Give you a guide to oscilloscope usage skills

An oscilloscope is an electronic measuring instrument with a wide range of uses. It can transform invisible electrical signals into visible images, making it easier for people to study the changing processes of various electrical phenomena.

The oscilloscope uses a narrow electron beam composed of high-speed electrons to hit the screen coated with fluorescent material to produce tiny spots of light. Under the action of the measured signal, the electron beam is like the tip of a pen, which can draw a curve of the instantaneous value of the measured signal on the screen. The oscilloscope can be used to observe the waveform curve of various signal amplitudes changing over time, and it can also be used to test various electrical quantities, such as voltage, current, frequency, phase difference, amplitude modulation, etc.

Below, Antai Test will briefly talk about the tips for using the oscilloscope:

1. For general oscilloscopes, adjust the brightness and focus knobs to minimize the diameter of the light spot to make the waveform clear and reduce the test error; do not let the light spot stay at one point, otherwise the electron beam will bombard one point and form a dark spot on the fluorescent screen, damaging the fluorescent screen.

2. Measurement system - such as oscilloscopes, signal sources; printers, computers and other equipment. The grounding wire of the electronic equipment under test - such as instruments, electronic components, circuit boards, power supply of the equipment under test, etc. must be connected to the public ground (earth).

3. When the TDS200/TDS1000/TDS2000 series digital oscilloscope is used with a probe, it can only measure the waveform of the signal (the measured signal - the signal ground is the earth, and the signal end output amplitude is less than 300VCATII). It is absolutely not allowed to measure the floating ground signal of the AC220V mains or electronic equipment that cannot be isolated from the AC220V mains. (The floating ground cannot be connected to the earth, otherwise it will cause damage to the instrument, such as testing an induction cooker.)

4. The housing of a general oscilloscope, the metal outer ring of the signal input BNC socket, the probe ground wire, and the AC220V power socket ground wire are all connected. If the instrument is not connected to the ground wire when in use, and the probe is used directly to measure the floating signal, the instrument will have a potential difference relative to the ground; the voltage value is equal to the potential difference between the point where the probe ground wire contacts the device under test and the ground. This will bring serious safety hazards to the instrument operator, the oscilloscope, and the electronic equipment under test.

5. If the user needs to measure switching power supplies (switching power supply primary, control circuit), UPS (uninterruptible power supply), electronic rectifiers, energy-saving lamps, inverters and other types of products or other electronic devices that cannot be isolated from the AC220V mains power for floating signal testing, the DP100 high-voltage isolation differential probe must be used.

Other precautions when using the oscilloscope:

(1) Thermal electronic instruments should generally avoid frequent startup and shutdown, and the same applies to oscilloscopes.

(2) If the waveform is found to be affected by external interference, the oscilloscope casing can be grounded.

(3) The voltage of "Y input" should not be too high to avoid damaging the instrument. It should not exceed 400V at maximum attenuation. When the "Y input" wire is suspended in the air, it will be interfered with by external electromagnetic interference and produce interference waveforms. This phenomenon should be avoided.

(4) Before shutting down, turn the brightness adjustment knob counterclockwise to the bottom to reduce the brightness to the minimum, and then disconnect the power switch. Analog oscilloscope.

(5) When observing the bright spots on the screen and making adjustments, the brightness of the bright spots should be moderate and not too bright.

12 questions and answers to teach you how to choose an oscilloscope correctly

1. What is the most valuable indicator of an oscilloscope?

Bandwidth is a grade-level parameter. Increasing bandwidth also increases costs at a grade-level.

2. How high does the sampling rate need to be to meet the requirements?

Generally speaking, the sampling rate can be 5 times the bandwidth. For example, an oscilloscope with a 200M bandwidth can be equipped with a 1G sampling rate.

The pursuit of higher sampling rates is nothing more than to catch small glitches, but these high-frequency glitches have been filtered out at the bandwidth layer, and higher sampling rates do not bring good benefits.

3. What is the difference between normal trigger and automatic trigger?

Normal: Normal (standard) trigger, the waveform will be sampled only when there is a trigger event that meets the conditions;

Auto: Automatic triggering. After waiting for a period of time, if no trigger event that meets the conditions occurs, it will be forced to trigger and sample the waveform;

Since the trigger position is random, the waveform display may be unstable. If this happens, use the Normal mode.

4. How to capture abnormal signals whose conditions cannot be determined?

Can be captured using template trigger.

When the template trigger is turned on, the template actually acts as a layer. It will continuously detect whether there is a waveform that touches the template area. When a waveform touches the template, a signal will be detected, and then it will be filtered and displayed.

5. Are the channels of the oscilloscope isolated?

The channels of the oscilloscope are not isolated; the ground of the oscilloscope is connected to the earth and cannot be directly connected to the neutral line;

It is indeed possible to directly measure 220V AC power by adding an isolation transformer, but this is not a recommended approach. The safest and most correct approach is to use a differential probe.

6. Which is more accurate for measuring voltage: an oscilloscope or a multimeter?

The vertical resolution of a general oscilloscope is 8 bits. The measurement accuracy is related to the vertical resolution and vertical scale.

The accuracy of a multimeter is much higher. The ADC of a six-and-a-half-digit multimeter can reach 24 bits, and that of a handheld meter is far more than 8 bits. The voltage value measured by a multimeter is more reliable.

7. What is the difference between the X1 and X10 positions of an oscilloscope probe?

There are two core points:

The attenuation bandwidth is different. The signal amplitude does not attenuate at X1, and the signal attenuates to one tenth of the original at X10.

The bandwidth is different. The bandwidth of X1 gear is only about 10M, while the bandwidth of X10 gear is about 250M.

8. Do general oscilloscope probes need to be calibrated regularly?

The standard does not have clear measurement regulations for probes, but for passive probes, probe compensation adjustment must be performed at least when the probe is replaced or the probe channel is exchanged.

9. What are the main factors that determine the price of oscilloscope probes?

The main determinants of price are, of course, bandwidth and features.

There are many types of oscilloscope probes with different performances, such as high voltage, differential, active high-speed probes, etc., and the prices range from a few hundred RMB to nearly $10,000.

The probe is the part of the oscilloscope that contacts the circuit. A good probe can provide the fidelity required for testing. To achieve this, even a passive probe must have a lot of passive device compensation circuits (RC networks) inside.

10. Is there any way to use an oscilloscope to measure the working conditions of a high-frequency transformer or inductor core?

You can rely on the power analysis software that comes with the oscilloscope. It has a function - BH curve analysis, which can reflect the working state of the magnetic core, measure the dynamic inductance value, and derive the core loss.

11. Can an oscilloscope perform Fourier decomposition?

Most modern digital oscilloscopes have FFT functions, but you need to pay attention to the number of points that FFT can analyze, which directly determines the accuracy of the FFT analysis results and avoids spectrum leakage.

12. Can an oscilloscope perform filtering? For example, low-pass filtering of PWM waves?

Oscilloscopes generally have a bandwidth limit of 20MHz, which is a hardware filter. Some oscilloscopes also support software filters with adjustable cutoff frequencies.