Frequently Asked Questions about software for oscilloscopes
Frequently Asked Questions about hardware for oscilloscopes
Frequently Asked Questions about using oscilloscopes
The Scopix is equipped with sophisticated triggering functions. It is possible to trigger signal capture according to a pulse width.
In this way, if you want to capture your signal when a pulse with a defined width is detected, you have to use the "Pulse" triggering mode so that you can set the required pulse width and trigger your signal correctly.
The Scopix is equipped with sophisticated triggering functions. It is thus possible to perform triggering according to the count of the number of events in order to achieve triggering on a specific edge.
When the count reaches the maximum defined, triggering will occur on the next edge.
The ".trc" trace files in the Scope or Meter mode are designed either to be re-opened in the oscilloscope via the "recall" function available in the "Memory" / "Trace" function, or to display the trace in Sx-Metro. To do this, select "File Manager" / "Open" and then select the ".trc" file to be opened.
These files can also be exported into Excel from Sx-Metro.
The ".rec" recording files in Recorder mode can be recalled by the oscilloscope for display later on or opened in Sx-Metro, just like the trace files. It is also possible to export them into Excel using Sx-Metro.
The ".txt" text files are designed to be imported directly into Excel. The import method is described in the explanatory datasheet on "Data processing on computer". They cannot be used in Sx-Metro.
The ".cfg" configuration files contain the oscilloscope configuration data: the oscilloscope's mode (Scope/Meter/Recorder/Analyser) and the various data for each channel: sensitivities, coupling, bandwidth limitation. These data are intended to be opened in Sx-Metro or used to restore a configuration in the oscilloscope.
The ".fct" mathematical function files contain a recorded mathematical function. These files can only be opened with the oscilloscope in the Math menu.
There are various file formats for screenshots.
The .prn, .pcl and .eps files are print files, which means they contain binary data formatted to be transmitted to a printer. This file format is for network printers.
The .gif and .bmp files are image files which can be imported onto your computer for display or for incorporation in a document. They are also used with Virtual Printer to enable networked printing via a computer.
The Scopix has two display modes which allow you to display the signal variations over time. The first is "envelope" mode. This mode displays the minimum and on the Y axis of each sample of the signal.
The second is the "total mode". It operates similarly to the envelope mode, but it stores the different acquisitions and displays the most recent in a brighter colour to distinguish them.
These two display modes allow effective analysis of signals that vary over time.
"Envelope" display with AM modulation
"Total" display with FM modulation
By adjusting the vertical scale manually, you can obtain a trace as required with the amplitude that you want. In the menu bar at the top of the screen, the vertical scale setting can be found in "Vert / chx / Sensitivity-Coupling" in Scope/Recorder/Analyser modes or "Vert / chx /Vertical scale" in Meter mode (where x represents the number of the channel to be modified).
It is also possible to adjust the amplitude using the buttons.
You can also adjust the horizontal sensitivity by double-clicking on channel CH1 and then indicating the required sensitivity.
By expanding the on-screen traces horizontally; you can observe any phenomena occurring over small time variations, without having to totally recalibrate the oscilloscope.horizontal zoom.
To enlarge the traces/harmonics on the screen, simply press the ZOOM ON/OFF button.
Another effective way of zooming on a part of the screen is to use the "touch zoom". This is possible by tracing the part to which the zoom must be applied.
The finger shapes the part to be zoomed. To do this, slide your finger as shown below to obtain a zoomed image:
The choice of the measurement range depends on several parameters. That is why you need to adjust the vertical scale of:
• the measurement type selected:
• the Probix probe connected to the input,
• the parameters in the "Vertical Scale" menu (if the parameters have been modified since connection of the Probix probe).
In the menu bar at the top of the screen, use the menu Vert / ch x (x = 1/2/3/4) / Sensitivity- Coupling to display the adjustment window. Then enter the required values in Range, while keeping the Autorange active.
In the ranges, it is also possible to add filters. Two are available: one 625 Hz filter and one 5 kHz filter (if the 625 Hz filter is activated, the 5 kHz filter is activated too).
These filters are used to remove the disturbances from the high frequencies of the signal to obtain a signal without too much disturbance to provide accurate measurements which are easy to understand.
To demonstrate how useful and powerful these filters can be, we injected a frequency-modulated signal on the inputs of a Scopix oscilloscope, initially in Scope mode:
a 90 Hz / 10 Vpp signal and a 5kHz / 10 Vpp signal which combine to give a modulated signal:
Once we have observed the signal in Scope mode, we must switch to Meter mode so that the instrument indicates the RMS voltage which it has measured. With a 10 Vpp signal, an RMS value of 3.53 V should be obtained, but the Meter mode measures an RMS value of 3.97 V because of the 5 kHz disturbance signal.
To solve this problem, we can activate the 625 Hz filter which also activates the 5 kHz signal. The RMS value of the signal voltage measured is then 3.59 V.
The filters have thus eliminated the disturbance signal. The filters are particularly useful in cases like this. The higher the carrier frequency, the greater the efficiency of the filtering. For example, for a carrier frequency of 115 kHz, we obtain an RMS voltage value of 3.57 V.
Another possible application for showing the effectiveness of the filters is an application involving a PWM variable speed drive. A test with a pulse-width modulator was therefore performed:
When we are using pulse-width modulation, the RMS value of the voltage as measured by the Meter mode is incorrect if the filters are not active. Indeed, the frequency measurement is not correct, causing an error on the RMS voltage value.
This phenomenon is due to the Meter mode which is not capable of following the frequency value proposed because it is drawn alternately towards 10 kHz and 20/60 Hz.
To solve this problem, we must activate the Meter mode's 625 Hz filter which automatically activates the 5 kHz filter. The PWM is then transformed into a sinusoidal with a single frequency, making it possible to perform the measurement.
The frequency value measured is then correct with the filter. We can conclude from this that the RMS value of the voltage is accurate because the voltage depends on the frequency in a PWM variable speed drive. However, this voltage value is still not optimized. For greater accuracy, we need to use a Probix HX0093 probe.
The Probix HX0093 has a built-in analogue filter which provides additional filtering in order to obtain the best possible result.
In Scope mode, as it is connected to the PWM variable speed drive without an internal Scopix filter, we obtain a sine wave directly thanks to the Probix filter:
Now that we are in Meter mode with all the possible filters, we obtain a precise frequency value, so the RMS voltage value is more accurate than before.
Frequently Asked Questions
Yes, the various options can be downloaded at any time. These options include:
FFT stands for Fast Fourier Transform. When this parameter is activated, the representation is frequency-based instead of time-based. In other words, the variable is no longer time, but frequency.
For example, measurement of an oscillator's distortion level or detection of a noise (audio) caused by a specific gear on a rotating machine. In both of these cases, the aim is to detect a sinusoidal signal with a lower amplitude than a dominant component. The best way of searching for this low-amplitude component is to use the frequency-based representation because it separates each component. This makes it easy to identify them, unlike the time-based representation in which they are mixed together.
For example, let us take the addition of two sine waves, one with an amplitude of 5 V at a frequency of 125 Hz, and the other with an amplitude of 0.5 V at 2,250 Hz.
The Math2 signal, in green, shows this representation. To determine the component at 2,250 Hz, the time-based representation is not very practical because of its amplitude.
If we change to frequency-based representation, the two components are separated. They are then simple to determine.
If we return to the previous example, we have a 5 V component and a 0.05 V component, giving a ratio of 100 between the two. If we display the FFT of this signal ion a linear scale, several choices are available: either the 250 Hz component is nearly impossible to see or the amplitude of the main component is truncated, unless the graphic is large enough to display both correctly.
If we use a logarithmic scale, it will compress the high-amplitude component and dilate the low-amplitude component, thus enabling them to be shown on the same graphic while allowing measurements. The logarithmic scale has its own unit: the Bel, more commonly used in its "tenth" form, the decibel (dB).
Db ratio = 20*log(voltage).
Linear scale: the component at 2,250 Hz cannot be seen.
Logarithmic scale: the two components are easily identifiable and measurable.
For a voltage ratio of 100, there are 40dB more, as shown on the FFT graphic opposite.
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