Abstract: A spectral photometer including a filter wheel driven by a synchronous motor and an analysis circuit. Interference effects of the power line on the output of the photometer are cancelled by provision of a speed changer to achieve each revolution of the filter wheel in the time required for a set, odd number of power line half-cycles to the motor.

Abstract: An alarm switch circuit includes an opto-isolator that is used as a high speed switch to control the pulse generation rate of an oscillator circuit which in turn maintains a set of normally open contacts of an interlock relay in the closed condition. The fail-safe design features are not negated should the following conditions occur: (1) a loss of power, (2) one or more independent failures of circuit elements, (3) open or short circuit failures of the set point (SP) or process variable (PV) voltages or their polarity reversals and (4) the background noise masks the PV signal.

Abstract: A fail-safe logic circuit which includes a pulse generator driven series arrangement of opto-isolators each of which generates a pulsating signal at its output as a function of the logic level state of its respective input terminal. If all input terminals are logic level highs, then a pulsating output signal is equivalent to a true state whereas either a DC or zero level signal is indicative of a false state.

Abstract: Method and system for the constant amplitude control of an electromechanical oscillator utilizing a phase locked oscillator to generate a secondary a-c setpoint which is compared to the oscillator output to provide a difference signal which is passed as a fast-acting negative feedback signal to stabilize the amplitude.