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What is an oscilloscope?

An oscilloscope is a measuring instrument for electronics. Represents a plot of amplitude on the vertical axis and time on the horizontal axis. It is widely used by students, designers, engineers in the field of electronics. It is often complemented with a multi-meter, a power supply and a function generator or arbitrary. Lately, with the explosion of devices with radio frequency technologies such as WiFi or BlueTooth, the workbench is complemented by a spectrum analyzer.

The oscilloscope displays the values of the electrical signals in the form of coordinates on a screen, in which normally the X (horizontal) axis represents time and the Y axis (vertical) represents voltage. In analog or digital phosphor oscilloscopes is usually included other input or control, called "Z-axis" that controls the brightness of the beam, thus highlighting or off certain segments of the trace depending on repetition frequency or rate of transition in time.

Down a modern digital oscilloscope shown:


On an oscilloscope three types of controls are used as regulators which adjust the input signal and allow consequently measured on the screen and thus can see the shape of the signal measured by the oscilloscope exist basically, this known technical way you can say that the oscilloscope is used to observe the signal measured.

The first control regulates the X (horizontal) axis and appreciates fractions of time (seconds, milliseconds, microseconds, etc., according to the resolution of the apparatus). The second regulates the Y axis (vertical) controlling the input voltage (in volts, millivolts, microvolts, etc., depending on the resolution of the apparatus).

The third is a set trigger (or trigger in English), this control allows you to synchronize the signals that are repeated so periodically using a characteristic reference signal, different shot types are used, being the most common triggering rising or falling edge of the signal, for which the trigger voltage is defined and whether the edge is rising or falling.

These regulations determine the value of the squaring dividing the display scale, allowing to know how this represents for each square, thus knowing the value of the signal to be measured, both in voltage and frequency or period.

 Screen of a digital oscilloscope digital representation of an 
unstable signal mode
Variable Persistence DPO (digital phosphor)

Analog Oscilloscope

The voltage to be measured is applied to the plates vertical deflection of a cathode ray tube (using an amplifier with high input impedance and adjustable gain) while the horizontal deflection plates a voltage is applied saw-tooth (named because, repeatedly, grows gently and then falls abruptly). This voltage is produced by a suitable oscillator circuit and the frequency may be adjusted within a wide range of values , which can be adapted to the frequency of the signal to be measured. This is what is called time base.

Figure 1. Schematic representation of an oscilloscope.

In Figure 1 you can see a schematic representation of an oscilloscope indicating the minimum basic steps. The operation is as follows:

In the cathode ray tube the electron beam generated by the cathode and accelerated by the anode reaches the screen, coated internally with a fluorescent layer that is illuminated by the impact of the electrons.

If a potential difference to either of the two pairs of baffles, occurs a deviation of the electron beam due to the electric field created by the applied voltage is applied. Thus, the sawtooth voltage, which is applied to the horizontal deflection plates, causes the beam to move from left to right and during this time, no signal in vertical deflection plates, draw a line horizontal line on the screen and then back to the starting point to start a new sweep. This return is not perceived by the human eye due to the speed at which is done because, in addition, during the same a shutdown (erase) Partial or beam deflection occurs.

If under these conditions the signal to be measured (via the adjustable gain amplifier) the beam, also moving from left to right is applied to the plates vertical deflection, it will move up or down depending on the polarity of the signal, and with greater or lesser extent depending on the applied voltage.

Being the coordinate axes divided by brands, you can establish a relationship between these divisions and sawtooth period in relation to the X axis and voltage in reference to Y. This corresponds to each horizontal division one specific time, just as each vertical division corresponds to a specific voltage. Thus in the case of periodic signals can be determined both his tenure as its amplitude.

Typical margin scales ranging from microvolts to a few volts and microseconds to several seconds, makes this very versatile instrument for the study of a variety of signals.

Limitations of analog oscilloscope

The analog oscilloscope has a number of limitations typical of operation:

  • The signals must be periodic . For a stable trace , the signal must be periodic as it is the frequency of the signal which cools the trace on the screen.
  • Very fast signals reduce glare . As the period of the signal is observed, the brightness is reduced because the refresh rate decreases.
  • Slow signals do not form a trace . Low frequency signals produce a very slow scan does not allow to integrate the trace retina . This is solved with high persistence tubes . There were also specially adapted Polaroid cameras to photograph the oscilloscope screen . Keeping exposure during a photo of the trace is obtained.
  • You can only see if they are repetitive transients.

Digital oscilloscope

Today analog oscilloscopes are being displaced largely by digital oscilloscopes, among other reasons for the facility to transfer the measurements to a personal computer or LCD.

In the digital oscilloscope previously signal is digitized by an analog to digital converter. Relying reliability display quality of this component, it must be maintained at maximum.

The features and procedures outlined for analog oscilloscopes are applicable to digital. However, these will have additional features such as the shot early (pre-triggering) for displaying short duration events, or memorizing the oscillogram transferring data to a PC possibilities. This allows comparing measurements made at the point of a circuit element. There are also teams that combine analog and digital stages.

These oscilloscopes added services and facilities to the user impossible to obtain with analog circuitry, such as:

  • Automatic measurement of peak signal maximum and minimum values. True RMS.
  • Measure signal edges and other intervals.
  • Transient capture.
  • Advanced calculations as the FFT to compute the spectrum of the signal.

MSO2024 Tektronix Digital Oscilloscope 200MHz with
4 analog channels and 16 channels digital that can be
used for logical analysis of states and times and analyze
options buses serial communication as RS232, CAN, LIN,
I2C, Etc.

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