In earlier days Automation was based on.

Manual Control

• in Manual Control all the action related to process control were taken by operators.

• Possibilities of human errors & consequently its effect on quality of the final product.
• The production, safety, energy consumption and usage of raw material are all subject to the correctness & accuracy the human action.

Pneumatic Control

• Industrial Automation  with its machine & process control, had its origin in the 1920s with the advent of "Pneumatic Controllers".
• Actions were controlled by a simple manipulation of pneumatic valves, which in turn were controlled by relays & switches.

• Bulky & Complex System
• Involves lot of rework to implement control logic
• Longer project duration

Hard Wire Logic Control

• The contactor & Relays together with hardware timers & counters were used in achieving the desired level of automation.

Drawbacks

• Bulky Panels
• Complex Wiring
• Longer Project duration
• Difficult Maintenance & Troubleshooting 

Electronic Control Using Logic Gates

• In 1960s with the advent of electronics, the logic gates started replacing the relays & auxiliary contactors in the control circuits.
• The hardware timers & counters were replaced by electronic timers.

Advantages

• Reduced space requirements
• Energy saving
• Less maintenance & greater reliability

Drawbacks

• Change in control logic not possible.
• Longer project duration.