An oscilloscope is a laboratory device that is mostly used to analyze and display the waveform of electronic signals. The device itself draws a graph of the instantaneous signal voltage that depends on time. Simply said, an oscilloscope is one tool that gives you the ability to track voltage changes over time by displaying the waveforms of electronic signals. Due to the fact that it enables oscillations, it was named an oscilloscope.
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Oscilloscope Functions
Oscilloscopes displays voltage signals in terms of waveforms. They show visual images of how voltage fluctuates over interval. The signal change is displayed on the screen on the vertical or Y-axis and the horizontal or X-axis shows time.
The two primary oscilloscope purposes cover sampling and triggering.
Triggering
The trigger controls let the oscilloscope user steady and show a multiple waveform. Edge triggering is commonly used because the slope and show the fundamental trigger points. The slope controls determine whether the trigger dot is going up or down at the signal’s edge. The level regulator governs the edge of the trigger control.
Triggering is useful when operating on complex signals such as series of pulses, where pulse-width triggering may be necessary. One thing that you to know is that during any set interval, the trigger-level setting and the next falling edge of the signal should take place. If these conditions are met, triggering the oscilloscope occurs.
One can also use the short-triggering process where the oscilloscope shows a mark whenever an input signal encounters the right trigger settings. In the process, the oscilloscope obtains and updates, and controls the display to show the mark.
Sampling
The procedure converts a portion of an input signal into several distinct electrical values that are used for display, processing, and storage purposes. The size of every sampled point is equivalent to an input signal’s amplitude during sampling time.
The waveform for input is displayed as a series of dots on the oscilloscope’s screen. If the dots are placed at a distance from each other, and they cannot be read well, they are connected through the interpolation procedure. In this procedure, the dots are connected with lines to show a continuous waveform that can be read.
Black dots show sampling while interpolation is shown by the black line.
Features of an Oscilloscope:
Screen
The first feature is the screen where the electron beam strikes. Conventional oscilloscopes have a cathode ray tube or the CRT.. Electronic circuits in the oscilloscope put on some voltage to one set of the deflection plates. The outcome is that the beam moves across the screen from the left side to the right at a constant speed which is the time axis.
Digital oscilloscopes have a flat-panel display or a CRT which operates like a computer’s monitor. The screen of a digital oscilloscope has a one-centimeter graticule on it.
Signal Inputs
These are channels and they are more than two. They are referred to as CH1, CH2, CH3, and so on. There is also one external trigger input which is known as “EXT TRIG.’
Control Collections for the Horizontal Part of Input Signal
These controls are responsible for setting the time axis and they are calibrated in terms of seconds per division. For example, 1µs/div translates to one main division that occurs in 1 microsecond. The horizontal controls are also referred to as “timebase” and the setting is known as the “sweep rate”.
Trigger Controls
These trigger controls synchronize an oscilloscope’s input signal to the horizontal display. The synchronization is important because there is no constant relationship between an internal timebase and an external signal. The trigger is responsible for making the oscilloscope wait until some set level in input is attained before starting its display.
Control Collections for the Vertical Part of Input Signals
Several controls are related to the vertical part of the display associated with the input signals. The controls are coupled to the “Direct Current “DC”, the one that passes through a capacitor, the “AC”, and the disconnected control “GND”. A knob controls the amplified amount that is applied to the signal and it is set according to screen units such as a “20mV/div” which means that a 10 millivolt change in the input signal will result in one major division which is traced vertically.
Essential Safety Tips for an Oscilloscope User
Now that you have learned about all the features of an oscilloscope, there are essential activities that you need to undertake before you start using it.
It is significant to ensure that you undertake proper grounding because of safety purposes. You must ensure that the integrated circuits (ICs) that you are testing are safe while also taking care of your body. You should ensure that all the oscilloscope is calibrated and the controls are set. The oscilloscopes probes should be well connected and compensated to ensure that you get the best readings.
Proper Grounding
Proper grounding is one of the essential steps you should observe to ensure that you can work on internal circuits.
You need to ground the oscilloscope correctly to protect yourself from shock and also safeguard the internal circuits from damage.
Steps on How to Conduct Proper Oscilloscope Grounding
- Connect the oscilloscope to an electrically neutral point, for example, earth ground.
- Plug the oscilloscope’s three-pronged power cord into an outlet that is grounded to earth ground to ensure that you are protected from shock. In the event of a high voltage from the contacts of an ungrounded oscilloscope including the knobs, it is easy to get a shock.
A properly grounded oscilloscope ensures that the current moves through the grounding part into the earth ground. It eliminates the risk of the user becoming the earth ground.
Accurate measurements can only be achieved when the oscilloscope is properly grounded. It should share the same ground as the internal circuits that you are testing. However, you should note that some oscilloscopes do not need earth ground because they are well insulated which protects the user from any hazards.
- Ground your internal circuits because they have miniature conduction paths that are vulnerable to damages by static electricity which can build up in your body. You should not that, it is easy to ruin an internal circuit by undressing and touching its leads. It is essential to weal a grounding strap that sends static body charges to earth ground.
ESD Anti-Static Wrist Strap Band
- One thing that you should note is that advanced oscilloscopes need an AC/DC ground coupling. An AC coupling is needed when you are using an AC signal and the same should be done for the DC signals.
AC coupling clears the DC component from the oscilloscope so that it oscillates about zero. The change of one signal to the other helps in getting an accurate and tight waveform. It plays a significant role when one is measuring small AC disturbances.
The advanced oscilloscope enables you to choose either to use the DC or AC coupling. Always note that an oscilloscope can notify you about coupling it to the ground.
Set the Controls
After you plug in the oscilloscope, take a critical look at the front panel. It has three sections which include the vertical, horizontal, and trigger. You also need to understand that oscilloscopes have different models and types and the others sections vary. Oscilloscopes have two input channels that display different waveforms on the screen.
Some oscilloscope models have DEFAULT or AUTO SET buttons that can set up the controls in a single step and take a signal. If your oscilloscope lacks these buttons, then it is significant to set the controls to ordinary locations before taking the readings.
Instructions for Setting the Oscilloscope
- Turn on your oscilloscope such that it shows channel 1 on the screen.
- Check the vertical volts/division scale and position controls are at the middle-range positions.
- Switch off all the magnification settings and variable volts division.
- Check the channel one input coupling to DC.
- Ensure that the trigger mode is on auto and also set the rigger to channel one
- You can turn the trigger source off or at the minimum point possible.
- Now, you can set the horizontal time/division and ensure that the controls are at middle-range positions
- Adjust channel 1 volts/division and ensure that the signal takes the space of 10 vertical divisions to avoid tampering with signal distortion.
How to Calibrate the Oscilloscope
Calibration of the oscilloscope involves setting the machine to ensure that it offers accurate measurements. Every week, you need to calibrate your oscilloscope at room temperatures. Usually, the oscilloscope changes by approximately nine degrees Celsius. Calibrations is also known as signal path compensation and it is significant in ensuring that the machine functions optimally.
Calibration Involves
- Connecting the Probes
- Compensating the Probes
Connecting probes is a significant procedure that occurs after the oscilloscope is well-grounded and has been set in standard positions. The next thing is connecting probes to the oscilloscope to ensure that it is well-matched and allows one to access power and performance. Probes set the quality and integrity of the signal that you will get when measuring. You need to understand that measuring a signal needs two connections which are;-
- The ground connection
- The probe tip connection
It is easy to identify probes since they are packaged with a clip attachment for grounding the probe to the internal circuits under test. Practically, you need to ground the clip to ground in the internal circuit, for example, a metal chassis of a product that you are working on. Then, just touch the probe tip to a test point in the internal circuit.
Compensate the Probes
Compensation of oscilloscopes probes requires passive attenuation voltage. Before you can use the probes, you must compensate them to balance their electrical properties. You should always compensate the probe before using the oscilloscope. Research has shown that when an oscilloscope is not well compensated, the results are inaccurate.
Digital oscilloscopes possess a square wave reference signal present at the terminals of the front panel and their purpose is to compensate the probe.
How to Compensate the Probes
- Connect the probe to the vertical channel
- The probe tip must be connected to the probe compensation to produce a square wave reference signal.
- The ground clip of the probe should be connected to the ground.
- Examine the square wave reference signal.
- Make the right adjustments of the probe and check if the corners of the square wave reference signal are square.
Oscilloscope Measurement Methods
These measurements include:
· Time
· Voltage
You need to learn that these two basic methods form the fundamentals of all other measurements that you will undertake when using an oscilloscope.
Taking the measurements visually needs an oscilloscope screen. The common method includes the examination and understanding of the on-screen displays of digital oscilloscopes.
The interesting part about digital oscilloscopes is that they are automated and they simply and hasten the analysis of common jobs. This means that their measurements are reliable and their confidence levels are high. You need to know how to check the measurements manually since it aids in understanding the automatic measurements.
How to Take Voltage Measurements Using an Oscilloscope
Voltage refers to the amount of electric potential between two points in an internal circuit, and its measurement is expressed in volts. At the ground point, the voltage is always zero.
Voltage can be measured in accordance to their variation from peak-to-peak which refers to the maximum point of signal to its minimal point. On this point, you must be careful about the kind of voltage that you need.
