An automated production line applies a polymer coating to a moving sheet. A beta source and detector monitor the total thickness of the coated sheet. The detector count rate remains below the target value, although the source activity and the source-to-detector arrangement are unchanged. Opening the flow valve deposits more coating and closing it deposits less coating.
Which action should the coating control system take?
Close the flow valve so that less coating is deposited and the count rate rises to the target value.
Reset the target to the lower count rate without changing the amount of coating deposited.
Open the flow valve because a low count rate shows that the coating is too thin.
Open the flow valve so that more coating is deposited and the count rate rises to the target value.