Platinum Metals Rev., 1961, 5, (4), 143
Miniature Moving Coil Relay
Iridium-Platinum Contact Assembly
In order to take the fullest possible advantage of the extremely limited operating power available, moving-coil construction is employed for very high sensitivity relays. The type S.115 relay by Sangamo Weston Limited is an example of miniature moving-coil construction, the unit measuring only 51 × 19.5 × 21.5 mm. It can be wound to operate on a current of only 50 microamp.
The contact arrangement comprises a blade of 20 per cent iridium-platinum attached to the lower end of the moving coil, this moving between the two dimpled iridium-platinum strip contacts in the base assembly shown on the right of the illustration.
The hairspring of the relay normally keeps the blade in the central or “off” position.
Provided that spark-quenching is employed, the contacts will handle powers of up to one watt, a.c. or d.c. (substantially non-inductive) and provided that the circuit voltage does not exceed 50 or the circuit current 100 microamp.
Iridium-platinum provides the combination of hardness and complete freedom from tarnish that is essential in this application.