How to reduce the inherent noise of the oscilloscope

The current probe uses the Hall effect and open-loop measurement principle to convert the measured current (AC, DC, or irregular waveform current) into a measurement module that follows the output current or voltage. The primary and secondary sides are highly insulated. The secondary side truly restores the waveform of the original side, which has the characteristics of high accuracy, high linearity, high integration, simple structure, long-term stability, and adaptability to various working environments.

As the current level drops, the noise inherent in the oscilloscope will become a real problem. All oscilloscopes have an extra featurevertical noise. When you measure low-level signals, the noise of the measurement system may cause the accuracy of the actual signal measurement to decrease. Since the oscilloscope is a wideband measuring instrument, the wider the bandwidth of the oscilloscope, the higher the vertical noise. Therefore, before measuring, you need to carefully test the noise characteristics of the oscilloscope. When a 500MHz bandwidth oscilloscope uses a sensitive V/div setting, its noise floor is generally about 2mV peak-to-peak. When making low-level measurements, you need to be aware that the acquisition memory on the oscilloscope may affect the noise floor. With the same bandwidth and other conditions, the deeper the acquisition memory, the greater the noise. On the other hand, modern AC/DC current probes can measure 5mA AC or DC current with a measurement accuracy of about 3%. The design of this current probe uses current input per ampere and voltage output is 0.1V. In other words, when measuring currents below 20mA, the 2mVpp noise of the oscilloscope itself may be the main noise source.

So, how can we reduce the inherent noise of the oscilloscope to a greater extent? For modern digital oscilloscopes, there are many options:

1) Bandwidth limit filter

Most digital oscilloscopes provide bandwidth-limiting filters. These filters can filter out excess noise in the input waveform and reduce the noise bandwidth, thereby increasing the vertical resolution. The bandwidth limiting filter can be implemented by hardware or software. Most bandwidth limiting filters can be enabled or disabled according to your needs.

2) High-resolution acquisition mode

Most digital oscilloscopes can provide 8-bit vertical resolution in normal acquisition mode. Some oscilloscopes can provide higher vertical resolution in high-resolution mode, usually up to 12 bits. This mode can reduce vertical noise and improve vertical resolution. Generally, when a slower time/div setting is applied, a lot of data points are captured on the screen, and the high-resolution mode has a great influence at this time. Since the acquisition in high-resolution mode will average the data points adjacent to a single trigger point, the sampling rate and bandwidth of the oscilloscope will be reduced.

3) Average mode

If the signal is periodic or DC, you can use the average mode to reduce the vertical noise of the oscilloscope. The average mode collects periodic waveforms multiple times and generates a running average to reduce random noise. The high-resolution mode reduces the sampling rate and bandwidth of the signal, while the normal average mode does not. However, the average mode slows down the waveform update rate because it requires multiple acquisitions to calculate the average value of the waveform before it can draw a trace on the screen. When you select a large number of averages, the noise reduction effect is more obvious than any of the above methods.

Therefore, if we want to reduce the noise generated by the current probe, we must first reduce the inherent noise of the oscilloscope. The above is PRBTEK's brief introduction for you to reduce current noise. If you have any problems in the process of using the probe, welcome to visit the official website of PRBTEK.