Measurement Systems in Electronics Dr inż. ZDZISŁAW PÓLKOWSKI Polkowice, 2015 University of Pitesti Dolnośląska Wyższa Szkoła Przedsiębiorczości i Techniki

Measurement Systems in Electronics

Dr inż. ZDZISŁAW PÓLKOWSKI

Polkowice, 2015

University of PitestiDolnośląska Wyższa Szkoła Przedsiębiorczości i Techniki

w Polkowicach

Simedre Mirel-Adrian

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 meter-kilogram-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.


• 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 .


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 y-axis 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.


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.


• 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.


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.


• 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


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


• 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.


Documents

Measurement Systems in Electronics Dr inż. ZDZISŁAW PÓLKOWSKI Polkowice, 2015 University of Pitesti Dolnośląska Wyższa Szkoła Przedsiębiorczości i Techniki