Network isolator

from Wikipedia, the free encyclopedia

A network isolator is a galvanic isolation device for Ethernet- based networks. It interrupts all electrically conductive connections between the connected network peripherals and the connected device. It usually offers protection against DC and AC voltages of 4KV and more. In addition, it enables almost loss-free transmission of high-frequency AC voltages> 1 MHz, which are used in the Ethernet protocol for signal transmission. There are already manufacturers whose network isolators are suitable for the standard-compliant electrical isolation of Ethernet-based signal interfaces (SIP / SOPs) in accordance with the requirements of IEC 60601-1 in the medical field .

Causes of tension in network lines

In the case of copper-based network cabling, it can happen that the cable shield or the line cores inadvertently receive an electrical connection to other live parts. Causes for this can include moisture, aging processes, installation or design errors.

The voltage applied to the network cabling in this way corresponds at most to the local mains voltage. For this reason, network isolators are designed for a permanent voltage of 250 VAC in most cases.

However, high overvoltages caused by switching processes occur briefly in the supply networks.

Because these overvoltages can often be a multiple of the mains voltage, network isolators have a high dielectric strength. In addition, network isolators prevent equalizing currents from flowing between the connected devices, which are caused by potential differences between the connection points.

application areas

In general, network isolators are used in copper-based network connections in public, commercial and private areas.

Common areas of application are:

Medical technology

Network isolators are used in the medical field to protect the patient from leakage currents . The network connection between an active medical device and an Ethernet network or a non-medical device, such as an office PC, is classified as a potential source of danger as a result of voltage differences in accordance with the IEC EN 60601-1 standard for medical electrical devices and systems between the ground potentials of the connected network parts can be the cause of a leakage current that could endanger the patient. Such voltage differences can also be caused by incorrect installation, e.g. B. incorrect assignment or metallic contact between the shield or data lines of a damaged cable and live parts within the cable routing.

Network isolators can be used as accessories or components of a medical electrical device or system. Network isolators themselves are subject to the requirements of EN 60601-1 and EN 60601-1-2 in the medical-electrical system, but are not medical products in the sense of the Medical Device Directive 93/42 / EEC, as they do not fulfill any therapeutic or diagnostic purpose on their own. However, the manufacturer of the network isolator can place it on the market as a general accessory for a medical device. This would also make it a medical product under the Medical Devices Act. As individual devices, they are usually not subject to the obligation to carry out safety checks , unless this is required by the manufacturer of the network isolator or the medical-electrical system consisting of the network isolator and active medical device in the accompanying documents.

However, if the network isolator has already been placed on the market as a medical product, this makes it easier for the manufacturer of the medical system to determine conformity. For this purpose, it is only necessary to check, in accordance with Section 10 (1) MPG , whether all subsystems of the medical device system are being used according to their intended purpose and whether they do not negatively influence each other or from outside. This is recorded in writing by means of a simple declaration.

However, the Medical Devices Act permits the operator of an active medical device to manufacture a medical-electrical system himself, according to Section 12 MPG, the so-called in-house production. After going through the simplified conformity assessment procedure, the risk assessment of the new system, measurements of the electrical safety and clinical assessment by a medical professional, the operator is permitted to use the system for his own needs in his own premises. For the use of a network isolator, this means that compliance with the limit values ​​according to EN 60601-1 and EN 60601-1-2 in the currently valid version must be ensured. This is usually only possible with proof of a standards test by an accredited test laboratory. However, with this method the "own manufacturer" has much more responsibility than with the variant mentioned above, since with the former he only has to check whether all medical products are operated and used in the area of ​​the intended use.

Network isolators should be arranged as close as possible to the medical device. In the medical field, they are often used together with isolating transformers , which also serve to protect the patient, but protect against excessive currents from the power supply network in the event of an insulation fault.

Measuring and monitoring equipment

Network isolators are also used for sensitive measuring and monitoring devices in electrical test fields, which are connected to a control center via Ethernet interfaces and have to be protected against interference voltages and potential differences.

Computer systems

Network isolators are also used in computer systems that are galvanically connected to one another over long distances via Ethernet cabling and in which potential equalization currents are to be prevented.

Audio applications

For some time now, network isolators have also been used for audio applications in which the transmission of low-frequency alternating voltages (mains hum) via the network connection is to be reduced.

Valuable and vulnerable devices

Network isolators are also used for applications in which valuable devices or devices in particular need of protection are to be protected against hum and surge voltages from the network peripherals.

technical requirements

The international standard IEC 60601-1 for medical electrical devices and systems and their national equivalents, for example DIN EN 60601-1, OEVE / OENORM EN 60601-1, result in high demands on the insulation structure for network isolators. There the requirements are significantly higher than in the standard IEC 60950 (information technology equipment), which is applicable in the non-medical area, since it is assumed that a patient may be unconscious, anesthetized or unable to move and therefore need greater protection.

For medical devices or systems, IEC 60601-1 (3rd edition) requires two independent protective measures for patient protection ( M eans O f P atient P rotection = MOPP). A network isolator can form one or two protective measures for patient protection, depending on its insulation structure. In the case of only one MOPP, a second protective measure must be taken for the device concerned, e.g. B. by a permanently installed equipotential bonding conductor.

The manufacturers confirm conformity with the requirements of the applicable standards and guidelines, in particular IEC 60601-1, with their own CE declarations and / or with test certificates from independent test centers. However, whether a network isolator has one or two MOPPs is usually not clear from the certificates and depends on the combination of the air and creepage distances implemented, the structure of the insulation and the dielectric strength. From the dielectric strength alone - 1.5 KV (AC) are required for one MOPP and 4 KV (AC) for two MOPPs - no statement can be made about the number of MOPPs implemented.

Unshielded cable connections, which are occasionally mentioned as an alternative to the use of network isolators, do not have a sufficient protective effect in terms of IEC 60601-1, since the data lines themselves can carry dangerous voltages.

The galvanic isolating elements used on network cards and other active network components built in accordance with IEC 60950 do not meet the requirements of a galvanic isolating device in the sense of IEC 60601-1, because on the one hand the shielding is connected and on the other hand the insulation structure does not usually meet the strict requirements of the IEC 60601-1 corresponds and therefore cannot replace network isolators in the medical field.

The transmission quality of a network isolator can be determined with the help of the typical parameters for cabling routes in network technology (e.g. insertion loss, return loss, near-end crosstalk). In the beginning it did not play an essential role in the medical field when data rates of 100 Mbit / s were still used. Network isolators with data rates of up to 1 Gbit / s have been developed for the continuously increasing demands on data volumes. The transmission quality was noticeable with these, because the attenuation properties resulted in a virtual shortening of the transmission path by more than 4 m in some cases. In practice, however, this only played a role if the cable length of 90 m was exhausted and poor quality components were used.

The high data rates that currently occur when transmitting video signals in medical networks have pushed conventional 1 Gbit / s network isolators to their limits. In order to provide network isolators for data rates up to 10 Gbit / s, even more care was taken to ensure the transmission quality, while at the same time adhering to the parameters required by IEC 60601-1. This makes it possible to certify 10 Gbit / s transmission links (channel) with built-in network isolators according to Class E A (Cat 6A).

The definition of a network isolator is to prevent any direct galvanic connection between the connected devices. Therefore, in addition to the data lines, the cable shield must also be galvanically isolated.

Designs

Network isolators are offered in different designs. As an external device in its own housing, as a built-in variant for device manufacturers, ultra-compact, for circuit board assembly, with cable and integrated in wall outlet boxes for networks.

Web links

swell

  • Hospital IT Journal Issue 05/2008
  • DeviceMed edition 10/2008
  • Meditronic Journal, edition
  • the hospital edition 2.2020

Individual evidence

  1. ↑ RD Böckmann / H. Frankenberger: Implementation Aids for the Medical Devices Act Volume 2 Chapter 3.10
  2. ↑ Phonosophy Network Isolator - HiFi Test | audiophil-online. Retrieved April 30, 2019 .
  3. ↑ World's first 10 Gbit / s network isolator for medical technology | the hospital. Retrieved May 5, 2020 .