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How to know whether the oscilloscope is accurate
- 2017/6/22 10:00:00 -

It’s enough for engineer when the waveform captured by oscilloscope occupy 2 divisions of the display area. They don’t think it’s necessary to zoom the waveform to a full screen size. And it’s wrong actually. Today we’ll see why we need to put the waveform at full size of the screen.

The difference between 2 division and full screen display is that the waveform would be “extended”. This cause the change of vertical scale value, which influence the accuracy of vertical measurement. The relation between 8-bits ADC and vertical measurement appears mostly important.

Take the ruler for example, if you take 1m ruler to measure 1.6cm object, it will be 2cm at result. And if you use 10cm ruler, it will come to 1.6cm. This is to say, the smaller the measure unit, the more accurate it is.

So, how does the change of vertical scale value influence the accuracy of measurement?

1. Influence from vertical resolution

The normal digital oscilloscope in the market integrates 8-bits ADC. Every

waveforms are reunited by 256 units of “0” and “1”. We assume that 8 divisions

are the full scale at vertical side, and the quantification level at 256. While the

vertical scale is 500mV/div, the vertical precision will be (500mV x

8)/256=15.625mV. For the same signal, when the vertical scale switch to

50mV/div, that is (50mV x 8)/256=1.5625mV. The vertical precision reaches

1.5625mV.

To make the measurement accurate, you can follow the tip:

Make the measured signal occupy around 6 div of the display screen. Like when you measure a 7Vpp Peak-Peak value sine waveform, the vertical scale should set at 1V/div instead of 2V/div or 5V/div. Furthermore, the voltage resolution is also involved in. Like when it’s on 1V/div voltage, the resolution will be 1V/25=40mV. When it is at 10V/div, the resolution will be 10V/25=400mV. It can be seen that at 1V/div, the resolution will be higher and the value more accurate.

This is also why OWON produce 12 and 14 bits oscilloscope. When using the high vertical resolution oscilloscope, engineers shall not worry for the mistake causing from signal reunite. 12-bits XDS oscilloscope is 16 times clearer against 8-bits one. That is 4096 units of “0” and “1” to reunite a waveform. Even more in XDS2000 series with 14-bits resolution and 16384 units to reunite the waveform. Not only will it makes your vision more clear, but also keep the measured value accurate. That is what OWON keeps doing – makes your best need.