Layout and Operating principle of an Oscilloscope
An oscilloscope has a screen, knobs to adjust the time base, controls for signal voltage, and input channels to connect a probe.
There are two kinds of oscilloscopes: analog and digital.
Layout and Operating Principle of an Analog Oscilloscope
An analog oscilloscope works using a cathode ray tube, similar to the tubes in old TVs.
Inside the tube, there is a heating wire that glows when an electric current passes through it.
This wire or an electrode behind it is negatively charged, called the cathode.
When heated, electrons are released from the cathode and are attracted to the positively charged anode.
This movement of electrons is based on the principle that opposite charges attract and like charges repel.
The tube has a vacuum, so the electrons don’t collide with air particles.
Around the heating wire, there’s a Wehnelt cylinder, which is slightly negatively charged at the opening.
This charge helps guide the electrons toward the opening.
However, if the negative charge is too strong, it will block the electrons from flowing.
After the cylinder, there are focusing optics in front of the anode, which use different electrical potentials to focus the electron beam.
The anode has a hole in it. Electrons are sped up so much that they fly past this hole instead of hitting the anode.
Without anything stopping them, the electrons hit the middle of the screen, creating a bright spot.
A plate capacitor, with one plate on top and one on the bottom, directs the electron beam up or down.
The measured signal is sent to these plates. If the top plate has a positive signal, the electrons move up.
If the signal is negative, the electrons move down, making the electron beam move in the Y direction according to the signal.
Two other plates in the X direction move the beam from left to right.
The oscilloscope sends a sawtooth signal to the X plates, making the beam move left to right.
In the Y direction, the beam follows the signal’s waveform.
The sawtooth signal’s frequency sets how often the analog signal is sampled, adjusted by the time base setting.
At the end of the tube, a fluorescent screen glows where the electron beam hits, displaying the signal for a few milliseconds.
Controlling the electron beam tube involves many gain factors and other settings.
Analog oscilloscopes can’t store waveforms digitally; they can only be captured with a camera.
Like old tube TVs, analog oscilloscopes have mostly been replaced by modern digital ones with LCD screens.
However, analog oscilloscopes are still useful for simple measurements and can be bought cheaply second-hand.
Layout and Operating Principle of Digital Oscilloscopes
The picture explains how a digital oscilloscope works. First, the signal being measured is boosted and filtered.
Filtering is necessary because the digital process can’t handle very high frequencies.
If the signal has frequencies higher than the oscilloscope’s limit, it can cause errors (known as aliasing).
The signal is then converted from analog to digital using an analog-to-digital converter, which samples the signal at fixed intervals.
The sampling frequency must be a multiple of the signal frequency to accurately capture sharp changes.
The oscilloscope’s bandwidth is crucial for choosing the right device. The signal’s strength is converted into specific values.
For example, a 10-bit converter can distinguish 1024 different values, while an 8-bit converter can handle only 256.
More bits in the converter provide better accuracy. The digital data is stored in memory, then processed and shown on the oscilloscope’s screen.
Since the data is already in memory, various algorithms like FFTs (Fast Fourier Transforms) can be applied.
The data can also be saved to a USB stick, Compact Flash, or an SD card. Older oscilloscopes might use adapters to switch from Compact Flash to SD cards.
Digital oscilloscopes have mostly taken the place of analog ones.
The easier hardware and lower cost have made digital oscilloscopes popular among hobbyists.
You can buy them for a few hundred dollars. They come in different bandwidths and memory sizes.
Devices with large memory are also known as storage oscilloscopes or transient recorders.
What is the principle of an oscilloscope?
An oscilloscope works by displaying electrical signals on a screen.
It takes these signals and shows their changes over time as a wave on the screen.
This helps us see how the signals behave, making it easier to measure and analyze them.