How to measure the refresh rate of oscilloscope

1、 Waveform refresh rate concept

Waveform refresh rate is also called waveform capture rate , It refers to the number of times the clock waveform is refreshed per second , Expressed as the number of waveforms per second （wfms/s）, The higher the waveform refresh rate , The greater the probability of capturing abnormal signals . Some people will be curious , Screen refresh is usually only a few dozen hz, You can only refresh dozens of pictures per second , Can so many waveform screens be displayed ？ in fact , There is also a waveform synthesizer in the oscilloscope , Pictured 1 Shown , The waveform synthesizer will combine multiple frames of waveforms into one picture , Although the screen only refreshes dozens of pictures per second , But each picture contains thousands of frames of waveforms , So no matter how high the waveform refresh rate is, the screen can be displayed .

chart 1 Waveform synthesizer

2、 The preparation of the instruments

The preparation of the instruments ： Be measured

Oscilloscope

、 Measuring instrument （ Oscilloscope 、 Logic analyzer ）、20Mhz Signal source .

Each frame of waveform sampled by the oscilloscope , Will be in Trig out Output a pulse signal , This Trig out The interface is usually on the back of the oscilloscope , So we can measure Trig out Signal to measure the waveform refresh rate of the oscilloscope . We will measure ZDS4000 Waveform refresh rate of oscilloscope , choose ZDS1000 As a measuring instrument , among ZDS4000 Pick up 20Mhz Signal source ,ZDS1000 Pick up ZDS4000 Of Trig out The signal , If you don't have an extra oscilloscope , Logic analyzer can also be used as measuring instrument .

3、 Oscilloscope settings

The nominal waveform refresh rate of the oscilloscope is usually the maximum value , In fact, the refresh rate of base gear is different at each level , We need to find the base gear with the highest refresh rate . First ZDS4000 The display type is set to dot ,ZDS1000 Turn on the hardware frequency meter , Real time measurement of the oscilloscope under test ZDS4000 Of Trig out signal frequency , And then ZDS4000 Horizontal time base from the minimum gear 500ps Spin big , Observe Trig out frequency , Find the maximum , You can see , Pictured 2 Shown ,ZDS4000 stay 10ns Time base gear ,Trig out The frequency is the highest .

chart 2 find Trig out The gear with the highest frequency

4、 Refresh rate calculation

A lot of people directly put Trig out Frequency as waveform refresh rate , Actually, it is not allowed , Because the waveform refresh rate refers to the number of waveform captures per second , And some oscilloscopes Trig out It is intermittent , Some are persistent , The best way is to count Trig out The number of pulses per second is the exact waveform refresh rate . Pictured 3 Shown , open ZDS1000 Statistical measurement function , The horizontal time base is set to 100ms gear , The total sampling time is 1.4s,RiseCount The rising edge counter is 1.4647M, Is equivalent to 1s by 1.046M about , explain ZDS4000 The maximum refresh rate of the oscilloscope is 1.046Mwfms/s.