BY THEO TEKSTRA, MARKETING MANAGER GAVITA HOLLAND

EMI CAN DISRUPT OR DEGRADE THE FUNCTIONING OF OTHER ELECTRONIC DEVICES E.M.I. A DOUBLE-EDGED SWORD BE SMART WHEN YOU DESIGN A CLIMATE ROOM

The introduction of high frequency electronic remote ballasts into the market has created a new problem: electromagnetic interference (EMI). EMI consists of high frequency signals which are either conducted (through for example your power cord back to the grid), or emitted in the form of radio waves (for example by your lamp cord connecting a high frequency remote ballast to the lamp). EMI can disrupt or degrade the functioning of other electronic devices. In some cases, this may even lead to life threatening situations, for example, if medical systems or emergency communication systems are influenced. So what is that EMI, and what can we do to avoid it? What are the rules and regulations?

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Standards Let’s get the dull stuff out of the way first: there are two classes which define how much EMI a device may emit: a) Class A for industrial use - Conducted EMI travels through the power cord of the b) Class B for residential or medical use device back to the grid, and is distributed over your mains ca- In industrial environments the EMI levels are allowed to be bles. All devices that are plugged into the same mains supply a bit higher. Class B, for residential use, is more strict than will receive this automatically. The interference does not stop the industrial standard. In Europe, as well as North America, at your house though: a complete block of houses or more, class A and B are used, and are connected to the same supply, can very similar. Manufacturers of THE INTERFERENCE be influenced. The frequencies are I. electrical devices need to make approximately 9 kHz to 30 MHz. sure they do not emit more than DOES NOT STOP AT Radiated EMI can, for example, the applicable standard. YOUR HOUSE hinder cell phone reception, wire- less devices such as intercom sys- EMI, however, is a double-edged sword: manufacturers of tems, monitoring systems and radio amateurs, but it can also electronic devices should also make sure that their electri- induce bad readings of sensitive instruments such as pH and cal devices are protected against the influence of EMI from ec meters. A DOUBLE-EDGED SWORD other apparatus to a certain degree. This, of course, makes Conducted EMI can influence anything that is connected to things a bit more complicated. Interference you experience the same mains supply, and can cause routers to disconnect, is not necessarily from a device emitting too much, it could computers to fail, loss in data, interference on audio and ca- BE SMART WHEN YOU DESIGN A CLIMATE ROOM well be that the receiving device is not sufficiently protected ble TV systems, etc. against EMI. Of the two, the conducted EMI may well be a worse problem than the emitted EMI. There are many devices that emit EMI, because they emit radio frequent radiation, for example, cell phones and radio transmitters. In certain environments it is therefore not al- Electronic ballasts and EMI lowed to use these, because they would possibly interfere Electronic ballasts have become popular because they are with sensitive systems. Examples are radio studios and the- efficient, lightweight, run relatively cool, provide a stable aters (interference with audio systems and wireless micro- output regardless of mains voltage fluctuations, and can be phones), hospitals and airplanes (possible interference with controlled. Traditional (low frequency) core-coil ballasts are critical electronic systems). Still, these devices all comply to quite heavy and become very warm. They can be noisy, as regulations. in humming, and some components degrade over time. But they are cheap, reliable, and cause no interference whatso- ever, because they work on the mains frequency: 50/60 Hz! Radiated and conducted EMI So why don’t manufacturers make a low frequency electronic There are two different types of EMI: ballast? They do. - Radiated EMI works like radio waves, and is emitted by There are low frequency electronic ballasts as well. Because the equipment like a radio transmitter. Radio waves are very of the electronic nature of the ballast they can still cause EMI high frequency: frequencies from 30 kHz and up (long wave) though, and because of the low frequency they are often big can cause radiated interference. Medium wave, for example, and more expensive. Especially square wave low frequency ranges from approximately 500 kHz to 1.7 MHz. This emis- ballasts can be noisy on lamps, resulting in (literally!) vibrating sion can be picked up by devices that are sensitive to these arc tubes. They are also less efficient than high frequency bal- frequencies, without any electrical connection to the device lasts, and more expensive to produce. generating the EMI.

gardenculturemagazine.com 75 Then there is a huge variety in operating frequency: traditional high frequency ballasts work around 35 kHz, but modern hor- Low versus high frequency ticultural double ended systems, for example, work at 120 kHz! It’s not only this base frequency that causes the problems. High Magnetic ballasts output the same frequency as the re- frequency equipment generates what we call harmonics, much ceive from mains, so 50 Hz in Europe, 60 Hz in the USA. higher frequencies than the base frequency. They easily reach This causes a “flicker” in the light, which actually switches the radio frequent spectrum your other devices are sensitive to. on and off 100/120 times per second. On digital photo- Harmonics are mostly responsible for emitted EMI problems. graphs you see this as light and dark banding. High fre- Sine wave and square wave both have higher harmonic frequen- quency electronic ballasts switch so fast that the arc in the cies. High frequency square wave ballasts in particular generate arc tube does not extinguish any more, leading to a higher lots of harmonics and EMI. output, and better efficiency.

How to avoid EMI It is almost impossible to avoid EMI with a high frequency re- higher frequency, possibly even destroying the ballast. This is mote ballast. The lamp cord connecting the (metal shielded) why in horticulture only complete fixtures are used, with ballast ballast to the reflector is the biggest problem for radiated EMI: and reflector integrated. The lamp cables are integrated in the it works like an antenna. The longer the cord the bigger the an- metal design, reducing the interference to a minimum. tenna. Shielding the lamp cord is not a solution in many cases, as Conducted EMI is caused by insufficient filtering inside the bal- it dampens the ignition pulse and can lead to lamps not starting last, or just plain bad design, causing high frequency signals to be any more, causes losses in output signal, and in some cases, it delivered back to the grid. This can happen in remote ballasts, actually causes the frequency of the ballast to go up to a much as well as complete fixtures.

Down to Earth Tel: +44 (0) 1223 610021 Email: [email protected] D E Kent Ltd Tel: +44 (0) 1223 500633 Website: www.downtoearthkent.co.uk E.M.I. I GARDEN CULTURE

There are several ways to keep your EMI to a minimum: HARMONICS ARE MOSTLY RESPONSIBLE FOR EMITTED 1. Best option: use complete fixtures! Ballast and reflector are integrated, so there is no loose lamp cord to emit lots of EMI. EMI PROBLEMS Also they are much easier to wire than remote systems. You just need to bring power to your climate room. 2. Make sure you have a good earth connection. The use of a protective earth connection is crucial to avoid EMI in shielded systems. Always use protective earth for safety, but specifically for high frequency devices to provide good shielding. 3. Keep lamp cords as short as possible, so keep the ballasts as close to the reflector as possible. And here I am talking about just 15 cm of cable instead of 5 meters or more! 4. Keep lamp cords apart from mains cords. If you they cross or run parallel you can get induction of the high frequency out- put on your mains supply, causing conducted EMI. This feedback signal can even destroy your ballast. 5. Never coil your lamp cords, make them too short! A coil EMI measuring rooms ideally do not contain metal objects close to the sources, de tables on which the objects are placed are made of wood. can influence the frequency of your ballast, and can amplify radi- ated EMI. Keep your family and So, what should I buy? neighbors happy and safe If a device carries an FCC or CE sign it should be compliant EMI can cause all kinds of mayhem in a domestic environment: to the EMI regulations. I say should be, as in reality there are Internet routers that lose connection, Wi-Fi access points that a lot of things wrong with the testing of electronic equipment. decrease in performance or lose connection, TV’s and satellite For CE, for example, the manufacturer may choose to test receivers that show interference, remote controls (for example, the equipment himself, and declare that it is compliant to CE. to open your garage door or arm your alarm system) that do If it turns out that it isn’t compliant he will probably get a slap not work anymore, intercom systems that become unusable be- on the wrist, which in many cases is cheaper than being really cause of a loud hum, false alarms in wireless systems, amateur compliant. Specifically manufacturers in cheap labor countries radio traffic interference, etc. When the neighbors call the cable outside the European Community (where the CE certification guy to search the cause of the problem you are already too late. is required) do not really care so much about compliance. The It is always better to prevent these problems. importer or distributor is responsible. For FCC compliance the device needs to be tested in a lab which is accredited by the FCC. In reality though, there is a huge difference in reports that are obtained from different (ac- Conducted EMI credited) labs from different countries, also depending on how they test. If you test a ballast, for example, with just 15 cm of lamp cord it will give you a much better result than with 4 me- ters coiled next to the ballast. An FCC approval is no guarantee for absence of EMI. Measuring graphs from a FCC Report of a complete fixture Be smart when you design a climate room. Think ahead, and (Gavita Pro 1000e DE) – all levels are below the limits that are indicated by the red line choose products from a reliable manufacturer. Realize that all high frequency remote ballasts (even the FCC approved) can Emmited EMI emit EMI and that in all cases it is better to use complete fix- tures. If you use remote ballasts, then place the ballasts as close to the reflectors as possible, and use very short leads. Never cross lamp cords and power cables, and make sure all your sys- tems have perfect ground connections. 3

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