Notes
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Description A voltmeter is an instrument used to measure differences of electric potential, commonly called voltage, in volts or units that are multiples or fractions of volts. As shown in the illustration on the right, the user can choose between the upper limit of volts to be used. Use Plug the probes into the meter. Red goes to the
positive (+) and black to the negative (-). Turn the selector dial or switch to the type of
measurement you want. To measure direct current - a battery, for
example - use DCV. To measure alternating current, such as a wall
outlet, use ACV. Choose the range setting. The dial may have
options from 5 to 1000 on the DCV side and 10 to 1000 on the ACV
side. The setting should be the top end of the voltage you are
reading. Not all voltmeters have this setting. Turn the meter on.
Hold the probes by the insulated handles and touch the red probe to
the positive side of a DC circuit or either side of an AC circuit.
Touch the other side with the black probe. Read the digital display or analog dial.
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Description
Ammeters, as well as voltmeters and ohmmeters, are designed with the
use of a sensitive current detector such as a galvanometer. An
ammeter is placed in series with a circuit element to measure the
electric current flow through it.
Ammeters are non-mechanical, or digital, and use an analog to
digital converter (ADC) to measure the voltage across the shunt
resistor. The ADC is read by a microcomputer that performs the
calculations to display the current through the resistor. Use: Must be placed in series. Potential Problem: One problem with ammeters is the need for these meters to be inserted into the circuit and become part of it.
Mistakenly placing ammeters in parallel with a circuit
will blow the fuse, possibly damaging the ammeter and causing injury |
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Description
An ohmmeter is an instrument used for direct measurement of the
electrical resistance of a material or electronic
component, usually in ohms.
Ohmmeters typically use an ammeter to measure current through the
material after it has been given some set voltage by the ohmmeter;
the direct-current resistance of the sample can then be directly
determined through Ohm's law.
Disconnect completely and/or turn OFF all power to the circuit you are testing. Connect in parallel across the resistor
You must have a completely dead wire or circuit in order to ensure
accuracy in measurement, as well as your own safety.The ohmmeter
will supply the voltage and current for your circuit so NO other
power is necessary
Connect testing wires to the ohmmeter. The
black wire goes to the ground (common) outlet, the red wire to the
volt/ohms outlet
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Description A multimeter or a multitester, also known as a volt/ohm meter or VOM, is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current, and resistance. There are two categories of multimeters, analog and digital (often abbreviated DMM or DVOM) Use: Typical Components A selector switch or knob.
This allows changing the function (volts,
ohms, amps) and scale (x1, x10, etc.) of the meter. Many functions
have multiple ranges. It is important to have both set correctly,
otherwise serious damage to the meter or harm to the operator may
result. Most meters employ the knob type like the one shown in the
image, but there are others. Regardless of the type, they work
similarly. Some meters (like the one in the image above) have an
"Off" position on this selector switch while others have a separate
switch to turn the meter off. The meter should be set to off when
stored. Test leads.
There should be
2 test leads or probes. Generally, one is
black and the other red. |
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ð Analog meters use a graduated scale with a pointer
ð DIgital meters provide a direct numerical readout
ð Terminal colors: The red terminal is positive and the black terminal is negative
ð Ammeter
Ø Measures current
Ø Must be connected in series with a circuit
ð Ohmmeter
Ø Measures resistance
Ø Does this by supplying a voltage and measuring the amount of current flowing through the resistor
Ø Resistor is removed from the circuit
ð Voltmeter
Ø Measures voltage
Ø Voltage exists between 2 points, it does not flow as current does
Ø It is connected in parallel with a circuit
ð Multimeter
Ø Multipurpose device
Ø Combines a voltmeter, ammeter, and ohmmeter into one device
ð Meters should be calibrated before use to ensure that you are starting at a known point.