Measurement Systems in Electronics-presentation-

DR INZ. ZDZISŁAW PÓLKOWSKI

Polkowice-2015

University of Pitesti andDolnośląska Wyższa Szkoła Przedsiębiorczości i Techniki w

Polkowicach

STUDENT: CONSTANTIN IONUT

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 physical devices, but the user as well.

Measurement of mechanical systems has long been an issue for engineers. Having been trained to deal with mechanical systems, the use of electrical or electronic system to make measurements on these mechanical systems are far from obvious. For a mechanical engineer to properly select and utilize electronic measurement devices requires both an understanding of the mechanical system and an understanding of the characteristics of the transducers. This is not to say that all measurement systems are electronic, because there are a number of purely mechanical measurement devices that far predate the high tech electronic systems that are used in many of today’s systems. To fully understand how a measurement system works, we have to first understand exactly what a measurement system is and what it is capable of.

http://www.thefreedictionary.com/

Derived SI units

• All measurements can be expressed using combinations of the seven base units (and angle if needed). These combinations are called derived units.

SI Fundamental Units

Quantity Unit SymbolLength Meter m

Mass Kilogram kg

Time Second s

Electric Current Ampere A

Temperature Kelvin k

Luminous Intensity

Candela cd

Amount of substance

Mole mol

http://www.shimadzu.com/

Some Important Electrical Units

• Except for current, all electric and magnetic units are derived from the fundamental units. Current is a fundamental unit.

Quantity Unit Symbol

Current Ampere A

Charge Coulomb C

Voltage Volt V

Resistance Ohm Ω

Power Watt W

http://www.shimadzu.com/

Some Important Magnetic Units

All magnetic units are derived from the fundamental units. These units are discussed in Chapter 10.

Magnetic field intensity H

Magnetic flux fMagnetic flux density B

Magnetomotive force Fm

Permeability m

Ampere-turns/meter At/m

Weber Wb

Tesla T

Ampere-turn At

Webers/ampere-turns-meter Wb/At.m

Ampere-turns/weber At/WbReluctance R

Quantity Symbol Unit Symbol

http://www.allaboutcircuits.com/

Generic scheme of a measurement

E n v i r o n m e n t

1

InfluenceInfluence

ObserverMeasurement System (noisy)

Measurement Object

Mat

chin

g

Mat

chin

g

Disturbance

y x +Dy +D x

Influence

BASIC PRINCIPLES OF MEASUREMENTS

Measurement is the acquisition of information about a state or phenomenon (object of measurement) in the world around us. This means that a measurement must be descriptive (observable) with regard to that state or object we are measuring: there must be a relationship between the object of measurement and the measurement result.

Characteristics of measurement systems

• To choose the instrument, most suited to a particular measurement application, we have to know the system characteristics.

• The performance characteristics may be broadly divided into two groups, namely ‘static’ and ‘dynamic’ characteristics.

• Static characteristics • The performance criteria for the measurement of quantities that

remain constant, or vary only quite slowly. • Dynamic characteristics• The relationship between the system input and output when the

measured quantity (measurand) is varying rapidly.

Generalized Instrument System

Thermal Variable

Generalized Instrument System

www.answers.com

Accuracy, errors and correction

No instrument gives an exact value of what is being measured. There is always some uncertainty in the measured value. This uncertainty is expressed in terms of accuracy and error. Accuracy of an indicated (measured) value may be defined as conformity with or closeness to an accepted standard value (true value). Accuracy of the measured signal depends upon the intrinsic accuracy of the instrument itself, variation of the signal being measured, accuracy of the observer and whether or not the quantity is being truly impressed upon the instrument. For example, the accuracy of a micrometer depends upon factors like error in screw, anvil shape, temperature difference, and the applied torque variations etc In general, the result of any measurement differs somewhat from the true value of the quantity being measured. The difference between the measured value (Vm) and the true value (Vt) of the quantity represents static error or absolute error of measurement (Es), i.e.

http://fetweb.ju.edu.jo/

Electronic Instruments-Oscilloscope-

• One of the most important tools is measured in electron is oscilloscope.

• Definition - The oscilloscope, or scope for short, is a device for drawing calibrated graphs of voltage vs time very quickly and conveniently. Such an instrument is obviously useful for the design and repair of circuits in which voltages and currents are changing with time. There are also many devices, called transducers, which convert some non-electrical quantity such as pressure, sound, light intensity, or position to a voltage. By using a transducer the scope can make a plot of the changes in almost any measurable quantity. This capability is widely used in science and technology.

• Why do we need an oscilloscope?

http://www.owlnet.rice.edu/

What are the major components?

• Display Screen– Displays an input

signal with respect to time.

• Control Panel– Adjusts how the

input signal is displayed.

George Washington University

What is the purpose of an oscilloscope

• The purpose of an oscilloscope is to measure a voltage that changes with time and show it in a graphical format.

George Washington Universityhttp://www.testandmeasurementtips.com/

1) Here is the oscilloscope in our lab

-Notice the X-Y axes

2) Here is our alternating voltage signal from before

3) If we measure our signal with the scope, it would look like this!

Oscilloscope: Screen

• Notice that the screen has ruled divisions both horizontally and vertically.

• The axes can be scaled, for example…

• If each vertical division is worth 5 seconds, what time is represented by this point?

• If each horizontal line represents 1 volt, what voltage is represented by this point?

http://commons.wikimedia.org/

Oscilloscope: Input Channels

• How do we get the voltage into the scope?• This area is broken into two parts

– Left Half for Channel 1 (X)– Right Half for Channel 2 (Y)

• In the center is a switch that determines which channel will serve as the input to the scope: 1, 2, Dual or Add.

• Why would we want more than 1 channel?

George Washington University

Channel 1 Channel 2

Equipment: Function Generator

• Purpose: Produces waves of different – Shapes (sinusoidal,

square, etc.)– Amplitude– Frequency

• Several available in the lab, but we will use the one built into the Instek Oscilloscope. (Shown)

George Washington Universityhttp://en.wikipedia.org/

OBJECTIVES

• In this module you will learn how use an oscilloscope to:

measure direct current (D.C.) voltage and measure alternating current (A.C.) voltage.

Equipment

Make sure that you have the following before you begin:

• an oscilloscope• a function generator• a six volt battery and • two cables

www.phys.nthu.edu.tw/

How to connect cable correctly

• A cable should be connected to the input of Channel A.

• The other end of the cable has 2 leads with alligator clips. These should not be connected to anything at this point (if they are, then disconnect them).

http://www.cctvforum.com/

Measure Electronic Waves: How to Calibrate an Oscilloscope

• An oscilloscope is an incredibly useful tool to have on your electronics workbench. Unfortunately, oscilloscopes are also expensive, costing at least a few hundred dollars. So most electronic hobbyists get by without one. But if you have one, you must first verify the settings of some key controls on your oscilloscope before you take a measurement.

• The exact steps you need to follow to set up your oscilloscope vary depending on the exact type and model of your scope, so be sure to read the instruction manual that came with your scope. But the general steps should be as follows:

• follows:• Examine all the controls on your scope and set them to normal positions.• For most scopes, all rotating dials should be centered, all pushbuttons should be

out, and all slide switches and paddle switches should be up.• Turn your oscilloscope on.• It it's the old-fashioned CRT kind, give it a minute or two to warm up.

• Set the VOLTS/DIV control to 1.

• This sets the scope to display one volt per vertical division. Depending on the signal you're displaying, you may need to increase or decrease this setting, but one volt is a good starting point.

• Set the TIME/DIV control to 1 ms.

• This control determines the time interval represented by each horizontal division on the display. Try turning this dial to its slowest setting. Then, turn the dial one notch at a time and watch the dot speed up until it becomes a solid line.

• Set the Trigger switch to Auto.

• The Auto position enables the oscilloscope to stabilize the trace on a common trigger point in the waveform. If the trigger mode isn't set to Auto, the waveform may drift across the screen, making it difficult to watch.

Connect a probe to the input connector.If your scope has more than one input connector, connect the probe to the one labeled A.Oscilloscope probes include a probe point, which you connect to the input signal and a separate ground lead. The ground lead usually has an alligator clip. When testing a circuit, this clip can be connected to any common ground point within the circuit. In some probes, the ground lead is detachable, so you can remove it when it isn't needed.Touch the end of the probe to the scope's calibration terminal.This terminal provides a sample square wave that you can use to calibrate the scope's display. Some scopes have two calibration terminals, labeled0.2 V and 2 V. If your scope has two terminals, touch the probe to the 2 V terminal.For calibrating, it's best to use an alligator clip test probe. If your test probe has a pointy tip instead of an alligator clip, you can usually push the tip through the little hole in the end of the calibration terminal to hold the probe in place.It isn't necessary to connect the ground lead of your test probe for calibration.

If necessary, adjust the TIME/DIV and VOLTS/DIV controls until the square wave fits nicely within the display.

If necessary, adjust the Y-POS control to center the trace vertically.If necessary, adjust the X-POS control to center the trace horizontally.If necessary, adjust the Intensity and Focus settings to get a clear trace.You're now ready to begin viewing the waveforms of actual electronic signals.Remember that the controls of every oscilloscope make and model are unique. Be sure to read the owner's manual that came with your oscilloscope to see if there are any other setup or calibration procedures you need to follow before feeding real signals into your scope.

http://www.dummies.com/how-to/content/measure-electronic-waves-how-to-calibrate-an-oscil.html

Others electronics measuring instrumentsVoltmeter and Ammeter

measuring current

Electric current is measured

in amps (A) using an

ammeter connected in series

in the circuit.

Measuring current

A

This is how we draw an ammeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUIT

AA

+ - + -

Measuring voltage

The ‘electrical push’ which the cell gives to the current is called the

voltage. It is measured in volts (V) on a voltmeter

v

Measuring voltage

This is how we draw a voltmeter in a circuit.

SERIES CIRCUIT PARALLEL CIRCUIT

V

+ -+ -

V V

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