Download International System of Units (SI)

University of Pitesti
Dolnośląska Wyższa Szkoła Przedsiębiorczości i Techniki
w Polkowicach
Measurement Systems in Electronics
Simedre Mirel-Adrian
Dr inż. ZDZISŁAW PÓLKOWSKI
Polkowice, 2015
Definition of a Measurement system
• The measurement system can be defined as the all the components
included from the interface to the physical property being measured,
pressure, vibration etc, to the recorded data storage. This not only
includes the physic
• The measurement system in its simplest form generates a human
readable interface that can be used for simple monitoring. In this
simple system any data must be recorded by the operator. The
measurement system may include an electrical interface, allowing
the data to be converted to some other format, or in some other
location before it is presented to the operator. Data in this
configuration is still recorded by the operator, but the additional level
of complexity allows for a certain amount of pre-processing to be
completedal devices, but the user as well.
http://web.mst.edu/~cottrell/ME240/Resources/Measurement%20systems/Measurment%20systems.pdf
International System of Units (SI)
• The International System of Units (abbreviated SI from systeme
internationale , the French version of the name) is a scientific method
of expressing the magnitudes or quantities of important natural
phenomena. There are seven base units in the system, from which
other units are derived. This system was formerly called the meterkilogram-second (MKS) system.
• All SI units can be expressed in terms of standard multiple or fractional
quantities, as well as directly. Multiple and fractional SI units are
defined by prefix multipliers according to powers of 10 ranging from
10 -24 to 10 24 .
• SI base units:
The meter (abbreviation, m) is the SI unit of displacement or length.
One meter is the distance traveled by a ray of electromagnetic (EM)
energy through a vacuum in 1/299,792,458 (3.33564095 x 10 -9 )
second.
http://whatis.techtarget.com/definition/International-System-of-Units-SI
•
•
•
•
The kilogram (abbreviation, kg) is the SI unit of mass. It is defined as the
mass of a particular international prototype made of platinum-iridium and
kept at the International Bureau of Weights and Measures. It was originally
defined as the mass of one liter (10 -3 cubic meter) of pure water.
The second (abbreviation, s or sec) is the SI unit of time. One second is the
time that elapses during 9.192631770 x 10 9 cycles of the radiation
produced by the transition between two levels of Cesium 133. It is also the
time required for an EM field to propagate 299,792,458 (2.99792458 x 10 8 )
meters through a vacuum.
The kelvin (abbreviation K), also called the degree Kelvin
(abbreviation, o K), is the SI unit of temperature. One Kelvin is 1/273.16
(3.6609 x 10 -3 ) of the thermodynamic temperature of the triple point of pure
water (H 2 O).
The ampere (abbreviation, A) is the SI unit of electric current. One ampere
is the current that would produce a force of 0.0000002 (2 x 10 -7 ) newton
between two straight, parallel, perfectly conducting wires having infinite
length and zero diameter, separated by one meter in a vacuum. One
ampere represents 6.24 x 10 18 unit electric charge carriers, such as
electrons, passing a specified fixed point in one second.
http://whatis.techtarget.com/definition/International-System-of-Units-SI
• The candela (abbreviation, cd) is the SI unit of luminous intensity. It
is the electromagnetic radiation, in a specified direction, that has an
intensity of 1/683 (1.46 x 10 -3 ) watt per steradian at a frequency of
540 terahertz (5.40 x 10 14 hertz).
• The mole (abbreviation, mol) is the SI unit of material quantity. One
mole is the number of atoms in 0.012 kilogram of the most common
isotope of elemental carbon (C-12). This is approximately 6.022169
x 10 23 , and is also called the Avogadro constant.
• SI derived units include the hertz, the newton , the pascal (unit of
pressure or stress) , the ohm , the farad , the joule , the coulomb ,
the tesla , the lumen , the becquerel , the siemen, the volt, and
the watt .
http://whatis.techtarget.com/definition/International-System-of-Units-SI
Types of Measurement Instruments
There are two main types of the measuring instruments: analogue and digital.
The analogue instruments indicate the magnitude of the quantity in the
form of the pointer movement. One has to learn reading such instruments
since there are certain markings on the scale. They usually indicate the values
in the whole numbers, though one can get the readings up to one or two
decimal places also. The readings taken in decimals places may not always
be entirely correct, since some human error is always involved in reading. The
digital measuring instruments indicate the values of the quantity in digital
format that is in numbers, which can be read easily. One doesn't needs any
prior training to read these instruments since they indicate the values directly
in the numerical form. They can give the readings in one or more decimal
places. Since there is no human error involved in reading these instruments,
they are more accurate than the analogue measuring instruments.
http://www.brighthubengineering.com/hvac/49317-what-are-measuring-instruments/
Methods of Measurement
• Measurement of any quantity involves two parameters: the
magnitude of the value and unit of measurement. For instance, if we
have to measure the temperature we can say it is 10 degree C. Here
the value “10” is the magnitude and “C” which stands for “Celsius” is
the unit of measurement. Similarly, we can say the height of wall is 5
meters, where “5” is the magnitude and “meters” is the unit of
measurement.
• The methods of measurement:
 Direct method
 Indirect method
 Comparative method
 Coincidence method
 Contact method
 Deflection method
 Complementary method
http://www.brighthubengineering.com/hvac/40280-methods-of-measurement/
Voltmeter
• A voltmeter, also known as a voltage meter, is an instrument used for
measuring the potential difference, or voltage, between two points in
an electrical or electronic circuit. Some voltmeters are intended for use
in direct current (DC) circuits; others are designed for alternating
current circuits. Specialized voltmeters can measure radio frequency
voltage.
• A basic analog voltmeter consists of a sensitive galvanometer (current
meter) in series with a high resistance. The internal resistance of a
voltmeter must be high. Otherwise it will draw significant current, and
thereby disturb the operation of the circuit under test. The sensitivity of
the galvanometer and the value of the series resistance determine the
range of voltages that the meter can display.
http://whatis.techtarget.com/definition/voltmeter
• A digital voltmeter shows voltage directly as numerals. Some of
these meters can determine voltage values to several significant
figures. Practical laboratory voltmeters have maximum ranges of
1000 to 3000 volts (V). Most commercially manufactured voltmeters
have several scales, increasing in powers of 10; for example, 0-1 V,
0-10 V, 0-100 V, and 0-1000 V.
http://whatis.techtarget.com/definition/voltmeter
Ammeter
An ammeter is placed in series with a circuit element to
measure the electric current flow through it. The meter must be
designed offer very little resistance to the current so that it does not
appreciably change the circuit it is measuring. To accomplish this, a
small resistor is placed in parallel with the galvanometer to shunt
most of the current around the galvanometer. Its value is chosen so
that when the design current flows through the meter it will deflect to
its full-scale reading. A galvanometer full-scale current is very small:
on the order of milliamperes.
a)digital ammeter
b)analog ammeter
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/ammet.html
Oscilloscope
• A test instrument that is used to measure and analyze electronic
signals (waves and pulses) displayed on its screen. The x-axis
represents time, and the y-axis represents an instantaneous view of
the voltage of the input signal. To allow viewing signals across a
wide frequency range, the rate and speed at which the sweep of the
x-axis occurs is configurable. The sensitivity of the inputs can also
be configured to accept signals from microvolts peak-to-peak to
many thousands of volts peak-to-peak.
http://www.pcmag.com/encyclopedia/term/48636/oscilloscope
• Both analog and digital oscilloscopes are available. In an analog
scope, the x-axis is controlled by an internal time base, and the yaxis is directly controlled by the input signal. In a digital model, the
input voltage is sampled at a preset frequency. The x-axis
represents the samples along a timeline, and the y-axis shows the
voltage levels of each sample.
• The main purpose of an oscilloscope is to graph an electrical signal
as it varies over time. Most scopes produce a two-dimensional
graph with time on the x-axis and voltage on the y-axis.
https://learn.sparkfun.com/tutorials/how-to-use-an-oscilloscope
Digital-to-Analog Convertors (DAC)
•
As the world’s leading provider of data converters, Analog
Devices has the industry’s largest portfolio of D/A converters (DACs)
ranging from 8 bits to 24 bits. ADI DACs are unmatched in their
ability to deliver performance and value by providing accurate and
reliable conversion for a range of applications including industrial
automation, programmable logic controllers, optical transceivers,
data acquisition, and more. Our portfolio includes integrated output
amplifier options for ease of use, dynamic range DACs for
multicarrier generation over a very wide bandwidth, and a variety of
other DACs to suit your design needs.
http://www.analog.com/en/products/digital-to-analog-converters.html
Analog-to-digital Convertor(ADC)
• Linear Technology offers a complete family of high performance
analog to digital converter products (ADCs), including 16-bit to 24-bit
delta sigma converters for precision measurements, up to 16-bit
high-speed pipeline ADCs for communications and 8-bit to 20-bit
low power successive approximation register (SAR) analog to digital
converter for everything in between. Our analog to digital converter
portfolio offers unmatched noise performance (SINAD, SNR and
SFDR), low power consumption and small package size.
http://www.analog.com/en/products/digital-to-analog-converters.html
Frequency meter
A frequency meter is an electronic instrument that displays
the frequency of a periodic electrical signal.
Frequency meter, device for measuring the repetitions per unit
of time (customarily, a second) of a complete electromagnetic
waveform. Various types of frequency meters are used. Many are
instruments of the deflection type, ordinarily used for measuring low
frequencies but capable of being used for frequencies as high as
900 Hz. These operate by balancing two opposing forces. Changes in
the frequency to be measured cause a change in this balance that can
be measured by the deflection of a pointer on a scale.
http://www.allaboutcircuits.com/textbook/alternating-current/chpt-12/frequency-and-phase-measurement/
Ohmmeter
Though mechanical ohmmeter (resistance meter) designs are
rarely used today, having largely been superseded by digital
instruments, their operation is nonetheless intriguing and worthy of
study.The purpose of an ohmmeter, of course, is to measure the
resistance placed between its leads. This resistance reading is
indicated through a mechanical meter movement which operates on
electric current. The ohmmeter must then have an internal source of
voltage to create the necessary current to operate the movement, and
also have appropriate ranging resistors to allow just the right amount of
current through the movement at any given resistance.Starting with a
simple movement and battery circuit, let’s see how it would function as
an ohmmeter:
http://www.tigerstop.com/tigertamer/Using_an_Ohm_Meter.htm
Functions of the Measuring Instruments
• Most of the measuring instruments indicate the value of parameter
in the form of the indicator movement, which gives us the magnitude
of that quantity. There are many other functions performed by the
instruments as indicated below:
• 1) Indicating the value of the physical quantity: The instruments
are calibrated against the standard values of the physical quantities.
The movement of the pointer directly indicates the magnitude of the
quantity, which can be whole numbers or also fractions. Nowadays,
the digital instruments are becoming very popular, which indicate the
values directly in numerical form and even in decimals thus making
them easy to read and more accurate.
• 2) Measuring instruments used as the controllers: There are
number of instruments that can be used as the controllers. For
instance, when a certain value of the pressure is reached, the
measuring instrument breaks the electrical circuit, which stops the
running of compressor. Similarly, the thermostat starts or stops the
compressor of the refrigeration system depending on the
temperature achieved in the evaporator.
• 3) Recording the data: Some measuring instruments can also be
used to record and also store the data. In this age of
computerization storing the recorded data has become quite easy.
There are number of instruments that are connected to the pen that
moves on the paper. As the pointer of the instrument moves as per
the changes in the magnitude of the quantity, the pen also moves on
the paper making the graph against certain parameter like time.
Attaching small memory to the PCB can also enable recording of the
instruments in the chip.
• 4) Transmitting the data: The measuring instruments can also be
used to transfer the data to some distant places. The instruments
kept in unsafe locations like high temperature can be connected by
wires and their output can be taken at some distant places which are
safe for the human beings. The signal obtained from these
instruments can also be used for operating some controls.
• 5) Do calculations: Some measuring instruments can also carry out
a number of calculations like addition, subtraction, multiplication,
division, etc. Some can also be used to find solutions to highly
complex equations.
http://www.brighthubengineering.com/hvac/49317-what-are-measuring-instruments/
Accuracy, precision & resolution
• Quantities can't be determined with absolute certainty.
Measurement tools and systems have always some tolerance and
disturbances that will introduce a degree of uncertainty. In addition,
also the distinctiveness is a limiting factor.
• The following terminology are often used in relation to the
measurement uncertainty:
• Accuracy: The error between the real and measured value.
• Precision: The random spread of measured values around the
average measured values.
• Resolution: The smallest to be distinguished magnitude from the
measured value.
• In practice these terms are often confused. This article discusses
these concepts.
http://meettechniek.info/measurement/accuracy.html
• Definition accuracy and precision
Often the concepts accuracy and precision are used
interchangeably; they are regarded as synonymous. These two
terms, however, have an entirely different meaning. The accuracy
indicates how close the measured value is from its actual value, i.e.
the deviation between the measured and actual values. Precision
refers to the random spread of the measured values.
http://meettechniek.info/measurement/accuracy.html
• Accuracy
Accuracy is an indication of the correctness of a measurement.
Because at a single measurement the precision affects also the
accuracy, an average of a series of measurements will be taken.
The uncertainty of measuring instruments is usually given by two
values: uncertainty of reading and uncertainty over the full scale.
These two specifications together determine the total measurement
uncertainty.
These values for the measurement uncertainty is specified in percent
or in ppm (parts per million) relative to the current national standard.
1 % corresponds to 10000 ppm.
http://meettechniek.info/measurement/accuracy.html
Sources of error in measurement systems
• If we sought the most general definition of error, we would define it
as the difference between the actual value and the measured value.
This difference can occur from many sources and in a wide range of
ways. We can break these down into three basic categories,
systemic errors, random errors and illegitimate errors. By far the
most common systemic errors are Calibration errors, more
specifically, non-linearity, hysteresis, repeatability and calibration
curve errors. These are generally fairly easy to determine and are
quite quantifiable. Probably the least quantifiable systemic error is
the tendency for a person taking a reading to consistently “jump the
gun” and take the reading before it actually gets there, anticipating
the data, rather than reading the data that actually exists. This
particular type of error is not only difficult to quantify, in many cases
it is difficult to even determine as existing.
http://web.mst.edu/~cottrell/ME240/Resources/Measurement%20systems/Measurment%20systems.pdf
• Errors will creep into all measurement regardless of the care which
is exerted. But it is important for the person performing the
experiment to take proper care so that the error can be minimized.
Some of the errors are of random in nature, some will be due to
gross blunder on the part of the experimenter and other will be due
to the unknown reasons which are constant in nature. Thus, we see
that there are different sources of errors and generally errors are
classified mainly into three categories as follows:
• a) Gross errors
• b) Systematic errors
• c) Random errors
http://web.mst.edu/~cottrell/ME240/Resources/Measurement%20systems/Measurment%20systems.pdf
Advantages and Disadvantages of the Digital
Instruments
These days there is greater trend of using the digital instruments for
measurement of all the important quantities like weight, length, temperature,
humidity, current, voltage, rpm and even the blood sugar level. There are
also digital instruments for measurement of the blood pressure, heart beat
rate, and others.
• Here are some of the advantages of the digital
instruments over the analogue instruments:
1) They are very easy to read.
2) Since there are very few moving parts in the electronic instruments, they are
usually more accurate than the analogue instruments. Even the human
error involved in reading these instruments is very less, which adds to the
accuracy of digital instruments.
3) The electronic items tend to be cheaper than the mechanical items.
4) The data from the instruments can be recorded for future reference.
5) The output of the digital devices can be obtained in the computer
http://www.brighthubengineering.com/hvac/49317-what-are-measuring-instruments/
• There are also some disadvantages of the digital
instruments. Here they are:
1) Sometimes they tend to indicate erratic values due to faulty
electronic circuit or damaged display.
2) In case of high humidity and corrosive atmosphere the internal parts
may get damaged and indicate the faulty values.
3) Sometimes these instrument show some readings even though there
is no applied measurable parameter.
On the whole, the advantages of the digital instruments outdo the
disadvantages, which is why they have become highly popular. You
can find digital instruments in the cars, air planes, motor cycles, and
also in places like air ports, railway stations, public places etc. The
digital clocks are one of the most widely used instruments for the
personal use and also in public and private places. The trend is
towards the digital instruments since they are convenient to use and
also have excellent looks. In future their use is sure to increase
much more.
http://www.brighthubengineering.com/hvac/49317-what-are-measuring-instruments/