Welcome to the Digital Scope.FAQ
Digital Storage Scope.FAQ
ver. 304
Frequently Asked Questions
Dear Technologist(s):
Thanks to the hundreds of respondees to the earlier versions of this FAQ!
Special thanks to David H. Whittum at Stanford University for this FAQ's
first HTML/WWW site (http://beam.slac.stanford.edu/www/library/w3/dso.html).
This newest Digital Storage Scope.FAQ file contains many (but not all) of your
answers to the more "Frequently Asked Questions" regarding Digital Storage
Oscilloscopes (DSOs).
The answers and suggestions come from more than a decade of my experiences as
a DSO sales engineer in the Boston, Massachusetts area.
This FAQ contains no links to other WWW sites although a few are mentioned.
The opinions are completely mine and represent no company or service - they
are meant simply to be helpful, generic, and easy to understand.
Feel free to contact me anytime if you have additional questions or comments.
Digital Scope.FAQ Main Menu (in order of appearance)
WELCOME! (This FAQ Welcomes YOU)
DSO INDUSTRY TRENDS (Whats happening in DSO technology this year?)
DSO FORM FACTORS (What types of DSOs are there?)
PRIMARY DSO FUNCTIONS (What can DSOs actually do?)
COMPARISONS (How can I best compare various models)
DSO APPLICATIONS (What are the most common DSO applications?)
ADCs (What speed do I really need on each channel?)
BANDWIDTH & TRIGGER (What numbers and functions are right?)
ARCHIVAL & MEMORY (How fast, how deep, and can I get more?)
DISPLAYS (What am I really looking at?)
MEASUREMENTS (How much is my signal changing over time?)
DIGITAL SIGNAL PROCESSING (How can I obtain more useful information?)
DEMOS & PURCHASING (How can I see and get the DSO I really need?)
DSO INDUSTRY TRENDS 1995
THE VAST MAJORITY OF THE DSOS THAT ARE SOLD IN THE UNITED STATES are
manufactured by US Corporations making delivery, service, calibrations,
and support most convenient.
UNITED STATES DSO MANUFACTURERS OFFER A NUMBER OF FREE SERVICES:
Catalogs with detailed specifications and pricing
FREE DSOs for evaluation on your signals with a "how to drive it" demo
Application notes that relate how to take specific measurements or tests
Seminars to teach basic DSO technology
Seminars to teach application specific measurement techniques
Competitive DSO COMPARISONS
TRAINING after delivery for most rapid return on investment
TOLL-FREE TELEPHONE APPLICATIONS ASSISTANCE to support their platforms
Software Drivers for remote control and analysis.
The primary US manufacturers of DSOs are:
Fluke Corporation 800 443-5853 in Everett, WA
http://www.fluke.com/
Hewlett-Packard 800 452-4844 in Palo Alto, CA
http://www1.hp.com/
LeCroy Corporation 800 553-2769 in Chestnut Ridge, NY
http://www.lecroy.com/
Tektronix Corporation 800 426-2200 in Beaverton, OR
http://www.tek.com/
The combination of Number of Channels, Sample Rate, Front End Bandwidth, and Memory
Depth are the primary cost determinants of digital scopes. The current market
suggests these sorts of performance/cost tiers.
Sample Rate BW Memory Depth Average Cost
=========== ======= ============ ============
100 MS/sec 100 MHz 10 K $ 3000
200 MS/sec 100 MHz 20 K $ 3500
1 GS/sec 100 MHz 1 K $ 4000
100 MS/sec 200 MHz 50 K $ 6000
2.5 GS/sec 300 MHz .5 K $ 7000
100 MS/sec 400 MHz 50 K $ 7500
500 MS/sec 500 MHz 50 K $10000
1 GS/sec 500 MHz 100 K $10000
2 GS/sec 500 MHz 200 K $14500
2 GS/sec 1 GHz 200 K $17500
4 GS/sec 1 GHz 50 K $35000
5 GS/sec 1 GHz 15 K $30000
8 GS/sec 2 GHz 32 K $60000
10 GS/sec 1.5 GHz 1 K $15000
DSO's go all the way to 50 GHz (the "sampling scope" variety) bandwidth.
MAINFRAME DSO POWER IS NOW IN THE NEWEST PORTABLES. DSOs now can include
memory depths > 1M samples per channel and offer processing options such as
HISTOGRAMMING or FFTs on up to 6M contiguous samples.
MOST US MAKERS OF ANALOG OSCILLOSCOPES are discontinuing their high BW
models. Some manufacturers are offering hybrid analog and digital scopes.
DSOs ARE THE HIGHEST BW OSCILLOSCOPES AVAILABLE and are usually less expensive
than their analog model equivalents. Several DSOs go well beyond 1 GHz.
DSO ACQUISITION MEMORY DEPTHS are expanding with 50 K (typical MINIMUMS) up to
8 Million samples (MAXIMUM).
SOME MODELS offer INTERLEAVING the CHANNELS so that, for example, in a 2 channel
model, twice the sample rate is achieved when using just 1 channel compared with
both channels being used.
SOME MODELS offer INTERLEAVING the MEMORIES so that, for example, in a 2 channel
model, twice the memory depth is achieved when using just 1 channel (and twice the
recording time) compared with both channels being used.
SOME MODELS offer INTERLEAVING CHANNELS and MEMORIES.
DSOs ARE THE PRIMARY DEBUGGING TOOLS FOR HIGH SPEED DIGITAL CIRCUITS since
they can now sample so rapidly, have large acquisition memories, and can trigger
on virtually all types of fault conditions involving multiple channels.
DSO TRIGGER CAPABILITIES ARE STRONGER THAN EVER. Emphasis is in minimizing
dead time between triggers and triggering on the most elusive events.
DSOs AREN'T JUST FOR SINGLE TRANSIENT CAPTURE. DSOs can now provide stand-alone
measurements and tests that apply waveform analysis right in the instrument.
SOME MANUFACTURERS NOW OFFER APPLICATION SPECIFIC MEASUREMENTS. For instance,
developers of disk drives can now have PW-50 and TAA measurements right in
their scopes.
MOST DSO USERS ARE NOW PURCHASING 4 CHANNEL models as the cost difference is
low and seeing what is happening on more than 2 channels is so beneficial.
DSOs ARE BECOMING EXTREMELY COMPUTATION INTENSIVE. Deeper memories, multiple
channels, high resolution displays, and enhanced DSP routines tax the fastest CPUs and
smartest firmware. Latest designs use multi-processor architectures.
FUNCTIONS ARE INCREASING SO THE USER INTERFACE IS GAINING INCREASING IMPORTANCE.
There is virtually no standardization as to the method of giving a user control
of a DSO. As you look, you'll see combinations of knobs, buttons, touch
sensitive screens, mice, computer interfaces, and even programmable buttons on
the probes. As a general rule of thumb, the more menus, the fewer the knobs.
DSOs WITH FLOPPY DISK DRIVES ARE THE RULE VS. THE EXCEPTION. Almost all new
units offer them - either as options or as standard features. Most store front
panel set-ups, screen shot graphics you can import into word processing, and waveform
data archival.
SOME MANUFACTURERS ARE NOW OFFERING BUILT IN HARD DISKS that are removable and
thus, transferable, (via PC Card interfaces) to laptops or PCs.
DSOS ARE BEING OPERATED BY MORE COMPUTERS as redundant tests and measurements
are being automated. Most DSOs come with IEEE-488 and RS-232 interfaces and
offer remote programmability and data transfer. Most DSOs have free or low
cost device drivers for popular software packages. (WWW http://www.natinst.com
for more information from National Instruments)
UPGRADE PATHS for firmware and hardware expansions are becoming common,
but not all models can be upgraded.
DSO FORM FACTORS
DSOs are now available in 5 different form factors:
1) PC CARD - A to D on a card that uses a PC's CPU and memory - PCB Style
Interesting due to low cost. Look out for noise problems from some PC's
backplanes.
2) STAND ALONE CARD - DSO on a card for embedded systems - PCB Style
Interesting due to low cost, small size, fewer noise issues - greater
functionality.
3) HANDHELD - Portable capabilities - Portable Style Battery operated for
field measurements.
4) PORTABLE - with some amount of upgrade capabilities - Portable Style
Performance approaching mainframes and low cost due to high competition,
high volume, and large scale integrations.
5) MAINFRAME - typically with plug-ins that determine performance - Lab Style
Highest cost but highest performance and greatest versatility.
PRIMARY DSO FUNCTIONS
The 5 Primary Functions of a DSO are to:
1) CAPTURE.....the signal
2) VIEW........the signal
3) MEASURE.....the signal
4) ANALYZE.....the signal
5) DOCUMENT....the signal
CAPTURE = consider SAMPLE RATES, MEMORY DEPTH, BANDWIDTH, TRIGGER,
NUMBER OF CHANNELS, DISPLAY UPDATE RATE and/or DEADTIME
BETWEEN ACQUISITIONS and PROBES.
(Here you should have a predetermined knowlege of the highest frequency
signal you need to digitize, what its full scale amplitudes are, and whether
or not you need to capture single shot or repetitive waveforms. If these issues
are unclear to you, review them with your sales engineer.)
VIEW = consider ADC resolution, DISPLAY resolution, Display size,
DSP results, and ZOOM EXPANSIONS.
MEASURE = consider PULSE PARAMETER requirements, CURSORS, and STATISTICS.
ANALYZE = consider DSP, PASS/FAIL Testing, MASK Comparisons, and EYE Diagrams.
DOCUMENT = consider PRINTING, SCREEN SHOTS to DISK, and DATA TRANSFERS.
COMPARISONS
DSOs STILL VARY IN PERFORMANCE IN A VARIETY OF WAYS. Each manufacturer provides
a certain degree of standard features, but their different design schemes
produce unique performance strengths and weaknesses. Compare and evaluate.
SMART CHOOSERS typically let their S I G N A L S determine the primary
specifications (Sample Rate, BW, Memory Depth, Trigger BW, etc.) and let
their A P P L I C A T I O N determine secondary specifications (I/O,
Measurement, DSP, etc.).
(SPECIFICATIONS TO COMPARE) Model X Model Y Model Z
=========================== ======= ======= =======
(FRONT END)
Max Transient Sample Rate
Max Repetitive Sample Rate
Analog BW
Timebase Range Max
Timebase Range Minimum
Volts/Div (Range)
Cust. Vertical Rescaling (Y/N)
Vertical Resolution (# of bits)
(STORAGE)
Number of Channels
Max Samples on each Channel
Max Samples on 1 Channel
Reference Memories (# kbytes)
High Density DOS Disk (Y/N)
Hard Disk (Y/N)
Built-In Printer (Y/N)
PC Card (Y/N)
(TRIGGER and ACQUISITION MODES)
EDGE TRIGGER (Y/N)
HOLDOFF by TIME (Y/N)
HOLDOFF by EVENTS (Y/N)
PATTERN (Y/N)
GLITCH (Y/N)
INTERVAL (Y/N)
STATE QUALIFIED (Y/N)
DROPOUT (Y/N)
EXCLUSION (Y/N)
Video Trigger (Y/N)
Maximum # of Triggers/second
Trigger Segments w/ Time Stamps (Y/N)
Trigger Pass/Fail w/ Masks & Parameters (Y/N)
External Trigger Input (Y/N)
PEAK DETECT w/ Timing (Y/N)
Roll Mode Acquisitions (Y/N)
Display Update Rate
(DISPLAY)
Display Size (Diagonal) (# inches)
Display Pixel Resolution (# pixels x # pixels)
Display Type (Color, Monochrome, etc.)
Multiple Zooms per Trace (Y/N if Y, #?)
Multiple Grids for full 8 bits (Y/N)
Multiple Cursors per Screen (Y/N if Y, #?)
(CPU PERFORMANCE)
CPU (Model and Clock Speed)
Math Co-Processer (Y/N)
Max Record Size on Math (Y/N)
(MEASUREMENTS and DSP)
Pulse Parameters (#Total/#Viewable)
Statistics on Parameters (Y/N)
Chained Math Operations (Y/N if Y, #?)
Histogramming (Y/N)
Advanced Mathematics (Y/N)
FFT (Y/N)
(TERMS AND CONDITIONS)
Standard Warranty (# of Years)
Free Firmware Upgrades (Y/N if Y, #?)
Memory Upgrades (Y/N)
Prices w/ all options ($)
APPLICATIONS
DUE TO EXPANDING FUNCTIONS AND CAPABILITIES, DSOs lend themselves to a
wider variety of application areas. Like a computer, the more applications you
can use an instrument, the greater value it has and the easier it is to
justify. Here are a few for you to consider:
The most obvious one is to use a DSO as an OSCILLOSCOPE. Typical
applications are electronic circuit design and debug and troubleshooting
faulty or intermittent circuits.
Another common application is as the front end of a DATA ACQUISITION SYSTEM.
DSO's cost per channel has become very competitive. Many people find that the
triggering flexibility, deep memory, "live" view of waveforms, and fast
transfer rates make the DSO a great candidate. If your experiment is short
lived, it is nice to have a DSO when you are done vs. a black box that gets
shelved and forgotten. Typical applications are research experiments, process
monitoring, and flaw detections.
DSOs lend themselves to being fully integrated into ATE SYSTEMS. In this
example, the DSO is under remote control from a host computer and conducts
its business by computer command. Typical applications are incoming Quality
Assurance of components, Manufacturing/Production Functional Test, Final
Test, and System Test.
DSOs can be used (card level or portable rack mounted form factors) and can
be embedded into systems that require Analog to Digital conversion and data
analysis. Here the DSO is used as a SYSTEM COMPONENT and eliminates the need
and time of engineering custom devices.
DSOs DISPLACE/REPLACE MANY DEDICATED INSTRUMENTS - i.e. DMMs, Spectrum
Analyzers, Impedance Analyzers, Time Interval Analyzers, Frequency Counters,
Pulse Counters, Power Meters, etc.
Some of the common DSO Application fields include:
Aerospace
Automotive Electronics
Avionics
Chemistry
Computer Backplanes/Interfaces
ElectricalComponents
Electric Power
EMP/EMI/EMC
LASERS
Lightning Studies
Magnetic Media
MATE
Medical
NDT
Networks/Communications
Noise/Acoustics
Power Supply Design/Manufacturing
Process Control
RADAR
Semiconductor Design/Manufacturing
SONAR
Telecomm (Switches, Cellular,Telemetry)
Ultrasound Vibration/Mechanical Analysis
ADCs
ADCs - SPEED
LOOK OUT for short record length DSOs that can only sample at maximum rates
for short periods of time. Ideally, the sample rate value should be displayed on
screen all the time. BE CERTAIN YOU CAN SAMPLE FAST ENOUGH IN REAL TIME
(SINGLE SHOT) MODE ON ALL CHANNELS SO YOU CAN RECORD WITHOUT ALIASING.
Another point of confusion! SAMPLE RATES specified for REPETITIVE vs.
SINGLE SHOT acquisitions. REAL-TIME refers to SINGLE SHOT. RIS refers to
Random Interleaved Sampling. RIS is sometimes called ET or EQUIVALENT
TIME sample mode and can only be used with repetitive waveforms.
Also referred to as "Random Repetitive Sampling".
The sample rate speed of the DSO's analog to digital converter is a very
important specification. It is the minimum time between each sample. For
instance, a 500 MS/sec. sample rate relates to 2 ns. per point resolution.
Multiply the number of sample points * the sample period to determine a
DSO's maximum recording time @ maximum sample rate.
Many people confuse the SAMPLE RATE speed with the BANDWIDTH. BANDWIDTH is
simply the analog front end performance (preamplifier and sample and
hold circuitry).
ADCS - RESOLUTION
This refers to full scale resolution. An 8 bit digitizer will divide full scale
input voltages by 255 counts. Thus the minimum discernible sampled value on a 1
volt full scale 8 bit DSO would be 1 / 256 or .00390 volts per step.
If you have repetitive waveforms, you can increase your vertical resolution
with AVERAGING.
If you have transient waveforms, you can increase your vertical resolution by
low-pass filtering each sweep for ENHANCED RESOLUTION.
ADCS - ACCURACY
Not all ADCs are created equally. The most common figure of merit is
EFFECTIVE BITS that relate the number of correct bits of a given ADC's actual
measurements vs.ideal.
BANDWIDTH & TRIGGER
BANDWIDTH
BW is the amount your signal will be attenuated by the DSOs front end amplifier
- specified at the -3dB point - as a function of input frequency. Remember
that BW ratings are at the input to the amplifier and that your PROBES might
also attenuate your signals. If you are looking at signals > 50 MHz, try a
FET probe.
Remember that -3dB is down in amplitude by almost 30%. You probably DON'T want
a 30% error in your amplitude measurements. Consider the higher BW DSOs so your
measurements will be accurate.
CAUTION! Many DSOs have BW ratings that reflect their best performance but
only in certain voltage ranges.
CAUTION! Some DSOs reduce sample rates by the number of channels activated.
This could cause aliasing by changing the relationship of how fast the DSO is
sampling vs. the BW of the signals you are digitizing.
Many DSOs have analog BW specifications far greater than their SINGLE-SHOT
sample rate's Nyquist (.5 sample rate) frequency. This is so that when
repetitive waveforms are viewed, the maximum BW signals can be seen.
TRIGGER
If you can't TRIGGER on the waveforms you need to see, you have a real
problem! This should be center stage for your demo if you are looking at a new
DSO. There are various trigger capabilities and a combination of them that are
easy to use that capture your waveforms is the most desirable.
Know how frequently you need to trigger. The maximum trigger rate is a key
specification that isn't often published in manufacturer's specifications as
there can be many variables. Evaluate and compare!
Some DSOs have a MEMORY SEGMENTATION feature that lets you trigger very
rapidly and fill just a portion (1 segment out of #n segments) per
trigger.
Most DSOs will let you trigger on the width of pulses , the INTERVALS
between pulses, the LOGICAL or PATTERN conditions between inputs, after
specific delays by events or time, drop out conditions, etc. Compare!
Look for TRIGGER ICONS that relate how the current trigger selection is
working. This is very helpful if you are looking at a screen dump later and
trying to reacquire with the same trigger conditions.
DSOs are valuable tools for looking at video signals but not all DSOs offer a
video trigger as a standard feature. Compare!
DSOs can almost always capture single shot events but not always with the
amount of pre or post trigger delay you might need. If your application
requires capturing a lot of transient waveforms, look into the span of trigger
delay as an important spec.
ARCHIVAL & MEMORY
ARCHIVAL
FLOPPY DISKS - They are nice - should be MS-DOS and should come with
file formatter so you can convert to ASCII and back then back to binary.
HARD DISKS - They are becoming available and offer the same kind of
convenience that is realized in PCs.
MEMORY CARDS - They are expensive but they are fast - up to 200 times faster
than a floppy. Requires a reader at PC to use the data.
PRINTERS/PLOTTERS - They are the best way of showing the world your waveforms
and your measurements. Plotters are great for elegant color - most impressive
for overheads.
ARCHIVAL DATA FILE TYPES:
WAVEFORM FILES - Binary but with conversions to ASCII for import into other
programs and from ASCII back to DSO's binary format.
SET UP FILES - Most DSOs have front panel setups that you can recall and store
either in nonvolatile memory in DSO or to disk.
SCREEN SHOTS - "Print to disk" graphics files that are screen dump imports
into your word processor.
MEMORY
CAUTION! Manufactures specify their largest numbers. Look out for some
DSO's acquisition memory values that divide by the number of active channels.
CAUTION! Don't confuse ACQUISITION memory with REFERENCE memory specifications.
Reference memory is used for copies of waveforms recorded earlier and made
available for comparison either by viewing or by mathematics. Some DSOs have
longer acquisition memories than reference memory. COMPARE!
Not all DSOs have the same number of reference memories. More are better. Make
sure they have the width to contain your processed data. You can't store 12
bit averaged waveform data in 8 bit reference memory. Compare.
Not all DSOs have the same number of memories for front panel set-up/storage
and recall. Compare.
Some manufacturers offer MEMORY CARDS for additional reference memory.
Some DSOs allow for MEMORY SEGMENTATION where you can acquire multiple trigger
events in a single sweep display. A few models will also record the time of
each trigger event that occurred.
DISPLAYS
NOT ALL DSOS ARE CREATED EQUALLY - ESPECIALLY THEIR DISPLAYS! IDEALLY the DSO
will compact an entire sweep of acquisition memory onto a single screen with a
min/max algorithm. The benefit is that you don't have to page thru screens to
see the interesting details in your data. Min/max compaction makes faults
obvious.
IDEALLY, THE SCREEN WILL BE LARGE enough so that you can see the WAVEFORMS and
MEASUREMENTS clearly at the SAME TIME. Look out for small diagonal measurement
displays that put measurements on top of the waveform data.
DSO displays are typically specified in terms of resolution and diagonal size.
The higher the resolution, the easier it will be to see fine details and the
better your publications that have imported DSO screens will appear. The
larger the diagonal size, the greater the chance of being able to see critical
information on screen all at the same time vs. pages of menus.
IDEALLY, YOU SHOULD HAVE ALL THE INFORMATION ON SCREEN THAT YOU WANT IN YOUR
REPORT. Consider things like trigger parameters, ICONS, measurements, input
and timebase settings for each trace, sample rate, cursors and their
measurements for each trace, clock/calendar. That is a lot of information on
screen. How does it look?
IDEALLY, YOU SHOULD HAVE THE ABILITY TO EXPAND OR ZOOM in on DIFFERENT PARTS
of your waveforms to see details more clearly and to limit your measurements
to within a given region of data. This means MULTIPLE EXPANSION WINDOWS are
best.
Ideally, the graticule should be done in software and allow multiple
traces to be displayed, each within their own grid. This preserves the full
scale voltage input ranges for best accuracy.
Ideally, the DSO display should have a report of what the front panel status
is so that the entire setup of the DSO can be observed, verified,
replicated, and printed.
MEASUREMENTS
NO MORE FINGERPRINTS ON THE SCREEN FROM COUNTING GRID SQUARES! Modern DSOs
display precise measurements of any waveform you capture.
Measurements are either made with CURSORS or automatically with PULSE PARAMETERS
such as as RISE TIME, RMS, FREQUENCY, etc. seen right on the display.
Ideally, the PULSE PARAMETERS should include STATISTICS so you can see and
measure HOW MUCH YOUR WAVEFORMS ARE CHANGING with every new trigger or
acquisition.
Cursors should show:
ABSOLUTE AMPLITUDE at a given point
ABSOLUTE TIME at a given point
RELATIVE AMPLITUDE
RELATIVE TIME
Ideally, EACH TRACE should have its own set of cursors for SIMULTANEOUS
measurements on all displayed traces.
You should be able to make measurements automatically on all displayed traces.
PAY CLOSE ATTENTION TO THE DSO'S ABILITY TO DETECT AND MEASURE SIGNALS THAT
ARE CHANGING. THIS IS OFTEN OVERLOOKED AND YET IT IS OFTEN THE MOST NEEDED
CAPABILITY.
DIGITAL SIGNAL PROCESSING (DSP)
DSP is doing math on the waveforms so additional information can be obtained.
Some instruments really slow down when DSP is being performed. Ask for benchmark
specifications on the key functions you need. Don't waste your time looking at
DSOs that just aren't fast enough.
Another DSP concern is that some manufacturers don't process an ENTIRE waveform
because of poor CPU power. Make sure the data you need processed is really being
processed!
Another DSP concern is that you may wish to do a SERIES of functions. How many
functions can be chained varies from model to model. Compare!
Consider these potential DSP functions:
Arithmetic (Add, Subtract, Multiply, Divide any traces)
Averaging (Remove random noise, improve resolution)
Enhanced Resolution (Smoothing, improves resolution at reduced BW)
Functions (Integrate, Differentiate, Envelope, etc.)
FFT (Spectral analysis of any trace)
Histograms (Distributions of measured values)
Mask Testing (Comparisons of live waveforms to masks)
Measurement Testing (Comparisons of live waveforms to measurements)
Trending (Time series of measured values)
DEMOS & PURCHASING
BEFORE THE DEMO
BE IN TOUCH WITH YOUR BUSINESS NEEDS as they relate to your DSO needs. Are you
going to faster designs soon that might impact the banner specifications
you'll need in the near future?
WRITE DOWN EXACTLY WHAT YOU EXPECT THE NEW DSO TO DO. Make it your "Wish
List". Try to find out what the most popular DSO is for your application.
GET A SENSE OF HOW SOLID YOUR BUDGET IS and how soon you can place an order
once you make a decision. If it is more than 6 months away and your short term
needs are critical, consider rental or lease.
PLAN SEVERAL DIFFERENT DEMOS WITH DIFFERENT MANUFACTURERS. Let them know it is
a "competitive situation" and you want the best DSO you can get that meets
your needs. You'll get a lot of attention and the best of services.
SCHEDULE THE DEMOS IN YOUR LAB INSTEAD OF YOUR CONFERENCE ROOM. You'll be
closer to your signals and the real environment where the DSO
will have to work.
YOU SHOULD PLAN TO SEE A DEMO OF THE EXACT MODEL DSO YOU ARE THINKING OF USING
- with all the options you believe you'll need - conducted by a Sales Engineer
that knows the instrument and what you need it to do extremely well.
THE DSO MANUFACTURER's SALES ENGINEER SHOULD BE A GREAT RESOURCE TO YOU. By
reviewing your application and assisting you with a model selection that is
technically correct, your demo will be much less likely to disappoint you or
anyone else.
If you have never met the Sales Engineer, plan to start with a quick tour of
your facility. Explain why you need the DSO showing them the area that it will
be used in and what you expect it to do. The tour may let your Sales Engineer
see things that will help you that you hadn't thought about.
DURING THE DEMO
A quick overview of the DSO's banner specifications and key features is a good
place to start the demo. Focus quickly on how to drive the front panel and
how to extract the various functions. If it looks complex, save front panels
you'll need to recall. Ask questions.
You should see your signals on screen EARLY into the demo and plan to borrow
the DSO for at least a few days to evaluate it if the demo goes well.
THE DEMO SHOULD PROVE THAT THE DSO MODEL BEING DEMOED CAN DO YOUR SPECIFIC
APPLICATION(S). If the demo can't do that, you are probably wasting time by
evaluating it further AFTER the demo. If the DSO has to do a specific task,
see it happen at the demo and learn how to replicate the settings so you can
do it after the Sales Engineer leaves.
PAY ATTENTION TO THE NUMBER OF BUTTONS that have to get pushed to go from one
operation to the next. If the demo is really canned, force some hopping around
so you see typical vs. streamlined operation.
Find out how long the DSO model you are looking at has been on the market. Ask
for MTBF figures . Find out where the closest
service center is and how long a typical repair or calibration turnaround
might take.
If you are a LARGE company, find out who else in your company is using the
same/similar DSO from the Sales Engineer. Chat with the other users.
If you are a SMALL company, find out who else in your industry within your
area is using the same/similar DSO from the Sales Engineer. Chat with the
other users.
Take as much time as you like. Don't rush it. Ask questions. Record answers.
Enjoy the process.
Check the demo DSO that will be left for evaluation to make sure:
That it will accept your full scale voltages
That it samples fast enough to capture your waveforms with high fidelity
That it is not affected by other signals in your environment
That it has the options necessary to take your measurements
That it has a manual covering operations
That you have the applications engineering telephone number for support
during your evaluation period
DURING THE EVALUATION
MAKE NOTES OF THE QUESTIONS YOU HAVE AND RECORD THE ANSWERS. It will keep you
focused.
CALL THE FACTORY'S APPLICATION'S GROUP AND TEST THEM to see how well they
answer your questions. Get application notes sent to you that address your
areas of interest.
DON'T BELIEVE THERE IS ONE DSO THAT DOES EVERYTHING. Most labs have a variety
of DSOs for various functions.
Try this experiment with the DSO you are considering. Connect a signal source
up to the DSO where you can vary the amplitude of the signal by very small
amounts. The waveform should have at least 3 or 4 complete cycles on screen
and be 90% of full scale. Once you have a stable trigger, store a copy of the
waveform into a reference memory. Then activate math so that all new waveforms
are being subtracted from the waveform in reference memory. See how little you
can change the amplitude level on the generator to see and measure the
difference with the DSO. A large part of the utility of a DSO is verifying
that things are exactly as they should be and seeing when they aren't.
AFTER THE EVALUATION
IF THE DSO DIDN'T MEET YOUR EXPECTATIONS, MAKE SURE YOU KNOW WHY and include
the new things you've discovered in your Wish List that you've learned.
PURCHASING
Get a list of ALL OPTIONS available for the DSO so that you can
order the exact configuration that really addresses your needs. Make sure you
and your Sales Engineer determine issues that might include:
Memory Expansion Options
Waveform Processing Options
Disk Drive Options
Printer Options
Hardware Options
Active Probes
Probes with different attenuations than those supplied with the DSO
Scope Cart
Rack Mount
Hard Shell Transit Case for safe shipping your DSO to remote sites
Probes for all channels
You should also explore the manufacturer's policies and costs regarding:
Applications Assistance
Calibrations- NIST, MIL, Performance Checks, ISO-9000, At-Site Service
Capabilities for Training Users
DSO System Software/Firmware Upgrades
Warranty Period - Extensions
GET A WRITTEN QUOTATION that relates the model, specifications, options, all
costs, delivery, and any discounts available. Most manufacturers offer
Educational, GSA, Quantity, and/or Demo discounts if you qualify.
You might also consider rental or leasing options. Most rental companies offer
equity rentals where rental/lease fees apply towards purchase. AT&T CAPITAL
CORPORATION is an excellent source of information concerning this
@ 800-874-7123.
John D. Seney |_|_|_|_| john@wd1v.mv.com
144 Pepperidge Dr. |_| |_| www http://www.mv.com/ipusers/wd1v
Manchester, NH 03103-6150 |_|_ _|_| wd1v@wb1dsw.nh.usa.noam
LeCroy Sales Engineer | | | | | 800-553-2769
(H) 603-668-1096 (F) 603-627-1623 (P) 800-SKYPAGE #5956779
All opinions are my own, including Digital Storage Scope.FAQ
Latest Site Update: December 16, 1995
Send comments to John D. Seney, WD1V
john@wd1v.mv.com