Time proportioning control: A. can be used on a PM550 programmable process controller B. is less efficient than normal PID control C. cannot use a TM990 micro¬computer D. a and b above. E. None of the above

The correct answer is: A. can be used on a PM550 programmable process controller.

Time proportioning control is a type of control that uses time to proportion the output of a controller. It is often used in applications where the process is slow to respond to changes in the setpoint. Time proportioning control can be used on a PM550 programmable process controller.

Option B is incorrect because time proportioning control is not necessarily less efficient than normal PID control. In some cases, it may be more efficient.

Option C is incorrect because time proportioning control can use a TM990 micro¬computer.

Option D is incorrect because only option A is correct.

Option E is incorrect because option A is correct.