Oscilloscope is one of the essential tools for electronic engineers. It can convert invisible electrical signals into visible images and display the changes of measured signals on the screen, which is convenient for people to design circuits and locate errors. In the components of oscilloscopes, the importance of the probe is needless to say, its quality is directly related to the accuracy of the measurement results of the oscilloscopes.
As the name suggests, the probe plays the role of detection. It is an important medium to connect the tested circuit with the input of oscilloscope. The simplest probe is a wire connecting the circuit under test and the input end of the electronic oscilloscope. The complex probe is composed of resistance capacitance elements and active devices. The simple probe without shielding measures is easy to be interfered by the external electromagnetic field, and its equivalent capacitance is large, resulting in the increase of the load of the circuit to be measured and the distortion of the measured signal.
When using inappropriate probe, it will have a greater impact on the measurement results, which can be divided into two aspects. In the first case, the probe changes the original shape of the waveform and the observed waveform deviates. In the second case, the oscilloscope is abnormal. Normal devices become inoperable.
To avoid these situations, it is necessary to be familiar with the type of oscilloscope probe, and then select and use it according to the actual situation. There are many kinds of probes commonly used, such as passive probe, active probe, differential probe, current probe, low capacitance probe, high voltage probe and so on. The following introduces the application scope of these probes, which is convenient for you to choose.
Active voltage probe: generally suitable for bandwidth greater than 500m? Hz, amplitude less than plus or minus 3 V single ended signal. Tektronix’s active voltage probe models are: p7260, p7240, tap1500, etc. Some models can measure 3dB bandwidth up to 6G.
Passive probe: generally used for testing bandwidth less than 500m? A single ended signal of 1 Hz. It is a kind of more economical probe. For example, p6139a has a wire length of 1.3 meters and a bandwidth of 500 meters? The compensation range is 8 to 12 PF, with the input impedance of 10 m Ω, the input capacitance of 8 PF, the maximum voltage of 300 VRMs.
Differential probe: generally used to test differential signal. It can be divided into high bandwidth and high voltage. High voltage differential probe can test up to 4400 V differential signal; high bandwidth differential probe can test up to 12.5g high-speed signal. Even some products can reach 16ghz.
Current probe: generally use Hall effect to test current signal. The test range is generally from DC to 2G. The amplitude is from 1mA to 20000A.
Low capacitance probe: This is a probe set for matching. At present, this kind of probe has few models in the market, and can measure up to 9g? Bandwidth? Hz。
High voltage probe: suitable for testing high voltage signal, can measure up to 4000 V voltage, can be divided into single ended and differential probes.
According to the practical experience, the most frequently used probe is passive probe, and the high resistance passive voltage probe accounts for the largest proportion. The passive voltage probe provides various attenuation coefficients for different voltage ranges, such as 1 ×, 10 ×, 100 ×. Among these passive probes, the 10 × passive voltage probe is the most commonly used one. For applications where the signal amplitude is 1V peak or lower, the 1 × probe may be more suitable or even essential. It is much more convenient to switch the 1 × / 10 × probe in the application of mixed low and medium amplitude signals (tens of millivolts to tens of volts). However, the switchable 1 × / 10 × probe is essentially two different probes in a product, with different attenuation coefficient, bandwidth, rise time and impedance (R and C). Therefore, these probes can’t match the input of oscilloscope and can’t provide the optimal performance of standard 10 × probe.
In general, passive probes are used most. Different attenuation coefficients can be selected according to different situations. In this paper, the importance of oscilloscope probe is explained, and the types of probe are introduced. In the end, explain the most frequent use of passive probe, I hope you novice after reading this article, can have a further understanding of the oscilloscope.
Editor in charge: GT