How Do I Choose the Best Multimeter with Oscilloscope?

The analog oscilloscope uses an analog circuit (oscilloscope, the basis of which is an electron gun). The electron gun emits electrons to the screen. The emitted electrons are focused to form an electron beam and hit the screen. The inner surface of the screen is coated with fluorescent substances. The point hit by the beam will emit light.

Chinese name: Analog oscilloscope
Foreign name: Analog oscilloscope

Principle: Electron beam deflection
Use: Measuring signal amplitude

Introduction to Analog Oscilloscopes

How to calibrate an analog oscilloscope

Oscilloscopes, like other instruments (such as multimeters), must be calibrated before use. The so-called calibration of the oscilloscope is to correctly debug the original waveform of the oscilloscope before testing. In other words, the corrected waveform must be consistent with the parameters set by the oscilloscope itself (these parameters are usually marked at the calibration test point). Take the GW GOS-602 oscilloscope as an example (left picture): the lower left corner of its panel is the parameter that requires the correction waveform, such as the voltage value is 2V, the frequency is 1KHz, etc. (right picture), it is the oscilloscope correction waveform (or positive) , Cosine wave, square wave), the peak-to-peak voltage is 2V, and the frequency is 1KHz. However, the oscilloscope usually cannot directly display the frequency of the waveform. Instead, the frequency is converted into a period according to the conversion between frequency and period (T = 1 / f), and then the frequency is represented by the periodic wave (the equivalent period of the frequency 1KHz is 1mS).

In the process of correcting the waveform, in order to facilitate the observation of the waveform, the center position of the waveform should be adjusted first. This requires the switch of the modal signal connected between the inputs to the GND position (bottom left). At this time, if the power is normally connected, a horizontal bright line should be displayed; if it is not displayed, then POSITION, DC BALT and INTER should be adjusted up and down. Among them, POSITION is the waveform up and down adjustment button (middle picture), DC BAL is the center adjustment of the horizontal bright line, and INTER is the brightness adjustment. If the bright line is unbalanced (relative to the X axis), use a non-inductive screwdriver to adjust it. In TEACE ROTATION near the FOCUS (bottom right), then adjust the convergence to the best state by adjusting the FOCUS.

Analog oscilloscope first job

After completion, convert GND to AC (Figure a); when inputting the correction waveform, adjust the attenuation or expansion button to the original position. If the dial is wrong, it will seriously affect the accuracy of the measured waveform value. The channel selection is completely controlled by the MODE selection key (Figure b); if the debugged waveform is flickering, then it is necessary to consider the synchronization function key, that is, LEVEL (horizontal synchronization adjustment)

Analog oscilloscope cycle number adjustment

And the adjustment that usually needs to be adjusted is the peak-to-peak voltage and the number of cycles, which is also the content of our waveform testing. These adjustments are completed by the cooperation of buttons VOLTS / DIV, TIME / DIV, SWP.VAR, and VOLTS / DIV. Which value is indicated by the mark on each button indicates that this value is the unit value of each cell on the display axis. . The abscissa indicates the period, and the ordinate indicates the voltage amplitude. For example: VOLTS / DIV white designated point is dialed at 1V (bottom left), which means that the voltage amplitude of each cell on the ordinate is 1V; it will be specified on TIME / DIV The dot points to 1mSV (bottom right), which means that the period of each small cell on the abscissa is 1mS. According to the number of unit cells occupied by the waveform, the amplitude and period of the waveform can be directly read (or read after empirical calculations), which can be used to judge whether it is straight or not, and analyze the cause of the failure. So before using

Before the analog oscilloscope is officially calibrated

Calibration is very important

Before the official calibration, according to the reference value of the lower left corner of the oscilloscope, the voltage range should be set to the unit of 1V and the period range to 1mS (of course, you can also choose other unit values). Confirm which CHANNEL is used or which CHANNEL is used together (which one is used depends on where you set the MODE selection function): CH1 (first trace), CH2 (second trace) , DUAL (use of both traces), ADD (double trace overlay). Press POWER to start the adjustment, and set the input coupling mode to GDN (input to ground). This is used to correct the center position of the waveform. In conjunction with this function key, there is POSTION (waveform up and down adjustment button). Because the waveforms we measure are often pulse signal waveforms, when the center position is adjusted, the gear is normally set to AC (AC input), while the DC gear (DC input) is less commonly used.

Analog oscilloscope input method

After setting the input mode to AC, connect the probe of the signal transmission line to the calibrated test port (bottom left), and you can see the square wave on the display. But the square wave at this time is not necessarily standard (correct). It is possible that the peak-to-peak voltage is insufficient and the period is incorrect. This time is to test your familiarity with the functions of this oscilloscope. There is a button in the center of the axis of the voltage button, which is used to compensate for the voltage value. Under normal circumstances, it is rotated right to the card position lock (middle picture), and it can be used normally. If the correction parameter value still cannot be restored after locking, this voltage amplitude compensation potentiometer should be used to compensate. The cycle adjustment button is not so hidden. It is located to the left of the large button set in the cycle unit, and it is labeled SWP VAP. It can adjust the waveform cycle. At the same time, there is a POSMCN button on the left side of the SWP VAPR, which is used to horizontally translate the waveform (bottom right), it is used to coordinate the use of the WSP VAP, allowing us to observe or adjust the waveform period more accurately and conveniently. The original waveform of the oscilloscope can be set to match the calibration reference value. If this happens, the waveform cannot stand still when the probe is connected to the calibration test port. It may be because the LEVEL located to the right of the large cycle button has not been debugged. The name of LEVEL is called "tracking level", and its actual function is to supplement the horizontal synchronization control. When two tracks are used at the same time, the level cannot be synchronized. At this time, the TRIC on the LEVEL head must be considered. ALT Press the key, this is a mandatory lock. If you are familiar with using these keys, it is not difficult to correct the original waveform of the oscilloscope.

Performance characteristics of analog oscilloscope

Simple operation-all operations are on the panel, the waveform response is timely, and digital oscilloscopes often take longer to process.

High vertical resolutioncontinuous and infinite. Digital oscilloscope resolution is generally only 8 to 10 bits.

Fast data updatecapture hundreds of thousands of waveforms per second, and digital oscilloscopes capture dozens of waveforms per second.

Real-time bandwidth and real-time display-The bandwidth of continuous waveforms is the same as that of single waveforms. The bandwidth of digital oscilloscopes is closely related to the sampling rate. If the sampling rate is not high, interpolation calculations are needed, which is prone to confusing waveforms.

Notes for Analog Oscilloscopes

One thing that can't be paid special attention to when correcting the waveform is: the signal attenuation line of the signal transmission line (see Figure 15). When it is dialed to * 1, it means no attenuation (usually set point); when dialed to * 10, it means 10 times attenuation, usually when the frequency of the input signal is too low, its corresponding period will become very large. It is necessary to perform attenuation before testing, but it is still necessary to improve by 10 times in the test results, this is the original waveform value. The other is the expansion button (* 10 disk MAC) located between SWP VAP and POSMCN (see Figure 16). When the cycle unit number is set to the lowest microsecond value and the waveform cannot be seen clearly, or when the frequency of the waveform is very high, this expansion button is used. In other words, the so-called expansion and attenuation are only for the period, but have no effect on the voltage amplitude, and whether it is for expansion or attenuation, the period multiple must be reduced or enlarged accordingly after adjusting the waveform. In order to make the waveform reading more accurate and clear, the original calibration waveform must be adjusted to the most accurate, clear, and finest lines. Only in this way, the reading will be the most accurate and the error will be minimized. This often plays a significant role in fault analysis. One last thing to note is that after the adjustment of the calibration waveform, all compensation buttons cannot be moved or changed (that is, SWP VAP and voltage compensation), otherwise the oscilloscope will be recalibrated again.

Requirements for the use of analog oscilloscope: pay attention to waterproof, drop-proof and dust-proof!

Application of analog oscilloscope in troubleshooting of instrument and equipment

An oscilloscope is an instrument that uses the deflection of an electron beam to reproduce the instantaneous image of an electrical signal. It can not only measure the amplitude of voltage, current, and other signal amplitudes, but also measure its period, frequency, and phase, and can intuitively, Visually display the waveforms of various electrical signals. Oscilloscopes are an important inspection and diagnostic tool in the troubleshooting of instruments and equipment. Many people compare them to the "eyes" of maintenance technicians. In fault inspection, we can apply waveforms Observation, signal tracking, signal injection, etc., to carry out surveillance observation, measurement observation and verification observation. By detecting the relevant test points of the circuit, understand the working condition of the circuit, check the quality of the electronic components, and determine and Judging the overall performance and existing problems of electronic instruments or equipment) ^[1] .

1) Check the ripple voltage of DC system

The ripple voltage of the power supply has a great impact on the operation of the instrument. The size of the ripple voltage in a DC stabilized power supply usually has corresponding technical indicators or requirements. If it exceeds its specified index, the instrument will not work well. In the actual work, the author has encountered many cases where the instrument cannot work normally due to the increased power supply ripple. For example: an imported COZ incubator worth tens of thousands of yuan, the set temperature during cell culture is 37 ° C, The actual displayed temperature only jumps between 24 ~ 30 , and the temperature always rises below the set value. The displayed temperature jump indicates that the display signal is mixed with interference signals; the temperature rises below the set value, which indicates the control circuit Runaway control. Check with oscilloscope and found that the ripple voltage is very large (nearly 4V). It is suspected that the filter capacitor capacity t has deteriorated. Replace the filter capacitor and the instrument is working normally. It is the ripple that affects the measurement and temperature control. When the instrument is unstable, don't forget to check the ripple of the power supply) ^[1] .

2) Check the relevant test points or relevant circuit waveforms in the circuit

Some instruments are attached with circuit diagrams, and the circuit diagrams are marked with test points and their waveforms. Check the test points with an oscilloscope, observe their waveforms, analyze their differences, and quickly find their faults. ^[1]

3) Check the working waveform of the loop-free paper circuit or related components. Before checking, the following preparations should be made

Observe the connection and structure of the circuit or device under test, refer to related materials, find similar circuits or devices, analyze and compare them, clarify the principle as much as possible, and draw the circuit block diagram. Make sure that the measurement is targeted. Modules that are wiped or blackened and cured can be regarded as a "black box". According to their pin conditions and peripheral components, describe their circuits, push their circuit structure, and look for input by people. Then check with waveform observation method) ^[1] .

In the above fault inspection, the oscilloscope is mainly used for monitoring observation. Its method is mainly the waveform observation method.

4) Side. Relevant technical parameters of the circuit or the whole machine

In this kind of detection, the oscilloscope is mainly used for measurement or verification observation. Its method mainly uses the signal injection method. Take audio amplifier as an example. Using auxiliary instruments such as oscilloscope and signal generator, you can measure the amplifier's voltage gain, output, etc. Human impedance, output impedance, output power, intermodulation distortion, etc. Similar to this, using this method, you can also measure the frequency response and rise time of the oscilloscope and verify some parameters of the oscilloscope) ^[1] .

5) Check the quality of the digital integrated circuit

Commercially available integrated circuit testers have full functions and wide use, but are not fully popular at present due to their high price. In the troubleshooting of instruments and equipment, often the problem of checking the quality of integrated circuits is encountered, and the conditions are limited. Next, we can do it ourselves and make some simple and practical instruments. For example, sine wave signal generator, square wave signal generator, high and low signal generator. There are many circuits in the former two instruments, and the latter generator is checking digital integration. The circuit has a large purpose. Use it as a signal source, use an oscilloscope as a monitor, and if necessary, add a wave generator to check a variety of digital integrated circuits. For example: various gate circuits, inverters, Buffer, decoder, flip-flop, bus data transceiver. In addition, it can also be used as the data line and address line of the microprocessor, to do some simple microprocessor experiments, or to check some simple processor failures. ^[1]

6) Check the quality of the sensor

Many sensors plus their preamps can form a special signal source. For example: temperature transmitter, pressure sensor, photoelectric sensor, infrared sensor, etc. Therefore, when repairing a digital temperature controller, we can use a heating method to warm up the sensor, and then use an oscilloscope to observe the change of its voltage at the output of the preamplifier. When repairing a digital balance, an intermittent force can be added to the balance. Use an oscilloscope to observe the change in voltage before AD conversion. Check the quality of the sensor, check the faults of the related circuits, and some sockets with signal output can also be used as signal sources. For example, R, B, etc. found on the computer monitor socket, G, H, V signals are very useful when repairing the display. With this, we can use oscilloscope traces to check the relevant circuits of the display. In addition, there are some hidden signal sources, such as electromagnetic field signals at specific frequencies in the air, plus Adjusting the harmonic circuit and its amplification circuit can constitute a high-frequency or ultra-high-frequency signal source. When inspecting equipment such as receivers and televisions, you can also use an oscilloscope to find faults (Note: only observe the signal With) ^[1] .