I'm trying to device an instrument comprising two infrared proximity sensors that can be used to check for the straightness of slender (tall) concrete columns. The proximity sensors would be placed at the top and bottom of a 2 metre tall metal pole. The two sensors should work at the same time. Their output are to be compared by a different circuit. If their output are not the same, a buzzer keeps sounding until their output becomes the same. But my problem is that i don't know of any circuit or circuit diagram that can compare the output of there sensors. Please can anybody help me out. The diagram for the sensor is at https://www.electronic-circuits-diagrams.com/alarmsimages/19.gif