74

BY THEO TEKSTRA, MARKETING MANAGER GAVITA HOLLAND

EMI CAN DISRUPT OR DEGRADE THE FUNCT

IONING

OF OTHER ELECTRONIC DEVICES

BE SMART WHEN YOU DESIGN A CLIMATE ROOM

A DOUBLE-EDGED SWORD

E.M.I.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?

75 gardenculturemagazine.com

E.M.I. I GARDEN CULTURE

- Conducted EMI travels through the power cord of the

device back to the grid, and is distributed over your mains ca-

bles. All devices that are plugged into the same mains supply

will receive this automatically. The interference does not stop

at your house though: a complete block of houses or more,

connected to the same supply, can

be influenced. The frequencies are

approximately 9 kHz to 30 MHz.

Radiated EMI can, for example,

hinder cell phone reception, wire-

less devices such as intercom sys-

tems, monitoring systems and radio amateurs, but it can also

induce bad readings of sensitive instruments such as pH and

ec meters.

Conducted EMI can influence anything that is connected to

the same mains supply, and can cause routers to disconnect,

computers to fail, loss in data, interference on audio and ca-

ble TV systems, etc.

Of the two, the conducted EMI may well be a worse problem

than the emitted EMI.

Electronic ballasts and EMIElectronic ballasts have become popular because they are

efficient, lightweight, run relatively cool, provide a stable

output regardless of mains voltage fluctuations, and can be

controlled. Traditional (low frequency) core-coil ballasts are

quite heavy and become very warm. They can be noisy, as

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!

So why don’t manufacturers make a low frequency electronic

ballast? They do.

There are low frequency electronic ballasts as well. Because

of the electronic nature of the ballast they can still cause EMI

though, and because of the low frequency they are often big

and more expensive. Especially square wave low frequency

ballasts can be noisy on lamps, resulting in (literally!) vibrating

arc tubes. They are also less efficient than high frequency bal-

lasts, and more expensive to produce.

StandardsLet’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

b) Class B for residential or medical use

In industrial environments the EMI levels are allowed to be

a bit higher. Class B, for residential use, is more strict than

the industrial standard. In Europe, as well as North America,

class A and B are used, and are

very similar. Manufacturers of

electrical devices need to make

sure they do not emit more than

the applicable standard.

EMI, however, is a double-edged sword: manufacturers of

electronic devices should also make sure that their electri-

cal devices are protected against the influence of EMI from

other apparatus to a certain degree. This, of course, makes

things a bit more complicated. Interference you experience

is not necessarily from a device emitting too much, it could

well be that the receiving device is not sufficiently protected

against 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-

lowed to use these, because they would possibly interfere

with sensitive systems. Examples are radio studios and the-

aters (interference with audio systems and wireless micro-

phones), hospitals and airplanes (possible interference with

critical electronic systems). Still, these devices all comply to

regulations.

Radiated and conducted EMIThere are two different types of EMI:

- Radiated EMI works like radio waves, and is emitted by

the equipment like a radio transmitter. Radio waves are very

high frequency: frequencies from 30 kHz and up (long wave)

can cause radiated interference. Medium wave, for example,

ranges from approximately 500 kHz to 1.7 MHz. This emis-

sion can be picked up by devices that are sensitive to these

frequencies, without any electrical connection to the device

generating the EMI.

THE INTERFERENCE DOES NOT STOP AT

YOUR HOUSE

BE SMART WHEN YOU DESIGN A CLIMATE ROOM

A DOUBLE-EDGED SWORD

I.

Tel: +44 (0) 1223 610021Tel: +44 (0) 1223 500633

Email: info@downtoearthkentltd.org.ukWebsite: www.downtoearthkent.co.uk

Down to Earth Kent LtdD E

higher frequency, possibly even destroying the ballast. This is

why in horticulture only complete fixtures are used, with ballast

and reflector integrated. The lamp cables are integrated in the

metal design, reducing the interference to a minimum.

Conducted EMI is caused by insufficient filtering inside the bal-

last, or just plain bad design, causing high frequency signals to be

delivered back to the grid. This can happen in remote ballasts,

as well as complete fixtures.

Then there is a huge variety in operating frequency: traditional

high frequency ballasts work around 35 kHz, but modern hor-

ticultural double ended systems, for example, work at 120 kHz!

It’s not only this base frequency that causes the problems. High

frequency equipment generates what we call harmonics, much

higher frequencies than the base frequency. They easily reach

the radio frequent spectrum your other devices are sensitive to.

Harmonics are mostly responsible for emitted EMI problems.

Sine wave and square wave both have higher harmonic frequen-

cies. High frequency square wave ballasts in particular generate

lots of harmonics and EMI.

How to avoid EMIIt is almost impossible to avoid EMI with a high frequency re-

mote ballast. The lamp cord connecting the (metal shielded)

ballast to the reflector is the biggest problem for radiated EMI:

it works like an antenna. The longer the cord the bigger the an-

tenna. Shielding the lamp cord is not a solution in many cases, as

it dampens the ignition pulse and can lead to lamps not starting

any more, causes losses in output signal, and in some cases, it

actually causes the frequency of the ballast to go up to a much

Low versus high frequency

Magnetic ballasts output the same frequency as the re-

ceive from mains, so 50 Hz in Europe, 60 Hz in the USA.

This causes a “flicker” in the light, which actually switches

on and off 100/120 times per second. On digital photo-

graphs you see this as light and dark banding. High fre-

quency electronic ballasts switch so fast that the arc in the

arc tube does not extinguish any more, leading to a higher

output, and better efficiency.

E.M.I. I GARDEN CULTURE

77 gardenculturemagazine.com

HARMONICS ARE MOSTLY RESPONSIBLE FOR EMITTED

EMI PROBLEMS

Keep your family and neighbors happy and safe

EMI can cause all kinds of mayhem in a domestic environment:

Internet routers that lose connection, Wi-Fi access points that

decrease in performance or lose connection, TV’s and satellite

receivers that show interference, remote controls (for example,

to open your garage door or arm your alarm system) that do

not work anymore, intercom systems that become unusable be-

cause of a loud hum, false alarms in wireless systems, amateur

radio traffic interference, etc. When the neighbors call the cable

guy to search the cause of the problem you are already too late.

It is always better to prevent these problems.

There are several ways to keep your EMI to a minimum:

1. Best option: use complete fixtures! Ballast and reflector are

integrated, so there is no loose lamp cord to emit lots of EMI.

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

can influence the frequency of your ballast, and can amplify radi-

ated EMI.

So, what should I buy?If a device carries an FCC or CE sign it should be compliant

to the EMI regulations. I say should be, as in reality there are

a lot of things wrong with the testing of electronic equipment.

For CE, for example, the manufacturer may choose to test

the equipment himself, and declare that it is compliant to CE.

If it turns out that it isn’t compliant he will probably get a slap

on the wrist, which in many cases is cheaper than being really

compliant. Specifically manufacturers in cheap labor countries

outside the European Community (where the CE certification

is required) do not really care so much about compliance. The

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-

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.

Be smart when you design a climate room. Think ahead, and

choose products from a reliable manufacturer. Realize that all

high frequency remote ballasts (even the FCC approved) can

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

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.

Measuring graphs from a FCC Report of a complete fixture (Gavita Pro 1000e DE) – all levels are below the limits that are indicated by the red line

Conducted EMI

Emmited EMI