Cover story
Figure 3: Left: very small signal deviation; Right: resolved vertically / horizontally and measured with the cursor
this value is over 8 bits across the entire bandwidth. This means that the ENOB value becomes important for high bandwidth and high resolution measurements. As described earlier, the higher vertical resolution can be
used to measure signals with a high dynamic range, which can occur in power measurements. However, it should be noted that the optimal use of the higher resolution is given when the signal can be displayed over the full screen. This means that when measuring, say, current and voltage using channels 1 and 2, it is recommended to use the full screen. However, due to the different colour representation of the traces, these curves are still easy to recognise; see Figure 2. In the power range, even the smallest mains fluctuations
at the AC input can have a negative impact on various functions. To be able to fully guarantee the devices’ functions, it is important to know how well the electronics in it deal with these fluctuations, which can result in voltage dips, noise or harmonics. An oscilloscope can acquire signals in these areas using a high-voltage differential probe and current clamp. The voltage and current curves are then measured with the oscilloscope. The accuracy and noise behaviour of the probes used must also be considered. While the measurement of the maximum/minimum values of the large signal components is very similar for 8-bit and 12-bit, the advantage of a 12-bit oscilloscope lies in the measurement of the small signal deviations that would not be visible in an 8-bit oscilloscope. Here the vertical setting can be refined so that very small signal components can be displayed with good resolution. These can now also be analysed and measured precisely; see Figure 3. With an 8-bit structure, the theoretical resolution due to the 256 levels with a vertical display representation of 8V (1V/DIV) is 31.25mV. On a 12-bit oscilloscope, the steps are 4096, which corresponds to a resolution of 1.95mV with the same vertical setting. This means that noise components and other deviations that can’t be seen in the step sections on an 8-bit oscilloscope can now be measured. As with the 8-bit oscilloscope, a mode (high-res) is
integrated in the RIGOL DHO series, which can be set to 14 or 16 bits, displaying the signals even more finely. This averaging technology is therefore in an even finer range than the 12-bit resolution (high-res) of the 8-bit oscilloscopes.
The optionally available power analysis function can also be used for general measurement of the AC input of a switched-mode power supply. Here values for current and voltages for e.g. active power, apparent and reactive power or the crest factor can be measured. With the math function it is also possible to show the performance in a curve. At the output of a switched-mode power supply, the power analysis can be used to analyse the output ripple in order to measure the signal quality. In signal analysis, and especially in error analysis,
it makes a lot of sense not only to concentrate on time analysis, but also to use frequency analysis. Here, for example, undesired non-linearities or harmonics can be represented well. Due to the improved interference-free dynamic range of the 12-bit oscilloscope, it is also possible to carry out the frequency analysis with a higher dynamic range. This means that in the frequency analysis, both the noise behaviour and the internally-generated interference amplitudes are below those of the 8-bit oscilloscope. Also, the FFT can convert up to one million samples into the frequency spectrum and thus achieve a very high frequency resolution. As with a spectrum analyzer, the spectrum can be set using start-stop frequencies or using centre/span. When the oscilloscope is set to 50Ω, the vertical unit can also represent (dBm) logarithmic representation with the reference “m” for “mWatt”. The oscilloscope also offers further measurements with
the new “UltraAcquire” function, where the memory is divided into different segments, each filled with different trigger events. This enables a very high waveform capture rate of 1.5Mwfms/s. The acquired signals can then be displayed in different ways (e.g., as a waterfall or 3D). Signals that change very quickly, which are otherwise difficult to detect due to the long blind time, can thus be better analysed. With the DHO1000 and DHO4000 series, RIGOL is
expanding its already extensive product portfolio for further applications. In addition to simple operation via touchscreen, keyboard or web control, the oscilloscopes enable versatile use in different areas such as research and development, education or other industrial applications that require a very high horizontal or vertical resolution.
www.rigol.eu
www.electronicsworld.co.uk February 2023 09
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