Accessory Use of Oscilloscope Passive Probes
Firstly, let's start with the earth wire. Usually, the standard 15cm long black ground clamp can be used to connect the earth wire, but such a long earth wire will generate large oscillations due to the inductive effect when measuring high frequency signals, and then coupled into the switching power supply occasions will also be very noisy. Many people may not know, commonly used 500MHz passive probe in the use of such a long ground with a bandwidth of 200MHz ~ 300MHz is not bad. So if you want to do high-frequency measurements, you need to use a short earth wire, such as some grounded spring pins or spring tabs. The use of such a short earth wire brings a problem that may not be able to find a suitable ground point near the detection point, and then lead to a long wire will increase the inductance, so through the corresponding grounding of the copper sheet to the reference ground near the detection point. Because of the large cross-sectional area of the copper sheet itself, its inductance is small and it can provide an ideal ground reference point. Below is an example of a test using a spring-loaded grounding lug in conjunction with a grounded copper sheet.
A little more about signal detection. We all know that the probe in front of the probe hooks can be removed with the front of the probe to do the measurement, but the probe if too thick if it is not convenient to measure some high-density pins, and too thin if the permanent and may be damaged. Therefore, some probes have some spare parts for the probe, which can be easily replaced by the user. When replacing the probe, use a pliers to pull off the original probe and replace it with a new one.
For some high density QFp or DIp package devices, if you want to use the probe directly on the chip pins to do the probe is usually more dangerous, because the probe may slide away from the two adjacent pins resulting in a short circuit. For this application, some probes are supplied with plastic IC tips. These tips are placed on the front of the probe and their wedge-shaped structure ensures that the tip of the probe does not slip off while making reliable contact, thus avoiding the risk of a measurement. These IC probes are colour coded for different chip pin spacings and can support pin spacings from 0.5mm to 1.27mm.
Another approach for on-board signal testing is to use sleeves or very small grappling hooks. Sleeves are better suited for direct connection with
Sleeves are better suited for direct connection to the pins on the board, while the grappling hooks attached to the front of the sleeve can be very easily hooked onto the pins or leads of the chip. Of course, this method offers convenience while also affecting the bandwidth of the probe due to the long ground and signal wires used. Smaller grappling hooks can also be supported down to a minimum pin pitch of 0.5mm.
Probe accessories are also available for special applications. For example, for some critical signals on the board, if you want to measure them as easily and reliably as possible, you can reserve a probe adapter on the pCB when practical. When you need to test, you just need to plug the probe into the adapter, which guarantees the bandwidth and facilitates the measurement. In addition, if the signal under test can directly provide the output of the coaxial connector, such as BNC interface, it can also be connected directly through the probe's BNC adapter and BNC cable, is also very reliable and convenient.
There are also some tests such as jitter, eye diagrams, templates, etc. that require off-hand testing because of the long measurement time required. The hand-held method is convenient but unreliable and does not last very long. The easiest way to test off-hand is to attach the probe to a 2-legged probe clamp and press it against the test point by gravity. For more complex situations, there is also the option of a 3-dimensional probe arm which clamps the probe in place and adjusts the position and angle of the probe as required. This 3-dimensional probe holder to do a good job if the price is very expensive, even more than the price of an ordinary passive probe, so only in some special measurement occasions will be used.
The hand-held method is convenient but unreliable and does not last very long. The easiest way to test off-hand is to put the probe on a 2-legged probe clamp and press it against the test point by gravity. For more complex situations, there is also the option of a 3-dimensional probe arm which clamps the probe in place and adjusts the position and angle of the probe as required. These 3-dimensional probe arms can be very expensive if they are well made, even more than the price of a normal passive probe, so they are only used in some special measurement situations.
In addition, passive probes usually come with a small screwdriver to adjust the matching capacitance, or there are colour rings that can be attached to the probe to distinguish between different channels.
