Abstract: A computer controlled device for accurately mixing two or more fluid materials into a continual stream over an extremely wide range of relative quantities and fluid characteristics. The device can additionally sequentially dispense different predetermined mixtures of said fluid materials to two or more destinations. Mixing may be automatically accommodated in two or more sequential dilution steps. Provision exists for exact temperature control of the fluid materials and the discharge stream. Self monitoring and operation documentation are included. The device is designed to feed ingredients into continuous-flow processes which include testing of aquatic organisms for toxicological response to a variety of carefully controlled concentrations and combinations of chemical toxicants.

Abstract: An economical astable multivibrator circuit provides a variable frequency, variable duty cycle digital signal for controlling a solid-state relay to provide power proportioning. An optical isolator receives analog input signals and converts those signals into a variable resistance signal for altering the RC time constant of the charge/discharge timing circuit. The controller is capable of driving several solid-state relays simultaneously and includes a powerstat adjustment for manually adjusting the range of power delivered to a load.