Oscilloscopes

About Oscilloscopes

What is an oscilloscope?

Oscilloscopes are electronic measuring devices that display several electrical voltages simultaneously on one screen. The main focus of the measurements is usually the temporal course and the temporal changes of the voltage curves. For this purpose, the voltage time series, also known as the progress graph, is displayed in a two-dimensional coordinate system with horizontal X-axis (time axis) and vertical Y-axis (voltage axis). The image shown on a small screen is the oscillogram .  While the conventional analogueue oscilloscopes were made of cathode ray tubes similar to the television picture tubes, their digital successors now use LC displays.

Depending on where the oscilloscope is used, hand or table oscilloscopes as well as oscilloscope attachments are recommended. Although the technology in the oscilloscopes is becoming increasingly compact and the devices are thus becoming smaller and smaller, conventional table oscilloscopes do not fall below a certain size. This is due to the size of the display and keyboard, which allows the user to see the history graphs more accurately and thus also to improve the troubleshooting. 

What types of oscilloscopes are available?

A distinction is made primarily between analogueue and digital oscilloscopes. Both visualize the voltage signal as well as the frequency, phase shifts, through characteristics or pulse diagrams.

As a storage oscilloscope, you can also make data available after measurement, store it on a storage medium or transfer it to a PC. The disadvantage is the more complicated operation compared to analogueue devices as well as the danger of a distorted representation by the alias effect. Higher frequencies are incorrectly interpreted as lower frequencies. However, DSOs are energy efficient with LCD technology and fast processors. In addition, they display the measured data much more precisely. Modern, digital oscilloscopes also provide extensive functions for signal analysis. Thereby, their view can be easily enlarged or scrolled.

What do you need to look for when buying an oscilloscope?

Before you buy an oscilloscope, you should ask yourself what you want to measure and whether you need it stationary at the workplace or while traveling. Particular attention must be paid to the sampling rate, the number of available channels, the bandwidth, the measuring accuracy and the memory depth. Below we will look at these and other factors in more detail.

Analogue or digital?

Digital oscilloscopes are ideal for high-frequency signals. With them, extensive frequencies, functions and signals can be recorded, stored and analyzed effectively. In addition, they have a greater range of functions and allow the parallel display of several signals. Analogueue oscilloscopes, on the other hand, store the image on the tube instead of the signal.

Bandwidth

The bandwidth determines the maximum frequency of all components of an analogue or digital signal that can be detected by the device. It is selected according to the desired application. To measure analogue signals, the bandwidth should be at least three times as high as the maximum frequency of the current signal, and at least five times as high for digital signals. Therefore, if the highest clock frequency is 100 MHz, the oscilloscope should be able to measure at least 500 MHz. In particular, high-frequency signals require a high bandwidth to be able to reliably measure and prevent distorted signals.

The input channels

Oscilloscopes have up to four input signal channels that can be used to display and compare up to four measurements simultaneously. The flexibility and accuracy of the channels is decisive. You can choose between analogueue and digital inputs. Specially insulated inputs also help to avoid short circuits when measuring power supplies.

The sampling rate

The sampling rate determines the resolution and the accuracy of the measurement. It determines how many details of the lines and waveforms consisting of individual sample points are recorded and stored by the oscilloscope. The higher the sampling rate of the oscilloscope, the more points the wave has and the more accurate and finer the graph is. We recommend that you select the sampling rate at least five times as high as the input frequency. For example, a bandwidth of one GHz would require a sampling rate of five gigamples.

The memory depth

The memory depth of the oscilloscope defines the memory volume for recording the signals. It specifies the number of points that can be saved for a complete signal recording. The higher the memory depth, the greater the amount and duration of signal recording. The memory depth is directly related to the sampling rate. In order to guarantee a high sampling rate during long periods of time, a memory that is as low as possible is required. The required memory depth is determined by multiplying the time to be recorded by the sampling rate.

Curve navigation and zoom

The screen section can be scaled horizontally and vertically using curve navigation. With it you can move along the saved graph and select the desired section. Zoom is essential for accurate analysis – especially at large storage depths and extensive waveforms.

Auto-measurement functions:

Automatic measurement functions are used for convenient graph analysis. Depending on your requirements, corresponding functions such as amplitude measurements, time measurements, rise times or period duration are available.

The probes

The probe takes the desired values from the object to be measured and forwards them as a signal. In this way, voltage for the oscilloscope can be viewed and evaluated. You can choose between active and passive probes. Passive probes are not only inexpensive and robust, but also have the appropriate impedance and a low influence on the measurement result. However, this only applies to the low frequency range. If the measuring point is not sufficiently low-resistance and a probe capacity of 10 to 20 pF is not permitted, an active probe is required.

The triggering

In order to obtain a static image for periodic signals, the recording must be stopped before each run until the signal to be measured reaches a defined state. This state is called "trigger". Most oscilloscopes have automated trigger mode. The device recognizes the recurring, defined state of the signal itself and can control the beam run accordingly. Triggers can also be used to start signal acquisition at a predefined time.
In addition to hardware and software triggers, there are also special forms such as “Visual Triggering”. Self-defined blocking and passage ranges can be placed above the graph. The trigger only starts when the signal interacts with the defined areas.

High-quality devices also provide practical features such as trigger delays or a second time base and setting options for complex trigger patterns. Short dead times between the trigger pulses are also useful to use a mode for multiple acquisitions and thus not to miss an event.  

Connectivity

Connectivity requirements vary depending on the scope of use. The higher the quality of the device, the more connections it has for evaluation, data transfer and storage. Among other things, there are the following options:

• Data transfer for MS Excel or Word for evaluation
• Printer connection
• GPIB
• Graphics card connector for connecting to an external monitor
• LabVIEW for detailed analysis
• Programming interface
• Memory card slot
• USB port

FAQ on oscilloscope

What does ISO calibration mean?

Since 1987, QA systems have been certified by industrial companies and now also by service companies, banks, insurance companies, retailers and hospitals. In addition, there are other industry-specific laws, standards and guidelines in the pharmaceutical industry (CFR,GMP), in the food sector (HACCP) and in the automotive sector (VDA, QS9000, ISO TS 16949). For all guidelines and standards, the introduction and maintenance of a test equipment management including calibration is an indispensable element.

Conclusion: How to buy the right oscilloscope

Before purchasing an oscilloscope, you must know what purpose the device is to be used for. Accordingly, you first select between an analogueue and digital device and then determine the necessary features. You can also partially filter our products on these:

• Bandwidth (at least three times the maximum frequency)
• Number and quality of input channels (for example, for graphic menu navigation)
• Scanning rate
• Memory depth (important for the extent and duration of signal recording)
• Curve navigation
• Zoom
• Triggering
• Connectivity
• Display