An oscilloscope is a widely used electronic measuring instrument. It can transform invisible electrical signals into visible images, making it easy for people to study the changing processes of various electrical phenomena.
An oscilloscope uses a narrow beam of high-speed electrons to strike a screen coated with a fluorescent material, producing a tiny spot of light. Under the influence of the signal being measured, the electron beam acts like the tip of a pen, tracing the instantaneous change curve of the signal on the screen. An oscilloscope can be used to observe the waveforms of various signals whose amplitude changes over time, and it can also be used to test various electrical quantities, such as voltage, current, frequency, phase difference, modulation amplitude, and so on.
Here are some simple tips for using an oscilloscope:
1. When using a general-purpose oscilloscope, adjust the brightness and focus knobs to minimize the diameter of the spot to ensure a clear waveform and reduce testing errors. Do not let the spot remain stationary at one point, otherwise the electron beam bombarding that point will create a dark spot on the fluorescent screen and damage it.
2. Measurement system – such as oscilloscopes, signal generators, printers, computers, etc. The grounding wire of the electronic equipment under test – such as instruments, electronic components, circuit boards, power supplies, etc. – must be connected to the common ground (earth).
3. When using the TDS200/TDS1000/TDS2000 series digital oscilloscopes with probes, only waveforms of signals (where the measured signal and signal ground are earth's earth, and the signal output amplitude is less than 300V CAT II) can be measured. It is absolutely forbidden to measure floating ground signals of electronic devices powered by AC220V mains or those not isolated from AC220V mains. (Floating ground must not be connected to earth's earth, otherwise it will damage the instrument, such as when testing an induction cooker.)
4. The casing of a general-purpose oscilloscope, the metal outer ring of the BNC socket for the signal input, the probe ground wire, and the ground wire of the AC220V power socket are all connected. If the instrument is used without connecting to the earth ground wire and the probe is used directly to measure floating ground signals, a potential difference will be generated between the instrument and the earth; the voltage value will be equal to the potential difference between the point where the probe ground wire contacts the device under test and the earth ground. This will pose a serious safety hazard to the instrument operator, the oscilloscope, and the electronic equipment under test.
5. When users need to measure the floating ground signal of products such as switching power supplies (primary and control circuits), UPS (uninterruptible power supplies), electronic rectifiers, energy-saving lamps, frequency converters, or other electronic devices that cannot be isolated from AC220V mains power, the DP100 high-voltage isolation differential probe must be used.
Other precautions for using an oscilloscope:
(1) Thermionic instruments should generally avoid frequent power-on and power-off, 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 even at maximum attenuation. When the “Y input” wire is suspended, it will be affected by external electromagnetic interference and will produce an interference waveform. This phenomenon should be avoided.
(4) Before turning off the power, turn the brightness adjustment knob counterclockwise to the end to reduce the brightness to the minimum, and then turn off the power switch. Analog oscilloscope.
(5) When observing and adjusting the bright spots on the screen, the brightness of the bright spots should be moderate and not too bright.
12 Questions and Answers to Help You Choose the Right Oscilloscope
1. What is the most valuable specification of an oscilloscope?
Bandwidth is a tier parameter; increasing bandwidth also affects the cost level.
2. What sampling rate is required to meet the requirements?
Generally speaking, the sampling rate should be 5 times the bandwidth. For example, a 200M bandwidth oscilloscope can be equipped with a 1G sampling rate.
Pursuing a higher sampling rate is simply to catch small glitches, but these high-frequency glitches have already been filtered out at the bandwidth layer, so a higher sampling rate does not bring good benefits.
3. What is the difference between normal triggering and automatic triggering?
Normal: Normal (standard) trigger, waveform will only be sampled if there is a trigger event that meets the conditions;
Auto: Automatic triggering. If no triggering event that meets the conditions occurs after waiting for a period of time, it will force triggering and sample the waveform.
Because the trigger location is random, the waveform display is often unstable. If this occurs, please use Normal mode.
4. How to capture abnormal signals when conditions cannot be determined?
Template triggers can be used to capture this.
Once the template is triggered and opened, it is actually treated as a layer. It continuously detects whether any waveforms will touch the area of the template. When a waveform touches the template, a signal is detected, and then it is filtered and displayed.
5. Are the oscilloscope channels isolated?
The oscilloscope's channels are not isolated; the oscilloscope's ground is connected to earth and cannot be directly connected to the neutral wire.
Adding an isolation transformer does allow you to directly measure 220V AC mains power, but it's not recommended. 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-purpose oscilloscope is 8 bits. Measurement accuracy depends on the vertical resolution and the vertical range setting.
Multimeters are much more accurate; a six-and-a-half-digit multimeter can reach 24 bits with its ADC, and handheld multimeters have far more than 8 bits. The voltage values measured by multimeters are more reliable.
7. What is the difference between the X1 and X10 ranges of an oscilloscope probe?
There are two key points:
With different attenuation bandwidths, the signal amplitude of the X1 level is not attenuated, while the signal amplitude of the X10 level is attenuated to one-tenth of its original value.
The bandwidth is different; the X1 tier has a bandwidth of only about 10M, while the X10 tier has a bandwidth of about 250M.
8. Do oscilloscope probes generally need to be calibrated periodically?
The standard does not have specific metrological regulations for probes, but for passive probes, probe compensation adjustment must be performed at least when replacing the probe or exchanging probe channels.
9. What are the main factors that determine the price of an oscilloscope probe?
The main factors determining the price are, of course, bandwidth and features.
There are many types of oscilloscope probes with different performance characteristics, such as high voltage, differential, active high-speed probes, etc., and the prices range from a few hundred RMB to nearly ten thousand US dollars.
The probe is the part of the oscilloscope's contact circuitry, and a good probe can provide the required fidelity for testing. To achieve this, even passive probes must have a large number of passive component compensation circuits (RC networks) internally.
10. Is there a way to use an oscilloscope to measure the operating status of a high-frequency transformer or inductor core?
You can use the power analysis software that comes with the oscilloscope. One of its functions is BH curve analysis, which can reflect the working state of the magnetic core, measure the dynamic inductance value, and determine the core loss.
11. Can an oscilloscope perform Fourier decomposition?
Most modern digital oscilloscopes have FFT functionality, but it's important to be aware of the number of points that FFT can analyze, as this directly determines the accuracy of the FFT analysis results and helps avoid spectral leakage.
12. Can an oscilloscope perform filtering? For example, can it perform low-pass filtering on a PWM wave?
Oscilloscopes typically have a 20MHz bandwidth limit, which is a hardware filter. Some oscilloscopes also support software filters with adjustable cutoff frequencies.
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