Relay No. 90A

This is essentially a change-over relay switch.  It is used for various purposes, the chief of which is used at the Central Telegraph Office (CTO) to transfer the hues from the telegraph apparatus to the Time Distribution Chronopher, or Sub-Chronopher as the case may be, for the transmission of the 10.00 a.m. and the 1.00 p.m. G.M.T. signals to provincial offices, Admiralty stations, etc.  They are also used on other time related equipment.

Relay, Type 90A (cover removed)
Figure 34

It consists of an electromagnet B, having two 600 ohm windings which can be connected either in series or in parallel as required.  This electromagnet has an armature A to which are attached two contact springs B and B1 connected to terminals T and T1 but insulated from each other and from the armature.  These springs, when the relay is not energized, make contact with separate contact screws C which are attached to the terminals S.  On the passage of it current the armature A is attracted downwards, carrying with it the contact springs B and B1.  These make contact with the lower contacts D, which are connected to terminals M until the cessation of the energizing current, when they return to their normal position against the upper contacts C.  Bias is given to the armature by the tension screw K and its associated spring.
 

Last revised: November 17, 2023