Basic six measurements and exercises of the hottes

Fundamentals of oscilloscope (VI) -- Measurement and practice

6.1 how to measure

in the first two chapters of this book, we introduced various control mechanisms on the oscilloscope that can be used to affect the display of signal waveform. In this chapter, we will talk about important waveform parameters, which increase the stretching space (it can be increased to more than 210 meters, and will also introduce how to use the oscilloscope to measure these parameters.

the oscilloscope can measure two basic quantities, namely voltage and time. Starting from these two quantities, use the cursor manually or use the automatic method to measure all other waveform parameters.

when measuring, it is important to understand the ability of your oscilloscope. Don't try to measure in a 20MHz Observe a 10MHz square wave on the oscilloscope, because it is impossible to see the real shape of the square wave in this case. The 10MHz square wave contains 10MHz sine wave fundamental wave, 30MHz, 50MHz, 70MHz and other harmonics. On a 10MHz oscilloscope, it is also possible to see some effects of 30MHz harmonics (although its amplitude is incorrect), but the frequency of the next harmonic component is 2.5 times the bandwidth of the oscilloscope! So at this time, the waveform you see on the oscilloscope will be more like a sine wave than a square wave (see Figure 50)

the same is true for the measurement of rise time. If you use an oscilloscope whose rise time is 10 times faster than the rise time of the measured signal for measurement, the influence of the rise time of the oscilloscope itself on the measurement will be almost negligible. However, if the rise time of the measured signal of the oscilloscope is the same, the measurement error can be as high as 41%

several standard waveforms for vertically extending the industrial chain

the three most common waveforms are sine wave, triangular wave and square wave (see Figure 51). These waveforms can be found in any function generator and are often encountered in practical work

sine wave contains a single frequency component; Square wave and triangular wave are composed of many different related sinusoidal harmonics. The square wave is composed of odd harmonics of the fundamental wave, and the triangular wave is composed of even harmonics of the fundamental wave. These waveforms are symmetrical in time and amplitude

these waveforms also have their deformation forms, which is usually the result of symmetrical changes in waveforms. In this way, the triangular wave becomes a sawtooth wave (named after its beginning), and the square wave becomes a rectangular wave

frequency is the number of cycles of the waveform that occurs in one second

so if we divide 1 second by the time required for a cycle, we get the frequency in Hz

for example, if the period =1ms, then there is a small platform of fluctuation in the frequency curve =1/10 ×= 1000hz=1khz

the waveform that occurs repeatedly is called repetitive waveform or periodic waveform. This is the easiest waveform to measure

another parameter most commonly measured for repetitive or periodic waveforms is the amplitude of the waveform. Amplitude is the voltage on a waveform from the highest point to the lowest point. This is also called peak (I) peak amplitude or Vp-p (see Figure 52)

6.2 basic exercises or how to explain sine waves

the exercises contained in this part can help users get familiar with the main control mechanism on the oscilloscope. Its content is divided into two parts. First, the control mechanism of analog oscilloscope is introduced, and then the control mechanism of digital oscilloscope is introduced. Specific exercises on DSO will be given later

required equipment:

▲ oscilloscope: an analog oscilloscope Xu pm3094 (for analog oscilloscope practice only) or a combined oscilloscope, which can be selected from pm3382a... Pm3394a series or similar products

▲ two 10:1pm9010/091 or pm9020/091 probes or similar products and fine-tuning tools are used for probe compensation and adjustment

▲ function generator that can generate sine wave, square wave and triangular wave with frequency of 2MHz or higher, such as pm5135 or pm5138 or similar products

▲ two 50 Ω BNC cables

start

if the cable is connected to the oscilloscope, remove it from the oscilloscope

use the correct power line to connect the oscilloscope to the mains power supply and turn on the power switch

connect the probe to channel 1 of the oscilloscope, and connect the probe to the probe adjustment connector on the front panel of the oscilloscope

if a combined oscilloscope is used, select the analog mode

press the AUTOSET key (the green key on the upper part of the front panel)

for the old oscilloscope without this function, set it according to the above items:

brightness - middle position

vertical position control - middle position

horizontal position control - middle position

time base 0.2ms/grid

ch1 sensitivity 0.2v/grid. Note that if the automation of the oscilloscope is not high, increase the probe attenuation

trigger - trigger source ch1, mode - Auto, peak peak level trigger

confirm that the probe has been compensated. For this reason, it may be necessary to adjust the LF compensation trimming capacitance on the probe. If necessary, refer to the section "probe compensation" in Chapter 4. Now we can start to study the control mechanisms

refer to the illustrations on the front and back covers of this book to find the location of each control mechanism

screen control

adjust the brightness and focus control mechanism and observe the impact on the screen display

adjust the focus control mechanism to obtain clear scanning display and clear text display

note that in order to observe the rising and falling edges of the square wave given from the probe adjustment output terminal, the brightness of the oscilloscope needs to be adjusted to be bright. This is because the electron beam moves faster on these edges

adjust the text brightness control mechanism to make the text brightness on the oscilloscope tube reach an acceptable level

disconnect the probe from the ch1 input, and then adjust the scanning knob so that the scanning is parallel to the horizontal ruler line of the oscilloscope

place the scale brightness control knob and observe that the scale becomes bright