A system is adapted to automatically maintain a desired yield level for a slurry flow. Measurements of the electrical conductivity of a slurry are taken and corrected for the effects of temperature and pressure. The corrected conductivity measurements are used to arrive at a value for system yield. The system automatically determines if the yield is too high or too low relative to a desired level, and controls the rate at which accelerator is added to the slurry in order to increase or decrease yield.