Hi, I hope you are having an awesome time. If you have read my other posts on this topic, you have seen, I am talking too much about the importance of a quality oscilloscope in your lab. I am not going to do the same here, I am just giving you a straight forward oscilloscope buying guide.
This post will be full of technical stuff, so keep this in mind before jumping into it. I am talking about the parameters that make a scope great, and that you should understand the importance of these parameters in buying your own cool scope.
What is an Oscilloscope?
An oscilloscope is the most fundamental instrument of every electronics engineer or hobbyist’s lab. Its best use is when it comes to time-varying signals, and a multimeter or all other measuring instrument seems to fail.
It gives you a two-dimensional graph of a function (measuring signal) with respect to time, so you can clearly measure the signal frequency, amplitude, shape, rise time, distortion, time intervals, and few other parameters.
There exist two main types of oscilloscopes, the digital and analog. There was a time for analog oscilloscopes. I do not know, maybe some people are still using it. My first oscilloscope was analog too, and the first time I introduced it was during my university first year. But the powerful analog to digital converters has changed everything.
Usage of an oscilloscope
- It gives you the power to see what’s going on with the signals in a circuit.
- If you are wondering how your sounds waves look like in the telephone line, which is a very crazy idea, an oscilloscope is there to make your wish a reality.
- The journey of an oscilloscope and electronics hobbyist starts at the very beginning. The first simple circuit he can design might be a passive low pass filter. Oscilloscope helps him to see the real-time frequency response of the filter, to analyze and verify the cutoff frequency for the designed filter.
- Sometimes, a design circuit for some unknown reasons fails. We turn it on, it works fine but a sudden it fails. To analyze this problem, to know what amplitude of impulse signals that are causing the circuit to fail, we need an oscilloscope.
- Pulse Width Modulated (PWM) signal can only be studied well if you can see it by eye. You can play around with duty cycles and amplitudes in a fun way if you can see it, in my opinion.
There are a lot of things to discover about this awesome instrument, the oscilloscope.
Parameters to look for in an oscilloscope
An electronic instrument is defined as good or bad based on some parameter judgments. A multimeter is good if it has high impedance and it is bad if it has bad safety measures. The same goes for an oscilloscope.
The following are the parameters that I think you should understand before you can judge any oscilloscope as good or bad. These parameters are not limited to just beginner oscilloscopes, you can apply it to any oscilloscope.
Bandwidth is the most important parameter of all. It limits the ability of the scope to measure a signal. It shows the frequency range that the oscilloscope can accurately measure.
According to IEEE 1057, bandwidth is defined as “the point at which the amplitude of a sine wave input is reduced by 3 dB (approximately 30%) relative to its level at a lower reference frequency.”
In other words, bandwidth is specified at the frequency at which a sinusoidal input signal is attenuated to 70.7% of the signal’s true amplitude.
An oscilloscope is made of complex circuitry. The important part of the circuitry is the front end amplifiers, which work at a certain band of frequencies and define the bandwidth of an oscilloscope.
If someone needs a high bandwidth he needs a sophisticated front-end circuitry, which makes the whole oscilloscope very expensive.
In summary, the more is the bandwidth, the more powerful the oscilloscope is, and the most expensive as well. But a rule of thumb for selecting a good bandwidth is to have the bandwidth 5 times greater than the fundamental frequency of your measuring signal.
A very good point for beginners. If you have high bandwidth and you are playing with a low-frequency signal, you do not get accurate results. You get a lot of noise instead of great results. Sounds crazy! I know.
So, basically, I keep all these things in mind and try my knowledge best to make the list of oscilloscopes having decent bandwidth, shared in my other post the link is given at the end of this post.
2. Sample Rate
The sample rate is the ability of an oscilloscope to how fast it can acquire the number of samples per second, or in simple words, it determines the amount of waveform information captured and displayed on the screen.
The greater the sample rate, the more resolution it has, and in the result, you have every detail of your signal on display.
The above equation is the Niquest criteria for sample rate. Oscilloscopes must obey this in order to be called a good or the best beginner oscilloscopes.
This is an industrial adopted rule of thumb. But some industry people also recommend a sample rate that is 3 to 5 times the bandwidth.
The reason they provide is, you need a high sample rate to see any unexpected glitches or anomalies. In summary, the more samples you have in each period, the more signal detail you’ll capture.
Let’s see what Keysight Labs have got for us about the sample rate and bandwidth.
A good point for the beginner, without proper bandwidth, you will end in an attenuated or distorted signal. While without enough sample rate you will end in having no information that is very necessary to display the exact frequency, rise and fall times of your signal. You can also miss any glitch or anomaly occurring instantly.
One important thing to double-check is the sample rate of the oscilloscope when all channels are turned on.
Typically, when multiple channels are in use, the sample rate is split up among the channels. If you are using more than one channel, you’ll want to make sure the sampling rate is still sufficient.
3. Memory depth
Memory depth is the measure of oscilloscope’s memory to store signals. The more memory depth means you can capture signal at the highest sample rate.
This is a very nice feature and a good oscilloscope must have a good size of depth memory. But it will make it costly.
The oscilloscope memory is directly tied to the sample rate. The more memory you have, the higher you can keep the oscilloscope’s sample rate as you capture a longer period of time.
The higher the sample rate, the higher the effective bandwidth of the oscilloscope.
4. Waveform update rate
It is the time oscilloscopes takes to update its screen. It is a very great and important feature to look for.
Of course, who cares for an oscilloscope when it takes too much time to update its screen. As in such a situation, there is a good chance you may miss an important signal.
Above are the key parameter to look for in a good oscilloscope. Some other following useful aspects can also be taken into consideration.
5. Size and cost
They may not be the important parameters but I feel I should talk about them a little bit. For me, size is not that issue because I love working in the lab. The one used in the lab is bench oscilloscope. There may be beginners who will use an oscilloscope for car diagnoses. For such people, who carry oscilloscope where and their, size is of a big problem.
The cost is a big issue. But you cannot have a cheap oscilloscope with great features. It just cannot happen. Good bandwidth, sample rates, built-in wave generator, FFT, extra channels, good memory depth are the parameters that will cost you money.
I keep these problems in mind and try my knowledge best to enlist oscilloscopes you can carry everywhere and are of a reasonable price at a beginner level, the link is given below at the end of this post.
6. Number of channels
An important thing I like to consider for an oscilloscope is the number of channels.
I think 2 channels are more than enough if you are just started with electronics. The reason is, if you are going to use more than two channels, the extra channels are just making the scope expensive.
For example, you want to see the communication of Arduino at the same time. Two channels will be enough to see what is coming to your Arduino and what is going away from it or to see the phase difference between 2 pulse trains or any two signals.
So, above are the key parameters that I think make an oscilloscope buying guide complete. Besides these, there are features you should also take in consideration. Let talk about those in the following.
- Having a friendly graphical interface. There are a lot of scopes that have so ugly graphics that people find it very difficult to operate the scope accurately.
- Mathes functions including FFT.
- External triggering
- USB storing option
- Remote controlling option
- Solid-body structure
- EMI/EMC free reading
- Low noise level
- High-quality probes to reduce signal distortion
With that, I think it is clear what you do before investing any money in any oscilloscope. I have done this research for you all people and listed a few oscilloscopes which you can see in my other post, the link is given below at the end of this post.
Buying an oscilloscope is not so easy. But it is not that complicated, just need a little understanding of a few parameters. Here in this post, I try to give you an easy oscilloscope buying guide.
I talk about some of the most important parameters such as bandwidth and sample rate in great detail to make it clear to you. These two parameters play a major role in determining the oscilloscope price. The higher the value of these parameters, the higher the prices of oscilloscopes.
For me, if you are going to buy any scope, you should ask the following question yourself.
Write all your answers on the paper.
- For what situation you need a scope?
- Do you need a benchtop or portable oscilloscope?
- How many signals do you want to measure at once?
- A guess of frequencies you will measure with the scope
- What are the amplitudes of your signals?
- Are the signals you are going to measure periodic or non-periodic?
- This question is so obvious, but let add it. What is your budget?
Take the above questions very seriously, it may save you a lot of money. Don’t buy a bandwidth oscilloscope if you don’t really need that high bandwidth. It sounds cool but if your not a professional, higher bandwidth will end on a high noise floor.
With this, above was my knowledge that I wanted to share with you. Hopefully, it was some kind of help you, and you enjoyed it.
Thank you and have a good life.
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