Familiarity with the oscilloscope
An oscilloscope is a measuring device that can be used to observe and measure voltage, frequency, periodicity, phase difference, as well as the voltage and amp characteristics of semiconductor elements (such as diodes, transistors, etc.).
Screen: Each oscilloscope has a screen that consists of two main parts:
A) time axis, b) voltage axis
In the oscilloscope, the grading is in centimeters (large houses are 1 cm and small houses are 2 mm).
Channel: The input of each oscilloscope is called a channel, and each oscilloscope is divided according to the number of catalysts that can be applied to it: one-channel, two-channel, three-channel, and four-channel, which are 3- and 4-channel digital oscilloscopes.
The keys on the oscilloscope are divided into three categories.
Although the control switches of different scopes are slightly different, but in general, there are a series of basic switches in analog scopes, which, although there are differences in appearance, but in the end their function is the same in different models and in shape. Below you can see one of the simplest models
1- vertical part :
: CH1 1-1 – Input Number One Oscilloscope
: CH2 1-2 Input No. Two Oscilloscope
1-3 keys (AC-GND-DC)
1-3-1 AC AC: If the switch is placed on this part, only the alternating current signal enters the oscilloscope and the DC voltage is prevented from being displayed.
1-3-2 DC mode: If the switch is set to this mode, any input signal (either DC or AC or a combination of both) is displayed on the screen.
1-3-3 GND method: If this mode is selected, the oscilloscope input is connected to ground and the electrical connection between the prop and the oscilloscope is cut off. This mode is used to set the oscilloscope to zero.
1-4 VARIABLE volume: which is located on the VOLT / DIV selector and is used to calibrate the device, which should always be at the extreme right (turn clockwise) to a factor of 1. (to zero Voltage error)
1-5 POSITION VOLUME: With this volume, the waveform on the screen can be moved vertically. 1-6) mode key: This key has four positions: a) CH1 b) CH2 c) DUAL د ADD
Depending on which of the inputs of the scope we want to use, we can set the MODE key, which, respectively, from top to bottom of the scope, on the screen, channel one, channel two, two simultaneous waves and in ADD mode, mathematical sum. Will show two waves
1-7 Volume VOLT / DIV: By changing this potentiometer, the amplitude of the wave that appears on the screen changes.
Note: By resizing (VOLT / DIV value) any waveform can be displayed on the screen. The oscilloscope does not interfere with any wave (range or period) and only changes the scale. Wave indication is that the waveform is at the maximum visible amplitude (largest peak-to-peak state) and has 1 or 2 periods.
1-8 ALT push button: By pressing this button, both channels give a wave to the oscilloscope together and the wave of both channels is drawn together, but its waveforms are not seen together on the oscilloscope screen at all times. Instead, they appear one by one on the sensitive screen.
1-9 CHOP push button: By pressing this button, channels 1 and 2 are both lit and two separate waves can be observed by the inputs of these two channels separately on the siloscope screen.
2- TRIGER part:
SOURSE 2-1: To display a stable waveform on an oscilloscope screen, it is necessary to have a sweeping waveform (SWEEPR) with a synchronous input waveform (synchronous), so to synchronize it is necessary to apply a waveform to this type of signal. The synchronizer in the SOURSE location is specified as follows.
CH1. In this case, if the wave is not fixed, we use the LEVEL key to hold the wave (
EXT 2-1-2: If placed in this position, the swept signal can be transmitted to the horizontal plates from the outside by the terminal (EXT-TRIG) of the external wavelength of the required frequency.
2-1-3 If the signal frequency is the same as the city power frequency, we use the INE button to supply the sweeper signal.
HEVEL 2-2: Used to hold the wave.
SLOP 2-3: Aligns the graph with the V axis.
TRIC 2-4: is a circuit exciter.
3- HORIZONTAL part:
3.1 POSITION volume: With this volume, the waveform on the screen can be moved horizontally.
3-2 TIME / DIV selector: By changing this key, the period of the wave changes. As a result, the unit of time on the T-axis changes. To read the true period value of a wave, we multiply the number of units seen by the number TIM / DIV. 0663 On this selector, there are three categories of settings in terms of seconds (S), milliseconds (MS) and microseconds (us), which should be considered when converting.
3-3 Volume SWP VAR: With this volume, more waveforms can be reflected on the screen (to zero the frequency error)
3-4 MAG10 pressure key: Pressing this key increases the wave 10 times.
PROBE: To view the waveform applied to the oscilloscope, first connect the electrical signal to the oscilloscope input with the probe.
The oscilloscope interface wire consists of three parts: 1) the metal core that connects to the oscilloscope channel and is called the B.NC 2) the probe that connects to the circuit 3) the shild wire that connects the probe to the bnc.
There are (1 *) and (10 *) switches on the probe. If the input signal amplitude is low, 1 * mode is used and if the input signal amplitude is large, 10 * mode is used. (In 10 * input mode, the input signal is 10 times. Is weakened).
Internal circuit of the probe
How to measure with an oscilloscope:
Before starting work with an oscilloscope, we must do two things:
A) Initial settings: Gain Variable Control keys, which are located as a smaller key on the Volt / DiV and Time / Div keys (gray) to end in a clockwise direction.
In analog oscilloscopes, the upward sliding switches and pushbuttons must all be out.
B) Set the three-mode AC GND DC switch to GND mode for both channels and set the vertical axis to zero with the Position knob. Use the Intensity and Focus keys to adjust the light intensity and wavelength, respectively, and set the keys to DC after adjusting the ground.
1- Voltage measurement (range):
Count the number of vertically enclosed cells from the peak to the lowest point of the wave and multiply by the Volt / Div of that channel. The number obtained will be the size of the amplitude of the PP wave. For example, if VOLT / DIV is equal to 3.4 and the number of cells enclosed by the wave in the vertical direction is 3.4, then multiply these two numbers to obtain the amount of voltage.
We have: amplitude (voltage) = number of volts / div × number of vertical cells
3.4 × 2 = 6.8 V
1-Period or frequency measurement:
A) Multiply the number of horizontal cells along a periodicity by the Time / Div unit and invert the number to get the wave frequency. For example, the number time / div on ms50 and the number of horizontal cells in A period equal to 5.2
Period) T = time / div × number of horizontal houses)
5.2 × 50ms = 260ms
F = 1 / T = 1 / 260ms = 3.8hz <= frequency
B) Matching method:
In this method we compare the wave whose frequency we want to obtain with the wave whose frequency we can measure, we change the known frequency so that it equals the unknown frequency so that we can read the unknown frequency value .
As we know, an oscilloscope can only be used to measure voltage and we can not measure current with it. To do this, we set a 1 ohm power in the circuit and according to the ohm law we have V = RI and R = 1? So we have V = 1 × I (meaning V will be equal to I) and by measuring the voltage we actually measure the current.
4- Measuring potential difference:
INV key: This key reverses the signal and is used to calculate the potential difference. If V1 is the input of CH1 and V2 is the input of CH2, we do the following for the potential difference of V2-V1:
We add CH1 with the inverse of CH2 (that is, we put it in ADD mode and two INV buttons are pressed for the channel).
CH1 [ADD] ([INV] CH2) = CH2-CH1 = V2-V1
5- Measurement Phase difference:
A) Time domain method: In this method, we put the oscilloscope in DUAL mode and display the channels 1 and 2 signals together, then we calculate the phase difference from the diagram according to the values of T and T0 and from the following relations.
B) Lissage method: In the lysing method to calculate the phase difference, we put the oscilloscope in XY mode and after the appearance of a stable Lisagus waveform, we calculate the phase difference according to the shape shown and the following relation. After connecting the two Signal to Channels First we place both channels on the GND mode to adjust the created point of light in the middle of the coordinate axis. Then we place it on the DC mode to get the phase difference.
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