TRANSDUCERS Device that converts one form of energy

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TRANSDUCERS • Device that converts one form of energy to another form for various

TRANSDUCERS • Device that converts one form of energy to another form for various purposes including measurement or information transfer. • Energy may be of any kind electrical, mechanical, chemical, optical.

Basic Requirements of transducers • Linearity : i/p – o/p characteristics should be linear.

Basic Requirements of transducers • Linearity : i/p – o/p characteristics should be linear. • Stability : o/p should be stable to change in temp & other environmental factors. • Ruggedness : capable of withstanding overloads, with measures of overload protection. • Repeatability : should produce identical output signals. • Dynamic Response: should respond to changes in i/p as quickly as possible. • Reliability: should withstand mechanical strains without affecting the performance of the transducer.

Classification of Transducers • Active Transducers self generating, does not require external source. Ø

Classification of Transducers • Active Transducers self generating, does not require external source. Ø Ø Ø Thermocouple Photovoltaic Cell Piezoelectric Transducer • Passive Transducer Requires an external power source. Ø Resistive Transducer Strain Gauge, Thermister, Thermometer. Ø Inductive Transducer Linear Variable Differential Transducer Ø Capacitive Transducer Photoemissive Cell Photomultiplier Tube

Strain Gauge • A device whose electrical resistance varies in proportion to the amount

Strain Gauge • A device whose electrical resistance varies in proportion to the amount of strain in the device. • The sensitivity of stain gauge is described in terms of Gauge factor. • Gauge factor-Change in resistance per unit change in length. G = ΔR/R Δl/l S

Bonded strain gauge • Consist of a grid of fine resistance wire cemented to

Bonded strain gauge • Consist of a grid of fine resistance wire cemented to the base. • Base may be thin sheet of paper or bakelite. • Covered with thin sheet of paper or thin bakelite sheet to avoid mechanical damage. • Bonded to the structure under study with an adhesive.

Bonded Strain gauge

Bonded Strain gauge

Unbonded strain gauge • Unbonded strain gages consist of a wire stretched between two

Unbonded strain gauge • Unbonded strain gages consist of a wire stretched between two points • Force acting on the wire (area = A, length = L, resistivity = r) will cause the wire to elongate or shorten. • This will cause the resistance to increase or • decrease proportionally according to: R = ρL/A and ΔR/R = GF· ΔL/L, where GF = Gauge factor (2. 0 to 4. 5 for metals, and more than 150 for semiconductors).

Unbonded Strain Gauge

Unbonded Strain Gauge

Thermistor • Two terminal resistor whose resistance changes significantly when its temperature changes. •

Thermistor • Two terminal resistor whose resistance changes significantly when its temperature changes. • The resistance of a thermistor decreases with increase of temperature. • Resistance at any temp is given by RT=R 0 exp β(1/T-1/T 0) Where RT = thermister resistance at temp T(K) R 0 = thermister resistance at temp T 0(K) β = A constant determined by calibration.

Miniature Epoxy Coated Thermistors Symbol

Miniature Epoxy Coated Thermistors Symbol

 • Three parameters characterizing thermistor are Ø Ø Ø Time Constant - time

• Three parameters characterizing thermistor are Ø Ø Ø Time Constant - time for thermistor to change its resistance by 63%. (1 to 50 ms) Dissipation Constant - power necessary to increase the temp of thermistor by 1ºC. (1 to 10 m. W/ºC) Resistance Ratio - ratio of resistance at 25ºC to that at 125ºC. (3 TO 60). • Uses: To measure temp, flow, pressure, composition of gases, liquid level etc.

Thermocouple • Junction between to dissimilar metals or semiconductors that generates a small voltage.

Thermocouple • Junction between to dissimilar metals or semiconductors that generates a small voltage. • The two junctions reference and sensing are maintained at different temp. • Each junction is made by welding the two dissimilar metals together. • Reference junction has a fixed temp usually 0ºC. • And the output voltage depends on the temp of sensing junction.

Thermocouple circuit iron Reference junction constantan iron Milli voltmeter constantan Sensing junction

Thermocouple circuit iron Reference junction constantan iron Milli voltmeter constantan Sensing junction

Inductive Transducers • In the first diagram the variable inductor is part of an

Inductive Transducers • In the first diagram the variable inductor is part of an oscillator circuit. • If the position of the core is moved then the oscillator frequency changes. • The change in frequency can be displayed as a change in millimetres.

variable inductance type

variable inductance type

Variable reluctance type • As the air gap changes the reluctance of the circuit

Variable reluctance type • As the air gap changes the reluctance of the circuit changes. • This causes a change of inductance.

 • This can be used as shown by the next illustration. • As

• This can be used as shown by the next illustration. • As the inductance changes so the frequency of the oscillator changes. • The output of the oscillator can be converted to DC for display on a digital meter calibrated in inches etc.

Linear Variable Differential Transformer • There is one primary and two secondary windings. •

Linear Variable Differential Transformer • There is one primary and two secondary windings. • If AC is applied to the primary then voltages are induced in the secondaries. • The secondaries are connected so their outputs are opposite. • When the core is central the two voltages are equal in amplitude and cancel out.

LVDT • If the core is moved then there will be more voltage in

LVDT • If the core is moved then there will be more voltage in one secondary than the other. • The voltages will not cancel out and there will be an AC signal at the output proportional to the distance the core has moved. • Using a phase detector circuit it is also possible to indicate the direction the core has moved. • The graph representation shows the output voltage/position characteristics.

LVDT Model Graph

LVDT Model Graph

Load Cell • A load cell is typically an electronic device that is used

Load Cell • A load cell is typically an electronic device that is used to convert a force into an electrical signal. • This conversion is indirect and happens in two stages. Ø Ø Through a mechanical arrangement, the force being sensed deforms a strain gauge. The strain gauge converts the deformation (strain) to electrical signals.

 • Normally, a load cell consists of four strain gauges in a Wheatstone

• Normally, a load cell consists of four strain gauges in a Wheatstone bridge configuration, but is also available with one or two strain gauges. • The electrical signal output is normally in the order of a few millivolts and requires amplification by an instrumentation amplifier before it can be used. • The output of the transducer is plugged into an algorithm to calculate the force applied to the transducer.

Pyrometer • It’s a non-contact instrument that detects an object's surface temperature by measuring

Pyrometer • It’s a non-contact instrument that detects an object's surface temperature by measuring the temperature of the electromagnetic radiation (infrared or visible) emitted from the object. • The wavelength of thermal radiation ranges from 0. 1 to 100 µm i. e. , from the deep ultraviolet (UV) across the visible spectrum to the middle of the infrared region (IR).

 • Pyrometers are essentially photo detectors which are capable of absorbing energy, or

• Pyrometers are essentially photo detectors which are capable of absorbing energy, or measuring the EM wave intensity, at a particular wavelength or within a certain range of wavelengths.

 • Common pyrometers include: Ø Optical Pyrometer : - Designed for thermal radiation

• Common pyrometers include: Ø Optical Pyrometer : - Designed for thermal radiation in the visible spectrum. - Utilizes a visual comparison between a calibrated light source and the targeted surface. - When the filament and the target have the same temperature, their thermal radiation intensity will match causing the filament to disappear as it blends into the targeted surface in the background. - When the filament disappears, the current passing through the filament can be converted into a temperature reading.

Ø Infrared Pyrometer: - Designed for thermal radiation in the infrared region usually 2

Ø Infrared Pyrometer: - Designed for thermal radiation in the infrared region usually 2 ~ 14 µm - Constructed from pyroelectric materials, e. g. , triglisine sulfate (TGS), lithium tantalate (Li. Ta. O 3), or polyvinylidene fluoride (PVDF). - Similar to the charge generated by stressed piezoelectric materials, a pyroelectric charge dissipates in time. - Hence, a rotating shutter is required to interrupt the incoming radiation to obtain a stable output.

 • Advantages: – Fast response time – Good stability – Non-contact measurement •

• Advantages: – Fast response time – Good stability – Non-contact measurement • Disadvantages: – Expensive – Accuracy maybe affected by suspended dust, smoke, and thermal background radiation

The Variable Area flowmeter • Also known as Rotameter, is one of the most

The Variable Area flowmeter • Also known as Rotameter, is one of the most economical and reliable of flow measurement instruments. • In various configurations it can be designed to withstand high pressures, corrosive fluids, high temperatures, and is completely independent of factors influencing electronic meters. • This is done using a uniformly tapered tube, a float whose diameter is nearly identical to the tube ID at the inlet, and a scale to correlate float height.

Variable Area Flowmeter

Variable Area Flowmeter

 • The flow tube is traditionally placed in a vertical position and fluid

• The flow tube is traditionally placed in a vertical position and fluid enters from the bottom, forcing the float up in the tube until a sufficient annular opening exists between the float and tube to allow the total volume of fluid to flow past the float. • At this point the float is in an equilibrium position and its height is proportional to the flow rate.

CLASSIFICATION OF MEASURING INSTRUMENTS

CLASSIFICATION OF MEASURING INSTRUMENTS

Depending on working principle • Moving iron type instruments • Moving coil type instruments

Depending on working principle • Moving iron type instruments • Moving coil type instruments a). Attraction type a). Permanent magnet type b). Dynamometer type b). Repulsion type

MOVING IRON INSTRUMENTS – ATTRACTION TYPE Principle • A soft iron piece gets magnetized

MOVING IRON INSTRUMENTS – ATTRACTION TYPE Principle • A soft iron piece gets magnetized when it is brought into a magnetic field produced by a permanent magnet. • The same phenomenon happens when the soft iron piece is brought near either of the ends of a coil carrying current. • The iron piece is attracted towards that portion where the magnetic flux density is more. • This movement of soft iron piece is used to measure the current or voltage which produces the magnetic field.

Construction • A soft iron disc is attached to the spindle • To the

Construction • A soft iron disc is attached to the spindle • To the spindle, a pointer is also attached, which is made to move over calibrated scale • The moving iron is pivoted such that it is attracted towards the center of the coil where the magnetic field is maximum

Principle • When the current to be measured is passed through the coil or

Principle • When the current to be measured is passed through the coil or solenoid, field is produced which attracts the eccentrically mounted disc inwards, thereby deflection the pointer which moves over a calibrated scale

Deflecting Torque • Produced by the current or the voltage to be measured. •

Deflecting Torque • Produced by the current or the voltage to be measured. • It is proportional to the square of the voltage or current. • Hence, the instrument can be used to measure d. c. or a. c. • Scale is non- uniform Control torque : Spring or gravity Damping : Air friction damping

MOVING IRON INSTRUMENT - REPULSION TYPE Principle • Two iron piece kept with close

MOVING IRON INSTRUMENT - REPULSION TYPE Principle • Two iron piece kept with close proximity in a magnetic field get magnetized to the same polarity. Hence, a repulsive force is produced. • If one of the two piece is made movable, the repulsive force will act on it and move it on to one side. • This movement is used to measure the current or voltage which produces the magnetic field.

Construction • There are two iron pieces-fixed and moving. • The moving iron is

Construction • There are two iron pieces-fixed and moving. • The moving iron is connected to the spindle to which is attached a pointer. It is made to move over a calibrated scale.

Working • When the current to be measured is passed through the fixed coil

Working • When the current to be measured is passed through the fixed coil it sets up its own magnetic field which magnetizes the two rods similarly the adjacent points on the lengths of the rods will have the same magnetic polarity. • Hence, they repel each other with the result that the pointer is deflected against the controlling torque of a spring or gravity. • The force of repulsion is approximately proportional to the square of the current passing through the coil • Whatever be the direction of current in the coil, the two irons are always similarly magnetised.

Deflecting torque • Produced by the current or the voltage to be measured. •

Deflecting torque • Produced by the current or the voltage to be measured. • It is proportional to the square of the voltage or current. • Hence, the instrument can be used to measure d. c. or a. c. Control torque : Spring or gravity Damping : Air friction damping

Advantages and disadvantages: • The instruments are cheap , reliable and robust • The

Advantages and disadvantages: • The instruments are cheap , reliable and robust • The instruments can be used on both A. C and D. C • They cannot be calibrated with high degree of precision with D. C on account of the effect of hysteresis in the iron rods or vanes.

MOVING COIL INSTRUMENT – PERMANENT MAGNET TYPE Principle : when a current carrying conductor

MOVING COIL INSTRUMENT – PERMANENT MAGNET TYPE Principle : when a current carrying conductor is placed in magnetic field it is acted upon by a force which tends to move it to one side and out of the field. This movement of coil is used to measure current or voltage.

Construction • This instrument consists of a permanent magnet and a rectangular coil of

Construction • This instrument consists of a permanent magnet and a rectangular coil of many turns wound on a light aluminium or copper former inside which is an iron core • The sides of the coil are free to move in the two air gaps between the poles and core • To the moving coil spindle is attached, a pointer is attached to the spindle to move over a calibrated scale.

Working • A magnetic field of sufficient density is produced by the permanent magnet.

Working • A magnetic field of sufficient density is produced by the permanent magnet. • The moving coil carries the current or a current proportional to the voltage to be measured. • Hence, an electromagnetic force is produced which tends to act on the moving coil and moves it away from the field. • This movement makes the spindle move and so the pointer gives a proportionate deflection

 • Deflecting torque : It is directly proportional to the current or the

• Deflecting torque : It is directly proportional to the current or the voltage to be measured. So, the instrument can be used to measure direct current and dc voltage. • Control torque : Spring control. • Damping torque : Eddy current damping. Damping is electromagnetic by eddy currents induced in the metal frame over which the coil is wound. Since the frame moves in an intense magnetic field, the induced eddy currents are large and damping is very effective.

The permanent-magnet moving coil (PMMC) type instruments have the following advantage and disadvantages: ADVANTAGES

The permanent-magnet moving coil (PMMC) type instruments have the following advantage and disadvantages: ADVANTAGES 1. They have low power consumption 2. Their scales are uniform and can be designed to extend over and arc of 1700 degree or so 3. They possess high (torque/weight) ratio. 4. They can be modified what the help o f shunts and resistances to cover a wide range of currents and voltages. 5. They have no hysteresis loss. DISADVANTAGES 1. Due to delicate construction and the necessary accurate machining and assembly of various parts, such instruments are somewhat costlier as compared to moving iron instruments. 2. Some errors are set in due to the ageing of control springs and the permanent magnets.

MOVING COIL INSTRUMENTS – DYNAMOMETER TYPE Principle An electrodynamic instrument is a moving coil

MOVING COIL INSTRUMENTS – DYNAMOMETER TYPE Principle An electrodynamic instrument is a moving coil instrument in which the operating field is produced, not by a permanent but by another fixed coil. This instrument can be used either as an ammeter or voltmeter but is generally used as a wattmeter.

Construction • Fixed coil (F) is made in two sections. • In the space

Construction • Fixed coil (F) is made in two sections. • In the space between two, Moving coil (M) is placed. • Moving coil is attached to the spindle to which pointer is attached. • The pointer is allowed to move over a calibrated scale

Working • The fixed coil and the moving coil carry currents. Thus, two magnetic

Working • The fixed coil and the moving coil carry currents. Thus, two magnetic fields are produced. • Hence, an electromagnetic force tends to act on the moving coil and makes it move. • This makes the pointer gives a proportionate deflection.

Deflecting torque As voltmeter: The two coils are electrically in series. Deflecting torque is

Deflecting torque As voltmeter: The two coils are electrically in series. Deflecting torque is proportional to square of voltage to be measured. Hence used for measuring ac and dc voltages. As ammeter: The two coils are electrically in series. Deflecting torque is proportional to square of current to be measured. Hence used for measuring ac and dc currents. As wattmeter: Fixed coils carry the system current. Moving coil carries a current proportional to the system voltage. The deflecting torque is proportional to V ICos φ i. e. Power to be measured Control torque : Spring control. Damping torque : Air damping.

The Oscilloscope

The Oscilloscope

 • The oscilloscope is basically a graphdisplaying device - it draws a graph

• The oscilloscope is basically a graphdisplaying device - it draws a graph of an electrical signal. • In most applications the graph shows how signals change over time: the vertical (Y) axis represents voltage and the horizontal (X) axis represents time. • The intensity or brightness of the display is sometimes called the Z axis.

The graph can give us information about many things about a signal. Here a

The graph can give us information about many things about a signal. Here a few: • You can determine the time and voltage values of a signal. • You can calculate the frequency of an oscillating signal. • You can see the "moving parts" of a circuit represented by the signal. • You can tell if a malfunctioning component is distorting the signal. • You can find out how much of a signal is direct current (DC) or alternating current (AC). • You can tell how much of the signal is noise and whether the noise is changing with time.

X, Y, and Z Components of a Displayed Waveform •

X, Y, and Z Components of a Displayed Waveform •

What does an oscilloscope do? • An oscilloscope is easily the most useful instrument

What does an oscilloscope do? • An oscilloscope is easily the most useful instrument available for testing circuits because it allows you to see the signals at different points in the circuit. • The best way of investigating an electronic system is to monitor signals at the input and output of each system block, checking that each block is operating as expected and is correctly linked to the next. With a little practice, you will be able to find and correct faults quickly and accurately.

How Does an Oscilloscope Work? To better understand the oscilloscope controls, we need to

How Does an Oscilloscope Work? To better understand the oscilloscope controls, we need to know a little more about how oscilloscopes display a signal. Analog oscilloscopes work somewhat differently than digital oscilloscopes. However, several of the internal systems are similar. Analog oscilloscopes are somewhat simpler in concept and are described first, followed by a description of digital oscilloscopes.

Analog and Digital Oscilloscopes • Oscilloscopes also come in analog and digital types. An

Analog and Digital Oscilloscopes • Oscilloscopes also come in analog and digital types. An analog oscilloscope works by directly applying a voltage being measured to an electron beam moving across the oscilloscope screen. The voltage deflects the beam up and down proportionally, tracing the waveform on the screen. This gives an immediate picture of the waveform. • In contrast, a digital oscilloscope samples the waveform and uses an analog-to-digital converter (or ADC) to convert the voltage being measured into digital information. It then uses this digital information to reconstruct the waveform on the screen.

Analog Oscilloscopes • When you connect an oscilloscope probe to a circuit, the voltage

Analog Oscilloscopes • When you connect an oscilloscope probe to a circuit, the voltage signal travels through the probe to the vertical system of the oscilloscope. Figure 6 is a simple block diagram that shows how an analog oscilloscope displays a measured signal • Depending on how you set the vertical scale (volts/div control), an attenuator reduces the signal voltage or an amplifier increases the signal voltage. • Next, the signal travels directly to the vertical deflection plates of the cathode ray tube (CRT). Voltage applied to these deflection plates causes a glowing dot to move. (An electron beam hitting phosphor inside the CRT creates the glowing dot. ) A positive voltage causes the dot to move up while a negative voltage causes the dot to move down.

 • The signal also travels to the trigger system to start or trigger

• The signal also travels to the trigger system to start or trigger a "horizontal sweep. " Horizontal sweep is a term referring to the action of the horizontal system causing the glowing dot to move across the screen. • Triggering the horizontal system causes the horizontal time base to move the glowing dot across the screen from left to right within a specific time interval. • Many sweeps in rapid sequence cause the movement of the glowing dot to blend into a solid line. At higher speeds, the dot may sweep across the screen up to 500, 000 times each second. • Together, the horizontal sweeping action and the vertical deflection action traces a graph of the signal on the screen. • The trigger is necessary to stabilize a repeating signal. It ensures that the sweep begins at the same point of a repeating signal

Triggering Stabilizes a Repeating Waveform

Triggering Stabilizes a Repeating Waveform

Analog Oscilloscope Block Diagram

Analog Oscilloscope Block Diagram

Analog Oscilloscope Front Panel

Analog Oscilloscope Front Panel

Digital Oscilloscopes • Some of the systems that make up digital oscilloscopes are the

Digital Oscilloscopes • Some of the systems that make up digital oscilloscopes are the same as those in analog oscilloscopes; however, digital oscilloscopes contain additional data processing systems. • With the added systems, the digital oscilloscope collects data for the entire waveform and then displays it. • When you attach a digital oscilloscope probe to a circuit, the vertical system adjusts the amplitude of the signal, just as in the analog oscilloscope.

 • Next, the analog-to-digital converter (ADC) in the acquisition system samples the signal

• Next, the analog-to-digital converter (ADC) in the acquisition system samples the signal at discrete points in time and converts the signal's voltage at these points to digital values called sample points. • The horizontal system's sample clock determines how often the ADC takes a sample. • The rate at which the clock "ticks" is called the sample rate and is measured in samples per second.

 • The sample points from the ADC are stored in memory as waveform

• The sample points from the ADC are stored in memory as waveform points. • More than one sample point may make up one waveform point. • Together, the waveform points make up one waveform record. • The number of waveform points used to make a waveform record is called the record length. • The trigger system determines the start and stop points of the record. The display receives these record points after being stored in memory.

 • Depending on the capabilities of your oscilloscope, additional processing of the sample

• Depending on the capabilities of your oscilloscope, additional processing of the sample points may take place, enhancing the display. • Pretrigger may be available, allowing you to see events before the trigger point. • Fundamentally, with a digital oscilloscope as with an analog oscilloscope, you need to adjust the vertical, horizontal, and trigger settings to take a measurement.

Digital Oscilloscope Block Diagram

Digital Oscilloscope Block Diagram

Sampling Methods • The sampling method tells the digital oscilloscope how to collect sample

Sampling Methods • The sampling method tells the digital oscilloscope how to collect sample points. For slowly changing signals, a digital oscilloscope easily collects more than enough sample points to construct an accurate picture. However, for faster signals, (how fast depends on the oscilloscope's maximum sample rate) the oscilloscope cannot collect enough samples. • The digital oscilloscope can do two things: A) It can collect a few sample points of the signal in a single pass (in real-time sampling mode) and then use interpolation. Interpolation is a processing technique to estimate what the waveform looks like based on a few points. B) It can build a picture of the waveform over time, as long as the signal repeats itself (equivalent-time sampling mode).

Real-time Sampling

Real-time Sampling

Digital Oscilloscope Front Panel

Digital Oscilloscope Front Panel

Digital and Analog Oscilloscopes Display Waveforms

Digital and Analog Oscilloscopes Display Waveforms

Performance Terms The terms described in this section may come up in your discussions

Performance Terms The terms described in this section may come up in your discussions about oscilloscope performance. Understanding these terms will help you evaluate and compare your oscilloscope with other models. • Bandwidth: The bandwidth specification tells you the frequency range the oscilloscope accurately measures. As signal frequency increases, the capability of the oscilloscope to accurately respond decreases. By convention, the bandwidth tells you the frequency at which the displayed signal reduces to 70. 7% of the applied sine wave signal. (This 70. 7% point is referred to as the "-3 d. B point, " a term based on a logarithmic scale. ) • Rise Time : Rise time is another way of describing the useful frequency range of an oscilloscope. Rise time may be a more appropriate performance consideration when you expect to measure pulses and steps. An oscilloscope cannot accurately display pulses with rise times faster than the specified rise time of the oscilloscope

 • Vertical Sensitivity : The vertical sensitivity indicates how much the vertical amplifier

• Vertical Sensitivity : The vertical sensitivity indicates how much the vertical amplifier can amplify a weak signal. Vertical sensitivity is usually given in millivolts (m. V) per division. The smallest voltage a general purpose oscilloscope can detect is typically about 2 m. V per vertical screen division. • Sweep Speed : For analog oscilloscopes, this specification indicates how fast the trace can sweep across the screen, allowing you to see fine details. The fastest sweep speed of an oscilloscope is usually given in nanoseconds/div. • Gain Accuracy: The gain accuracy indicates how accurately the vertical system attenuates or amplifies a signal. This is usually listed as a percentage error.

 • Time Base or Horizontal Accuracy: The time base or horizontal accuracy indicates

• Time Base or Horizontal Accuracy: The time base or horizontal accuracy indicates how accurately the horizontal system displays the timing of a signal. This is usually listed as a percentage error. • Sample Rate: On digital oscilloscopes, the sampling rate indicates how many samples per second the ADC (and therefore the oscilloscope) can acquire. Maximum sample rates are usually given in megasamples per second (MS/s). The faster the oscilloscope can sample, the more accurately it can represent fine details in a fast signal. The minimum sample rate may also be important if you need to look at slowly changing signals over long periods of time. Typically, the sample rate changes with changes made to the sec/div control to maintain a constant number of waveform points in the waveform record.

 • ADC Resolution (Or Vertical Resolution): The resolution, in bits, of the ADC

• ADC Resolution (Or Vertical Resolution): The resolution, in bits, of the ADC (and therefore the digital oscilloscope) indicates how precisely it can turn input voltages into digital values. Calculation techniques can improve the effective resolution. • Record Length : The record length of a digital oscilloscope indicates how many waveform points the oscilloscope is able to acquire for one waveform record. Some digital oscilloscopes let you adjust the record length. The maximum record length depends on the amount of memory in your oscilloscope. Since the oscilloscope can only store a finite number of waveform points, there is a trade-off between record detail and record length. You can acquire either a detailed picture of a signal for a short period of time (the oscilloscope "fills up" on waveform points quickly) or a less detailed picture for a longer period of time. Some oscilloscopes let you add more memory to increase the record length for special applications.

Types of Waves • • Sine waves Square and rectangular waves Triangle and sawtooth

Types of Waves • • Sine waves Square and rectangular waves Triangle and sawtooth waves Step and pulse shapes

Sine Waves The sine wave is the fundamental wave shape for several reasons. It

Sine Waves The sine wave is the fundamental wave shape for several reasons. It has harmonious mathematical properties - it is the same sine shape you may have studied in high school trigonometry class. The voltage in your wall outlet varies as a sine wave. Test signals produced by the oscillator circuit of a signal generator are often sine waves. Most AC power sources produce sine waves. (AC stands for alternating current, although the voltage alternates too. DC stands for direct current, which means a steady current and voltage, such as a battery produces. ) • The damped sine wave is a special case you may see in a circuit that oscillates but winds down over time.

Square and Rectangular Waves • The square wave is another common wave shape. Basically,

Square and Rectangular Waves • The square wave is another common wave shape. Basically, a square wave is a voltage that turns on and off (or goes high and low) at regular intervals. It is a standard wave for testing amplifiers - good amplifiers increase the amplitude of a square wave with minimum distortion. Television, radio, and computer circuitry often use square waves for timing signals. • The rectangular wave is like the square wave except that the high and low time intervals are not of equal length. It is particularly important when analyzing digital circuitry.

Sawtooth and Triangle Waves • Sawtooth and Triangle waves result from circuits designed to

Sawtooth and Triangle Waves • Sawtooth and Triangle waves result from circuits designed to control voltages linearly, such as the horizontal sweep of an analog oscilloscope or the raster scan of a television. The transitions between voltage levels of these waves change at a constant rate. These transitions are called ramps.

Step and Pulse Shapes • Signals such as steps and pulses that only occur

Step and Pulse Shapes • Signals such as steps and pulses that only occur once are called single-shot or transient signals. The step indicates a sudden change in voltage, like what you would see if you turned on a power switch. The pulse indicates what you would see if you turned a power switch on and then off again. It might represent one bit of information traveling through a computer circuit or it might be a glitch (a defect) in a circuit. • A collection of pulses travelling together creates a pulse train. Digital components in a computer communicate with each other using pulses. Pulses are also common in x-ray and communications equipment.

Waveform Measurements • Frequency and Period : If a signal repeats, it has a

Waveform Measurements • Frequency and Period : If a signal repeats, it has a frequency. The frequency is measured in Hertz (Hz) and equals the number of times the signal repeats itself in one second (the cycles per second). A repeating signal also has a period - this is the amount of time it takes the signal to complete one cycle. Period and frequency are reciprocals of each other, so that 1/period equals the frequency and 1/frequency equals the period. So, for example, the sine wave in Figure 7 has a frequency of 3 Hz and a period of 1/3 second. • Voltage : Voltage is the amount of electric potential (a kind of signal strength) between two points in a circuit. Usually one of these points is ground (zero volts) but not always - you may want to measure the voltage from the maximum peak to the minimum peak of a waveform, referred to at the peak-to-peak voltage. The word amplitude commonly refers to the maximum voltage of a signal measured from ground or zero volts. The waveform shown in Figure 8 has an amplitude of one volt and a peak-topeak voltage of two volts.

 • PHASE: Phase is best explained by looking at a sine wave. Sine

• PHASE: Phase is best explained by looking at a sine wave. Sine waves are based on circular motion and a circle has 360 degrees. One cycle of a sine wave has 360 degrees, as shown in Figure 8. Using degrees, you can refer to the phase angle of a sine wave when you want to describe how much of the period has elapsed. • Phase shift describes the difference in timing between two otherwise similar signals. In Figure 9, the waveform labeled "current" is said to be 905 out of phase with the waveform labeled "voltage, " since the waves reach similar points in their cycles exactly 1/4 of a cycle apart (360 degrees/4 = 90 degrees). Phase shifts are common in electronics.

Applications of CRO • Oscilloscopes are used by everyone from television repair technicians to

Applications of CRO • Oscilloscopes are used by everyone from television repair technicians to physicists. They are indispensable for anyone designing or repairing electronic equipment. • The usefulness of an oscilloscope is not limited to the world of electronics. With the proper transducer, an oscilloscope can measure all kinds of phenomena. A transducer is a device that creates an electrical signal in response to physical stimuli, such as sound, mechanical stress, pressure, light, or heat. For example, a microphone is a transducer. • An automotive engineer uses an oscilloscope to measure engine vibrations. A medical researcher uses an oscilloscope to measure brain waves. The possibilities are endless.

Scientific Data Gathered by an Oscilloscope

Scientific Data Gathered by an Oscilloscope