T&M Coaxial Shunts: User Guide

In pulse testing, the coaxial shunt, as an indispensable part of pulsed current testing, is being used more and more widely,

However, many engineers still have questions about the use and installation of coaxial shunts. This article answers these questions.

Coaxial shunts can be divided according to the test current magnitude into coaxial shunts for general pulse testing and coaxial shunts for high pulsed-current testing of modules.

We will provide usage instructions for these two types.

SDN-414 series and SDN series

The SDN-414 series and SDN series are mainly used for current testing in general pulse testing; their power dissipation is relatively low and they cannot withstand the energy of high currents.

These two series of coaxial shunts are generally divided by the way they are connected to the circuit into nut type and pin type. For the use and installation of the nut type, refer to the 探头之家 video guide,

The following are usage instructions for the pin type.

The dimensional and appearance illustration of the pin type is shown below (this image is a randomly selected pin-type image).

In the above figure, red box 1 is the ground pin.

In the above figure, red box2 is the signal pin.

As can be seen from the figure, the part of the pin type that connects to the oscilloscope is a BNC connector, and a BNC cable can be used to connect directly to the oscilloscope.

Because the coaxial shunt measures current using Ohm's law as the principle, the signal output from the coaxial shunt to the oscilloscope is a voltage signal,

Considering the port voltage rating of the oscilloscope, an attenuator can be connected to the port according to test requirements to scale down the signal voltage proportionally, thereby protecting the oscilloscope port.

The part of the pin-type coaxial shunt that connects to the circuit is shown in the figure as two separate pins; connection to the circuit can be made by soldering lead wires to introduce it into the circuit.

Note: when soldering the signal pin, the solder joint should be as close as possible to the end with the insulating layer; this operation can minimize the introduced stray inductance.

The actual diagram of the pin type connected to the circuit is as follows:

An example of the pin type connected to a PCB is as follows:

In addition, the following is an introduction to the nut type; the appearance and composition of the nut type are shown in the figure:

Red box in the figure above1Connect to the positive terminal (signal)

Red box in the figure above2 connects to the negative terminal (ground)

As can be seen from the figure, connection to the oscilloscope can be made directly with a BNC cable. When connecting the coaxial shunt into the circuit, the threaded section where the small nut is located connects to the positive terminal,

The threaded section where the large nut is located connects to the negative terminal. This structure makes connection to the circuit board more convenient. When drilling holes in the circuit board to connect the coaxial shunt,

Adding a washer between the large and small nuts can protect the shunt from being damaged by tightening; a suitable socket can of course also be used for connection.

Schematic diagram of nut-type connection to a circuit board is as follows:

A series and M series

Testing large pulse currents requires the coaxial shunts in the test module; the most typical A series and M series are selected from them.

The A series can be divided into two types according to body length: one with a short body and one with a long body. The short-body type has low power dissipation, and the long-body type has high power dissipation.

In addition, the A series does not distinguish between pin-type and nut-type; all products of this type are nut-type.

Dimensional drawing of the short-body type is as follows:

For this type of coaxial shunt, connection to the oscilloscope port can be made directly with a BNC cable; when connecting it into the circuit, the yellow threaded section connects to the positive terminal,

The threaded section above the gray part connects to the negative terminal. Generally, for connection to a circuit board, holes are drilled in the circuit board or lead wires are brought out to connect to the coaxial shunt,

Bringing out lead wires is generally not recommended because this introduces unnecessary interference. When connecting into the circuit through drilled holes, washers can be added at the circuit connection positions or a suitable socket can be used,

which can reduce interference in the measurement.

Dimensional drawing of the long-body type is as follows:

The method of using this type of product for circuit testing is basically the same as that for the short-body type, but considering that it is longer and heavier,

therefore these properties need to be taken into account during use.

The M series can also be divided into two categories according to physical length; likewise, the longer version has higher power dissipation, and the shorter version has lower power dissipation.

M series products are also all nut-type; the dimensional drawing for the short version is as follows:

The connection between the M series coaxial shunt and the oscilloscope port also directly uses a BNC cable; when connected to the circuit, the threaded part is connected to the positive terminal,

The grounding part is its housing; the distance between the ground terminal and the signal terminal should be as short as possible, which can make the measurement more accurate and reduce introduced stray inductance.

The dimensional drawing for the long version is as follows:

The usage method of this model is basically the same as that of the short M series products, but because it is longer and heavier, attention must be paid to this aspect during use.

Of course, in addition to the above models, there are many other coaxial shunt models; the above models are relatively common and more frequently used by customers.

Other models can be found on the T&M official website; in addition, products can be customized according to the power dissipation and bandwidth required by the user.

If you have other questions or related technical inquiries, you can contact our staff for consultation.