159-117G00 Datasheet, PDF (1/6 Pages) Tyco Electronics – Mercury-Wetted Reed Relays

Catalog 1308242
Issued 3-03
P&B
159/160 series
Mercury-Wetted
Reed Relays
Users should thoroughly review the technical data before selecting a product part number.
It is recommended that users also seek out the pertinent approvals files of the
agencies/laboratories and review them to ensure the product meets the requirements for
a given application.
2 Ampere
Capsule
General Information
The mercury-wetted contact relay represents one of the more sophisticated types of relays
made today. The early pioneer work in mercury-wetted contact switching dates back to the
1950’s, as telephone laboratory scientists sought out the “perfect contact”. Mercury-
wetted contacts represent the nearest thing to the perfect contact yet developed, being
characterized by such parameters as: bounce-free operation; very low and stable contact
resistance; hermetic protection; fast operating speeds; Form C or Form D contact, action
contact life measured in billions of operations. The only major weakness of a mercury-
wetted contact relay is the necessity to mount the relay within 30° of a vertical position, due
to its position sensitivity.
While there are several variations of the mercury-wetted contact relay on the market, the
basic contact element has essential concepts in common. The mercury-wetted contact
element consists of a glass-encapsulated nickel-iron reed with its base immersed in a pool
of mercury. The free reed cantilever projects upward between sets of stationary contact
electrodes, which have been glass-sealed in proper juxtaposition at the top of the glass
chamber. The mercury is induced to flow up the cantilever by capillary action, wetting
mercury on both the cantilever contact tip as well as the stationary contacts. Thus a
mercury-to-mercury contact is maintained on both the normally-closed and normally-open
contacts, and the system is self-replenishing. The 2-ampere mercury-wetted capsule is
shown far left.
Along with the inherent fast actuation of the capsule and excellent load-handling capacity,
the mercury-wetted contacts exhibit extremely long life, as the mercury films re-establish at
each closure and contact erosion is eliminated. Contact interface resistance is very low and
stable, and as the mercury films are elastic, contact bounce is eliminated. A dynamic
sequence of the mercury-wetted contact action is shown below.
While the below sequence portrays a Form D (make-before-break) contact action, a true
Form C (break-before-make) contact can be provided by proper control of the mercury film
dynamics and the contact electrode spacing.
The mercury-wetted contact capsules generally are mounted within a coil assembly, and
with appropriately mounted bias magnets, mounting base and magnetic shielded
enclosures. The more popular assemblies contain one or two capsules in a convenient
printed circuit mounting module.
Mercury-wetted relays can be adjusted to operate with very low levels of input power, in the
order of 10-20 milliwatts. Thus, power gain switching of as great as 10,000 can be
realized. For all but very light contact loads, contact protection is required to limit the current
or voltage rise time across the contacts.
Form D Mercury-Wetted Contact Action As Seen In High-Speed Sequence
(1) Mercury (shown in black) covers armature and contact points; (2) and (3) as armature moves from open to closed position, mercury filament joins both contacts momentarily;
(4) ruptured mercury surfaces accelerate away from each other, providing rapid breaking action; (5) as contact surfaces join, mercury wetting dampens rebound, eliminates
electrical chatter, and provides contact reliability.
SPDT (Form C or Form D) Contact Specifications
Material
Mercury-wetted
platinum contacts
hermetically
sealed in an
inert atmosphere
Rating (Switched Load)
2 amperes
maximum
500 volts maximum
100 VA maximum
(Carry Load)
5 amperes
maximum
Not switched
Dimensions are shown for
308 reference purposes only.
Dimensions are in inches over
(millimeters) unless otherwise
specified.
Bridging and Transfer Time
When operated by a single
DC pulse, the bridging or
transfer time will be greater
than 50 microseconds, but
less than 500 microseconds.
Contact Resistance
14 milliohms typical;
20 milliohms maximum
Stable within
±2 milliohms
throughout life.
Specifications and availability
subject to change.
Life Expectancy
1 billion
operations
minimum
at rated load
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Technical support:
Refer to inside back cover.