Abstract: A stepping motor control circuit for precisely controlling the motion thereof. The control circuit energizes the motor windings according to the design sequence for rotation in a given direction. Each winding is energized by a signal having an ascending staircase for its leading edge, a descending staircase for its trailing edge and a steady state level between the leading and trailing edges. The ascending staircase and the descending staircase each comprise one quarter of the terms for each winding energizing signal. The steady state level occurs for one half the time of each energizing signal. The total number of steps in all ascending and decending staircases is controlled and selects the total rotation of the motor. When the motor reaches the desired position whether in the middle of a staircase or not, the signals coupled to the stepping motor windings are frozen at the level when the total step count is reached.

Abstract: In a double beam, optical-null type infra red spectrophotometer, an optical system including a movable dispersive optical element causes transmission of a spectrum of light in respective beams through an adjustable optical attenuator and through a sample and thence to a sensing circuit. The sensing circuit provides an error voltage having an amplitude proportional to the difference between the intensites of the beams passing through the sample and through the attenuator respectively. The position of the attenuator is adjusted in proportion to the integral of the error voltage to cause a reduction thereof while, in response to the magnitude of the error voltage in excess of a threshold value, there is a reduction in the rate of movement of the dispersive element.