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Perform fast & accurate signal measurement and recording in the workshop or on the go with this compact, fully- featured digital instrument. pico Virtual Instrument Review by Peter Smith 14  Silicon Chip www.siliconchip.com.au I developing “virtual” PC-based digital f you’ve recently purchased an cally very expensive pieces of test gear, oscilloscope or are in the process often affordable only by top training instruments. By utilising the display capabilities and processing power of of doing so, you’ve undoubtedly institutions and R & D labs. noticed that the traditional analog Companies like Pico Technology, the PC, the hardware cost of the digital ’scope (or other digital instrument) models have gone the way of the a leading UK-based test equipment can be reduced dramatically, while dinosaur. manufacturer, have changed all that by actually increasing funcWith ever increastionality. ing semiconductor ADC-212 Virtual Instrument specifications performance, the digOf course, the “virtuNumber of channels 2 ital oscilloscope can al” tag is simply hintAnalog bandwidth 50MHz now do everything, ing at the lack of the Sampling rate 100MS/s (single channel); 50MS/s (dual channel) and more, that its physical switches and Resolution 12 bit analog cousin can – knobs. Instead, measureBuffer size 128k words for a lower price. ments are displayed on Dynamic range 80dB a PC screen, with mouse Digital storage osVoltage range ±50mV to ±20V in nine ranges clicks and menus replaccilloscopes (DSOs) Overload protection ±100V ing rotary dials. are not new, at least Scope timebase 10ns/div to 50s/div in the traditional We at SILICON CHIP Trigger modes Free run, repeat, single stand-alone sense. still tend to prefer real Input impedance 1MΩ Just like their analog switches and knobs in Input coupling AC, DC counterparts, they preference to the mouse Accuracy ±1% include the usual and keyboard control Power supply 12V DC 500mA (mains adapter supplied) front panel display that’s part of all virtual Interface PC parallel port compatible output via D-25 connector instrumentation. and arrays of switchDimensions: 190 x 140 x 45mm (L x W x H) es and knobs. In this Having said that, the Software: PicoScope, PicoLog & various drivers and examples format, they are typilow-cost, portability www.siliconchip.com.au September 2002  15 Pico ADC-212 Virtual Instrument Fig.1: PicoScope’s spectrum analyser, oscilloscope and meter views, all running simultaneously. Here we’re measuring the noise and distortion from the SILICON CHIP Digital Sine/Square Generator. The generator is producing a sine wave at 10kHz (the peak), but note the smaller spikes. These harmonics originate in the digital circuitry and have passed through the generator’s output filter network. and ever-increasing performance of virtual instruments simply cannot be ignored. Pico Technology’s ADC-212 Virtual Instrument is a fine example of the functionality that can be included in a small package without it costing the earth. Being PC-based, this product includes both hardware and software components. Let’s look at the hardware component first. Hardware The ADC-212 is housed in a 190 x 140 x 45mm plastic (internally shielded) enclosure. The unit hooks up to your PC via a free parallel port and the supplied one-metre cable. If you don’t have a free parallel port, you can purchase an optional USB-to-parallel port adapter designed specifically for the task. Power is provided by a 12V DC 500mA plugpack adapter. For portable use with a laptop PC, Pico Technology offers an optional 5-hour battery pack. The pack is supplied in a look-alike case and can be recharged in about 4 to 5 hours from the standard AC adapter. The “front panel” consists of just three BNC connectors and a red LED. As this is a dual-channel instrument, 16  Silicon Chip two of the BNC connectors provide the ‘A’ and ‘B’ channel inputs. The third BNC can function either as a trigger input or signal generator output. The digital signal generator produces a square wave with a selectable frequency of between 0 and 250kHz. The hardware specifications are among the best that we’ve seen for a virtual instrument. The analog bandwidth is quoted as 50MHz, with 100MS/s (million samples per second) possible in single-channel mode. In plain terms, this means that you can accurately measure frequencies to 50MHz, although in ’scope mode at this frequency, viewed waveforms will not be “true to life”. As with any digital ’scope, the incoming signals need to be sampled at between five and ten times their frequency for accurate on-screen representation. For high sampling rates to be truly effective, a large storage buffer is mandatory. Obviously, the larger the buffer, the greater the portion of a signal that can be sampled at the maximum rate. A commonly employed method of dealing with limited buffer size is to reduce the sampling rate with each increase of the timebase setting. In the ADC-212, common sense prevailed and a large 128k sample buffer memory is standard fit. In contrast with many DSOs on the market, the ADC-212 boasts 12-bit vertical resolution rather than the more common 8-bit. This pushes the dynamic range out to 80dB, with 1% basic DC accuracy. As pointed out in Pico Technology’s marketing blurb, 8-bit resolution can detect at best only 0.4% signal change. This is no problem in digital electronics work, but in audio electronics, even 0.1% noise can be a disaster. 12bit analog to digital (A-D) resolution and low front-end noise allows the ADC-212 to detect changes as small as 0.024% (244ppm). The software Pico Technology’s virtual instrument software consists of two independent packages, called PicoScope and PicoLog. If your PC runs DOS or Windows (any version), then you should be able to successfully load and run the software. Naturally, higher-performance PC hardware will result in smoother display updates, but Pico are confident that the DOS version will even run on that old 486DX2! Note, however, that the DOS version does not include all of the functionality discussed below. For custom applications, Pico have supplied drivers for DOS, Windows (16 & 32-bit) and Linux. Additional information, examples and various support files are included on the CD for C/C++, Pascal, Visual Basic, Delphi, LabVIEW, Testpoint, Agilent Vee and Excel. PicoScope PicoScope includes a digital oscilloscope, spectrum analyser and meter. All of these instruments can operate concurrently and with surprisingly little performance penalty. All functions are controlled from within a single window (see Fig.1), which can be maximised to fill the entire screen if so desired. Buttons and drop-down menus along the top toolbar (the View bar) and the bottom www.siliconchip.com.au toolbar (the Sampling bar) provide quick access to all commonly used settings. New oscilloscope, spectrum analyser, meter and X-Y oscilloscope windows (called “views”) can be opened at any time. In addition, up to four active views can be displayed in a single window (called “composite” view) in a variety of useful formats. For example, the “overlay” format renders the selected views transparent and overlays them for quick waveform comparison. Window background, grid, text, ruler and trace colours can all be customised to taste. In addition, oscilloscope and spectrum analyser traces can be programmed to one of three possible widths. Oscilloscope By default, horizontal timebase settings range from 100ns/div to 50s/ div. When ETS is enabled (see below), additional ranges of 10, 20 and 50ns/ div are available. Optionally, timebase settings can be displayed by X-axis period rather than by time per division. In this mode, timebase settings range from 100ns to 500s. For detailed signal examination, the X-axis can be magnified up to 50 times in 1-2-5 steps. This is an indispensable feature when working with complex waveforms and large buffer sizes. A horizontal scroll bar appears when the magnified signal exceeds the display limits, allowing easy panning through the sample buffer to find the areas of interest. As the timebase settings increase, it takes a proportionally longer time to fill the sample buffer and update the display. With this in mind, Pico have provided a “maximum samples” setting, allowing you to balance speed with sample size to suit measurement requirements. Designed to eliminate noise from your measurements, another useful feature called “oversampling” averages a programmable number of samples (1 to 16) before updating the display. The newest version of PicoScope (R5.08) includes a new feature www.siliconchip.com.au Fig.2: This view, borrowed from Pico’s library of waveforms, shows the output of an inductive pickup sensing the secondary side of an ignition system. Note the markings along the horizontal axis, which indicate a -50% delayed trigger. Also note the vertical axis, which has been scaled up from mV (the sensor’s output level) to read in kV. dubbed “ETS” (Equivalent Time Sampling). In ETS mode, PicoScope oversamples the incoming signal to provide a higher overall effective rate – up to 5GS/s. In common with the averaging method described above, ETS is only suitable for repetitive waveforms. Maximum ETS oversampling rate and display update speeds are programmable in the Setup menu. Vertical axis Vertical settings range from ±50mv to ±20V in nine steps. An auto-range option is included to save repeatedly reaching for the mouse when you’re probing your way through a circuit. Another useful feature allows scaling of the Y-axis to match the attenuation of the probe in use. Available ranges are x1, x10, x20 and x100, covering all probe variants that you’re likely to encounter. Now all you have to do is remember to change this setting whenever you slide the probe switch! Like the horizontal axis, the Y-axis can be magnified at will via a dropdown menu on the View bar. Up to x10 magnification is supported, and once again scroll bars provide a means of viewing the entire signal excursion should it exceed the bounds of the display. Custom ranges If you’re measuring the output of a sensor, then why not display the relevant units (°C, kilopascals, etc) on the vertical scale instead of volts? This is a must-have feature for documentation purposes, and it certainly eases the strain on the grey matter. Any custom ranges that you define are automatically added to the available vertical range settings on the View bar. Fig. 2 shows how it works. Here, PicoScope is measuring the output of an inductive pickup attached to the secondary side of an automotive ignition system. Note the vertical scale – it’s graduated in kilovolts (kV)! Triggering PicoScope includes comprehensive triggering capabilities, with most settings instantly accessible from the Sample bar. In addition to the usual triggering modes (“auto”, “repeat”, “single” and “none”), the desired trigger threshold in millivolts can be entered directly. Alternatively, the trigger threshold and polarity can be set by clicking September 2002  17 Pico ADC-212 Virtual Instrument Fig.4: The Recorder view. We’re logging the current and voltage from a (simulated) battery pack and using PicoLog’s calculated parameter function to add “Power Dissipated”. and dragging a little grey “bug” to the desired level. A useful feature of DSOs is their ability to begin storing data at some time before or after the trigger condition is met. PicoScope calls this “trigger delay”, and it’s programmable on the Sample bar as a percentage of sweep time. Easier still, you can drag the same “bug” (in a horizontal direction this time) to visually position the trigger point anywhere within the buffer. The benefits of delayed triggering are clearly visible in Fig.2. By selecting a -50% trigger point, the rising edge of the discharge pulse is positioned in the middle of the buffer, allowing examination of the entire coil charge and discharge cycle. Lastly, a “save on trigger” function is provided for trapping intermittent or random events. This function writes a copy of the sample buffer to disk every time the trigger condition is met. Each write to disk creates a separate file, reloadable later for waveform analysis and documentation. Making measurements Once you’ve got the signal “tuned in” the way you want, you can apply one or more of a whole host of measurements. The simplest measurement involves clicking and dragging horizontal and vertical cursors to the desired positions and reading off the computed voltage levels and times. For more challenging work, PicoScope includes 19 automatic measurements. These include frequency, high pulse width, low pulse width, 18  Silicon Chip Fig.5: Zoom and scroll buttons make it easy to find what you want in Graph view. duty cycle, cycle time, DC voltage, AC voltage, minimum, maximum, risetime, falltime, and voltage and time at the cursor positions. In addition, a range of statistical functions can be applied across all measurements, including average, standard deviation, minimum, maximum and pass/fail. Naturally, you can define the upper and lower limits for the pass/fail function, which includes the ability to display an alert message and save the buffer to disk when either limit it exceeded. Measurements can be made over the entire buffer or in relation to the set cursor positions. To include any of these measurements at the foot of a Scope view, you simply add them to a measurement list. Separate measurement lists can be defined for each active view, too. Exporting measurements Measurements are updated in real time, so providing a “snapshot” of each sweep. However, there is often a requirement to analyse measurements over time to discover signal trends, abnormalities, etc. Commonly, a second application, such as Excel or MathCAD, would be used for the data analysis. PicoScope provides an easy method of exporting data to other applications. Data from the active view can be copied to the clipboard and pasted into the target application. DDE (Dynamic Data Exchange) is supported too, so you can paste a link to have the data in the target application updated in real time, if so desired. Display format Analysing bunches of numbers can be a time-consuming task, especially if you have to write additional code in a spreadsheet or other application to do it. A far simpler method is to have PicoScope do the statistical work and present the results in a format that can be interpreted at a glance. This is the purpose of the “data display” settings, which include “current”, “average”, “minimum & maximum” (envelope) and “accumulate”. Let’s look at what these do. The “current” setting is the default (normal) display mode, with the trace redrawn for each cycle (sweep). “Average”, on the other hand, draws a trace that represents the average of all cycles since you hit the Go button. Then there’s “minimum & maximum” mode, which displays a shaded area representing the minimum and maximum of all cycles. Finally, “accumulate” draws a new trace for each cycle without erasing the previous one. Several combinations of these modes are supported as well. Chart recorder mode For timebase settings of 100ms/div or longer, PicoScope can emulate the classic chart recorder. Instead of rewriting the display each cycle (“standard” mode), you can switch to “chart recorder” or “block” modes. In chart recorder mode, data is www.siliconchip.com.au Fig.6: Data is easily exported to other applications via Spreadsheet view. continuously collected and displayed, with the display “rolling left” when the trace reaches the right-most extremity. Alternatively, in block mode, an entire block of data is collected before being displayed. X-Y Scope So far, we’ve only talked about the oscilloscope instrument, which plots amplitude (the Y-axis) against time (the X-axis). PicoScope also includes an X-Y oscilloscope, which instead plots the amplitude of channel A against the amplitude of channel B. This view is generally used for comparing the phase of two sine waves. Most of the measurement options mentioned above do not exist in X-Y Scope view, although the Sampling bar settings are almost identical. Of course, the channel A & B timebases are locked in X-Y mode, so only one timebase is visible. Spectrum analyser Unlike the oscilloscope, which plots waveforms in the time domain, the spectrum analyser displays information in the frequency domain. This provides a means of discovering the amount of “energy” present in a signal, up to a defined frequency limit. In spectrum view, the horizontal axis is divided into bands of frequencies, displayed in either linear or logarithmic format. The vertical axis is graduated in decibels or volts RMS, representing power. PicoScope’s spectrum analyser operates up to 50MHz, with the upper www.siliconchip.com.au limit programmable on the Sample bar. The number of frequency bands displayed across the horizontal is selectable via the main Settings menu. The default of 256 allows fast display updates, but up to 4096 points can be selected for the highest accuracy. As with all digital spectrum analysers, PicoScope employs a mathematical technique called Fast Fourier Transforms (FFTs) to convert the sampled data from the time to the frequency domain. The application of this conversion causes some distortion of the spectrum peaks, so to minimise the effects on your measurements several compensatory (or “windowing”) techniques can be applied. Selections include Rectangle, Triangle, Gaussian, Hamming, Blackman, Parzen and Hanning. Spectrum measurements Cursors operate in a similar manner to the Scope view, allowing easy measurement of frequency, amplitude and phase. It is also possible to display average and peak values of successive cycles. Like Scope views, Spectrum views support a range of automatic measurements. These include peak frequency, peak amplitude, total power, total harmonic distortion (THD), total harmonic distortion + noise (THD+N), spurious free dynamic range (SFDR), SFDR frequency, signal to noise and distortion ratio (SINAD), signal to noise ratio (SNR), intermodulation distortion (IMD), gain, and ampli- Fig.7: Instead of mental notes, make real one in Notes view. Notes views are saved along with data files, so they provide a simple means of documenting your recordings. tudes at the third, fourth, fifth and sixth harmonic. Meter PicoScope’s Meter views can display either voltage or frequency. The voltmeter display is similar to traditional 4-digit true RMS meters. You can choose between AC, DC and decibel measurement. Input ranges are identical to the ‘scope instrument, including the auto-ranging functionality. Also in common with the ‘scope is the ability to create custom ranges, allowing you to display your measurements in whatever units you desire. Exporting and printing views PicoScope provides a means of copying individual views to the clipboard for pasting into your favourite application. In addition, you can save the selected view as a Windows Bitmap (BMP), Windows Metafile (WMF) or JPEG (JPG) file. Of course, if you want an image of the entire desktop, you can copy it to the clipboard using standard Windows keystrokes. You can also print any or all views on demand. Saving your settings PicoScope allows you to save settings and data files for the selected view, or the entire desktop. Any number of individual settings files can be saved and reloaded later as needed. With a little work, you can even add buttons to the main menu bar to allow September 2002  19 Pico ADC-212 Virtual Instrument instant reloading of commonly used settings – no need to remember what you named those files! The ability to save data files is useful for documentation and analysis, and it’s great for training purposes, too. Check out Pico Technology’s library of waveforms, accessible on their web site, to see how it all works. Some of these waveforms are included in the demo version of PicoScope. If you’d like to control PicoLog remotely, you can do that too. The latest release of the software (R5.08) includes IP connectivity so that you can connect two machines running PicoLog over a network. One machine acts as a server and supplies the data. The other acts as a client, behaving exactly as if the data were available locally. Up to 10 clients can connect to one PicoLog server. PicoLog Graph A real bonus with this package is the inclusion of Pico’s data logging software, PicoLog. In short, PicoLog collects data in real time and provides a means of analysing, displaying and exporting the results. In a similar vein to PicoScope, data is displayed in a number of different “views”, specifically: Recorder, Spreadsheet, Notes, XY Graph, Graph and Player. Let’s touch briefly on the highlights of some of these views. The Graph view looks and feels a lot like a chart recorder. Buttons arranged at the top and side of the view provide quick access to all settings and controls. Display format is entirely customisable. Multiple traces can be displayed on a single graph or on separate graphs (all within the Graph view). Axis scaling and markings can be formatted to suit all tastes. Manual control over “pen” and “paper” is provided by the surrounding buttons, and there’s even a magnifying glass (zoom)! When multiple traces are displayed on one graph, PicoLog can insert markers (circles, triangles, etc) on the traces for easy identification. Two clicks save the current view to disk as a Windows Bitmap (BMP), Windows Metafile (WMF) or JPEG (JPG) file. With the “auto-save” option enabled, all settings are saved to disk when the Graph view is closed. Recorder view All other views are launched from the Recorder view, which essentially defines and controls all recording runs. Go, Stop, Pause and Rewrite buttons control recording state once a run has been defined. The sampling interval, number of samples per run (up to a million) and number of readings per sample are all individually programmable. Once a run is complete, PicoLog can be programmed to “stop”, “repeat immediately”, “repeat after delay” or “scroll”. In scroll mode, oldest samples are discarded to make room for new as the run repeats. An unlimited number of runs, complete with associated settings, can be saved to disk or previous runs reloaded at will. For multiple runs, an incrementing number is automatically appended to the specified file name. A powerful feature of PicoLog is its ability to perform calculations on measured data using inbuilt mathematical operators and functions. Expressions can contain up to five parameters and can include the results of other calculations. Each calculated parameter can have its own, programmable, units of measure and scale factor. 20  Silicon Chip Spreadsheet This view provides a convenient method of locating and exporting data. As the name implies, readings are displayed in columnar format and can be listed numerically, by “time since start”, “time of day”, or “date/time”. In addition, each row can display an aggregate of values over a specified number of samples. Readings can be aggregated to “first reading”, “average” and “maximum & minimum”. Once you’ve formatted the list and selected the area of interest, you can print it, copy it to the clipboard or just save the data to disk in tab-delimited format. As with the Graph view, all settings are retained when the “auto-save” option is enabled. Notes view A simple method of identifying and otherwise annotating recordings is provided by the Notes view. Notes you type here are displayed at the foot of printed reports as well. Player view The Player view is just like the Recorder view – but without the recording capability. This enables you to work with data from a previous recording run while another is in progress. In fact, the Player can be launched as a stand-alone program, allowing you to open data files on any PC with a minimum of additional software. Impressions PicoScope and PicoLog appear to include just about every possible option without resorting to burying anything in multilevel menu selections. The on-line help is quite helpful, too. On the hardware side, the specifications for a package at this price are very respectable. If you’ve used a DSO before, you’ll have no problems driving the ADC212 out of the box. New users will need to invest some time learning the ropes to get the most from their purchase. More information Check out the demo versions of PicoScope and PicoLog, available free from the Pico Technology web site at www.picotech.com You can also download the ADC-212 and PicoScope/PicoLog user manuals in PDF format. At time of press, the ADC-212/100 was priced at $2,284 (excluding GST). This price includes all of the above software on CD, printed installation guide, parallel cable, plugpack AC adapter and one-year warranty. The PP-123 battery pack will set you back another $350 (excluding GST). Pico Technology products are distributed in Australia by Emona Instruments, telephone (02) 9519 3933 or email testinst<at>emona.com. au They’re also on the web at www. SC emona.com.au www.siliconchip.com.au