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The Fork Relay
Slide 1
Photo of Fork Relay
The Fork Relay was the first stage in the regeneration system.
It detected the polarity of the current coming into the station from the cable - i.e. whether a positive or negative had been sent from the station at the other end of the line.
Slide 2
Close-up of Fork Relay showing the coil in more detail.
Line current passed through a coil suspended between the poles of an electromagnet…
…this created a magnetic field which caused one of the two 'forks' to touch a contact, or butt.
It then sent either a positive or negative signal to the Interpolator.
Slide 3
Photo of Fork Relay with the relevant section highlighted.
Earth currents added a 'bias' to the signal, which caused the forks to drift and transmit one polarity longer than the other.
A feedback mechanism moved the contact butts to the left or right to compensate for this.
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