The Importance of Oscilloscope Probes
1. Safety
When using probes for measurements, the most important issue is safety. For example, when using a passive probe, the ground wire of the probe is connected to the ground of the oscilloscope. When the oscilloscope is safely grounded, the probe is safe. However, when the oscilloscope is not safely grounded, there will be a certain voltage in the ground wire of the probe, which will cause danger to the user.
2. Connection sequence
The probe is indirectly grounded through the ground wire of the oscilloscope's power cord, and the system under test may be a suspended system. To avoid danger, the ground wire must be connected to the ground first, and the oscilloscope and the system under test must be grounded together before the probe can be touched. on the test point. When disconnecting the probe, disconnect the probe first and then disconnect the ground wire.
3. Impedance
When using a probe, you need to consider the matching issue with the oscilloscope. Common passive probes generally require an oscilloscope with an impedance range of 1MΩ. Some active probes require 50Ω impedance. Before using the probe, read the instructions on the corresponding impedance in the manual to select the corresponding oscilloscope gear to match it.
4. Bandwidth
When using a probe for measurement, the bandwidth of the entire system is composed of two parts: the probe bandwidth and the oscilloscope bandwidth. If either bandwidth is insufficient, the final measurement result will not meet the requirements. For example, if you choose a 100M probe to match a 500M oscilloscope, the bandwidth will only be about 100M at most, so you cannot take advantage of the bandwidth advantage of the 500M oscilloscope. Therefore, only by selecting the oscilloscope and probe appropriately can the test bandwidth meet the requirements.
5. Voltage
When selecting a probe, you also need to consider the voltage of the test signal. On the one hand, you must ensure that the test voltage is not higher than the maximum input voltage of the probe. On the other hand, you must also ensure that the signal output by the probe is within the measurable range of the oscilloscope. This requires the tester to select the probe based on the voltage of the test signal. For example, if you want to measure a voltage signal of 600Vpp, you need to choose a probe with a withstand voltage exceeding 600Vpp. Generally, the maximum measurement voltage of an oscilloscope is 80V, so you need to choose a probe with an attenuation ratio greater than 8. If the signal that needs to be measured is a voltage signal of 10mVpp, a non-attenuated probe needs to be used for measurement.
6. Influence of ground wire
According to traditional usage habits, the grounding method of the oscilloscope is the long ground clamp wire. This grounding method is indeed a simple and convenient grounding method, but it is not a rigorous and accurate grounding method.
