Transcript Measurement Systems in Electronics

University of Pitesti and
Dolnośląska Wyższa Szkoła Przedsiębiorczości i Techniki w
Polkowicach
Measurement Systems in Electronics
-presentation-
STUDENT: CONSTANTIN IONUT
DR INZ. 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 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
Symbol
Length
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.
Quantity
Symbol Unit
Magnetic field intensity
Magnetic flux
Magnetic flux density
Magnetomotive force
H
f
B
Fm
Permeability
Reluctance
m
R
Symbol
Ampere-turns/meter
Weber
Tesla
Ampere-turn
Webers/ampere-turns-meter
Ampere-turns/weber
At/m
Wb
T
At
Wb/At.m
At/Wb
http://www.allaboutcircuits.com/
Generic scheme of a measurement
Environment
Disturbance
Influence
Influence
Measurement
System
(noisy)
Matching
Measurement
Object
Matching
x +D x
y +Dy1
Influence
Observer
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.
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!
George Washington University
http://www.testandmeasurementtips.com/
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?
Channel 1
Channel 2
George Washington University
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 University
http://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 instruments
Voltmeter and Ammeter
measuring current
Electric current is measured
in
amps
(A)
using
an
ammeter connected in series
in the circuit.
Measuring current
This is how we draw an ammeter in a circuit.
+
+
-
-
A
A
A
SERIES CIRCUIT
PARALLEL CIRCUIT
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.
+
-
V
SERIES CIRCUIT
+
-
VV
PARALLEL CIRCUIT