The Programmable Logic Controller or PLC, which was specially developed to cater to the needs of the automobile manufacturing industry, is robust and flexible and has proved itself capable of withstanding the demands of harsh industrial environments.Fifty years ago, the mainstay of automatic special purpose machine control was hard-wired relay logic which was supported by electro-pneumatic/motorised timers, electromagnetic digit-wheel counters, step selectors, and latched relays.Special purpose machines had come into being for carrying out reliable, repetitive and sequential machining operations in the mass manufacturing of automobile components.Then came electronic logic gates, hard-wired gate modules, timers, counters and shift registers followed by basic microprocessor control which did not gain ready acceptance (resistance to change).The first microprocessor-based PLCs catered only to logic functions using input, output, timer, counter and latch modules. Proficiency in relay logic made 'Ladder Diagram' programming / trouble-shooting easy and that enabled the take over of automatic special purpose machine control by PLCs.Later, introduction of arithmetic and process control functions made the PLC quite versatile. Then came servo control & computer numerical control and the rest is history!In the test and measurement field the industrial PC rules, with the support of dedicated modules for data acquisition & control, including software, from reputed manufacturers._______________________________