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 waveform curves of various signals' amplitudes changing over time, and it can also be used to test various electrical quantities, such as voltage, current, frequency, phase difference, modulation amplitude, etc. Below 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 stage, control circuit), UPS (uninterruptible power supplies), electronic rectifiers, energy-saving lamps, frequency converters, or other electronic equipment that cannot be isolated from AC220V mains power, the DP100 high-voltage isolation differential probe must be used. Other precautions for oscilloscope use:
(1) Frequent power-on and power-off should be avoided for thermoelectronic instruments, 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 the "Y input" should not be too high to avoid damaging the instrument, and should not exceed 400V even at maximum attenuation. When the "Y input" wire is suspended, interference waveforms will appear due to external electromagnetic interference, and this phenomenon should be avoided. (4) Before powering off, turn the brightness adjustment knob counterclockwise to the end to reduce the brightness to the minimum, and then turn off the power switch. (5) When observing and adjusting the bright spot on the screen, the brightness of the bright spot should be moderate and not too bright. 12 Questions and Answers on How to Correctly Select an Oscilloscope
1. What is the most valuable specification of an oscilloscope? Bandwidth. This is a high-end parameter; increasing bandwidth increases the cost and thus the oscilloscope's performance level.
2. How high should the sampling rate be to meet the requirements? Generally, a sampling rate of 5 times the bandwidth is sufficient. For example, a 200MHz bandwidth oscilloscope only needs a 1GHz sampling rate. Pursuing a higher sampling rate is simply to catch small glitches, but these high-frequency glitches are already filtered out at the bandwidth level, so a higher sampling rate does not bring significant benefits.
3. What is the difference between normal trigger and automatic trigger? Normal: Normal (standard) trigger requires a trigger event that meets the conditions to sample the waveform; Auto: Automatic trigger, after waiting for a period of time, if no trigger event meets the conditions, it will forcibly trigger and sample the waveform. Because the trigger position is random, it often leads to unstable waveform display. If the above situation occurs, please use Normal mode.
4. How to capture abnormal signals with uncertain conditions? You can use stencil triggering to capture them. When stencil triggering is enabled, the stencil is treated as a layer. It continuously detects whether a waveform touches the stencil's area. When a waveform touches the stencil, a signal is detected, filtered, and then displayed.
5. Are the oscilloscope channels isolated? The oscilloscope channels are not isolated; the oscilloscope ground is connected to earth ground and cannot be directly connected to the neutral wire; adding an isolation transformer can indeed allow direct measurement of 220V mains power, but this is not recommended. The safest and correct approach is to use a differential probe.
6. Which is more accurate for measuring voltage: an oscilloscope or a multimeter? A general-purpose oscilloscope has a vertical resolution of 8 bits. Measurement accuracy depends on the vertical resolution and the vertical range selected. A multimeter is much more accurate; a 6.5-digit multimeter can reach 24 bits with its ADC, and handheld multimeters offer far more than 8 bits. Voltage values measured by a multimeter are more reliable.
7. What is the difference between the X1 and X10 ranges of an oscilloscope probe? There are two main differences: the attenuation bandwidth is different. The signal amplitude is not attenuated in the X1 range, while the signal amplitude is attenuated to one-tenth of the original value in the X10 range; the bandwidth is different. The bandwidth of the X1 range is only about 10 MHz, while the bandwidth of the X10 range is about 250 MHz.
8. Do oscilloscope probes generally need to be calibrated periodically? There are no explicit metrological regulations for probes, but for passive probes, at least when replacing the probe or changing the probe channel, probe compensation adjustment must be performed.
9. What are the main factors determining the price of oscilloscope probes? The main factors determining price are, of course, bandwidth and functionality. Oscilloscope probes come in many types with different performance characteristics, such as high-voltage, differential, and active high-speed probes, with prices ranging from a few hundred RMB to nearly ten thousand USD. The probe is the part of the oscilloscope's contact circuitry; 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 built into the oscilloscope. One function is the BH curve analysis, which can reflect the operating status of the 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 the 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, such as low-pass filtering of a PWM wave? Oscilloscopes typically have a 20MHz bandwidth limit; this is a hardware filter. Some oscilloscopes also support software filters with adjustable cutoff frequencies.
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