cache of http://www.buyusa.gov/europeanunion/mercury.pdf. It's a snapshot of the page taken as our search engine crawled the Web.
The web site itself may have changed. You can check the current page or check for previous versions at the Internet Archive. Yahoo! is not affiliated with the authors of this page or responsible for its content.
Test and Measurement Coalition



Test and Measurement Coalition

RoHS Scope Review of Category 9 Products

Mercury Dossier


1.

Use of Mercury in test and measurement equipment

1.1

General
There are several uses of mercury and its compounds in electrical and optical equipment
because of its special properties including liquid metal state at room temperature and its
high electromagnetic frequency of radiation compared to other metals.

In manometers, which measure and control pressure;

In thermometers;

In electrical and electronic switches;

In fluorescent lamps;



In batteries (as mercuric dioxide); and

In sensors


Usage has been reduced considerably in the interest of safety and the environment wherever cost-
effective and technically equivalent substitutes have been found for applications of mercury.
Mercury in the test and measurement (T&M) sector has been greatly reduced in the last decade and,
excluding sensors, is in limited use in switches (including relays) and display lamps. The actual
amount in use is small. Five major companies in the T&M sector estimate their products account
for no more than 14 grams in switches and 340 grams in display lamps shipped into the EU
annually.

Further information on uses of mercury including dental and other medical applications can be
found at
http://www.chem.unep.ch/mercury/Report/Final%20Assessment%20report.htm


A simple introduction to switches and relays is available at
http://www.cougarelectronics.com/pdf/reed_relays.pdf



1.2

Technical characteristics

1.2.1

Lamps:
Mercury has the ability to enable electron/photon interaction processes at much
lower energy levels compared to other metals. This property has been used in
mercury lamps in education, research and in low energy fluorescent lamps for many
years.
Photon energy from a mercury lamp hitting a zinc plate will release electrons from
the zinc and this is a common demonstration of the photovoltaic effect due to the
photon energy exceeding the work function of the zinc. Tungsten filament lamps
will not show the effect independent of their brightness because the photon energy
produced is proportional to the electromagnetic frequency of the light. (Mercury
electromagnetic frequencies are in the violet/ultraviolet spectrum compared to the
lower frequencies of filament lamps.)
Mercury lamps consume lower energy than other lamps for equivalent light output.
They are used as lamps for room lighting, backlighting in liquid crystal displays
(LCDs), laser printers and photocopiers. LCDs are a common display type in T&M
equipment. No other commercially available backlighting technology gives
equivalent brightness and contrast ratio. LCDs with lamps having 3-5 milligrams of
mercury have largely replaced cathode ray tube displays in our sector. Other new
mercury free display lighting possibilities have been announced but we anticipate it
will be several years before a cost-effective suitable alternative becomes available.
There is great commercial incentive to bring mercury free display lighting to market
given the widespread usage of mercury lamps in many domestic and industrial
products.

1.2.2

Switches and Relays:
Using the properties of low resistance and surface tension, mercury wetted switches
and relays have been used in the past. Generally they have the disadvantage of being
directional in operation and are sometimes called tilt switches. Companies in the
T&M sector have replaced mercury switches with other types in the majority of
applications through mercury reduction programs, however there remain some
applications that require no contact bounce, high isolation, low contact resistance or
long life (number of operations over expected product lifetime) where mercury
switches and relays (activated by mercury switches) are still in limited use.
Application requirements of switches and relays generally include:

Reliable and stable low contact resistance
High operational life
Switching frequencies sometimes into the RF region
Wide range of ambient temperature operation
Switching voltages and currents


1.2.3

Other uses:
There are no products with mercury based manometers or temperature measuring
2
equipment in our companies. One company provides sealed elemental mercury that
has no electrical power for temperature standards applications.


1.3

Trends
1.3.1

Our companies have restricted mercury to LCDs, relays and switches in electronic
products. The majority of applications for switches and relays do not employ
mercury-wetted types which use in the order of 10 milligrams. Equivalent types two
decades ago used 20 or more times the quantity or mercury.

1.3.2

Our own reduction of mercury is in-line with reports of world usage of mercury that
indicate use of mercury is an order of magnitude less than the amount of mercury
used twenty years ago. Further details can be found at
http://www.chem.unep.ch/mercury/Report/7.3





2.

Substitutes for Mercury

Lamps
In the test and measurement sector LCDs are employed for visual text and graphical representation
of measured and derived data with screen sizes much smaller than large screen TVs. Alternative
plasma and LED display types are employed where the quantity of information is small and
numeric in nature. Our members have no additional information on substitutes for mercury lamps in
display backlights that have not been made available to ERA for their review of the first round of
RoHS exemptions.


Switches
There are vast numbers of switch/relay technologies available for different applications. Most are
electromechanical but there is a growing trend to use solid-state switches and relays in the guise of
CMOS or FET devices:

In any electromechanical relay, contact operation relies on an energising element or switch.
Depending on the design this can be a purely mechanical device or a magnetic element producing
armature movement when energised. The by-product of coil energization is heat. This is not an
ideal situation in relays required to offer stable low-level switching since heat generates significant
thermal emf voltages across switching contacts.

Different materials and technologies are employed in the following applications:
Power switching (high voltages and currents),
RF (Radio Frequency) switching at high speed and
Low-level signal switching.


Power switches
3
In power switches the issue to mitigate is arcing of contacts. In most applications power switches
do not require large operational life as they change state relatively infrequently (10 times/ hr) and a
switch life of 10
5
operations is often more than adequate. To mitigate arching, power switches use
cadmium oxide to keep contact resistance low, and may have air evacuated and subsequently sealed
to operate in a vacuum, or are filled and sealed with inert gas. Gold plating is an alternative used
that improves stability in gas filled relays and switches passing high currents. High voltage
switches normally have tungsten or molybdenum contacts that are hard and have high melting
temperatures.
Solid-state switches are unable to pass sufficient power without melting. Our companies do not use
mercury in power switches and we are not aware of any available.

RF Switches
Operating any relay at radio frequencies to switch analogue or digital signals imposes current and
voltage limitations due to the skin effect where current migrates from the centre of a conductor
towards its outer surface as frequency increases. This results in localised heating at the surface of
the conductor. In many applications at these frequencies a relay life of 10
8
operations or greater is
required as it may have to operate many times per second for considerable time. Wherever possible
solid-state switches are used however contact resistance is higher than equivalent electromechanical
relay switches and they suffer from poor isolation.
Electromechanical RF switches with a lifetime of 10
6
operations without mercury operate at
switching speeds up to 50 MHz. Wetting contacts with a small amount of mercury extends lifetime
to 10
8
operations and frequency response up to 1 GHz. The quantity of mercury used is in the order
of 10 milligrams. The equivalent switches twenty years ago contained 100 milligrams or more of
mercury.

Low-level signal switches
For low frequency applications more choices are available to designers. Unless very low contact
resistance or high isolation is required, solid-state switches are norma