Why Must Be Grounded In Shielded Cables?

There are many cables in life that we can't tell apart. One of these cables is called shielded cable, which is now more and more popular. Here follow the ZMS cable editor to understand some general knowledge of shielded cable.

A shielded cable is a transmission line that uses a metal mesh braided layer to wrap the signal line. The braid layer is generally red copper or tinned copper.
It is used for transformers and similar equipment.

A shielded cable is a metal shield with a shield layer grounded metal shield is an important measure to attenuate and prevent electrical interference. It includes the total shielding of the core, sub-shield, and double-layer type total shielding.

The choice of metal shielding type of control cable should be based on the strength of the impact of electrical interference that may arise. Then take into account the comprehensive suppression of interference measures to meet the requirements of reducing interference and overvoltage.
The higher the requirements for the anti-interference effect, the greater the corresponding investment.
When steel tape armored, steel wire braided total shielding is used, the price of the cable will increase by 10% to 20%.

With Shielding Cable Role

1 Anti-interference, prevent the intrusion of the external magnetic field.
2 Can be used as an auxiliary grounding body, cable breakage to ground leakage conductive circuit.
3 Anti-tension, compression, and resistance to digging enhance mechanical strength.
4 flame retardant, prevent heat sources, and a short period to grill.

Although shielded cables have more advantages, not all shielded cables are better than non-shielded cables.
In practice, it is also necessary for customers to choose the right type of cable according to their requirements to avoid unnecessary waste.

What are The Benefits of Shielding in Cables?

A shielded cable is a transmission line that uses a metal mesh braid to wrap the signal line.
The braid layer is usually red copper or tinned copper, but aluminum foil is also added.

When Is Shielded Cable Used?

In an environment where electromagnetic noise is radiated or conducted, electromagnetic noise may seriously interfere with the normal operation of electromechanical equipment. And a variety of cables used in the equipment is an important carrier of electromagnetic noise propagation class, so the need for cable shielding treatment.
Some of the objects of cable shielding are the noise source, and some other is the object of interference.
As a noise source, the cable will be like a radio transmitting antenna, the noise will be spread to the surrounding lines and equipment. As the object of interference, the cable will act like a receiving antenna, absorbing noise interference from other sources of radiation.

Shielding is to ensure that the system's interference-resistant transmission performance in an electromagnetic interference environment, while the interference resistance includes two aspects.
That is, the ability to resist external electromagnetic interference and the ability of the system itself to radiate electromagnetic interference to the outside.

The benefit of cable shielding is to reduce the interference of external electromagnetic fields to the power supply or communication lines, which affects the normal operation of the equipment. At the same time, shielded cables also have the role of preventing the line from radiating electromagnetic energy to the outside.
The vast majority of shielding systems currently used in the method of wire and cable and connections wrapped in a metal material shielding layer on the exterior can effectively filter out unwanted electromagnetic waves.

But for the shielding system, in the environment of noise interference, only the use of shielding is not enough, but also the shielding layer for good grounding.

How to Ground Shielded Cables?

Shielded cables are commonly used in industrial environments, especially in servo systems and encoders.

Shielding is used to ensure the transmission performance of the system in the presence of electromagnetic interference.
On the one hand, shielding protects against external electromagnetic interference, and on the other hand, shielding prevents the system itself from radiating electromagnetic interference to the outside.

How is the Shielded Cable Grounded?

There are two main methods of wiring shielded cables
1. Grounded at One End and Overhanging at the Other
When the signal line transmission distance is relatively far, due to the different grounding resistance at both ends or the PEN line having a current, may lead to two grounding potentials being different.

At this time, if both ends are grounded, the shield layer will be electrically popular, instead of forming interference with the signal.
Therefore, in this case generally take a point of grounding, the other end of the suspended approach, to avoid the formation of such interference.
2. Both Ends are Grounded
Both ends of the grounded shielding effect are better, but the signal distortion will increase.
And it should be noted that the two layers of shielding should be mutually insulated isolation type shielding.
If not insulated from each other should still be considered a single-layer shield.

The outermost shield is grounded at both ends to induce a current due to the potential difference introduced, thus generating a magnetic flux that reduces the strength of the source magnetic field.
This essentially cancels out the voltage induced when there is no outer shield.
The innermost shield, on the other hand, is grounded at one end and is only used for general anti-static induction because there is no potential difference.

The control cable metal shielding grounding method should comply with the following provisions

1. Computer monitoring system of the analog signal circuit control cable shield, shall not constitute two or more points of grounding, it is appropriate to use a centralized point of grounding.
2. In addition to the first item, such as the need for a point of grounding control cable shield, when the interference of electromagnetic induction is larger, it is appropriate to use two points of grounding.
The interference of electrostatic induction is larger, available one point grounding.
In double shielding or composite total shielding, it is appropriate to use one point for internal and external shielding, and two points for grounding.
3. In two points of grounding selection, it is also appropriate to consider the role of transient currents in the shield layer is not burned melt.

When using shielded cables, the shield should be connected at least at two ends equipotential.
When the system requires an equipotential connection at only one end, two layers of shielding should be used, and the outer shield should be handled according to the aforementioned requirements.

The principle is as follows

1. Single-layer shielding grounded at one end, does not form a potential difference, generally used to prevent electrostatic induction.
2. Double shielding, the outermost shield ends grounded, and the inner shield end equipotential grounding.

At this point, the outer shield due to potential differences and induction of current, so the magnetic flux reduces the strength of the source magnetic field, thus basically offsetting the voltage induced when there is no outer shield.
If it is to prevent electrostatic interference, it must be grounded at a single point, whether it is a layer or a two-layer shield. Because the single point of grounding electrostatic discharge is the fastest.