How do you check voltage with a voltmeter? To use your voltmeter, first attach the positive input terminal lead to the positive end of the circuit. Then attach the negative input terminal lead to the negative end of the circuit. The voltmeter will turn itself on and do the measuring automatically.
How do you read a voltage meter? A digital voltmeter will display the exact voltage in precise numbers. An analog voltmeter will use a needle to point out the voltage on a scale. What is a voltmeter used for?
What is the difference between a voltmeter and a multimeter? While a voltmeter can measure the voltage that passes between two points, a multimeter can measure that and more. Multimeters can measure ohms, amperes, resistance and current. Cite This! Try Our Crossword Puzzle! To avoid electric shock when measuring voltage or current, always hold only the plastic insulation on the probes. DO NOT touch the metal pins.
Exercise 1 : To measure the voltage at a wall outlet, insert one probe in one hole and the other probe in the other hole. Try it with your meter:. If you mix this up and reverse the wires, then the meter will read backwards. That is, on analogue meters, the pointer will quickly move off the left-hand side of the scale.
If this happens, no permanent damage normally occurs, simply reverse the way you have the probes. Exercise 2 : To measure the voltage of a car battery. A common use for a multimeter is to detect which lead from a battery or power supply is positive and which is negative. If, on an analogue meter, the pointer moves off to the left, then swap the probes over.
When the meter reads correctly, the red probe is connected to the positive wire or positive battery terminal. Exercise 3 : Detect the positive end of a small flashlight battery. This may seem like a logical statement, but many people have been trapped by not understanding the difference. This is not a very practical way of measuring the output, but it does give an interesting display.
To properly measure the output capabilities of your HiFi amplifier you need other test equipment. A useful feature of multimeters is their ability to measure the resistance in a circuit.
Although the exact resistance in a circuit may not be useful to you, often knowing the relative resistance is. However knowing that there is some resistance that of the heating element tells you that it should work. No resistance indicates a broken connection which needs to be fixed. The best way known to destroy your meter is to try to measure high voltage like volts AC while still on the resistance range. Always ensure the power is turned off and disconnected before measuring resistance.
The method of setting your multimeter for measuring resistance is different for analogue and digital meters. Therefore, we will look at each separately. This usually indicates that there is no connection between the probes. Note: When there is an open circuit, the meter can sometimes suggest some resistance often measured in Mega-ohms. This is normally caused by touching the probes with your hands, and the meter is actually measuring your skin resistance.
As mentioned earlier, knowing the exact resistance in a circuit is often not as important as knowing if there is a circuit at all, if there is a short circuit, or if there is an open circuit.
Try the following exercises as examples. Exercise 5 : Test a lead to see if it is faulty or not. This could be a lead from your HiFi, a power extension lead or a microphone lead.
Note: Some stubborn leads will only show an open circuit after bending the lead severely at either end. This suggests the lead is broken but still making intermittent connection. It also should be cut shorter and re-joined.
Exercise 6 : Check a light bulb to see if it is OK. Note: the resistance of a light bulb increases greatly when power is applied. This is because, as with most resistances, the resistance increases with temperature. Exercise 7 : Check if a fuse is blown or not.
If you think a fuse is blown, the best way to know for sure is to remove the fuse with the power off! Most multimeters have the facility to measure small amounts of DC current. Some meters also allow the measurement of AC current. Although the measurement of DC current is explained here, the procedure for AC current follows similar principles.
When we measure voltage, we are measuring the difference in voltage from one probe to the other. That is, we measure the voltage across a particular resistance. Example : Here we have two 1. By placing the probes as shown we can measure the voltage 3 volts across the light bulb. To measure the current in a circuit we need to measure the current flowing through the resistance. So what is the secret? In the article on The Dreaded Ohms Law , we learned that the current flowing through a series circuit is the same throughout the whole of the circuit.
Therefore if we can measure the current flowing through any part of the circuit, we are effectively measuring the current flowing through the resistance. That is, the current flowing through the resistance is the same as the current flowing through the wire, which is the same as that flowing through the batteries to use our example. So how do we do all this?
We could cut the wire between the battery and the light bulb. Then connect one probe to each of the cut ends, with the multimeter selected to measure DC current. This would work as we are measuring the current flowing through the wire and the multimeter. Because it is a series circuit, we are also measuring the current flowing through the light bulb and the batteries.
However it is not always wise to cut wires unnecessarily. In our example, an obvious place to break the circuit and insert our probes would be at the end of one of the batteries. Most battery holders have a spring to help make a good contact. It is normally possible to separate the batteries and insert a small piece of cardboard to isolate the batteries from each other.
Then it is a matter of simply placing a probe on either side of the cardboard. Whichever way it is possible to break the circuit, it is at that point that the probes need to be inserted. On DC it does matter. The black negative probe should go on the positive side of the break. That is, on analog meters, the pointer will quickly move off the left-hand side of the scale. When measuring AC current if your meter has that selection , be very careful not to touch the metal points of the probes.
This is because most often when measuring AC, it is at dangerous high voltages. Many meters only allow the measurement of very small DC currents. Often 25 milli-amps mA is the maximum. Many meters also have the capacity to measure 10 Amps. To do this you normally need to move the red probe to a different socket on the meter. This is often 10 amps AC only, not DC. Be sure to read the manual closely to know what you meter can and can not do.
Many digital meters allow a maximum of mA. If this limit is exceeded, a fuse in the meter will probably need replacing. It is wise to have a good stock of replacement fuses on hand. Inserting the probes between two batteries is an easy way of checking the charging current being delivered to Ni-Cad batteries. When measuring DC voltages, the red positive probe goes to the positive side of whatever is being tested. When measuring resistance, ensure there is no power applied to the resistance being tested.
When measuring current, it is necessary to break the circuit in an appropriate place and insert the probes in series with the circuit under test. The black probe goes to the positive side of the break. This site uses Akismet to reduce spam. Learn how your comment data is processed. Contact Geoff: geoffs geoffthegreygeek.
Sign in. Log into your account. Forgot your password? Privacy Policy. Password recovery. Recover your password. Understanding Audio Understanding Amplifier Power. Amplifier power is probably the most misunderstood and abused parameter of amplifiers and speakers. Yet, it is often the first and possibly only parameter Understanding Audio Understanding Speaker Sensitivity. Speaker sensitivity is a measurement of how well a speaker converts the amplifier power to to acoustic energy.
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Viewed 46k times. Jeffsbach Jeffsbach 91 1 1 gold badge 1 1 silver badge 2 2 bronze badges. He said I should know I went to school for electronics Add a comment. Active Oldest Votes. If the meter is analog, you can damage the needle with negative voltages in some cases.
Also, the sockets where the leads plug into the voltmeter are usually well labeled. In case of bannana plugs, its really how you decided to plug in the leads. Of course the only dignified way to do so is to plug the red into positive and black into negative. If you connect the lead "incorrectly" to a battery or other DC source, the meter should still work, but will show a "-" sign.
It should work with either polarity when measuring AC. Spehro Pefhany Spehro Pefhany k 12 12 gold badges silver badges bronze badges.
A plus may mean positive input or positive output and so in negative also. Saying a casual plus or minus causes a lots of misunderstanding on basics.
I measure diodes, etc. And black, the negative input terminus, is by default the positive output terminus.
But digital multimeter's probes really change their behavior when measuring battery, diode, etc. That is interesting.
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