Probe is a necessary tool for engineers. It is used to connect and detect the device under test, which is very important for testing and measurement. In the face of different application requirements and different brands of probes, there are often many problems in the selection and use of probes, so how should engineers solve the many questions about probes?

1、 What is a probe?

Oscilloscope probe is a kind of equipment or network that connects the signal source to the input of oscilloscope. No matter what the probe is actually, it must provide a convenient and high-quality connection between the signal source and the oscilloscope input. The probe is the bridge between the oscilloscope and the object to be measured. Without this bridge, the oscilloscope can not read the information of the object to be measured.

2、 Why are there so many probes?

A wide range of oscilloscope models and functions are available, which is only one of the basic reasons for the emergence of a large number of probes in the market. Different oscilloscopes require different probes. 400MHz oscilloscope requires a probe with 400MHz bandwidth. However, many probes with the same function and cost will compete for 100MHz oscilloscope. Therefore, a set of different probes must be designed to support 100MHz bandwidth. Generally speaking, the probe that matches the bandwidth of oscilloscope should be selected as far as possible.

3、 How to choose a probe?

What is the effect of adding an oscilloscope to the test point?

Due to the wide application and demand of oscilloscope measurement, there are many oscilloscope probes available in the market, so the process of probe selection is easy to cause confusion. In order to reduce a lot of confusion and narrow the selection process, it is very important to always follow the probe recommendations of the oscilloscope manufacturer, because different oscilloscopes are designed for different bandwidth, rise time, sensitivity and input impedance considerations. To make full use of the measurement function of the oscilloscope, the probe should match the design considerations of the oscilloscope.

4、 How does the probe affect the measurement?

In order to obtain the oscilloscope display of the signal, a part of the signal must be converted into the input circuit of the oscilloscope. The circuit behind the test point (TP) is represented by the signal source es and the impedance ZS1 and ZS2 of the related circuit, which is the normal load on es. When the oscilloscope is connected to the test point, the probe impedance ZP and the oscilloscope input impedance Zi become part of the load on the signal source. According to the relative value of impedance, adding probe and oscilloscope in the test point leads to various load effects.

5、 What are the probe indicators?

Distortion (general index), accuracy (general index), ampere second product (current probe), attenuation coefficient (general index), bandwidth (general index), capacitance (general index), CMRR (differential probe), decay time constant (current probe), direct current (current probe), frequency current rating decrease (current probe), rise time (general index), etc Tangent noise (active probe), temperature range (general index), threshold voltage (Logic Probe)

Editor in charge: PJ

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