The correct answer is: D. (a) and (b) above
A programmable controller (PLC) is a rugged, solid-state electronic device that uses a programmable memory to store instructions for controlling various types of machines. PLCs are used in a wide variety of industries, including manufacturing, process control, and transportation.
One of the main advantages of PLCs is that they are reconfigurable, meaning that they can be easily programmed to control different types of machines. This makes them ideal for applications where the production process changes frequently.
PLCs are also relatively easy to use and maintain. They typically have a user-friendly interface that allows operators to enter and modify programs without any special training. In addition, PLCs are often equipped with self-diagnostic features that can help to identify and troubleshoot problems.
Overall, PLCs are a versatile and reliable control solution that is well-suited for a wide range of applications.
Option A is correct because PLCs can be used on more than one machine during their lifetime. This is because they are reconfigurable, meaning that they can be easily programmed to control different types of machines.
Option B is also correct because PLCs can be reprogrammed in the field. This means that they can be updated or modified without having to be taken out of service.
Option C is incorrect because PLCs do not require considerable training before they can be used. They typically have a user-friendly interface that allows operators to enter and modify programs without any special training.
Option E is also incorrect because both options A and B are correct.