Mercury relay
A mercury relay (mercury displacement relay, mercury contactor) is a relay that uses mercury as the switching element.
They are used as high-current switches or contactors, where contact erosion from constant cycling would be a problem for conventional relay contacts.
Owing to environmental considerations about the
Operation
Mercury relays consist of a vertical (usually glass) tube containing liquid mercury. They have isolated contacts at the bottom of the tube and partway up, usually in a side arm of the glass. The relay works by
Around the top part of the tube is placed the
For the more traditional
The mercury relay thus allows for switching of higher currents with a small control current, for a large number of cycles. They are often installed into automatic controllers that required extended periods of unattended continuous switching operation. The mercury surface is self-restoring after an arc, and the contact resistance is low and stable.[1]
The glass tube of a mercury relay must be mounted near-vertically. The sensitivity of these relays can be altered by adjusting their angle relative to vertical. As sensitivity depends upon angle, they are unsuitable for use on mobile equipment or with conditions of high vibration.
Impulse relays
Mercury relays have also been produced as latching or
High-speed operation
Owing to the mass of mercury moved during switching, compared to that of the armature and spring leaves of a conventional relay, the mercury relay is not a high-speed device. Despite this, the mercury relay does have a very low
For high-speed use, the
Other mercury switching devices
- Mercury-wetted relay
- Mercury switch
References
- magnetiseditself.
- ^ Steel is less dense than mercury, so that the slug floats on top of the mercury, rather than sinking through it. Despite this, the reduced volume of mercury displaced is still sufficient to bridge the contacts.
- ^ Iron (and steel) is magnetic and can be attracted, mercury is not.
- ^ ISBN 1420026410Section 3.12 "Mercury displacement relays"
- ^ US 2778900, Lenning, Alvar, "Mercury relay of impulse type", published 1957-01-22, assigned to Inreco AB