I always enjoy reviewing about new products from Pico Technology. Since its inception in 1991, Pico Tech has built up an interesting portfolio of cost-effective oscilloscope wares and dataloggers, spectrum analyzers, and the like.
When you consider the very reasonable price tags on these latest probe scopes, you may just want to buy a few and sprinkle them across your benches.
The $219 single-channel 10-MHz-bandwidth PicoScope 2104 and its $348 25-MHz counterpart PicoScope 2105 comprise PC-hosted virtual oscilloscopes. They're compatible with PCs equipped with 480-Mbit/s USB 2.0 (Universal Serial Bus) ports.
However, don't lament if you're running an earlier PC. The scopes are useful with slower USB 1.1 systems, too.
Spec-wise, each probe/scope has a 1-Mohm input impedance, and input voltage ranges can be set from your PC on ranges between ±100-mV and ±20-V. Signals can be either AC-coupled or DC-coupled. The timebases can be set from 20-ns/div to as slow as 50-s/div for the PicoScope 2104 and from 10-ns/div to 50-s/div for the PicoScope 2105.
Plug-And-Play Handhelds
Thanks to USB's plug-and-play, and its ability to deliver power to plugged-in peripherals, these handheld scopes require no outboard power supplies.
The PicoScopes are also ergonomically designed. So, whether you're left-handed or right-handed, or whether you're ham-fisted or have the fingers of a surgeon, the PicoScope handhelds are comfortable to hold and elegantly simple. Pico Technology even includes a light beam that illuminates the tip of the probe.
Indeed, single-handed operation is the rule. A button on top of the probe puts you in the driver's seat. When you press the button to start the oscilloscope, the button itself flashes green to indicate the instrument is running. Once a signal is captured, you press the button again, and the button glows red to indicate the scope has stopped.
If you hold down the button continuously, you can activate the PicoScope's auto-setup function. This automatically sets up timebase and trigger configurations to best display the signal the PicoScope finds on its input.
The firm's press release (on the left) mentions the PicoScope software that lets you operate these instruments as an oscilloscope; not mentioned is that you can also use these probes as spectrum analyzers. And, as mentioned in Pico Tech's release, you can use the company's PicoLog software to run them as dataloggers.
As dataloggers, a PicoScope can collect up to one million samples, handling realtime data collection, analysis, and display. Programmable alarm limits can be set and your data can be exported to spreadsheets and databases. Waveforms can also be saved, printed, faxed, or e-mailed from your PC.
Multiple Probes
It's also possible, using either PicoLog or your own coding, to collect data from as many as four PicoScopes. The only constraint is that each scope must be connected to a separate USB port, and if a USB hub is used, it must be a powered hub.
Pico Technology also supplies two example programs written in C. One is a GUI (graphical user interface) application. The other is a console mode program that demonstrates all of the facilities of the system's driver. The GUI example is a generic Windows application, so it doesn't use Borland AppExpert or Microsoft AppWizard.
You can also program your own interfaces using popular languages such as VisualBASIC, Delphi, Excel, Agilent VEE, or National Instruments LabVIEW.
Normalized Readings
In use, the PicoScope hardware provides 8-bit vertical resolution, but the system's driver normalizes all readings to 16 bits. This enables the system to take advantage of noise reduction from over-sampling (when enabled).
The driver is supplied in the form of 32-bit Windows DLLs. The driver is used by the PicoScope and PicoLog software, mentioned in the press statement, to control the scopes.
In use, your host PC must run a Pentium-class processor (or equivalent) and have at least 32-Mbytes of RAM. You'll also need a spare 10-megs of hard disk space.
Also, your PC must run Microsoft Windows 98SE, Windows ME, Windows 2000, or Windows XP. Once you install a PicoScope's software, Windows automatically installs the drivers when a PicoScope is plugged in for the first time.
Signal Buffering
Complementing their 100-Msample/s realtime sampling rates (boostable to 2-Gsamples/s using digital equivalent time sampling) these scopes use a 24,000-sample buffer memory.
When using equivalent time sampling, a PicoScope collects data over a number of cycles of a repetitive waveform to give a higher effective sampling rate than what's possible for a single cycle. Equivalent time sampling permits the scope to use faster time-bases than those available in realtime mode.
The first figure shown below indicates a 25-MHz sinewave captured using a realtime sampling rate of 100-Msamples/s. The second figure shows the same 25-MHz sinewave sampled using digital equivalent time sampling.
You can see that the realtime sampling gives a wave shape that’s very distorted. The equivalent time sampling trace, however, gives a much more accurate representation of the input signal. On repetitive waveforms, a Pico oscilloscope with equivalent-time sampling can provide the same accuracy as higher-cost oscilloscopes that have higher real-time sampling rates.
Sampling Modes
A PicoScope can also run in one of several sampling modes. At high sampling rates, the scope collects data faster than a PC can read it. To compensate, the oscilloscope stores a block of data in an internal buffer, delaying transfer to your PC until a pre-set number of data points has been sampled. This is called Block Mode.
Block Mode is the best mode to use when the input signal being sampled contains high frequencies. As Mister Nyquist would explain, to avoid aliasing, the sampling rate must be greater than twice the maximum frequency in the input signal. In any case, a PicoScope can sample at a number of rates, which correspond to the maximum sampling frequency divided by 1, 2, 4, 8, etc.
When the scope is operating in Block Mode at speeds less than maximum, it's possible to oversample (taking more than one measurement during a time interval) and return an average. Doing this reduces the effects of noise and increases effective vertical resolution.
Data can be sampled with a period between 1-ms and 60-seconds, and data is transferred by to your PC in either a Normal or Windowed mode. In Normal mode any data collected since the last data transfer operation is returned in its entirety. This is useful if your PC's software requires fresh data on every transfer.
In Windowed Mode, a fixed number of samples are returned, even if the oldest samples have been returned before. Windowed Mode is useful when the program requires data from a constant time interval.
At very low sampling rates, you can switch to Streaming Mode. In Streaming Mode you can get accurately timed data to be transferred back to the PC without gaps. A realtime Continuous Mode is also provided for use at low sampling rates. This continuous mode supports capture of data from multiple converters.
In terms of triggering, the scope's can either start collecting data immediately, or be programmed to wait for a trigger event. A trigger occurs when a signal at the probe's input crosses a threshold voltage on either a rising edge or a falling edge.
Click here for a user guide (in Adobe Acrobat .PDF format).
For more details contact Pico Technology Ltd., Mill House, Cambridge St., St Neots PE19 1QB, England. Phone: +44 (0)1480 396 395. Fax: +44 (0)1480 396 296
Pico Technology, +44 (0)1480 396 395, www.picotech.com
