Update from EMC standards committees

Update from EMC standards committees

On behalf of the association, I follow what is happening within NEC EMC and every now and then I will inform you about it. I must admit that a large part of the standards that are discussed there are sometimes a bit far removed from my bed, because they usually concern measurement methods of EMC measurements in laboratories. Through my employer RH Marine & Bakker Sliedrecht I am also involved in standardization, but then within NEC 18. NEC 18 deals with electrical installations on board ships and on mobile and fixed units in the water. I would like to share some experiences from this working group with you.

RH Marine and Bakker Sliedrecht are companies that supply electrical installations and do automation projects on board ships. My interest lies more on the interface of EMC and the installations that I encounter on board. Fortunately, there is also room for this within standardization and that is why I represent the Netherlands from NEC 18 in various international working groups and am chairman of MT21. The latter is an international working group that deals with writing and maintaining EMC standards in the maritime sector and is part of the IEC (International Electrotechnical Commission).

The biggest challenge I face is that international treaties require equipment to be used that meets specific maritime EMC standards, such as IEC 60533. The problem is that this equipment is often not available on the market. This is logical, when you consider that a large ship can be comparable to a village with all the facilities and infrastructure. You also need equipment that you encounter on land, but the market segment for, for example, maritime coffee machines, is so small that a coffee machine manufacturer does not design separate products for the maritime sector.

The proposal that I am currently working out with my committee members in the IEC 60533 is to move from equipment requirements to system requirements, from a 'rule based' approach to a 'risk based' or 'goal based' approach. In the current version of the IEC 60533, very specific EMC requirements are set for each device that is brought on board (rule based). These EMC requirements rightly deviate so much from the requirements for equipment used on land, because of the different goals that must be achieved, that a replacement set of EMC tests must be performed. Depending on where the device is placed on board, for example close to the antennas or at the bottom of the ship, the requirements are often too strict, but sometimes not strict enough, which still causes disruptions. That is why we want to set requirements at system level (risk/goal based) in the new approach, such as: can my radio receiver receive weak signals; is my system disrupted by a walkie-talkie; does my computer network achieve the specified speed? How the future user of the IEC 60533 that is under development achieves this is no longer relevant from the perspective of the standard. This can be done by finding equipment that meets the specific maritime EMC requirements, which will remain in the standard; by taking smart shielding measures during the installation of the equipment; or by a combination of both: critically examining which EMC standards the equipment meets and taking a limited number of installation measures. Below I would like to name a few challenges that we are currently facing.

Radio reception on board ships is essential because, for example, SOS calls that come in via the radio can be received well. Even if a ship in distress is a bit further away and the radio signals are weak, you want to be able to receive them, so they must not be drowned out by interference signals generated on board. This sounds like a simple requirement, but how do you make this measurable? We have chosen a two-pronged approach for this. Some equipment, such as navigation lights, that is placed close to the antenna, is specifically designed for the maritime environment and is therefore logically also tested against maritime EMC standards. For manufacturers of maritime equipment, we have defined zones on board and the closer a zone is to the antenna, the stricter the emission limits will be to which the antenna is sensitive. The test is carried out in an anechoic chamber, with the standard settings for measuring equipment (CISPR 16). Many other generic equipment is not tested according to these standards and can, for example, be placed in a closed metal housing, or far away from the antenna to ensure radio reception. However, it must then be checked whether these measures are effective. For this, the draft standard requires that a measurement is performed via the antenna installed on board, with the bandwidth used by the system. The latter can be a challenge, because these bandwidths deviate from the standard measurement bandwidths defined by IEC / CISPR and not every measuring device will be able to handle this. Furthermore, the question is which limits should be used. Any limit above the sensitivity of the radio receiver can mean that a distress call, which could have been received, is drowned out by interference signals. On the other hand, the sensitivity of radio receivers is often below the level of the natural background radiation, which varies over time, so how do you perform such a measurement? A complete ship does not fit in an anechoic space. The challenge we have within the working group is to define a limit that is just above the background radiation, but not too far.

On board, walkie-talkies are often used, set to their maximum transmitting power, to ensure that they still have some range with all that steel on board. At short distances, 10 to 50 cm, these walkie-talkies can generate field strengths of 30 to 100 V/m. Domestic appliances are tested against 3 V/m, heavy industrial equipment against 10 V/m, so requiring that all equipment on board can withstand fields of 100 V/m across the entire frequency spectrum is not realistic. That is why the draft standard for IEC 60533 requires that the risks of interference on board must be inventoried and appropriate measures taken. Specific reference is also made to walkie-talkies in this respect, where the idea is to check whether the equipment used can withstand the field strengths that are resistant to the walkie-talkies used on board. In general, this works fine, but there is a risk that adjustments or other equipment may be necessary at a late stage in a project. The consideration of whether it is acceptable for a device to fail briefly also plays a role. For a coffee machine this is not a problem, for a radar installation it is.

As a final example, I would like to discuss interference caused by common mode phenomena, which is a major challenge for ships in particular, which can result in computer networks not reaching their speeds, for example. According to the proposal in the draft standard, it would only be permitted to check whether all signals are received correctly and quickly enough when the ship is put into operation. However, the risk that this is not the case is considerable, which is why we already want to offer solutions in the standard to reduce this risk. A very important cause of disrupted communication is common mode interference. Common mode interference is caused by switching power supplies and frequency converters, among other things. On land, this interference can be reduced by applying filters to earth. However, on board many ships, the neutral point of the network is floating, which means that applying filters with capacitors to earth is undesirable. This results in high common mode interference levels on board ships. These are also difficult to quantify because a LISN contains large capacitors to earth, which influence the place where the common mode voltage is expressed in a network with a floating neutral point. In addition, a lot of common mode interference is in a frequency range (2 kHz – 150 kHz) for which there are no requirements. Here too, we want to offer a two-pronged approach. Firstly, we have proposed a new measurement method so that manufacturers can determine how much common mode interference their device generates in a network with a floating neutral point. A network defined in the standard is connected to both the primary and secondary sides of the device, creating a neutral point. This neutral point is not connected to earth. The voltage between these two neutral points is then measured with a differential mode probe. The interference per frequency band is then determined on an oscilloscope, for example, and then compared with a limit. This measurement method deviates significantly from the measurement methods within IEC, so this still requires consultation within IEC. The other part of the responsibility lies with the installer. He will have to demonstrate that the amount of common mode interference on the network is not too high. This can be done with the same network to create a neutral point and then measure with a differential mode probe in relation to earth. The alternative is to simultaneously connect a differential mode probe between earth and each power line and then mathematically calculate the common mode voltage. Since there are many things on board that can influence the height of this voltage, the design standard does not currently specify a hard limit, but a value that, if exceeded, gives rise to an additional risk analysis.

It is far from certain whether, and if so how, the ideas described above will ultimately be included in the standard and whether that standard will ultimately be approved. However, it does give an idea of the issues that play a role within a standards committee, new ideas are put forward, it must be checked whether the proposals are feasible in practice and do not conflict with other standards. Furthermore, there is the challenge of convincing other parties of the usefulness and necessity of the proposals made and ultimately reaching a compromise that everyone can agree on. If you are interested in standardization work, you can always contact me. Both if you want to follow the standardization work that takes place in the ESD and/or EMC field via the association or if you are interested in standardization work in general. My contact details are known to the secretariat.

Jan-Kees van der Ven,

Representative of the Dutch EMC association within NEC EMC