Newsgroups: rec.radio.amateur.homebrew From: john@wd1v.mv.com (John Seney) Subject: Digital Storage Scope.FAQ Date: Mon, 7 Aug 1995 10:13:56 GMT (monaco 9 pt.) Summer, 1995 Digital Scope.FAQ - Version 1.09 ::::::::::::::::::::::::::::::::::::: ::Date/Time | O O :: :: /\ | :: :: / \ | O O :: :: / \ /\ | :: ::__/ \ / \ /`| O O :: :: \ / \/ | :: :: \ / | O O :: ::1 GHz BW \/ 2 GS/s |________:: ::________________________|A B C D :: :: rise 1.5 ns | x x x :: :: fall 4.9 ns | x x x :: ::_________________________________:: ::(*) (*) (*) (*) (*) (*) :: ::::::::::::::::::::::::::::::::::::: ::: ::: Dear Technologists: This Digital Scope.FAQ file contains many (but not all) of your answers to the more "Frequently Asked Questions" re: Digital Storage Oscilloscopes (DSOs). Key Issues reviewed in this file include: * DSO INDUSTRY TRENDS (Whats happening in DSO technology in 1995?) * DSO FORM FACTORS (What types of DSOs are there?) * PRIMARY DSO FUNCTIONS (What can DSOs actually do?) * 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?) Feel free to contact me anytime (john@wd1v.mv.com) if you have additional questions or comments. *If you want the latest version of this file sent to you automatically, send an EMAIL where the subject field contains the text "subscribe scope.faq". ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| | DSO INDUSTRY TRENDS 1995 MORE DSOs ARE NOW SOLD THAN ANALOG SCOPES. Expect most new scope models to be DIGITAL and have faster sampling, higher bandwidths, deeper memories, and lower costs than in 1994. COMPARABLE MODELS HAVE FALLEN IN PRICE BY ABOUT 50% IN THE LAST 4 YEARS. The DSO market is very competitive - thats good news for buyers. 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. Specifications: Model X Model Y Model Z ============================= ======= ======= ======= 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) Number of Channels Max Samples on all Channels Max Samples on 1 Channel Display Size (Diagonal) Display Resolution Display Type CPU (Type and Clock Speed) Math Co-Processer (Y/N) Maximum FFT Record Size Multiple Zooms per Trace (Y/N if Y, #?) Multiple Grids for full 8 bits Multiple Cursors per Screen (Y/N if Y, #?) Pulse Parameters (#Total/#Viewable) External Trigger Input (Y/N) Time Stamps on Segments (Y/N) Timing on Peak Detects (Y/N) Statistics on Parameters (Y/N) Roll Mode Acquisitions (Y/N) Pass/Fail Masks & Parameters (Y/N) Chained Math Operations (Y/N if Y, #?) Free Firmware Upgrades (Y/N if Y, #?) Memory Upgrades (Y/N) Video Trigger (Y/N) High Density DOS Disk (Y/N) Hard Disk (Y/N) High Speed Built-In Printer (Y/N) FFT (Y/N) Histogramming (Y/N) Advanced Mathematics (Y/N) Standard Warranty (Number of Years) Prices w/ all options ($) 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.). MAINFRAME 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 samples. DSOs ARE GETTING 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. SMART CHOOSERS must know the CPU specifications as well as the key DSP benchmarks. DSOs AREN'T JUST FOR TRANSIENT CAPTURE ANYMORE. Latest DSOs can now process multiple sweeps and generate envelopes, compute statistics, do complex DSP functions, conduct stand-alone tests, archive and print data, and even FAX DSO screens with measurement and test results to/from remote sites. 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. DSOs ARE THE HIGHEST BW OSCILLOSCOPES AVAILABLE. The highest BW "ANALOG" scope currently in production is only 400 MHz. while several DSOs go well beyond 1 GHz. The future is clearly digital! MAXIMUM REAL-TIME SAMPLE RATES (Single Shot) can now go to 10 Giga-samples in 1 new portable DSO model just announced. ACQUISITION MEMORY DEPTHS are expanding from 10 K to 50 K (typical MINIMUMS) and up to 8 Million samples (maximum). CLOSENESS TO SOURCES IS ALSO GOOD NEWS FOR SMART CHOOSERS. 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. UPGRADE PATHS for firmware and hardware expansions are becoming common. but not all models can be upgraded - another issue of concern for SMART CHOOSERS. DSOs ARE THE PRIMARY DEBUGGING TOOLS FOR HIGH SPEED DIGITAL CIRCUITS since they can now sample so rapidly and trigger on so many different fault conditions. TRIGGER RATES are becoming an important specification with varying amounts of information per trigger or sweep. SOME DSO MANUFACTURERS ARE OFFERING COLOR DISPLAY OPTIONS. Some versions utilize the colors cleverly with COLOR GRADED PERSISTENCE. While many applications only require a single channel DSO, MOST USERS ARE NOW PURCHASING 4 CHANNEL DSOs. SOME manufacturers can INTERLEAVE the CHANNELS of their DSOs 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 manufacturers can INTERLEAVE the MEMORIES of their DSOs 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 manufacturers can INTERLEAVE CHANNELS and MEMORIES. *SOME OFFER THIS FEATURE ONLY WITH THEIR DEEPEST MEMORY OPTIONS - be careful. Functions are increasing so the USER INTERFACE IS GAINING INCREASING IMPORTANCE. Features need to be extracted as needed - quickly and without a lot of button pushing, knob twisting, or frequent trips to the user's manual. DSOs WITH FLOPPY DISK DRIVES ARE THE RULE VS. THE EXCEPTION. Almost all new units offer them - either as options or as standard features. SOME MANUFACTURERS ARE NOW OFFERING BUILT IN HARD DISKS that are removable and thus, transferable, (via PCMCIA interfaces) to laptops or PCs. MOST DSO MANUFACTURERS OFFER A NUMBER OF FREE SERVICES: o Full line catalogs and price sheets o DSOs for evaluation on your signals with a "how to use it" demonstration o Application Notes that relate how to take specific measurements or tests o Seminars to teach basic DSO technology o Seminars to teach application specific techniques o Competitive DSO COMPARISONS o TRAINING after delivery for most rapid return on investment o TOLL-FREE TELEPHONE APPLICATIONS ASSISTANCE to support their platforms o Drivers for third party SOFTWARE used for remote control and analysis. The primary American manufacturers of DSOs are: o Fluke Corporation 800 443-5853 in Everett, WA o Hewlett-Packard 800 452-4844 in Palo Alto, CA o LeCroy Corporation 800 553-2769 in Chestnut Ridge, NY o Tektronix Corporation 800 426-2200 in Beaverton, OR (If you are outside of the United States, contact a local sales office) á ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| | 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, 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. ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| | 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 for, the more valuable it is and the easier it is to justify. Here are a few for you to consider: o 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. o 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. o 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. o 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. o 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: o Aerospace o Automotive Electronics o Avionics o Chemistry o Computer Backplanes/Interfaces o ElectricalComponents o Electric Power o EMP/EMI/EMC o LASERS o Lightning Studies o Magnetic Media o MATE o Medical o NDT o Networks/Communications o Noise/Acoustics o Power Supply Design/Manufacturing o Process Control o RADAR o Semiconductor Design/Manufacturing o SONAR o Telecomm (Switches, Cellular,Telemetry) o 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 NEEDED FOR THE RECORDING TIME NEEDED SO AS NOT TO ALIAS! Another point of confusion are SAMPLE RATES specified for REPETITIVE vs. SINGLE SHOT acquisitions. REAL-TIME refers to SINGLE SHOT and RIS refers to Random Interleaved Sampling. RIS is sometimes called ET or EQUIVALENT TIME sample mode. 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. LOOK OUT! Many DSOs have BW ratings that reflect their best performance but only in certain voltage ranges. LOOK OUT! 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. Require 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 Tricky! Manufactures specify their largest numbers. Look out for some DSO's acquisition memory values that divide by the number of active channels. 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! The best 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 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) Pass/Fail Testing (Comparisons of live waveforms to masks or 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. If you get saturated, take a break and return. Check the demo DSO that will be left for evaluation to make sure: o That it will accept your full scale voltages o That it samples fast enough to capture your waveforms with high fidelity o That it is not affected by other signals in your environment o That it has the options necessary to take your measurements o That it has a manual covering operations o 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. Is there ever a telephone or service charge for contacting them? 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. Remember: 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: o Memory Expansion Options o Waveform Processing Options o Disk Drive Options o Printer Options o Hardware Options o Active Probes o Probes with different attenuations than those supplied with the DSO o Scope Cart o Rack Mount o Hard Shell Transit Case for safe shipping your DSO to remote sites o Probes for all channels You should also explore the manufacturer's policies and costs regarding: o Applications Assistance o Calibrations- NIST, MIL, Performance Checks, ISO-9000, At-Site Service o Capabilities for Training Users o DSO System Software/Firmware Upgrades o Warranty Period - Extensions You should 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. -eof- -- ================================================================== John D. Seney, WD1V Internet: john@wd1v.mv.com 144 Pepperidge Drive America On Line: jseney@aol.com Manchester, NH 03103-6150 AX.25 Pkt: wd1v@wb1dsw.nh.usa.na (H) 603-668-1096 Ampernet: wd1v@wd1v.ampr.org (O) 603-627-6303 (F) 603-627-1623 (P) 800-SKYPAGE #5956779 * Source for Digital Scope.FAQ *To obtain the latest copy automatically, simply send me an EMAIL with "subscribe scope.faq" in the subject field. ==================================================================