By Eng. Mahmoud Hamdy, CEO of RAM Electronics
With my years of experience selling oscilloscopes at RAM Electronics, I've noticed that many customers often feel a bit confused about certain features when they're looking to buy a new oscilloscope.
Selecting the right oscilloscope can vary greatly from one customer to another, depending on individual needs, intended use, and budget constraints. In this article, I will focus on the key specifications of oscilloscopes to assist RAM Electronics customers in finding the ideal model for their specific applications. Always keep in mind that technological advancements are ongoing, so consider upgrading your measurement tools whenever necessary.
the technical information and graphs presented in this article were developed by our partner UNI-T's technical support team - thank you for your invaluable help!
Oscilloscopes are key instruments that visualize waveforms, supporting tasks such as circuit design, equipment testing, and various other applications. They serve as the "eyes" for electronic engineers, allowing for the quick identification of design errors, ensuring accurate test results, accelerating the development cycle, and reducing research and development costs. Below are the essential considerations for selecting the right oscilloscope.
Here are the key factors to keep in mind when purchasing a new oscilloscope:
1. BANDWIDTH
When it comes to selecting an oscilloscope, the most important aspect to consider is its bandwidth, as this determines the highest frequency signals that can be accurately measured. For instance, an oscilloscope with a bandwidth of 100MHz may not provide reliable results when testing a 100MHz sine wave, due to the 3dB (30%) attenuation that occurs at the specified bandwidth. To enhance the accuracy of amplitude measurements, it is advisable to follow the "five times rule," which recommends using an oscilloscope with at least 500MHz bandwidth for testing signals at 100MHz.
Insufficient bandwidth not only affects amplitude accuracy, but also significantly impacts edge testing. This is especially critical for digital engineers who are concerned with pulse and square wave signals. Following the "five times rule" is important since the edges of a signal contain a lot of high-frequency information, and using an oscilloscope with at least the fifth harmonic information can provide better waveform details.
2. SAMPLE RATE
The sample rate of an oscilloscope refers to the number of times it captures a sample of the input signal every second. A higher sample rate leads to improved detail and clarity in the displayed waveform, which helps to prevent missing critical information or events. When the same signal is tested at different sampling rates, the resulting waveforms on the oscilloscope will show noticeable differences.
It is logical to assume that a greater sampling rate will enhance the accuracy of signal restoration. However, if there is an unexpected signal between two samples, it might be missed, which could result in defects during the product design process. Therefore, it is vital to choose an oscilloscope with a suitable sample rate to ensure reliable testing and the identification of any irregularities.
It is advisable to use the "five times rule" when selecting the sampling rate for an oscilloscope. This rule states that the sampling rate should be no less than five times the highest frequency of the signal under test. For example, for an oscilloscope with a bandwidth of 200MHz, the sampling rate should be 1GSa/s or higher.
It's important to note that when using multiple channels simultaneously, the sampling rate will be evenly divided, which is known as interleaved mode. In this mode, the sampling rate can drop to 500MSa/s per channel when two channels are turned on, increasing the risk of missing signal details.
3. NUMBER OF CHANNEL
Oscilloscopes generally offer either 2 or 4 analog channels, and the number of channels plays a crucial role in determining how many signals can be observed simultaneously. For specific tasks, such as BUS timing tests or synchronizing multiple clock signals, having more than 2 channels may be necessary. Furthermore, multi-channel oscilloscopes can facilitate communication between channels, making research and development testing more versatile and user-friendly. However, these models can be on the pricier side, so it's important to evaluate your current and future project needs when selecting an oscilloscope.
It's important to note that when using multiple channels, some oscilloscopes may operate at a reduced sampling rate. This should be taken into account when choosing a scope.
4. Waveform Capture Rate
The rate at which an oscilloscope captures waveforms is referred to as the waveform capture rate. During the waveform acquisition process of a digital oscilloscope, a dead zone occurs. By increasing the waveform capture rate, it is possible to significantly minimize this dead time. If abnormal signals arise during the dead time between acquisitions, they may go unnoticed. Thus, it is essential to choose an oscilloscope with a higher waveform capture rate to reduce dead zones effectively.
5. Memory Depth
The memory depth of an oscilloscope represents the quantity of waveform points it can capture in a single acquisition. A greater memory depth is preferable for obtaining more comprehensive details. This depth is influenced by the sampling rate and the duration of the recording session.
To achieve a "Single Shot Acquisition" with a memory depth of 4 Mpts, you need to sample the signal at 1 GSa/s, which will allow you to store 4 ms of signal data. For an oscilloscope with a memory depth of 1 Mpts, you can store 1 ms of waveform data at the same sampling rate.
6. Triggering
An oscilloscope's trigger function plays a vital role in determining when data collection starts and how the waveform is visualized. Digital oscilloscopes provide the flexibility of both pre-trigger and post-trigger waveform options. Effective triggering guarantees a steady waveform display, which aids in swiftly identifying particular parts of a complex signal.
All oscilloscopes feature an edge trigger function, but this may not be enough when working with complex waveforms. For example, edge triggering can lead to an aliased waveform display when analyzing PRBS codes or signals with multiple edges. In such cases, it is crucial to employ advanced triggering functions to successfully complete testing tasks.
7. Automated Measurement
To enhance the efficiency of waveform analysis, oscilloscopes offer a range of automated measurement options. Utilizing these features effectively can significantly boost measurement productivity. Automated measurements enable engineers to complete testing tasks more swiftly, and they also provide more precise results compared to manual cursor measurements.
Most oscilloscopes provide basic measurement parameters like amplitude, period, frequency, and rise/fall time. UNI-T oscilloscopes, however, elevate the standard by offering a comprehensive suite of 36 measurement parameters. These include Max, Min, High, Low, Ampl, Pk-Pk, Middle, Mean, Cycmean, RMS, CycRMS, AC RMS, Period, Freq, Rise, Fall, RiseDelay, FallDelay, +Width, -Width, FRFR, FRFF, FFFR, FFFF, FRLF, FRLR, FFLR, FFLF, +Duty, -Duty, Area, CycArea, Oversht, Presht, Phase, and Pulse, effectively addressing a wide range of R&D requirements.
8. Expansion Or Upgrade
Sometimes, your current oscilloscope may not meet the requirements for testing in a new project, which might lead you to consider purchasing an additional scope for specific features. In such cases, having an oscilloscope that can be upgraded would be ideal.
9. Connectivity
Oscilloscopes can be connected to various devices, including PCs, through interfaces like LAN or USB ports, and sometimes even a VGA port for external monitor connections. Utilizing a USB connection allows engineers to conveniently store waveform data and screenshots for later analysis, which is particularly beneficial for remote operations.
10. Cost
In the end, choosing an oscilloscope that fits your budget is key! Whether you're looking for something for a short time or a long-term investment, there are plenty of options out there that won't break the bank.
Finally, choosing to buy your instruments from a trusted retailer is a wise decision. At RAM Electronics, we guarantee that all our instruments meet international standards and are from some of the most recognized brands worldwide, including UNI-T, Rigol, Hantek, OWEN, FNIRSI and more....
Explore our selection of oscilloscopes at RAM Electronics store: