adjacent wiring, terminals or tracks on a PCB.

Note: A lead with a 4mm banana plug on one end and a crocodile clip on the other end is very handy. The croc clip can be connected to ground in the circuit, freeing up one of your hands.

Most meters come as standard with pointed, needle tip probes. An alternative is crocodile (alligator) probes that have spring loaded clips. These are useful so that one or both probes can be connected to a circuit without holding the probes in place by hand.WARNING !!!

Safety First When Measuring Mains Voltages!Before using a meter to measure mains voltages, visually inspect it first. Check the meter, probes and accessories are free from damage. Never use test leads with exposed conductors which could be touched inadvertently or a meter with cracks in the casing or exposed metal. Make sure probes are pushed securely into sockets.

Only use meters and test leads that have a CAT rating suitable for the measuring job. Choose leads with proper insulation, finger guards and shrouded plugs.

Double check that test leads are plugged into the common and voltage sockets of the DMM (see photo below) and not the current sockets. This is essential to avoid blowing up the meter.

Ideally use test leads with shrouded crocodile clips on the ends, power off the circuit, connect the leads and power up again so you don"t have to hold leads. TV repair technicians used to have a saying that the safest place to keep one of your hands is in your pocket when making measurements. When holding a probe in each hand, there"s always the danger of making contact with neutral or ground with one hand and hot (live) with the other if the probe or leads are damaged, resulting in a shock across the heart, a potentially lethal scenario. Alternatively the negative probe lead can be connected to neutral using a crocodile connector so that measurements can be taken with one hand using the positive needle probe.

If you have to measure voltage at a socket outlet, turn off power before inserting probe tips. If this isn"t possible, always insert the probe tip into the neutral terminal of the outlet first and then insert the other probe into the live (hot) terminal. If you insert the probe tip into the hot first and inadvertently touch the tip of the other probe, or it makes contact with a metal surface, you can get a shock or potentially be electrocuted.

Ideally buy and use a meter with a least CAT III or preferably CAT IV protection for testing mains voltages. This type of meter will incorporate high rupturing capacity (HRC) fuses and other internal safety components that offer the highest level of protection against overloads and transients on the line being tested. A meter with less protection can potentially blow up causing injury if it is connected incorrectly, or a transient voltage generates an internal arc.

Autoranging meters detect the magnitude of the voltage and select the range automatically to give the most amount of significant digits on the display. You must however set the mode to resistance, volts or current and also connect the probe leads to the proper sockets when measuring current.

This Fluke "VoltAlert™" non-contact voltage detector from Amazon is a standard tool in any electricians tool kit, but useful for homeowners also. I use one of these for identifying which conductor is live whenever I"m doing any home maintenance. Unlike a neon screwdriver tester (phase tester), you can use one of these in situations when live parts/wires are shrouded or covered with insulation and you can"t make contact with wires. It also comes in useful for checking whether there"s a break in a power flex and where the break occurs.

Plug the red positive probe lead either into the mA socket or the high current socket which is usually marked 10A (some meters have a 20 A socket instead of 10A). The mA socket is often marked with the maximum current and if you estimate that the current will be greater than this value, you must use the 10 A socket, otherwise you will end up blowing a fuse in the meter. On some meters, there is no additional socket for measuring current and the same socket is used as for measuring voltage (usually marked VΩmA).

Turn the dial on the meter to the highest current range (or the 10A range if the probe is in the 10A socket). If the meter is autoranging, set it to the "A" or mA setting. (See the photo above for an explanation of symbols used).

Remember to return the positive probe to the V socket when finished measuring current. The meter is practically a short circuit when the lead is in the mA or 10 A socket. If you forget and connect the meter to a voltage source when the lead is in this position, you may end up blowing a fuse at best or blowing up the meter at worst! (On some meters the 10A range is un-fused).

Fluke, a leading US manufacturer of digital instrumentation, promotes the Fluke 113 model for general purpose use in the home or for car maintenance. This is an excellent meter and can measure AC and DC volts, resistance, check continuity and diodes. The meter is auto-ranging, so ranges don"t have to be set. It is also a true-RMS meter. It doesn"t measure current, so If you need to measure AC and DC current, the Fluke 115 has this added facility.

An alternative is the Fluke 177 model which is a high accuracy instrument (the specification is 0.09% accuracy on DC volts). I use this model for more accurate testing and professional use and it can measure AC and DC voltage and current, resistance, frequency, capacitance, continuity and diode test. It can also indicate max and min values on each range.

On most multimeters, the highest current range is 10 or 20 amps. It would be impractical to feed very high currents through a meter because normal 4 mm sockets and test leads wouldn"t be capable of carrying high currents without overheating. Instead, clamp meters are used for these measurements.

Clamp meters (as the name suggests), also known as tong testers, have a spring loaded clamp like a giant clothes peg which clamps around a current carrying cable. The advantage of this is that a circuit doesn"t have to broken to insert a meter in series, and power needn"t be turned off as is the case when measuring current on a standard DMM. Clamp meters use either an integrated current transformer or hall effect sensor to measure the magnetic field produced by a flowing current. The meter can be a self contained instrument with an LCD which displays current, or alternatively the device can output a voltage signal via probe leads and 4mm "banana" plugs to a standard DMM. The voltage is proportional to the measured signal, typically 1mv represents 1 amp.

To use a current clamp, you simply clamp over a single cable. In the case of a power cord or multicore cable, you need to isolate one of the cores. If two cores carrying the same current but in opposite directions are enclosed within the jaws (which would be the situation if you clamp over a power cord), the magnetic fields due to the current flow would cancel out and the reading would be zero.

Disconnect one end of the component if it"s in a circuit. This may involve pulling off spade leads or desoldering. This is important as there may be other resistors or other components having resistance, in parallel with the component being measured.

If the display indicates "1", this means that resistance is greater than can be displayed on the range setting you have selected, so you must turn the dial to the next highest range. Repeat this until a value is displayed on the LCD.

A multimeter is useful for checking breaks in flexes of appliances, blown filaments in bulbs and blown fuses, and tracing paths/tracks on PCBsTurn the selecting dial on the meter to the continuity range. This is often indicated by a symbol which looks like a series of arcs of a circle (See the photo showing symbols used on meters above).

If resistance is less than about 30 ohms, the meter will indicate this by by a beep tone or buzzing sound. The resistance is usually indicated on the display also. If there is break in continuity in the device being tested, an overload indication, usually the digit "1", will be displayed on the meter.

A multimeter can be used to check whether a diode is short circuited or open circuited. A diode is an electronic one way valve or check valve, which only conducts in one direction. A multimeter when connected to a working diode indicates the voltage across the component.Turn the dial of the meter to the diode test setting, which is indicated by a triangle with a bar at the end (see the photo showing symbols used on meters above).

When the black probe is in contact with the cathode of the diode (usually indicated by a bar marked on the component) and the red probe makes contact with the anode, the diode conducts, and the meter indicates the voltage. This should be about 0.6 volts for a silicon diode and about 0.2 volts for a Schottky diode. When the probes are reversed, the meter should indicate a "1" because the diode is open circuit and non-conducting.

If the meter reads "1" when the probes are placed either way, the diode is likely to be faulty and open circuit. If the meter indicates a value close to zero, the diode is shorted circuited.

So to measure the power in watts of a load/appliance, both the voltage across the load and the current passing through it must be measured. If you have two DMMs, you can measure the voltage and current simultaneously. Alternatively measure the voltage first, and then disconnect the load so that the DMM can be inserted in series to measure current. When any quantity is measured, the measuring device has an influence on the measurement. So the resistance of the meter will reduce current slightly, and give a lower reading than the actual value with the meter not connected.

Three ways to measure current drawn by an electrical appliance:The safest way to measure the power consumption of an appliance powered from the mains is to use a power adapter. These devices plug into a socket and the appliance is then plugged into the adapter which displays information on an LCD. Typical parameters displayed are voltage, current, power, kwh, cost and how long the appliance was turned on (useful for fridges, freezers and air conditioners which cut in and out). You can read more about these gadget in my article here:

An alternative way of safely measuring current drawn by an electrical appliance is to make up a test lead using a short piece of power cord with a trailing socket on one end and a mains plug on the other. The inner neutral core of the power cord could be freed and separated from the outer sheath, and current measured with a clamp meter or probe (Don"t remove the insulation!)

Some meters have a button which sets the meter to read max and min RMS voltages and/or peak voltages (of the waveform). An alternative is to use a DVA or Direct Voltage Adapter. Some components such as CDI (Capacitor Discharge Ignition) modules on vehicles, boats and small engines produce pulses which vary in frequency and can be short duration. A DVA adapter will sample and hold the peak value of the waveform and output it as a DC voltage so the component can be checked to see whether it"s producing the correct voltage level. A DVA adapter typically has two probe leads as input for measuring voltage and either two output leads with banana plugs or a connector with fixed plugs attached for plugging into a meter with standard spaced sockets. The meter is set to a high DC voltage range (e.g. 1000 volts DC) and the adapter typically outputs 1 volt DC per 1 volt AC input.

In this application, the adapter is used for measuring the primary voltage of a stator/ignition coil, not the secondary voltage, which could be about 10,000 volts or more.

The voltage supply to your home is AC, and voltage and current vary in polarity over time. The waveform is sinusoidal as in the diagram below and the change of direction of current is known as the frequency and measured in Hertz (Hz). This frequency can be 50 or 60 Hz, depending on which country you live in. The RMS voltage of an AC waveform is the effective voltage and similar to the average voltage. If the peak voltage is Vpeak, then the RMS voltage for a sinusoidal voltage is Vpeak / √2 (approx 0.707 times the peak voltage). The power in a circuit is the RMS voltage multiplied by the RMS current flowing in a load. The voltage normally printed on appliances is the RMS voltage even though this is not usually stated.

A basic multimeter will indicate RMS voltages for sinusoidal voltage waveforms. The supply to our homes is sinusoidal so this isn"t a problem. However if a voltage is non sinusoidal, e.g. a square or triangular wave, then the meter will not indicate the true RMS voltage. True RMS meters however are designed to correctly indicate RMS values for all shaped waveforms.

If you need to measure voltages and log them over time, you can use a datalogging multimeter. A product such as the Fluke 289 True-RMS datalogging multimeter can record 15,000 readings. Another feature of this meter is that it can be setup with a wireless connector to communicate with an Android mobile device, allowing readings to be viewed remotely, while the meter is located elsewhere.

Plug the black probe into COM and the red probe into the socket marked VΩ. Set the range to DC or AC volts and touch the probe tips to the two points between which voltage needs to be measured.

For this it"s best to stay safe and use a non-contact volt tester or phase tester screwdriver. These will indicate if voltage is e.g > 100 volts. A multimeter can only measure the voltage between live and neutral or live and earth if these conductors/terminals are accessible, which may not always be the case.

Voltage drop occurs across a resistance or along a power cable. So follow the same procedure as for measuring voltage and measure voltage at the two points of interest and subtract one from the other to measure voltage drop.

If voltage drop is excessive, appliances may not work properly. Cable should be sized adequately to minimise voltage drop for the current it needs to carry and the distance over which current travels.

Digital multimeter: What is the accuracy, range and resolution? (2021, May 9). Fluke. https://www.fluke.com/en-ie/learn/blog/digital-multimeters/accuracy-precision

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Question: To be clear, am I correct in my interpretation that if I want to check that there is 230v in my electrical connections in a light fitting that is glowing dimly, I need the lamp in first to complete the circuit, then I check either end of the fitting placing the meter in parallel? Conversely, if I were to use the meter in lieu of the lamp, then this would be in series and the reading would be false or the meter would simply not work?

Answer: If the fitting is wired correctly, it doesn"t matter much if the lamp is in place or not as regards measuring the voltage. Yes, you do connect a meter in parallel with a load (i.e. the lamp in your case) to measure voltage. But because a lamp doesn"t take much current, it doesn"t drop voltage significantly. Now if the load was high powered e.g. a heater, the voltage would drop a few volts. The open circuit voltage of a voltage source is always higher than the output voltage on load because a real voltage source always has internal resistance, plus the connecting wires have resistance also. So if the connecting wires are long or cross-sectional area is small, the voltage drop can be considerable if the wiring is sized inappropriately. If you connect the meter to the fitting without the lamp, it"s in parallel with the output terminals on the fitting and because it"s set to "volts", no current flows through it (well actually just a little, but microamps because it has such a high resistance). If the meter was set to "amps" it would be like a short circuit and effectively in series with the supply and a fuse would blow. Maybe the concept of parallel and series is a bit confusing. Just remember that when the meter is set to volts, it measures the voltage between two points and when set to amps, it measures the current flowing between the two points.

A meter has a very high impedance and sensitivity to voltage. Even though the black isn"t connected to anything, there is capacitance between the metal probe tip and wire of the black lead and ground. So a minute current can actually flow backwards and forwards through the air as this tiny capacitor charges and discharges as the AC continually changes direction, If you"ve ever put your hand on a plasma ball, a discharge flows through the ball to the glass at the point where your hand touches it. This is pretty much for the same reason. Look up capacitors on Wikipedia for more info.

I am replacing a ceiling fan. In checking the voltages i find i get a reading of 9 - 10 volts when I connect only the red lead of my test meter to the hot wire. The black is not connected to anything. Is there an explanation? If touch the black lead to ground or the common wires I get 120 volts (+/- a couple)

Having just enrolled on a auto electrical course at Cardiff and the Vale College, Cardiff and no nothing about vehicle electrics. I find your article about multimeters fascinating. Thank you!

Hi Mark, it possibly could. Sometimes adapters aren"t regulated and 12 volts output means the voltage it gives on full load, but this can rise when off load. A regulated adapter gives a constant voltage, independent of load. If it"s an AC adapter, it"s probably just a transformer, without any regulating electronics. 17.4 volts sounds very high though for a 12 volt adapter off load, a volt or two would be normal.

Does the microscope definitely require AC, rather than DC? Without being able to load the adapter with a current equivalent to what the microscope takes and see if voltage falls, I can"t say whether or not it would cause damage.

I just bought a 12v (written on on it) AC adapter. I measured the voltage at the tip of it with a Fluke meter. I am reading 17.4v, is this normal? My device (a LED illuminated microscope) requires 12v. Will I damage the LED bulb if I use this AC adapter?

Only if they"re connected to a high voltage source. Above about 50 V, a voltage source will begin to produce a sensation. However the intensity and actual threshold level depends on several factors such as location on the body of the point of contact, nature of the skin e.g. smooth or calloused, whether skin is dry or moist etc. An ohmmeter or multimeter set to the ohms range, outputs a voltage and uses this to feed a current through a connected resistance in order to calculate its value (R = V / I). However this voltage is relatively low. A Megger type insulation tester as used for checking insulation quality in electrical installations however, generates much higher voltages which will shock.

Hi Pranjal. Yes you can measure AC current if the meter has an AC current range. The procedure is the same as for measuring DC current described above. If measuring mains currents, precautions must be taken, including but not limited to the following:

3 If you estimate that the current will be higher than the maximum range, use the high current setting and use the high current (e.g. 10A or 20A) socket

4 If you don"t know the current, but think it may be greater than the value of the highest current range, you will need to use a clamp meter. The high current range may not be fused.

I"m not an electrician, but I presume a "Megger" type instrument would be required for testing insulation plus another for testing earth loop impedance and a third for testing RCDs. Alternatively a multifunction tester to all tests could be used. A multimeter would be of limited use.

Thanks Eugene. I have some of them already. Can you suggest any decent journal articles or published papers .. I realy need to use excessive literature review for my work and would appreciate any suggested sources

I had an electrician who used a multi meter to carry out an EICR ( PERIODIC TESTING ) USING A MULTI METER. I WAS SUPRISED AS I DIDN"T THINK IT WAS POSSIBLE HE ASSURED ME IT WAS. NUT QUESTION IS .IS IT POSSIBLE TO DO A FULL EICR ( PERIODIC TEST ) USING A MULTI METER.i know for a fact that he couldn"t get a tripping time for the rcd

Important! - For anyone using a DVA adapter mentioned below. These adapters are for measuring the primary voltage of a stator/ignition coil, not the secondary voltage, which could be about 10,000 volts.

The meter is practically a short circuit when the the leads are connected to measure current. If you connect it to a voltage source, it will blow the fuse in the meter. The high current range (10A/20A range) may not be fused on a cheap meter, so the meter will likely be destroyed if the voltage source can potentially supply a large current (the mains or a battery).

A digital multimeter has a high impedance, typically 10 megaohms. When one probe is contacting a 220 volts supply and the other end is in free air, you effectively have a potential divider circuit. A potential divider (Google it for more details) consists of a number of resistors connected in series. When the divider is connected to a voltage supply, a reduced voltage is available at the junction between the resistors (an example is the volume control on a radio). In the most simplest of examples, two resistors of equal value will give half the input voltage at the junction. In your case, the meter forms one part of the potential divider. The other part consists of the resistance from probe through the air to ground (practically infinite), the resistance from the probe through your hand to ground (could be hundreds of megaohms if there is high humidity) and the reactance of the probe to ground (due to capacitance). The latter three are in parallel.

Digital multimeter two probes. One probe places in phase 230VAC, another probe placed in open air. But meter reading shows 30V. Meter reading is correct? Pls explain.

Thank you very much for such helpful information, I"m passionate with electronics and inventing some cool devices, and my aim is to make free energy/electricity, so my problem is that I don"t know how do we determine voltage a diode can handle like 1N4008 or 1N540 and Voltage regulator and transistor, my question is how do we determine their voltage rating because some of them are not even written or they"re faded and where and in which circumstances do we use suppression capacitor, I"d like it if u poke me on my email when u get chance to answer my question and where to follow my answer Makhokha93@gmail.com thank you for your knowledge.

You can use a potential divider circuit to measure high voltages with a low voltage range meter. In fact this is how the internal circuitry in a meter reduces voltage for the various ranges. However the effort required isn"t really worth it. You would also have to build everything into a box so that there are no wires/terminals/components exposed which could cause shock. You can buy a multimeter for about $10 from Dealextreme or other similar gadget suppliers which will measure voltage, current and resistance.

When measuring current, a meter usually has two current sockets. The lower current socket is usually fused, but the higher current socket may or may not be fused. If you estimate the current being measured will be higher than the value indicated on the lower current socket, connect the probe to the higher current socket, otherwise you"ll nd up blowing a fuse.

by test leads being damaged, I mean any insulation scuffed, peeled back or cut to the extent that the inner copper cores are exposed and liable to be touched. Also insulation can crack, and leads pull out from the probe or plug end of the test lead, again exposing the conductor. I think I have a damaged set of leads, so I"ll upload a photo.

Very Good info , can you explain what some of the things are for people like myself that are Very Very unfamiliar with the terminology ? In the safety first alone I was lost on leads not being damaged , (maybe a picture glossary of lingo) or what a series or parallel is etc. love this hub ,just from my lack of certain words or terms and their meaning I was lost from the start. Thank You

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 mAVΩ. The fuse between 10A and COM is rated for 10A, so to measure high currents, you plug the black probe into COM and the red probe into the port labeled 10A.

Do you have a multimeter but are confused about how to use it or are getting unexpected readings? If so, the sections below will help you sort through what to do. If there are words or concepts you do not understand, or symbols on your multimeter that puzzle you, return to the Multimeter Overview tab. If you are looking for multimeter usage ideas or labeled photographs of assorted multimeter models, then visit the other tabs in this multimeter tutorial.

Plug your black and red probes into the appropriate sockets (also referred to as "ports") on your multimeter. For most multimeters, the black probe should be plugged into the socket labeled "COM," and the red probe into the socket labeled with a "V" (it might also have some other symbols). Remember to check out our image gallery, the Multimeter Overview tab, or your multimeter"s manual if you have trouble identifying the right socket.

Choose the appropriate voltage setting on your multimeter"s dial. Remember that most battery-powered circuits will have direct current, but the setting you select will depend on the science project you are doing. If you are working with a manual-ranging multimeter, you can estimate the range you need based on the battery (or batteries) powering your circuit. For example, if your circuit is powered by a single 9V battery, it probably doesn"t make sense to select the setting for 200V, and 2V would be too low. If available, you would want to select 20V.

Touch the probe tips to your circuit in parallel with the element you want to measure voltage across (refer to the Multimeter Overview tab for an explanation of series and parallel circuits). For example, Figure 6 shows how to measure the voltage drop across a lightbulb powered by the battery. Be sure to use the red probe on the side connected to the positive battery terminal, and the black probe on the side connected to the negative battery terminal (nothing will be harmed if you get this backwards, but your voltage reading will be negative).

Figure 6. Measuring voltage across a lightbulb by attaching the multimeter probes in parallel. Current flow is represented by the yellow arrows. In voltage-measurement mode, the multimeter"s resistance is very high, so almost all of the current flows through the lightbulb, and the multimeter does not have a big impact on the circuit. Notice how the knob has been set to measure DC voltage (DCV) and the red probe is plugged into the correct port for measuring voltage (labeled "VΩ" because it is also used to measure resistance).

If your multimeter is not auto-ranging, you might need to adjust the range. If your multimeter"s screen just reads "0," then the range you have selected is probably too high. If the screen reads "OVER," "OL," or "1" (these are different ways of saying "overload"), then the range you have selected is too low. If this happens, adjust your range up or down as necessary. Remember that you might need to consult your multimeter"s manual for specifics about your model.

Plug your red and black probes into the appropriate sockets (also referred to as "ports") on the multimeter. For most multimeters, the black probe should be plugged into the socket labeled "COM." There might be multiple sockets for measuring current, with labels like "10A" and "mA". Note:It is always safer to start out with the socket that can measure a larger current. Plug the red socket into the high-current port.

Choose the appropriate current setting on your multimeter. Remember to check if your circuit is direct current or alternating current, and that almost all battery-powered circuits will be direct current. If your meter is not auto-ranging, you might need to guess at the scale to use (you can change this later if you don"t get a good reading).

Connect the multimeter probes in series to the current you want to measure (refer to the Multimeter Overview tab for an explanation of series and parallel circuits). For example, Figure 7 shows how to measure the current through a lightbulb that is powered by a battery. Be sure to use the red probe toward the battery"s positive side, otherwise your current reading will be negative.

To measure the current through a lightbulb the multimeter becomes part of the circuit and transfers electricity from the battery to the lightbulb. The positive probe of the multimeter (red) is connected to the positive side of a battery while the negative probe of the multimeter (black) is connected to one lead of a lightbulb. The free lightbulb lead is then connected to the negative side of the battery using wire. Current will flow from the battery to the multimeter and then into the lightbulb.

Figure 7. Measuring the current through a lightbulb by attaching a multimeter in series. Current flow is represented by the yellow arrows. In current-measurement mode, the multimeter"s resistance is very low, so the current can easily flow through the multimeter without affecting the rest of the circuit. Notice how the knob has been set to measure direct current (DCA) and the red probe is plugged into the port for measuring current, labeled with an "A."

If your multimeter is not auto-ranging, you might need to adjust the range. If your multimeter"s screen just reads "0," then the range you have selected is probably too high. If the screen reads "OVER," "OL," or "1" (these are different ways of saying "overload"), then the range you have selected is too low. If this happens, adjust your range up or down as necessary. Remember that you might need to consult your multimeter"s manual for specifics about your model.

Plug your red and black probes into the appropriate sockets on your multimeter. For most multimeters, the black probe should be plugged into the socket labeled "COM," and the red probe should be plugged into the socket labeled with an "Ω" symbol.

Choose the appropriate resistance measurement setting on your multimeter"s dial. If you have an estimate for the resistance you will be measuring (for example, if you are measuring a resistor with a known value), that will help you pick the range.

Important: Turn off the power supply to your circuit before measuring resistance. If your circuit has a power switch, you can do this by turning the switch "off." If there is no switch, you can remove the batteries. If you do not do this, your reading might be incorrect. If your circuit has multiple components, you might need to remove the component you want to measure in order to accurately determine its resistance. For example, if your circuit has two resistors in parallel, you will have to remove one resistor to measure their resistances individually.

Connect one of your multimeter"s probes to each side of the object whose resistance you want to measure. Resistance is always positive and the same in both directions, so it does not matter if you switch the black and red probes in this case (unless you are dealing with a diode, which acts like a one-way valve for electricity, so it has a high resistance in one direction and a low resistance in the other direction). Figure 8 shows how to measure the resistance of a lightbulb.

Figure 8. Measuring the resistance of a lightbulb using a multimeter. Notice how the lightbulb has been disconnected from the circuit. The multimeter supplies its own small amount of current, which allows it to measure the resistance. Notice how the knob has been set to the "Ω" to measure resistance, and the red probe is plugged into the proper port to measure resistance (labeled "VΩ" since it is also used to measure voltage).

If your multimeter is not auto-ranging, you might need to adjust the range. If your multimeter"s screen just reads "0," then the range you have selected is probably too high. If the screen reads "OVER," "OL," or "1" (these are different ways of saying "overload"), then the range you have selected is too low. If this happens, adjust your range up or down as necessary. Remember that you might need to consult your multimeter"s manual for specifics about your model.

Set your multimeter to the continuity check symbol. Remember that this symbol might not look the same on all multimeters (and some multimeters do not have it at all), so check out the Multimeter Overview tab or our multimeter image gallery to see examples.

Plug your probes into the appropriate sockets. On most multimeters, the black probe should go into the socket labeled "COM," and the red probe should go into the same socket you would use to measure voltage or resistance (not current), labeled with a V and/or an Ω.

Touch two parts of your circuit with the probes. If the two parts of the circuit are electrically connected with very little resistance between them, your multimeter should beep. If they are not connected, it will not make a noise and might display something on the screen such as "OL," "OVER," or "1," which all stand for "overload." The easiest way to test this function with your multimeter is to check it with a single piece of conductive material (most metals) and a piece of non-conducting material, like wood or plastic. See Figure 9 for an example.

Figure 9. Using a multimeter to do a continuity test. If a conductive path is formed between the probe tips, the multimeter will beep. If the conductive path is broken (possibly due to a wire that has come loose in your circuit, or a bad solder connection), the multimeter will not beep. Notice how the knob has been set to the symbol for continuity and the red probe is plugged into the VΩ port (this port is not always labeled with the continuity symbol).

The diode check feature is useful to determine in which direction electricity flows through a diode. The exact operation of the "diode check" function will vary for different multimeters, and some multimeters do not have a diode check feature at all. Because of this variety, and because the feature is not required for most Science Buddies projects, we have not included directions here. If you need to do a diode check, consult the manual for your multimeter.

If your multimeter is not auto-ranging, knowing which scale to pick can be tricky, especially if you are not very familiar with metric prefixes. Here are two rules of thumb you can follow for measuring voltage, current, and resistance:

Voltage: Many manual-ranging multimeters have settings for 200mV, 2V, and 20V. It is very unlikely that battery-powered circuits will exceed 20V (for example, two 9V batteries connected in series will provide a maximum of 18V). A single AA or AAA battery supplies 1.5V. Two AA or AAA batteries combined in a battery pack will provide 3V, four will provide 6V, and eight will provide 12V. So, if you know what type of batteries (and how many), are powering your circuit, you can pick a starting range to measure voltage. Remember that you want to pick the next highest voltage setting (just like with measuring distance; you would need a yardstick— not a 12-inch ruler— to measure something that is 18 inches long). So, for a circuit powered by a single AA battery (1.5V), you would select the 2V setting. For a circuit powered by a 9V battery, you would select 20V.

Current: When measuring current, it is always a good idea to start out with the highest possible current setting (and the appropriate high-current socket, if your multimeter has multiple sockets to measure current), in order to avoid blowing a fuse. If the current you measure is low enough to safely use your low-current setting