Brief introduction to four common oscilloscope probes

Oscilloscopes are the most familiar test instruments, but there is no way to do testing without a probe. Oscilloscope probes are indeed an indispensable member of the oscilloscope family. The performance of the probe will have a direct impact on the final test results. There are four common types of oscilloscope probes: passive probes, active probes, differential probes, and current probes. Let's give you a brief introduction.

1. Passive probe

Attenuated passive voltage probe is the most commonly used probe. The bandwidth of common passive probes is below 500MHz. Most low-end and mid-range oscilloscopes are equipped with two or four passive probes. It is a very convenient and relatively cheap probe.

High voltage probes and transmission line probes also fall into the category of passive probes.

2. Active probe

Active probes have high input impedance and can achieve very high bandwidth. The disadvantages of active probes are high cost, large size, and the need for power supply.

3. Differential Probe

Differential probes are divided into active differential probes and high-voltage differential probes. When testing high-speed signals, especially differential signals, only the corresponding active differential probes can be used for testing. Active differential probes have the characteristics of low loading effect, higher signal fidelity, high dynamic range and extremely small temperature drift. In many high-voltage signal tests, high-voltage differential probes are generally used for testing.

4. Current probe

When using an oscilloscope to test current, a current probe is used. Commonly used current probes are made using the Hall principle. They obtain current signals by measuring changes in the magnetic field around the circuit.

When choosing a current probe, you should pay attention to several main parameters: the current size of the object to be measured, the current frequency, AC or DC, the shape and size of the jaws, the power supply method, the interface form, etc.

In the actual test process, we should choose a suitable oscilloscope probe. Only in this way can we get accurate test results.

5. Probe accessories

Oscilloscope probes usually come with some accessories, such as the color rings, adjustment rods, and probe protection caps shown above.

1. Color wheel

In the picture above, the red, yellow, green and blue circles are color rings. You can see that the probe has two blue ones. This color ring is made of plastic and has an open end. It can be removed at any time and replaced with another color. The color ring will not affect the circuit being tested. It only serves as an auxiliary identification and is used when the oscilloscope has multiple probes. Look at the probe socket of the oscilloscope in the picture below. Do you see that the socket has two colors?

If your probe is matched with an oscilloscope, you can find that your probe has been equipped with red and blue color rings. You only need to plug it into the oscilloscope probe socket according to the same color when using it. Inserting it in the wrong direction will not affect the measurement circuit, but it is just easier to distinguish during measurement. Before you know this knowledge, you will definitely take the oscilloscope probe and follow the cable to see if it is channel 1 or channel 2. Did I say it right?

If your probe is broken and you buy a new one from Taobao or a market, you must first install the corresponding color ring so that it is easier to distinguish the probe channels.

2. Adjustment rod

In the picture at the beginning of the article, the darkest stick is the adjustment stick. There is a flat stainless steel in the front, which looks like a screwdriver. This adjustment stick is a screwdriver, which is used to adjust the compensation capacitance of the probe . Take out your probe and find the screw hole, as shown in the following figure:

Note: Some probe compensation capacitor adjustment holes are located at the socket, as shown above, and some are located at the probe end.

The question is, when should it be adjusted? And to what extent?

Adjustment method: Have you found the calibration signal output port of the oscilloscope? See the picture above. Connect the probe to the signal output port, and the oscilloscope will show a 1KHz square wave signal. Observe the waveform of the signal and adjust it until it is very regular. For example, if the signal starts with the waveform on the left side of the figure below, adjust it to the waveform on the right side of the figure below.

3.Probe protection cap

The above picture shows the probe tip after the probe hook is removed. It is often used to test IC pins. Looking at the probe tip, when you use it to measure a certain IC pin, will you accidentally touch the surrounding pins or short-circuit two pins? At this time, the probe protection cap comes into play. Choose a suitable probe protection cap and put it on directly.