How to use oscilloscope correctly?
How to use oscilloscope correctly? At the beginning of choosing an oscilloscope, you already have a price range in mind. The price of an oscilloscope depends on a number of factors, including bandwidth, sampling rate, number of channels, and storage depth. If you only buy it based on price, you may not end up getting the performance you need.
Methods to choose one oscilloscope
(1) Confirm whether you need one analog or digital oscilloscope?
Both digital and analog oscilloscopes have its advantages and disadvantages.
With the development of modern technology, the function of digital oscilloscope is stronger, the response is faster and the price is lower.These advantages make it difficult for analog oscilloscopes to compete with advanced digital oscilloscopes. At present, almost all customers choose the digital oscilloscope, analog oscilloscope has been OUT of the basic.
(2) Confirm your demand on bandwidth
Instruments that measure ac waveforms usually have a frequency upper limit, and if the frequency of the waveform is above that the accuracy of the measurement will deteriorate.The upper limit of the frequency is the bandwidth of the instrument. Usually defined as the response of the instrument to lower the frequency by 3bB, the value of the bandwidth of the instrument you need depends on the characteristics of the signal being measured and the accuracy of the measurement you wish to obtain. An oscilloscope has two types of widths, namely, repeat (or analog) bandwidth and real time bandwidth. Many digital oscilloscopes provide analog bandwidths that are higher than their basic sampling rates. This is possible. If a signal repeats, the oscilloscope does not have to complete all the collection at one time. Instead, it can obtain part of the waveform when each trigger occurs, and constitute the display waveform after several cycles of triggering. (This process is usually so fast that you won't notice it happening.) the repeat-bandwidth metric is independent of the oscilloscope's sampling rate.In fact, this indicator is usually used to measure the bandwidth of the oscilloscope analog amplifier portion.Real - time bandwidth is suitable for non - repeating or single signal. The oscilloscope completes digitization in a trigger process, so the real-time bandwidth depends on the sampling rate of the oscilloscope, and the ratio between the sampling rate and the bandwidth is not fixed.If the oscilloscope is digitally reconfigurable, the ratio is closer to 4:1. If it is not refactored, the ratio is usually 10:1.
(3) Confirm numbers of channels you need
In general, the number of channels you need depends on the subject to be measured. At present, dual channel oscilloscopes are the most popular. For most engineers, however, a four-channel oscilloscope is more useful for some applications. The following points should be considered: do you need to capture multi-channel signals at the same triggering event?If so, choose an oscilloscope with each channel available for simultaneous sampling or independent A/D conversion. If the signal you are observing is a repeated signal, then it is not necessary to collect at the same time. Some oscilloscopes are in 2+2 form, that is, two channels are fully functional, and the other two channels are auxiliary channels with limited attenuation range. In this case, two A/D converters are Shared by four channels. Auxiliary channels provide additional flexibility when you are observing digital signals. For dual channel oscilloscopes, external triggers may be useful. It can use a signal without observation as an external trigger source without occupying the input channel of an oscilloscope. If you want to make digital timing measurements that require more than four channels of oscilloscopes, you may wish to consider using a logic analyzer. Although at this point you give up the vertical resolution of the measurement, you gain multiple channels and additional triggering and analysis capabilities.
(4) Confirm sampling rate you need
For a single signal measurement, the most critical performance indicator is the sampling rate, that is, the rate at which the oscilloscope takes a "quick picture" of the input signal. High sampling rate can produce high real - time bandwidth and high real - time resolution. Most oscilloscope manufacturers use a ratio of sampling rate to real time bandwidth of 4:l (if digital reconfiguration is used) or 10:1 (no digital reconfiguration) to prevent false waves. Some oscilloscopes provide the ability to independently control the sampling rate so that you can adjust both the sampling rate and the amount of data (time base) displayed on the screen so that the two Settings do not have to be tied down. This feature allows you to observe the waveform at the desired temporal resolution.
(5) Confirm storage depth you need
The storage depth of your oscilloscope depends on the total time range required and the time resolution required. If you want to store long periods of time at high resolution, you need to choose a deep storage oscilloscope. In this way, you can use a high sampling rate when the horizontal scanning speed is low. This will greatly reduce the chance of false waves and obtain more detailed information about the waveform.
(6) Examine and evaluate the triggering capability
Many general oscilloscope users are used to using edge trigger. In some applications, if an oscilloscope has other trigger capabilities, you will find it useful for your measurements. Advanced triggering features can isolate the events you wish to observe. In digital applications, an oscilloscope that triggers a specific pattern between multiple channels is useful for problem solving. In addition, the state trigger can be used to synchronize the mode trigger with the outer clock edge. Burr trigger occurs when positive or negative burr occurs or when a pulse is wider or narrower than the set width. These characteristics are especially important for fault detection. When the fault occurs, the forward event (using delay or horizontal position knob) is observed to determine the cause of the problem. If you need more advanced logic triggering capabilities, you can still consider using a logic analyzer. The TV trigger can trigger the presence as well as the specific line you need to observe.On some oscilloscopes, this feature is an option function.
(7) Evaluate burr catching ability
Three important factors affect the oscilloscope's burr capture ability: update rate: the digital oscilloscope must first capture data, then process it, and finally display it. The number of times an oscilloscope can complete these three processes in one second is called update rate. An oscilloscope with a fast update rate has a higher chance of capturing incidental burrs. The multi-processor structure oscilloscope has a faster update rate than the traditional single-processor structure oscilloscope, which makes it more suitable for capturing the occasional events. A multiprocessor architecture can produce display throughput and response times similar to analog oscilloscopes.
Peak detection capability: most digital oscilloscopes lose sampling points at low sweep speeds, thus reducing the effective sampling rate.This leads to the problem that narrow pulses, which are easily observed when set to a fast time base, disappear at low sweep speeds.However, for the special sampling mode of peak detection or burr detection, the maximum sampling rate is maintained at all scanning speeds, and the maximum and minimum values obtained in each sampling period are recorded.The smallest burrs that can be detected are related only to the sampling rate of the oscilloscope.
Burr trigger: an oscilloscope with burr trigger enables you to isolate burr that is difficult to detect and trigger when burr occurs. This feature can help you find the cause of abnormal conditions during circuit operation.
(8) Confirm the analysis function you need
With automatic measurements and the analytical capabilities built into an oscilloscope, you can get your work done easily and in less time. Digital oscilloscopes usually have sequential measurement functions and analysis options that analog oscilloscopes cannot have. Arithmetic functions include addition, subtraction, multiplication, division, integration and differentiation. Statistical measurements (minimum, maximum, and average) can quantitatively describe the uncertainty of a measurement, which is valuable in measuring noise characteristics and timing limits. Some digital oscilloscopes can also provide FFT function. An oscilloscope with all of the above advanced features might cost more, so you should decide for yourself whether the extra money is worth it. You'd better choose an oscilloscope with these characteristics according to the actual application.
(9) Evaluation of archiving capability
Most digital oscilloscopes can be connected to a PC, printer, or plotter via GPIB, rs-232, or a parallel port. But you should find out what kind of interface you can provide and what type of printer it will match. You should know that the output from laser and inkjet printers is of much higher quality than that from thermal printers. Using a digital oscilloscope with a floppy disk drive or software package, you can easily transfer waveform images and waveform data to a PC. These features will save time if you want to include a captured screen image in a report or if you want to convert waveform data into a table.
Analog and digital oscilloscope in the observation of the details of the waveform, which has the advantage?
1. Which is more advantageous, analog or digital oscilloscope, in looking at the details of the waveform (e.g., looking at parasitic waveforms of less than 1% at zero and peak crossing)?
2. Digital oscilloscope generally provides online display of root mean square value, its accuracy is generally what?
Answer: 1) observe parasitic waveform of less than 1%. The observation accuracy is not very good either in analog oscilloscope or digital oscilloscope. The vertical accuracy of the analog oscilloscope may not be higher than that of the digital oscilloscope. For example, the vertical accuracy of the analog oscilloscope with a certain 500MHz bandwidth is ±3%, which is not more advantageous than that of the digital oscilloscope (usually the accuracy is 1-2%). Moreover, the automatic measurement function of the digital oscilloscope is more accurate than the manual measurement of the analog oscilloscope for details.
How to use digital oscilloscope to distinguish analog bandwidth from digital real - time bandwidth?
Bandwidth is one vital index of oscilloscope. Bandwidth of analog oscilloscope is one certain value, however, bandwidth of digital oscilloscope has two kinds, analog bandwidth and digital real-time bandwidth. Digital oscilloscope to repeating the signal in a sequential sampling and random sampling technology can achieve the maximum bandwidth of the oscilloscope digital real-time bandwidth, real-time digital bandwidth and the highest frequency and digital waveform reconstruction technology related factor K = (digital real-time bandwidth digital highest rate/K), generally not directly given as an indicator. It can be seen from the definition of the two kinds of bandwidths that the analog bandwidths are only suitable for the measurement of repeated periodic signals, while the digital real-time bandwidths are suitable for the measurement of repeated signals and single signals at the same time.
The manufacturer claims the bandwidth of oscilloscope can achieve how many megabytes, it is analog bandwidth actually, digital real time bandwidth is below this value. For example, if the bandwidth of an oscilloscope is 500MHz, it actually means that its analog bandwidth is 500MHz, while the highest digital real-time bandwidth can only reach 400MHz, which is much lower than the analog bandwidth. Therefore, when measuring a single signal, it is necessary to refer to the digital real-time bandwidth of the digital oscilloscope, otherwise it will bring unexpected errors to the measurement.