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Chapter Four

Basic Test and Measurement Instruments 3:

Miscellaneous Instruments

Fall 2015

ME-3504

Sensors, Actuators and Instrumentation

5th Semester (Mechatronics)SZABIST, Karachi

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Nasreen BanoLecturer

(Department of Mechatronic Engineering)[email protected]

Office: 100 Campus 3rd Floor R-304

Course Support: Zabdesk

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Course Outline1. Fundamentals

2. Basic Test & Measurement Instruments

a. DC (Electro-mechanical)

b. AC Measurements

c. Digital Measurements

d. Data Acquisition

e. Display & Graphical Instruments

3. Sensors

4. Actuators

5. Mechatronic Systems

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Chapter ContentsData Acquisition

Digital Measurements

1. Digital Voltmeter

2. Digital Frequency Meter

3. Digital RLC Meter

Display & Graphical Instruments4. Cathode Ray Oscilloscope

5. Signal Generators

6. Signal Analyzers

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Data Acquisition

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Data AcquisitionData Acquisition:• Introduction

• General ADC Process

• ADC

• DAC

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Data AcquisitionData Acquisition:

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Data AcquisitionData Acquisition:• Naturally occurring signals: Analog

• Efficient devices: Digital

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• To properly acquire an analog voltage signal for digital processing, the following components must be properly selected and applied in this sequence:

1. Sensors 2. Buffer amplifier3. Filter 4. Analog-to-digital converter5. Computer

Data AcquisitionData Acquisition:

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• Sensor: First acquisition device (a sensor/transducer) to sense the (usually) physical quantity to be acquired

• Buffer Amplifier: Isolates the output from the input (i.e., it draws negligible current and power from the input) and provides a signal in a range close to but not exceeding the full input voltage range of the A/D converter.

• Filter: Usually a low-pass filter is necessary to remove any undesirable high- frequency components in the signal that could produce aliasing. The cutoff frequency of the low-pass filter should be no greater than ½ the sampling rate.

• ADC: Analog signal to digital version for processing with a digital hardware/system.

• Computer: For control (as central processing unit), and processing of the acquired data.

ADCs

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ADCsAnalog to Digital Conversion:• General Block Diagram of ADC

• ADC

• DAC

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IN OUTADC

Electrical Symbol

ADCsAnalog to Digital Conversion:

General Block Diagram:

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Sampler

Quantizer

Encoder

Analog input

Digital Bit Stream

0101 0110 0110 0110 1010 0011 0000 0000 0000 1110

ADCsADC General Block Diagram:

1. Sampler:

– Discretization of signal along horizontal axis

– Usually a simple switch with fixed sample time ‘n’ (e.g., S/H circuit)

– Sampling error and Nyquist frequency/rate

– Sampling rate affects bandwidth, signal quality & transmission rate

2. Quantizer:

– Definition of horizontal levels (Quantization levels)

– Rounding of discrete signal’s amplitudes w.r.t defined QLs

– Quantization error and quantizer’s resolution

– Resolution affects bandwidth, signal quality, transmission rate, bit rate and encoder’s length

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ADCsADC General Block Diagram:

3. Encoder:

– Assignment of binary code to each quantization level

– Translates decimal valued signal to equivalent binary signal

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0 1 0 1 0 1 1 0 0 1 1 0 0 1 1 0 1 0 1 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 0

Types

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DAC/ADCDAC Types:

1. Ladder

ADC Types:

2. Flash ADC

3. Successive approximation

4. Sigma-delta

5. Ramp type

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Ladder DAC

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MSB & LSB:

3- bit Truth Table

Ladder DAC

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DAC:

DACDAC:

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Example 6-1

A 500mA level is to be converted into a 7-bit digital code. Determine the resolution of the conversion and the analog levels represented by the LSB & MSB, & calculate the analog level represented by 1111111.

DACR/2R Ladder DAC:

• Two values of resistors R and 2R

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𝑉 𝑜=(2𝑛− 1𝐷𝑛……+23 𝐷3+22𝐷2++21 𝐷1+20 𝐷0 )𝑉 𝑠

2𝑛− 1 𝑣𝑜𝑙𝑡𝑠

DACR/2R Ladder DAC:


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DACR/2R Ladder DAC:


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DACR/2R Ladder DAC:

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Example 6-6

Calculate the output voltage from 5-bit DAC ,when the digital input is 00001,10000 & 1111 and Vi = 10V.

Example

Sketch a 4 bit DAC n/w and explain its operation.

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ADC Types

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ADCDigital representation of analog quantity:

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ADCDigital representation of analog quantity:

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ADCRamp Type ADC:

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ADCRamp Type ADC:

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ADCExample 6.5:

A linear-ramp ADC uses a 10-bit counter and a 15KHz clock frequency. The counter output is to be 1111111111 when the input voltage is 100mV. Calculate the required ramp rate-of-change and the ADC conversion time.

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ADCStaircase Ramp Type ADC:

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ADCStaircase Ramp Type ADC:

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Digital Voltmeters

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Digital VoltmetersRamp-generator type Digital Voltmeter:

Components:

• ADC

• BCD-7-seg driver

• 7-seg display

Working principle:

• Generation of a time pulse proportional to the input voltage

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Digital Voltmeters36Misc

Digital Voltmeters37Misc

Digital VoltmetersExample 6-1:

Calculate the maximum time t1 for the digital voltmeter (ramp-type), if the clock generator frequency is 1.5 MHz. Also, suggest a suitable frequency for the ramp generator. Where maximum counted pulses: N = 1999 (1.33 ms, 600 Hz).

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Digital Multimeter Meters

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Digital MultimetersBasic Hand-held Digital multimeter:

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Digital MultimetersHigh performance Hand-held Digital multimeter:

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Digital MultimetersBasic Hand-held Digital multimeter:

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Digital Frequency Meters

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Digital Frequency MetersFrequency Measuring Systems:

Waveform generation

ADCDigital

measurements

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Digital Frequency MetersFrequency Measuring Systems:

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Basic Frequency Meter:

• Time base

• Digital counting circuit

• Input waveform shaping circuitry

• Counter driver circuitry

Digital Frequency Meters46

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Digital Frequency Meters47

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Range Changing:

Example 6-3:

A digital frequency meter has a time base derived from 1 MHz clock generator frequency-divided by decade counters. Determine the measured frequency when a 1.512 kHz sine wave is applied and the time base uses (a) six decade counters and (b) four decade counters.(1.512 kHz, 1.5 kHz)

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Digital L & C Measurements

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Digital L & C MetersInductance Measurement:

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Digital L & C MetersCapacitance/Inductance Measurement:

Mono-stablePulse

generatorTrigger

A-stable multi-vibrator

Calibrationn/w

AND Pulse Count

7-seg-DisplayRC n/w

R Cx/Lx

Binary-Dec- Decoder Driver

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Cathode Ray Oscilloscope

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Cathode Ray Oscilloscope:

• For the study of all types of waveforms

• Measures:

– Peak voltage

– Frequency

– Phase difference

– Pulse width

– Delay time

– Rise time

– Fall time

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CRO Major Components:

• Cathode Ray Tube

• Working Principle

• Display

• Front Panel

• Controls and Measurements

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Cathode Ray Tube

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Cathode Ray Tube• A vacuum tube (an evacuated glass envelope of large size, heavy, and relatively

fragile) contains:

1. Electron gun: a source of electrons2. A fluorescent screen 3. Electron beam deflection and acceleration mechanism4. Graticule

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Cathode Ray TubeCRT Basic Components :

1. Electron gun– Heater – Control grid – Cathode

2. Anode3. Electron beam4. Focusing coils5. Deflecting coils6. Florescent screen 7. Graticule

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Cathode Ray Tube58Misc

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CRT Basic Components

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Cathode Ray TubeCRT Basic Components :1. Electron gun: to generate narrow, intense & high energy beam of electrons

– Heater: heats the filament up (tungsten), heated by electric current – Control grid: controls flow of electrons

– Cathode: filament or (metal oxides, Cesium cathode heated at 954o C)

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Cathode Ray TubeCRT Basic Components :

2. Anode: +vely charged electrode, accelerates & focuses electrons

3. Electron beam: stream of electrons; produces tiny, bright & visible spot on the phosphor-coated screen

4. Focusing coils: magnetic coils control the correct positioning of the electron beam on the required point on the screen

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Cathode Ray TubeCRT Basic Components :5. Deflecting coils: generates extremely low frequency EMF to deflect EB in vertical and horizontal directions

(input signals connection)6. Florescent screen: 7. Graticule

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Ray Tracing Mechanism

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Cathode Ray TubeCRT Ray Tracing Mechanism:1. Electron Gun

a. Triode Sectionb. Focusing

2. Deflection a. Vertical deflection platesb. Horizontal deflection plates

3. Post deflection acceleration4. Aquadag5. Screen6. Graticule

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Cathode Ray TubeCRT Ray Tracing Mechanism:Deflection Section:

• Deflection factor: Voltage required to produce one division of deflection (V/cm)

• Deflection Sensitivity: Deflection produced by 1 V (cm/V)

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Cathode Ray TubeCRT Ray Tracing Mechanism:Deflection Section:

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+V

-VAngle of deflection

Deflection plates

Electron beamScreen

Deflection

D

d

lL

𝑑𝑒𝑓𝑙𝑒𝑐𝑡𝑖𝑜𝑛𝑠𝑒𝑛𝑠𝑖𝑡𝑖𝑣𝑖𝑡𝑦=𝑉 𝑑

𝐷 =2𝑑𝑉 𝑎

𝐿𝑙

Cathode Ray TubeCRT Ray Tracing Mechanism:Deflection Sensitivity:

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Example 8-1: (Buchla)

A CRT with 3 cm plates, separated by a distance of 1.0 cm is operated with an accelerating voltage of 1.0 kV. The length of the CRT from the deflecting field to the face of CRT is 22 cm. What voltage is required b/w the deflection plates to deflect the beam by 4 cm on the screen? (121 V)

Waveform Display

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DisplayWaveform Display:

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Display70Misc

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Example 9-1:

Waveform Display:

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Horizontal Sweep Generator:

Amplifier Sweep Time Control

Schmitt Trigger

v1

v2

Ramp generator

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Display73Misc

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Trigger voltage levels:

Ramp voltage:

Transistor current:

± (𝑉 𝐶𝐶−1 )𝑅6

𝑅5

∆𝑉 1=𝐼 1𝑇𝐶1

𝐼 1=𝑉 𝐵1−𝑉 𝐵𝐸

𝑅3

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Horizontal Sweep Generator:Example 9-2:

CRO Controls

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CRO Controls76Misc

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CRO ControlsSystems of CRO used to maintain a clear and steady trace on the screen and overall proper functioning:

• Graticule: A calibrated flat piece of hard plastic for precise measurements and protection of the screen

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• Beam Finder: Push button to locate a display, shifted off the screen

Intensity control: for adjustment of brightness of the spot on the screen (accomplished by varying voltage b/w focusing and accelerating anodes)

• Focus control: for adjustment of fineness of electron beam on the screen (by varying the potential of middle anode with the help of a potentiometer)

• Trace rotation: Notch to adjust trace angle

Calibrator: an oscillator, which generates a known and fixed voltage in square waveform built in CRO for calibration purpose

Probe adjust: Usually 2 KHz and 0.2 to 2V p-p square wave output for testing purpose

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CRO Channels A and B

Horizontal/Vertical position controls: for moving the beam on any part of the screen. (by applying a dc voltage to H/V plates)

Vertical Sensitivity: scaling of the display to the input voltage (Volts/Div)

Vernier Knob: V/Div calibration adjustment

Input connectors

Wave type selector Mode selector• Channel• Dual• ADD• Inv B/A

Horizontal Sensitivity: time scaling factor Time/Div (common for both channels)• Vernier knob for calibration

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CRO Trigger Section:

Trigger Source:

• Internal Trigger : Time base connected to internal signal generator

• External Trigger : Time base connected to external source (EXT) with a coaxial cable

• Line: Signal from power line

• CH1/CH2: Time base takes trigger from channels

TV : For TV video study

A-B Sweep: (or X-Y sweep): Channel B for vertical deflection and channel A for horizontal deflection

Trigger level knob: for trigger point adjustment of the input wave

Measurements

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Measurements1. Peak-peak voltage

2. Frequency determination

3. Phase measurementa. Sweep methodb. Lissajous pattern (x-y mode)

4. Rise time, fall time and delay time

5. Pulse distortion

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Amplitude and frequency

Measurements

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MeasurementsPeak-peak voltage

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MeasurementsPeak-peak voltage

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MeasurementsFrequency determination:

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MeasurementsFrequency determination:

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Measurements87Misc

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Example 9-3: Determine the amplitude, frequency and phase difference b/w the two given waveforms

Pulse measurements

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Measurements89Misc

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Pulse Measurement:

• Pulse amplitude• Pulse width• Space width

• Rise time• Fall time• Delay time

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Pulse Measurement:

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Example 9-4: Determine the pulse amplitude, frequency, rise time and fall time of the given waveform

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Pulse Distortion:

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Pulse Distortion:

Example 9-6, 7:

Phase Measurements

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MeasurementsPhase Measurement:

Sweep method

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Measurements

Lissajous Pattern m

ethod

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Phase Measurement:

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Phase Measurement:

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X –Y Displays

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X –Y Displays

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X –Y Displays

Measurements101

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X –Y Displays

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X –Y Displays

Lab Work

Measurements

Determine the phase shifts of the four patterns of the following figure:

1 0sin 02

o

1 1sin 302

o

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Example

Measurements

Determine the phase shifts of the four patterns of the following figure:

1 2sin 902

o

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Example

Signal Generators

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Signal Generator• Generates Sine, Square, & Triangular waves• Basic wave form: Triangular (rest are driven from it)• Range: a fractions of Hz to 2MHz• Modulation capabilities: Amplitude, frequency, phase, pulse width and VCO control

• Primary waveform type: – Sine wave in AF and RF generators– Triangular in FG

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Signal GeneratorSignal Generator Types:• Audio Frequency Generators• Radio Frequency Generators• Function Generators• Pulse Generators

• Random signal generators• Pattern generators

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Signal GeneratorSignal Generator Types:

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10 MHz Pulse Generator:The B&K Precision Model 4030 is a versatile signal source which combines four functions into one unit--waveform generation, pulse generation (through variable symmetry), frequency sweep operation, and triggered operation.

The 4030 offers low rise and fall time pulsed signals up to 10MHz to meet many test and measurement applications.

10 MHz Pulse Generator


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Arbitrary Function generator with Counter

o Wide frequency range of 1 uHz up to 120 MHz for Sineo Sine and square output plus 27 additional built-in arbitrary

waveformso Clean and stable output of very small signals down to the 1 mV to

10 mV range (50 ohms)o Support of internal and external modulation sources as well as

internal, external, and gated trigger sourceso Convenient data input via numeric keypad or knobo Adjust modulation parameters precisely and over a wide rangeo Fully programmable via the standard RS232 interface using SCPI

compatible commandso 100 MHz Universal Counter with frequency measurement and

totalize function


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5 MHz Function Generator

• 0.5 Hz to 5 MHz• Sine, Square, Triangle, Pulse, & Ramp output• Coarse and Fine tuning• 4 digit LED display• Variable duty cycle• Variable DC offset• Variable amplitude output plus 20dB attenuator• 20Vpp output into open circuit (10Vpp into 50 Ωs)


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• 50 MHz Function/Arbitrary Function Generator

• 14-bit, 125 MSa/s, 16k point arbitrary waveform generator• Large 3.5-inch LCD color display with waveform preview• Linear and logarithmic sweep• AM/DSB-AM/ASK/FM/FSK/PM/PWM modulation functions• Variable DC offset• Adjustable duty cycle• Two independent channels with individual output On/Off buttons• Internal/external triggering• Gate and burst mode• 48 built-in predefined arbitrary waveforms• Store/recall up to 10 instrument settings and 10 arbitrary waveforms• Built-in counter• USB device port (USBTMC-compliant) with front panel USB host port• GPIB connectivity with optional USB-to-GPIB adapter (model AK40G)• SCPI-compliant command set• Short circuit protection on outputs• LabVIEW drivers available

Function Generators

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Signal GeneratorBlock Diagram of a basic Function Generate:

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“+” current source

“-” current source

Switch A1 A2 Attenuator

Sine shaper

Squaring circuit

Level detectorSymmetry

control Switch Output Line

Frequency Dial

Triangular wave generator

Range switch

Output

Mode switch

Signal GeneratorBlock Diagram of Function Generate:

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Triangular Wave Generator• A +ve constant current source feeds a capacitor• Capacitor develops a linear output• For –ve ½ cycle of the triangular, capacitor’s charging switched to –ve constant source

• Rate of change depends on varying either • The size of the capacitor• Amount of charging time

• slope : I or size of C• slope : I or size of C

• slope pulse repetition rate (vise versa)• Thus size C and I can both be controlled

𝑉 𝑐𝑐

𝑉 𝑜

C

Signal GeneratorBlock Diagram of Function Generate:• Sine shaper

• Square wave generation

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Frequency Analyzers

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Signal Analyzers• Used to analyze the spectral composition of the signals• Analog: band-pass filter bank• Digital: DF`T computations

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Signal Analyzers• Spectra Types:

– Line – Continuous

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References1. Electronic Instrumentation & Measurement (2e) David A. Bell

2. Berlin and Getz

3. Traderscity.com, Alibaba.com, embedds.com, radiomuseum.com

4. B and K Precision

5. Wikipedia Encyclopedia

6. Instapex.com

7. Allaboutcircuits, hobbyprojects, ntu.edu.sg , nitehwk.com, level1.physics.dur.ac.uk

8. www.virtual-oscilloscope.com

9. GW instek

10. Picture Credits (pic crdt.pdf)

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http://www.virtual-oscilloscope.com/

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