Glossary Cable Assemblies

Industrial communication with BUS- and Fiber-technology

Become aware of more details of our products.  Learn more about standards, backgrounds and technology aspects. For you we did prepare everything in detail, separated according to the product groups. Enjoy by reading more!

BUS Technology

Industrial Ethernet
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Industrial Ethernet is the word for an identical infrastructure within local area networks, but with a modified protocol. The protocol is not the standard Ethernet one. This is how networks exceed the office communication and integrate industrial field devices by using the same hardware platform. At the same time process security is improved by the modified protocols and your productivity stays high. There are different protocols for industrial ethernet standard, established are such as Profinet, Ether-CAT, EthernetIP, Powerlink and Sercos III with runtimes down to 100?s. Therefore protocols are capable of real-time applications and thus motion control. This standard has established in the market more and more. There are 2 pin configuration defined by the standard A and B, B is used more often. Whenever it does not come to Gigabit networks, the use of the pins 1, 2, 3 and 6 is sufficient.

Profibus

The profibus (process field bus) distinguishes between 2 different types. There are the versions Profibus DP (decentral periphery) and Profibus PA (process automation). Within the mechanical engineering the Profibus DP standard is used. This type of bus is described by the international norm IEC 61158. Profibus DP is a 2-wire bus with 9600bit/s
to 12Mbit/s adequate for distances from 100m to 1200m. This bus is used for the electrical transmission via copper in a line based infrastructure. By using fiber optics for the transmission the distances can be extended up to 15km.

Device Net

The Device Net system is commonly used in the field of industrial automation for connecting control units to one another. Device Net uses the controller area network as its basis.

Attenuation

The attenuation describes the reduction of the signal level on the cable. Therefore signal loss. To keep the attenuation low, the make-up length is supposed to be high. But this collides with inferior conditions for drag chain applications of a long make up length. See drag chain capabilities.

Can-Bus
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The Can-Bus (controller area network bus) is an accepted technology applied within vehicles. It is a field bus with a string/line infrastructure, additional strings/lines are possible in a limited way. The Can-Bus has to be terminated with 120 Ohm at its ends. This is necessary to prevent signal reflections and therefore communications errors. It is also possible to set up this bus with a star topology. The Can-Bus works on basis of voltage level differences, hence this bus is insensitive for external interferences. This is due to the fact that interferences influence both signal wires inside the cable and the voltage difference continues to be the same, the signal remains stable.

In accordance to the required data performance, the length and the corresponding loop resistance result the following cross sections for Can-Bus cables:

Drag chain capabilities

In order to achieve better drag chain properties, there is worked with a twisted wire make-up. It works like this: The lower the make-up length, the higher  the mechanical properties for drag chains. The reason for it is the compensation of the compressing and stretching within a single wire during drag chain motions. If the wires are not twisted, they will be damaged by the compressing and stretching in the drag chain. For drag chain applications the jacket of a cable is made generally of PUR (polyurethane).

Wave impedance

The wave impedance is usually a real value (e.g. 50 ? or 100 Ω). This value is independent regarding the cable length, but it is not independent regarding the frequency. The frequency dependency is up to the dielectric material and has to be considered for all signal transmission. Another word for it is dispersion. The wave impedance is not the ohmic resistance, it is considered to be the emitter gate resistance of a endless homogeny cable without signal reflection.

Shielding

The shielding is a electrical conductive cover for the functional wires of a cable. The shielding has 2 functions. It prevents interferences from decoupling off the cable, at the same time it prevent interferences from coupling into the cable. Both functions are equally important. There are 4 different shielding designs existing:

Fiber Optic Technology

Principle design of optical fiber cable
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1 Core: The core of an optical conductor is the inner part of an optical fiber cable. Within the core there is transmitted the light, so its transmission properties  are the main quality criteria.

2 Cladding: Without the cladding a light transmission wouldn’t be possible. The cladding is responsible for keeping the light inside the conductor and is  reflected in an oriented way. With a lower refraction index the claddings is the counterpart of the core and enables the TIR principle to work (total internal reflection). The cladding makes the light stay in the core.

3 Buffer: The buffer is a mechanical protection for the cladding and in particular for the core of the optical fiber cable. The buffer has no functionality in terms of the light transmission.

4 Jacket: The jacket is the contact of the fiber cable to its environment. In accordance the jacket needs to be adapted to the cables mechanical expectations and environmental conditions. In general there is distinguished in between static and dynamic use as well as indoor and outdoor applications.

Advantages and disadvantages of optical fiber compared to copper cable

Advantages

  • Higher transmission rates (Giga- to Terabit per second)
  • At the same time high transmission distances (up to some hundred kilometers without amplifier)
  • Lighter cable weight, occupying less space, less amplifiers and so lower installation and maintenance costs
  • No signal coupling to parallel conductors (noise coupling)
  • No influence due to electro-magnetical interferences (EMC), which enables the use together with high voltage lines
  • Ensures a galvanic separation of the signal and the system
  • Unempfindlichkeit gegenüber elektromagnetischen Einflüssen

Disadvantages

  • Requires a higher effort and accuracy demand for its assembly
  • Sensitive for mechanical stress and restricts the installation because of higher bending radius
  • Power over Ethernet (PoE) is not possible, this requires a copper conductor
Principle TIR (total internal reflection)
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The TIR-principle is the basis of the optical fiber transmission. Without this physical principle there wouldn’t be any fiber optics possible. The TIR principle is responsible for keeping the signal inside the conductor. An example of TIR with water and air: The TIR principle appears day to day, whenever we watch fishes or other subjects, standing at the waterside, below the water surface. Do we try to pick up e.g. a stone, it is not where it is expected to be. That’s TIR.

Jacket modes

This is the word for light beams coupled to the cladding. Within the cladding there are undefined reflection conditions, as it is not designed to transmit light. Its attenuation is that high, that signals die even on short distances. Modes do couple to the cladding whenever the light hits the surface of the cladding more vertical than the maximum angle allows. According to the TIR principle the beams decouple from the core and couple to the cladding.

Dynamic area

The dynamic area describes the attenuation, the system can stand without losing its functionality. It is highly recommended to put 6dB as a safety backup on top.

Dimensions of optical fibers
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Example: 50/125μm means 50μm of core diameter, 125μm of diameter for the cladding.

Modes / mode coupling

The word “mode” is used as another word for “light” in the technical language. Nothing else. From this words like “multimode” or “single mode” are derived. The physical effect making modes try to run next to each other is called “mode coupling”. This effect appears within all optical fiber conductors and leads to an increasing bandwidth. It enhances the transmission capability of the cable.

Multimode

Multimode means, that many light beams are coupled to the fiber at the same time and represent the signal. For multimode purpose there are used the gradient index fiber and the 200/230μm HCS fiber (core made of quarz glas, cladding made of plastic) with a maximum distance of 1km to achieve (Siemens calls HCS fiber PCF fiber). There are also used 980/1000μm POF fibers with a core made of PMMA, its maximum distance is 100m due to the high attenuation of the PMMA core.

Chromatic dispersion
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Light with a short wave length moves slower in optical mediums than light with longer wavelength does. Common LEDs emit the light within a tolerance from 600 to 700nm, although there rated value is 650nm. This leads to the fact, that some modes arrive earlier and some later at the receiver. This physical effect is relevant for all distances of 20km and higher.

Single Mode

Transmitting via “single mode” doesn’t literally mean to couple just one light beam into the cable, like the name mentions. But it is just a few light beams (modes), which are coupled to the conductor. It might be up to 20. Usually this type of transmission is used for long distances and therefore uses step index fibers. The use of e.g. 9/125μm SI fiber and 3/125μm fiber is common for transatlantic cable.

Gradient index fiber (GI)

This type of fiber has a creeping transition from the core to the cladding material. From the pure core material towards the cladding, the material of the cladding gets more and more intense. Finally it ends up with the pure cladding material. The refracting index from the core to the cladding changes creepingly as well. This cable design forms the signal mode to a wave. The use of this type of fiber compensates the effect of mode dispersion. See the figure “mode dispersion”. Examples for common fibers are the 50/125μm GI fiber in the EU and the 62.5/125μm GI fiber in the USA. Both achieve distances up to 3km.

Step index fiber

This type of fiber is applied for long distances. The step index fiber has a sudden change of material from core to cladding. This means the refracting index doesn’t change in a creeping way, like it does with GI fibers, it changes abruptly. The disadvantage of this technology is diversity in between the signal runtimes with multimode signals. For long runs there is used the single mode technology, thus the disadvantage of the mode dispersion is much lower.

Mode dispersion
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The mode dispersion describes the effect of varying signal runtimes on a cable. These signal runtimes result from different angles the modes are hitting the cladding surface and so the different distances to go. Depending on the coupling of the light waves to the cable, there are different reflection angles to take. This leads to earlier and later arriving modes at the end of the cable. So it is not only the signal runtime increasing, it is also the signal length. In the case there are 2 signals coupled in a rapid succession, it might happen that the mode dispersion makes the 2 signals join. Finally there is 1 long signal at the end arriving, which the receiver cannot understand.

Bandwidth

The bandwidth is defined as the frequency at which the signal level decreases to 50% of the reference value taken with 0Hz (DC). In the area of light transmitting technologies, the mode dispersion influences the bandwidth in a negative sense. The mode dispersion (impulse extension) is almost linear to the length of the cable. That is why it is called bandwidth length product (MHz x km). It is recommended to plan the transmission rate / data rate 3 to 5 times higher. A transmission rate of 150Mbit would theoretically lead to a bandwidth of 50MHz. Although the right dimensioning requires 150 to 250MHz. Additional signal drops due to bending radius or applied connectors are the reason.

Degree of transmission and wavelength
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With a wavelength of 515nm the green light has a minimum attenuation within the different colors, another minimum is up to the red light with 650nm. Due to the fact that green LEDs were difficult to get and hard to pulse, there is usually applied red light to fiber applications. This is taking advantage of the low attenuation of red light for the entire infrastructure for fiber optics.

Bending drop
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A bending radius on optical fiber cables of some centimeters means accepting signal losses. Whenever the cable goes straight again, after making a curve, some modes hit the cladding more steeply than the maximum angle allows. So this light is decoupling from the cable core and causes a signal drop. This happens to the light hitting the cladding at the end of a bend.

POF: Polymer optical fibre

Polymere optical fibers are most important on short distances for data transmission. Its core exists of Polymethylmehtacrylat (PMMA) and is 1mm thick in diameter. Its processing is easy and quick, because splicing and polishing can be skipped. The standard temperature for applying POF fibers is up to 60°C, its numeric aperture is about 0.5. Its use is limited to short distances due to its high attenuation. The PMMA core is responsible for this fact. The attenuation of e.g. glass is much lower. But for short distances it achieves a sufficient signal quality and makes this type of fiber very interesting for industrial applications.