An oscilloscope, informally known as a scope, is an electronic test instrument that is used to measure and graphically displays varying signal voltages, as a function of time. The measured waveform can then be further analyzed for the properties such as amplitude level, rise time, time interval, frequency, distortion, etc and display these properties directly on its screen.
Oscilloscopes are used in all most all aspects of the design and maintenance of electronic equipment and laboratory works in the sciences, engineering, automotive, medicine, telecommunications industries. Special-purpose scopes are used in the measurement applications like a heartbeat as an electrocardiogram, analysis of automotive ignition system, etc.
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A Typical oscilloscope will have the display, trigger, vertical and horizontal controls along with the probe to connect the signal to the input. The probe will have typically a resistance often ten times to the input impedance of the oscilloscope.
For the probe, the open wire test leads are not suitable for low-level signals as it likely to pick up interference and not suitable for high frequencies due to high inductance. Probes of the scope are usually shielded coaxial cable which has lower inductance, and higher capacitance, typical 50 ohms and a resistance of 1 megohm.
In the earlier time of analogue scope, there are many control knobs are available in the front panel to control and set the oscilloscope for the measurement. The number of control knobs in a digital oscilloscope is very less and most of them are multifunctional to control many features of the oscilloscope.
The Analog scope will have a CRT monitor for the display. Below are the features available to make the display visually suitable for the user.
Focus control: Focus control is used to adjust the CRT focus to obtain the most-detailed trace by increasing the sharpness.
Intensity control: Intensity control is used to adjust the trace brightness.
Astigmatism: Astigmatism control is used to control the "spot shape" by adjusting the voltage on the last CRT anode.
Timebase controls: Timebase controls are used to select the horizontal speed, this process is commonly referred to as the sweep.
Hold-off control: Hold-off control is used to hold the sweep for a preset time after a trigger. During this time sweep circuit will be under hold.
Finder: The beam finder circuit help to overrides any blanking and limits the beam deflection.
Graticule: The graticule is a grid of lines. By enabling graticule it serves as reference marks for the displayed trace measurements.
Vertical sensitivity: Vertical sensitivity is used to accommodate a wide range of input amplitudes by vertical deflection.
Horizontal sensitivity control: Horizontal sensitivity control is used to adjust the horizontal sensitivity when the instrument is in X-Y mode.
Digital scopes are mostly will have a touch screen to set the horizon and vertical scales for the measurements. In the advanced version of the digital oscilloscope, most of the settings like resolution, scaling etc will be set automatically for the measurements. Below are the most common knobs in digital oscilloscopes.
Multipurpose knob: Multipurpose knob is used for setting multiple features like waveform navigation, zoom, trigger, cursor position etc.
Save and Recall: In a Digital scope, one of the prime features available is the feature to save and recall the setting and the measurements. By using this knob, the user can save the setting as well as the measurements.
Scale: The scale is used to manually set the vertical and horizontal scale of the display for the measurements.
There are different types of oscilloscope are available, starting from the cathode ray-based oscilloscope then the digital scope becomes most common, now the PC based oscilloscope is the most cost-effective time-domain measurement system used for the research and development activities.
The earliest and most simple oscilloscope is the cathode ray oscilloscope, which consisted of a cathode ray tube, a vertical and horizontal amplifier, and a power supply. This analogue scope is used for signal analysis by feeding one reference signal into the first axis and an electrical signal to be measured to another axis.
The dual-beam oscilloscope can simultaneously display two signals by using a dual-beam CRT generator. The dual-beam oscilloscope can trace and switch quickly between traces and capture two fast transient events. It will cover all the limitations of the cathode-ray oscilloscope.
Analogue storage oscilloscope is an advanced version of the analogue oscilloscope which can directly display the traces and store the trace pattern. I.e it can retain the traces on the screen for several minutes, that normally decay in a fraction of a second.
Digital oscilloscopes use digital numbers corresponding to the voltage samples by using an analogue-to-digital converter (ADC) and a processor to process the data and display the results. The digital storage scope ( DSO) is used in the majority of industrial applications, due to low costs and the capability to store analogue data in digital format in memory, as long as required without degradation. The processed data using digital signal processing circuits can be displayed without the brightness issues as in CRTs.
A mixed-signal oscilloscope (or MSO) will have a few numbers of analogue channels and digital channels together. A mixed-signal oscilloscope solves the requirement of the separate oscilloscope and logic analyzer for the measurements.
A mixed-domain oscilloscope (MDO) will have both the time domain ( Oscilloscope) and frequency domain ( Spectrum analyzer) measurement capabilities. These scopes will have an additional RF input for the FFT-based spectrum analyzer functionality along with the other analog input channels. Display and other settings control knobs will be common for the analog and digital measurement setups.
Handheld oscilloscopes are mostly digital sampling oscilloscopes with lightweight and useful for field test and service applications. Most of the hand-held oscilloscopes will have more than one measurement channel and all the input signals must have the same reference voltage and differential preamplifier. The handheld scope will have an internal battery for field test applications.
In PC- based oscilloscope, the PC platform is used for the control of the instrument, measurement and display. In the PC based Scope, probs of the scope are connected to the PC through USB or LAN for the measurements and display. There will be dedicated software associated with the hardware for the data processing. These are the most cost-effective solution as a common PC can be used for the measurements.
Digital and Analog Scopes have a wide variety of test and measurement applications in automotive, voltage signal analysis, network, EMI pre-compliance analysis, power measurements and many more by using a suitable probe. Below listed are the top domains on which oscilloscope is used for test and measurements.
Oscilloscope type, number of channels and bandwidth are the prime specifications that need to consider in the selection of oscilloscope for the test and measurement applications.
Oscilloscope types like analog or digital or Mixed oscilloscopes need to select as per the test requirement. For field applications, a handheld type oscilloscope will be an ideal choice.
Analog and digital Scopes come with various numbers of channel options like single channel, dual, multi-channel etc. The number of channels needs to select as per the number of measurements and investigations channels required at a time.
The bandwidth of the oscilloscope is related to the speed or frequency of the waveforms, it can measure and display accurately. The electrical bandwidth is defined as the point at which the amplitude level of a waveform is reduced by 3 dB, with reference to the level at a lower frequency.
The rise time of the oscilloscope is one of the important parameters that need to consider for the situation where digital signals need to measure where the edges of the pulse signal or square waves determine the data. The rise time of the scope must be fast enough to capture the rise time transitions accurately, to avoid the missing of any important information.
In an oscilloscope, the signal to be measured is fed usually by using a coaxial connector such as a BNC, Binding posts or banana plugs on the base of frequencies of operation. A specialized cable called a "scope probe", which will have an impedance match is usually supplied along with the scope for the general-purpose measurements. Need to select the input connector to match the DUT connectors.
The oscilloscopes vertical channel resolution determines the "granularity" of the input signal and is based upon the digital to analogue converter in the digital scope.
The sample rate of an oscilloscope specifies the number of samples per second (S/s) it can measure. The higher the oscilloscope samples rate, the greater will be the resolution on the waveform and the lower will be the chance of losing the critical information.
The Screen size of the Oscilloscope indicates the size of the display on which the measured waveform and readings are projected to the users.
Oscilloscopes are available with various form factors and dimensions. Most modern devices are lightweight with portable handles to carry to the field for testing. For Lab applications, rack-mountable scopes are generally available with remote display options. Need to select as per the test requirements.
An oscilloscope is a test and measurement instrument used to measure, analyze and display the electronic signals in the time domain. A typical oscilloscope can display alternating current waveforms having a low frequency in the range of 1 hertz (Hz). High-end oscilloscopes are available with the features of a spectrum analyzer which can display signals in the gigahertz (GHz) frequency range.
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