CartPicoscope 3000 On Test
A new series of computerscopes in practice
By Harry Baggen (Elektor Netherlands Editorial)
Reproduced from Elektor June 2011 with the written
permission of Elektor International Media b.v.
Pico Technology have completely updated their middle–of–the–range series of USB–oscilloscopes. The new PicoScope 3000 series has quite a bit to offer, such as, for a USB–powered scope, a very high sampling frequency of 500 Msamples/s and a built–in AWG/function generator. What is it like to use such a scope in practice? We spent some time using the type 3206B.
USB oscilloscopes are forever becoming more powerful and more versatile. An electronics engineer is therefore increasingly tempted to buy a USB oscilloscope instead of a stand–alone version. The main motivation is not necessarily the potential to save some money, but more the advantages that a USB version could offer. The device has small dimensions and you have a very nice (computer) screen that is incomparable to that of an ordinary oscilloscope. In addition, a USB–scope combined with a laptop can be used for quite a while without being connected to an AC outlet and this combination has the further benefit of being completely isolated from the AC grid. And the supplied software often has a many more features which you are not likely to find on a comparable stand–alone version. But a stand–alone scope also has its advantages. The advantages of such an instrument are evident mainly at higher sampling frequencies, because the entire hardware of the instrument can be tuned to obtain the necessary operating speed. With a USB version you are stuck with the limitations of the data transfer between ‘scope and PC. This could be mitigated, for example, by adding more very fast memory to the scope hardware. This solution however, has the drawback that the hardware becomes increasingly more elaborate, with the consequence that the price advantage becomes smaller. But as already noted, a USB scope still has a few trumps in hand!
The new 3000 series from Pico
Pico Technology is a UK manufacturer who have specialised in the design and production of USB measuring instruments. They now have more than 20 years experience in that! Their range of USB oscilloscopes is very broad, starting with entry level models for about 125 pounds up to very fast models costing more than 13,000 pounds.
The popular medium range 3000 series has recently been completely updated. This range comprises six 2–channel models with prices ranging from about 500 to 1100 pounds. The entire series has a maximum sampling rate of 500 Msamples/s, and according to Pico — these are the most powerful USB–powered USB scopes available at the moment. The input bandwidth increases in steps and price from 60 to 100 and 200 MHz. In addition there are A– and B–versions, which have a different signal generator built in. The A versions have a function generator which can generate a number of fixed waveforms, while the B version has an AWG (Arbitrary Waveform Generator) which allows the user to make his own waveforms. They all have a built–in buffer memory, which, depending on the model, ranges from 4 to 128 Msamples. Pico sent us the most expensive model from this series, the 3206B, which we used for a few days. This is our report.
Hardware
Figure 1. The inner workings of the new 3000 series from Pico. Note the shielded input sections.
For starters, we could of course not resist the temptation to open the enclosure of the Picoscope, so that we could inspect the hardware it contains. Figure 1 shows the opened enclosure, where the nicely screened input sections stand out. The heart of the scope consists of a powerful Spartan–6 FPGA from Xilinx, which takes care of the digital processing of the measuring signals as well as producing the signals for the signal generator. To this is connected a fast DD3 memory chip for storing the data samples.
The two input channels are digitised using an unsigned A/D converter we understand was codesigned by Pico. The signal generator data created by the FPGA is converted into an analogue value by an AD9706, a 12–bit DAC from Analog Devices with 175 Msamples/s. Finally, a USB transceiver made by Cypress (CY7C68013A) takes care of the communications with the PC.
Software
Pico supply all their USB scopes with the same software, which has no limitations when it comes to features. The only limitations are those of the options and specifications of the connected hardware. The standard application is the oscilloscope screen, which shows the signals in a certain colour on a white background. There is a special ‘persistence’ mode, which imitates the afterglow of a classic CRT oscilloscope screen (on a black background). The trigger options are very extensive. With the aid of a few buttons you can walk through the buffer memory in blocks and call up interesting signals. There is also an ‘XY’ mode. In addition there is an FFT analyser, which shows a continuous frequency analysis of the input signal. This allows from a choice of different types of sampling windows (Hamming, Blackman, etc.).
Furthermore, the software has the option of displaying and analysing different types of serial data such as I²C, RS232/UART, SPI and CAN bus. This shows both the original measured signal as well as the decoded data on the screen at the same time. Using the generator button you can summon the menu for the built–in signal generator, where you can select the desired waveform and output voltage. With the B models from the 3000 series you also have the option of creating waveforms yourself using a graphical window (just draw the wave shape using the mouse) or from a CSV file.
In addition there are many more features and options, too many to discuss in detail, such as the option of making special scope profiles, the ability to make masks for, among other things, tolerance measurements in production processes, the various types of measurements that can be made on the displayed signals and carrying out mathematical functions.
Figure 3. The contents of the buffer memory is easily observed thanks to the division in blocks which are shown as postage stamps in the overview.
Figure 2. Here different windows of the main program have been opened.
In practice
The PicoScope 3206B is supplied with two probes in a storage pouch, a USB cable, an installation CD and a Quick Start Guide. The inconspicuous plastic enclosure has four BNC sockets on the front and one USB connector on the back. The installation of the software from the CD is done in five minutes, this went without any problems. After this the scope can be connected to the PC with the supplied cable and we can get started.
The first impression after starting the program is that of a plain appearance, all operating elements are accommodated in a few bars above and below the scope screen. The large screen format is immediately obvious, compared to our standard scopes in the lab! You really should start by reading the Help menu which explains the operation and features in detail, but as an electronics engineer you would much prefer to start experimenting immediately. That means connecting a probe and then clicking the handy Auto Setup button. The software will then try to find the correct settings (for, amongst others, X, Y and triggering) to give a steady image and a easily recognisable waveform. In most cases this button appears to work well, you can then fine-tune some of the settings yourself. The screen reacts pleasantly quick to signal changes and this gives you the feeling that you’re measuring in ‘realtime’. With a resolution of eight bits and a large screen you would expect the displayed waveform to look quite course, but thanks to mathematical averaging (adjustable from 8 to 12 bits) it appears much more detailed.
The design of the operating interface does require some familiarity, because its structure is completely different compared to a normal scope. But after working a few days with this software it all becomes much more fluent. Pico have not tried to emulate the operating interface of a conventional scope and this is perhaps a good thing, otherwise it would have become a mixture of a few scope buttons next to a few menus for the special functions. Now you are obliged to think differently. The menus have been kept minimalistic, where only the most important functions are accessible with a single mouse click. All other things are hidden deeper into the menu structure, but most of it is fairly obvious. You can easily switch between one and two input channels or adding a new window with another signal or waveform analysis. The advanced trigger functions are very extensive and clearly documented. All the trigger options appear in a separate menu with a brief explanation and a small picture. It is easy to step through the buffer memory, which is displayed as a few screens in postage stamp format in a separate window, after which the desired data can be displayed in a large format.
Figure 4. In the window for the Arbitrary Waveform Generator
an unusual signal can be generated quickly.
The built-in AWG/function generator of the 3000 series makes it possible to test circuits without the need for a separate generator. The frequency range is more than enough for most applications (1 MHz). The AWG in the model we tested has the additional option of designing different waveforms graphically in a kind of mini editor. In this way it only took me five minutes to make a sine–burst signal, which is very suitable to judge the delay response and ringing of audio filters and loudspeakers. Although this is a very complex signal for getting a scope to trigger on consistently (without having the sine waves ‘jumping around’ all the time) I was quickly able to find an advanced trigger setting that worked perfectly.
Thanks to the high sample frequency of the new 3000 series (500 Msamples/s for one channel, 250 for two channels) it is possible, even at higher signal frequencies, to see the exact shape of the signal edges and look for any tendencies of oscillation or ringing. Especially in combination with the large buffer memory this gives many options for signal analysis. The maximum sample- rate for continuous (repetitive) signals (this is 10 Gsamples/s for the 3206A/B) is something we haven’t tried, but it can be useful in some situations.
Excellent combination
The new 3000 series from Pico offers an excellent combination of a USB scope with a reasonably large sample frequency and a function generator/AWG with a useful frequency range. Starting from 399 pounds (excl. VAT) you have a 3204A with built–in function generator and 60 MHz input bandwidth. That gives you a fully–fledged scope with many features and a large screen (the computer monitor), which does not need its own power supply and is therefore very suitable in combination with a laptop.
Depending on your requirements for bandwidth, AWG and buffer memory size you can choose a more expensive version. The 3206B that we tested is very satisfactory in daily use. It is so good that it is difficult to return to using a conventional oscilloscope. With this 3000 series, Pico have made a versatile series of measuring instruments with state–of–the–art components, excellent performance and a great price/performance ratio.
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