Automatic block signalling and kiln: what they have in common

1. Step 1. Automatic block signalling — has part — Track circuit. Track circuits.
2. Step 2. Track circuit — has part — Relay. Track relays.
3. Step 3. Relay — evolved into — Programmable logic controller. It replaced relay cabinets.
4. Step 4. Programmable logic controller — is part of — Chemical plant. Process control automation.
5. Step 5. Chemical plant — is made of — Brick. The furnaces and towers are brick.
6. Step 6. Brick — uses — Kiln. Fired brick is stronger than mud brick.

Open Evothings