Network isolator
Encyclopedia
Network isolators are installed as part of a copper Ethernet
system, as galvanic isolators
.
Network data continues to be transmitted across an electrically non-conducting barrier, through the applied principle of electromagnetic induction
, whereby high frequency AC voltages conveying data
are induced
across an isolating gap.
The network isolator is therefore a passive device, and functions without any requirement of an external power supply.
Network connections between medical device
s and Ethernet
networks (and other non-medical devices, such as personal computer
s) must be in accordance with the IEC
standard IEC 60601-1 (3rd edition). This standard specifically deals with medical electronic and electrical equipment and systems, and classifies non-medical devices as potential hazard sources. A specific hazard stems from possible differences in ground potentials between network components, which when not properly isolated can result in a leakage current that can flow through the patient, which is dangerous, and potentially lethal. Such voltage differences can also arise through incorrect installation and wiring of network systems, electrical shorting within damaged cables and cabling, or shorting between damaged network cables and other voltage sources.
Network isolators work to remove this hazard, by electrically disconnecting medical devices from a network. Isolators may be used as network accessories, built into medical devices, or installed within a medical network system. Networks isolators should be installed as close as possible to the medical device in question.
As they serve no therapeutic or diagnostic purpose, network isolators themselves are not classed as medical electronic equipment according to the standard IEC 60601-1, nor do they fall within the scope of the Medical Devices Directive
93/42/EEC.
They are often installed in the medical field in conjunction with isolation transformer
s, which serve to protect the patient from electrical faults.
The IEC 60601-1 standard requires that two independent precautionary measures (Means of Patient Protection, or MOPPs) are set in place, to protect the patient from electrical shock in the medical system. A network isolator can be constructed to provide one or both required MOPPs. In the case where only a single MOPP is present in a system, a second measure of protection for the medical device must be made. This can be achieved, for example, by installing a fixed, low-resistance earthing cable, bar, or strap, referred to as a potential equalisation conductor. Conformation to the requirements of applicable standards and guidelines, in particular the IEC 60601-1 standard, involves manufacturers themselves declaring CE
compliance and/or gaining certification from an approved independent testing laboratory.
The number of MOPPs a network isolator provides will be stated in the certification of the device. These are achieved by a combination of clearance and creepage distances, and the breakdown voltage
of the insulating materials.
Although requirements on breakdown voltage levels are 1.5 kilovolts for one MOPP, and 4 kilovolts for two MOPPs, the number of MOPPs actually provided cannot be derived from the breakdown voltage alone.
Network connections made with unshielded cables are occasionally used as a form of isolation, in that no shield connection
exists between the device and the network. However, this fails to provide sufficient protection in the scope of IEC 60601-1, as the data lines themselves are not isolated, and may be floating at dangerous voltage potentials.
Network cards and other active network components which are designed to meet IEC 60950 (Safety of Information Technology Equipment), will usually not comply with the more demanding isolation requirements of IEC 60601-1 (Medical Electrical Equipment), and therefore require additional isolation before being used in medical applications.
The transmission quality of a network isolator can be determined by measuring the industry standard parameters or characteristics, for example, insertion loss
, return loss
, and near end crosstalk.
By definition, a network isolator completely eliminates each and every direct electrical connection between devices connected through a network connection - specifically all the data lines, and the cable shield
.
Voltage ratings (rated in kilovolts) and maximum transmission speeds (e.g. 1000BASE-T) vary between models.
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
system, as galvanic isolators
Galvanic isolation
Galvanic isolation is a principle of isolating functional sections of electrical systems, thus preventing the movement of charge-carrying particles from one section to another, i.e. no direct current flows between the sections. Energy or information can still be exchanged between the sections by...
.
Network data continues to be transmitted across an electrically non-conducting barrier, through the applied principle of electromagnetic induction
Electromagnetic induction
Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....
, whereby high frequency AC voltages conveying data
Data (computing)
In computer science, data is information in a form suitable for use with a computer. Data is often distinguished from programs. A program is a sequence of instructions that detail a task for the computer to perform...
are induced
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
across an isolating gap.
The network isolator is therefore a passive device, and functions without any requirement of an external power supply.
Medical
Network isolators are used in the medical industry to protect patients against leakage currents.Network connections between medical device
Medical device
A medical device is a product which is used for medical purposes in patients, in diagnosis, therapy or surgery . Whereas medicinal products achieve their principal action by pharmacological, metabolic or immunological means. Medical devices act by other means like physical, mechanical, thermal,...
s and Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
networks (and other non-medical devices, such as personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
s) must be in accordance with the IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
standard IEC 60601-1 (3rd edition). This standard specifically deals with medical electronic and electrical equipment and systems, and classifies non-medical devices as potential hazard sources. A specific hazard stems from possible differences in ground potentials between network components, which when not properly isolated can result in a leakage current that can flow through the patient, which is dangerous, and potentially lethal. Such voltage differences can also arise through incorrect installation and wiring of network systems, electrical shorting within damaged cables and cabling, or shorting between damaged network cables and other voltage sources.
Network isolators work to remove this hazard, by electrically disconnecting medical devices from a network. Isolators may be used as network accessories, built into medical devices, or installed within a medical network system. Networks isolators should be installed as close as possible to the medical device in question.
As they serve no therapeutic or diagnostic purpose, network isolators themselves are not classed as medical electronic equipment according to the standard IEC 60601-1, nor do they fall within the scope of the Medical Devices Directive
Medical Devices Directive
The Medical Device Directive is intended to harmonise the laws relating to medical devices within the European Union...
93/42/EEC.
They are often installed in the medical field in conjunction with isolation transformer
Isolation transformer
An isolation transformer is a transformer used to transfer electrical power from a source of alternating current power to some equipment or device while isolating the powered device from the power source, usually for safety...
s, which serve to protect the patient from electrical faults.
Other applications
Network isolators have many other applications in overcoming the problems of differing ground potentials across networks, or between network components. For example:- Electrical testing facilities, where measurement and monitoring equipment are connected to a central control centre through an Ethernet;
- For redundantRedundancy (engineering)In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....
server systems, which are physically connected via a copper network; - For private or commercial networks, where inherent potential differences within a building, or between buildings, become problematic, and a fibre-opticFiber-optic communicationFiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. The light forms an electromagnetic carrier wave that is modulated to carry information...
solution is not economically viable; - General usage as filters for shield currents in Ethernet connections.
Technical requirements
The international standard IEC 60601-1 Medical Electrical Equipment (3rd edition) specifies stringent criteria on the safety and isolation of medical devices. These requirements are of course much more stringent than those of a typical consumer product standard (i.e. IEC 60950 Safety of Information Technology Equipment), as the patient may be unconscious, anaesthetised, or otherwise unable to move, and the need for patient protection is therefore paramount.The IEC 60601-1 standard requires that two independent precautionary measures (Means of Patient Protection, or MOPPs) are set in place, to protect the patient from electrical shock in the medical system. A network isolator can be constructed to provide one or both required MOPPs. In the case where only a single MOPP is present in a system, a second measure of protection for the medical device must be made. This can be achieved, for example, by installing a fixed, low-resistance earthing cable, bar, or strap, referred to as a potential equalisation conductor. Conformation to the requirements of applicable standards and guidelines, in particular the IEC 60601-1 standard, involves manufacturers themselves declaring CE
CE mark
CE marking is a mandatory conformity mark for products placed on the market in the European Economic Area . With the CE marking on a product the manufacturer ensures that the product conforms with the essential requirements of the applicable EC directives...
compliance and/or gaining certification from an approved independent testing laboratory.
The number of MOPPs a network isolator provides will be stated in the certification of the device. These are achieved by a combination of clearance and creepage distances, and the breakdown voltage
Breakdown voltage
The breakdown voltage of an insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive.The breakdown voltage of a diode is the minimum reverse voltage to make the diode conduct in reverse...
of the insulating materials.
Although requirements on breakdown voltage levels are 1.5 kilovolts for one MOPP, and 4 kilovolts for two MOPPs, the number of MOPPs actually provided cannot be derived from the breakdown voltage alone.
Network connections made with unshielded cables are occasionally used as a form of isolation, in that no shield connection
Shielded cable
A shielded or screened cable is an electrical cable of one or more insulated conductors enclosed by a common conductive layer. The shield may be composed of braided strands of copper , a non-braided spiral winding of copper tape, or a layer of conducting polymer. Usually, this shield is covered...
exists between the device and the network. However, this fails to provide sufficient protection in the scope of IEC 60601-1, as the data lines themselves are not isolated, and may be floating at dangerous voltage potentials.
Network cards and other active network components which are designed to meet IEC 60950 (Safety of Information Technology Equipment), will usually not comply with the more demanding isolation requirements of IEC 60601-1 (Medical Electrical Equipment), and therefore require additional isolation before being used in medical applications.
The transmission quality of a network isolator can be determined by measuring the industry standard parameters or characteristics, for example, insertion loss
Insertion loss
In telecommunications, insertion loss is the loss of signal power resulting from the insertion of a device in a transmission line or optical fiber and is usually expressed in decibels ....
, return loss
Return loss
In telecommunications, return loss or reflection loss is the loss of signal power resulting from the reflection caused at a discontinuity in a transmission line or optical fiber. This discontinuity can be a mismatch with the terminating load or with a device inserted in the line...
, and near end crosstalk.
By definition, a network isolator completely eliminates each and every direct electrical connection between devices connected through a network connection - specifically all the data lines, and the cable shield
Shielded cable
A shielded or screened cable is an electrical cable of one or more insulated conductors enclosed by a common conductive layer. The shield may be composed of braided strands of copper , a non-braided spiral winding of copper tape, or a layer of conducting polymer. Usually, this shield is covered...
.
Models
Network isolators are commercially available in various designs, to suit customers’ requirements:- stand-alone devices, ready for immediate and simple installation;
- isolating components, suitable for OEMOriginal Equipment ManufacturerAn original equipment manufacturer, or OEM, manufactures products or components that are purchased by a company and retailed under that purchasing company's brand name. OEM refers to the company that originally manufactured the product. When referring to automotive parts, OEM designates a...
manufacturers; - integrated into network wall sockets, for permanent installations.
Voltage ratings (rated in kilovolts) and maximum transmission speeds (e.g. 1000BASE-T) vary between models.
External links
- EMO Systems range of network isolators
- International Electrotechnical Commission
- Baaske Medical USA range of medical grade network isolators