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Electronics Manufacturing – M528

Analog Vs Digital Oscilloscope


The goal of this article is to compares and analyzes choose a new oscilloscope that would be good for you and to compare and contrast between Instek GOS-6112 100 MHz Analog Oscilloscope and Agilent U1604A Handheld Digital oscilloscope (40 MHz). There are hundreds of different models to choose from with widely varying costs and specifications. I can not possibly tell you what the best oscilloscope would be. There are a lot of factors that come into play.

Most people want one oscilloscope and they want the best oscilloscope. Some people believe the more that you spend the better is the oscilloscope and that is not always the best option. Other people believe the cheap option; cheap is not always the best. The more time you spend doing research, the more money you save, the better the quality and the more technical specifications you get. If you can not afford a new oscilloscope then buy a used oscilloscope and make sure it has been recently calibrated before you buy and all the controls move. After you purchased oscilloscope you next purchase might be a function generator.

The factors involved that whether one oscilloscope is better than other and why are: bandwidth, number of channels, sampling rates, memory depth, resolution and accuracy (display capacity), triggering capability, probe requirement, connectivity and analysis capability.
Choosing a Oscilloscopes
Instek GOS-6112 100 MHz Analog Oscilloscope
Handheld OscilloscopesU
In the above figure showing Instek GOS-6112 100MHz Analog Oscilloscope and for about £531.20 ($1,035) you can buy it. In the figure to the right showing Agilent U1604A Handheld Digital Oscilloscope and for about £1,134.46 you can buy it.

The Handheld Digital Oscilloscope is small-size, less heavy, easy to carry, high-performance and high-price then 100MHz Analog Oscilloscope. Both Analog and Digital Oscilloscopes are used to display and analyze the waveform of electronic signals. The 100MHz Analog Oscilloscope has more mechanic switch (for example: trigger) then the Digital Handheld Oscilloscope.

Both Analog and digital oscilloscopes are used in laboratories, education, industries etc... However, the Handheld Digital Oscilloscopes are used at a customer’s site. Both Analog and digital oscilloscopes are used electronics technicians and engineers, students, lecturers, scientists etc.

Oscilloscope types include, analog, digital, PC, handheld, mixed signal, digital (storage, sampling and phosphor). The work you are require to do and location will determine what type of oscilloscope is best to use.

Digital oscilloscopes can display signal that may happen only once and Analog Oscilloscopes display signals as they happen.

The History of the Cathode Ray Tube


Karl Ferdinad Braun: The great Germany inventor and he displayed the first oscilloscope (Brun tube) in 1987.
Karl Ferdinad Braun
Inside Brun tube
Brun tube

Bandwidth


The bandwidth is the difference in frequency between the highest and lowest frequency roll-offs where response has fallen by – 3dB. However, modern oscilloscopes respond to DC (which is 0 Hz), then they are said to be DC coupled and the bandwidth is simply the highest frequency of operation (roll-off).

Today a 20MHz oscilloscope is the slowest oscilloscope (1/20MHz=50ns) that you could buy. A 40 MHz handheld digital oscilloscope will display 40 MHz waveforms and a 100 MHz Analog oscilloscope will display 100 MHz waveforms, are not at its correct amplitude (29% error), but attenuated by 71% of its true amplitude (- 3 dB point).

Distortion of 29%, because as the frequency increases, the gain (output/input) decreases and making the display less accurate. For example, a Sawtooth wave has componets at 2, 4, 6, 8, 10 … times the fundamental frequency. As the frequency increases these components become smaller, a 2KHz Sawtooth wave will contain components at 2KHz, 4KHz, 6KHz, 8KHz, 10KHz… Hence, a sufficient number of these harmonics must be present to accurately represent this sawtooth wave.

Therefore, 100 MHz Analog oscilloscope has a larger bandwidth then 40 MHz handheld digital oscilloscope and it will display more accurate. A useful rule of thumb is that you should purchase an oscilloscope with a bandwidth 5 times higher than the maximum frequency signal you will require (Oscilloscope Bandwidth Required = Frequency Component of Measured Signal * 5). However, high bandwidth oscilloscopes are expensive because higher bandwidth will likely provide more accurate reproduction of your signal.

Number of Channels


Most oscilloscopes in use today are dual-channel models. Before you purchase an oscilloscope make sure if it is a 2 or 4 channels. Single-channel oscilloscopes can display one waveform at once, dual-channel oscilloscopes can display two waveforms at once and 4-channels oscilloscopes can display four waveforms at once.

The 4-channel oscilloscopes are use to view the relationship of several signal and it allow to make precision measurements fast and efficiently. The 100 MHz Analog and Handheld Digital oscilloscope are both dual-channel. For Handheld Digital oscilloscope, when use two channels at maximum sampling rate, the DAC converts the signal in each channel in turn and resulting in a half of the digitizing rate per channel compared with that available when using one channel.

For a 4-channel Digital oscilloscope, when use four channels at maximum sampling rate, the DAC converts the signal in each channel in turn and resulting in a quarter of the digitizing rate per channel.

Sample Rate


The sample rate is the rate at which the input signal is converted to a digital signal and sampling rate is the inverse of the resolution. For example, if you are interested in 20ns resolution between point A and B, then the sampling rate that can provide this resolution is 1/20ns = 50*10^6 sample/sec.

The faster the oscilloscope can sample, the more accurately (greater the resolution) it can represent fine details in a fast signal and less likely that critical information or event will be lost. The minimum sample rate may also be important if you need to look at slowly changing signals over longer periods of time. Remember that the Nyquist theorem says that the signal must be sampled at least twice as fast as its highest frequency. If waveforms are periodic then you can save money by selecting an oscilloscope that provides equivalent time or random periodic sampling.
FFT
The main advantage of Handheld Digital Oscilloscope over 100MHz Analog Oscilloscope are the memory depth, 200*10^6 sample/sec (5ns resolution), and you can use Dual Waveform Math (DWM) and Fast Fourier Transform (FFT) function to perform quick waveform analyses in both time and frequency domains.

DWM function to perform math functions for signal addition and subtraction from multiple channels and FFT function allows you to view the waveform in a frequency domain using four windowing techniques (Rectangular, Hanning, Hamming and Black-Harris).

Free dynamic range (SFDR) is the difference (in dB) between the signal power and the power of the highest harmonic in the band of interest as shown in the spectral plot of figure on the right (result of calculating the FFT of a signal and a few of the measurements).

Memory Depth


The Handheld Digital Oscilloscope is up to 250 times the memory depth with 125 kilobytes of memory depth per channel and you can capture long time spans and non-repeating signals while maintaining a maximum sampling rate of 200 MSa/s.
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software

The memory depth is the number of samples which can be stored in memory, memory depth and sampling are related.
Memory depth required depends on the time selected need to measure and the time resolution require.

The digital storage oscilloscopes (DSOs) store captured samples in a buffer memory and for a given sampling rate, the size of the buffer memory determines how long it can capture a signal for before the memory is full. The memory depth benefits are fast sampling at long timebases, timebase zoom, and memory segmentation to let you capture a sequence of events.

However, high-speed waveform memory is expensive because it takes time to process a longer memory.


Display Capability

waveforms
Both Analog and Digital Oscilloscopes allow you to display phase shift, rise time, fall time, delay, pulse width, duty cycle, frequency and period. If the oscilloscope stop work, you can not repair it and you need to send it to the manufacture because the manufacture want you to go back there to use their service and repair, and oscilloscopes are not water resistant.

The Handheld Digital Oscilloscope comes with a color display to allow you to quickly and clearly identify your signal between two channels.
The large 4.5 inch LCD display with 320 x 240 resolutions extends the simplicity and makes it easier for you to see more information.

The 100 MHz Analog Oscilloscope provides a high intensity 6-inch retangular type cathode-ray tube with red internal graticule. It displays clear readable traces even at high sweep speeds. Internal graticule lines eliminate parallax-viewing error between the trace and the graticule line.
It has two-channel, dual-sweep and each channel has 11 basic deflection factors from 2mV to 5V per division. The horizontal defection system provides single, dual or delayed sweeps from 0.5s to 50ns per division (delayed sweep, 50ms to 50ns per division).

Triggering Capability


Both Analog and Digital oscilloscope allow you to trigger and display non-periodic signals such as single pulses, as well as periodic signals such as sine waves and square waves. The types of trigger include: Trigger Modes (AUTO, NORM, TV), trigger Source (CH1, CH2, LINE, EXT), Trigger Coupling (AC, DC, HFR, LFR), Trigger ("+" or "-" polarity or TV sync polarity) and Trigger Sensitivity. The trigger can also be delayed by the predefined time interval. Analog Oscilloscopes only display the signal after receiving the trigger and Digital Oscilloscopes, the trigger tells the oscilloscope to save the present data in memory.

The Handheld digital Oscilloscope comes with flexible triggering capabilities that allow you to isolate and capture the condition you want to characterize. The advanced triggering includes edge, pulse width, pattern, and video functionality to help you isolate the signal you want to see. The Autoscale enables the instruments to quickly display any active signals, and automatically adjust the vertical and horizontal settings with trigger control for best-possible signal display.

Probe Requirement

probes
To make measurements with an oscilloscope, you can use oscilloscope probe to connect the circuit to be tested to the channel 1 or 2 input of your oscilloscope, and you will get more precise measurements.

There are three types of oscilloscope probes, first is 1X probe and it supplies an input signal that is of the same amplitude as the signal being measured. The second is 10X probe and it provides and input signal that is attenuated by a factor of ten. The third types of oscilloscope combines the first two types and it has a small switch that allows you to switch between the 1X setting and the 10X setting

The U1604A comes with a blue (not red) and a black oscilloscope probe, the unit’s BNC connectors are blue and red. The color difference is in the safety ratings.

Blue represents 600 V CAT. III while black is 300 V CAT.III. DMM Probes include insulated alligator clip attachments, because the BNC connectors are recessed.


Connectivity


The 40MHz Handheld Digital Oscilloscope comes with USB 2.0 full-speed interface and the he waveform can be saved (as a data file for further analysis or as an image file for documentation), printed, annotate, manipulated and displayed as a computer file. You can also use a USB flash drive as an option to save and retrieve configuration setups or waveforms to and from the USB flash drive.

Analysis Capability


The 100 MHz Analog and Handheld Digital oscilloscopes have similar triggering capabilities and to store analog oscilloscope waveform you have to photograph it. On the other hand, the Handheld oscilloscope's capability with the PC Link application software and you can control the instrument remotely from PC, retrieve your waveform and print it using a connected printer. The average battery life is 4 hours and the charging time is 5 hours.

Where to purchase oscilloscopes


Digital oscilloscopes are replacing analog oscilloscopes in the marketplace. If you buy oscilloscopes from Farnell then you will save money, the less money you will spend to purchase oscilloscopes the more oscilloscopes you will get. The others oscilloscopes that you do not want then you can sell it to your mates or on eBay website. For example:
Mixed Signal Oscilloscope
Qty Price Description
1+ £159.20 buy one oscilloscope for £159.20 and you will NOT save money
3+ £153.60 buy three oscilloscopes for £153.60 and you will save £324
5+ £150.40 buy five oscilloscopes for £150.40 and you will save £645.6
10+ £145.60 buy ten oscilloscopes for £145.60 and you will save £1,446.4


You can buy Mixed Signal Oscilloscopes and Mixed Signal Oscilloscopes have spectrum analyser, higher sampling rates and provides larger number of channels and about 16 logic channels so that it can display both the analog and digital operation of a mixed signal on its display. For example, on the right is a MSO4104 Mixed signal Oscilloscope 1GHz and it has 2 or 4 analog channels plus 16 digital channels.

Farnell http://uk.farnell.com/electrical-electronic-test
Amplicon Liveline Ltd http://www.amplicon.co.uk/MandC/product/Test-64.cfm



Reference:

Julian Rubin, Cathode Ray Tube (CRT) http://www.patent-invent.com/electricity/inventions/cathode_ray_tube.html
Tektronix, XYZs of Oscilloscopes, Introduction to How Oscilloscope Work http://www.scribd.com/word/download_preview/23256?secret_password=9dmhrcnr60e7r
Howstuffworks, oscilloscope types http://science.howstuffworks.com/framed.htm?parent=question8.htm&url=http://www.radio-electronics.com/info/t_and_m/oscilloscope/oscilloscope_types.php
ZTEC Instruments, Oscilloscope Measurement Fundamentals, more information on FFT http://www.ztecinstruments.com/oscilloscope-measurement-fundamentals-part-3-of-3
REBECCA SUEMNICHT (2005), how to choose a mixed-signal oscilloscope http://www2.electronicproducts.com/How_to_choose_a_mixed-signal_oscilloscope-article-agilent-sep2005-html.aspx
Ian Hickman, Oscillospes: How to use Them, how they work
http://books.google.co.uk/books?id=p0HZMUkYgiwC&pg=PA67&dq=oscilloscope,+number+of+channel&lr=&sig=cMPXNLG28e6wQz3l1IeWWkmw4sE#PPA67,M1
Michael E. Brumbach, Industrial Electricity http://books.google.co.uk/books?id=N6JpAs199AIC&pg=PA54&dq=oscilloscope+probe&sig=twBvCSXbc9NhkZEZTZwHsMRuVJU#PPA54,M1
Instek Analog Oscilloscope http://www.instek.com/GOS-6103.htm
Instek Analog Oscilloscope Data Sheet http://www.valuetronics.com/vt/assets/pdfs/INSTEK_GOS6103_6103C_6112.pdf
Agilent U1604A Handheld Digital Oscilloscope http://www.home.agilent.com/agilent/product.jspx?nid=-536906711.536910945.00&cc=US&lc=eng
Agilent U1604A Handheld Digital Oscilloscope Data Sheet http://cp.literature.agilent.com/litweb/pdf/5989-5576EN.pdf
Martin Rowe (2007), Review: Agilent Technologies U1604A, Part 1 of 2 http://www.tmworld.com/blog/1430000143/post/810010281.html
MetricTest, Agilent U1600A Series Handheld Oscilloscopes http://www.metrictest.com/catalog/brands/agilent/agilent_u1600a.jsp



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