Swimming pool chemical control system

A system for controlling the chemical balance within a given range of a swimming pool of water having at least a recirculating water line and a pump in the recirculating water line which, when operating, forces water through the recirculating water line, the system including:

• a least one sensor in the recirculating water line for continuously determining the chemical balance of the pool and for producing an output indicative of that chemical balance:
• means for dispensing a chemical to the pool downstream of the sensor to adjust the chemical balance of the pool towards the desired balance;
• and
• control means, said control means comprising:
• (i) comparator means for comparing the output of the sensor with a predetermined value and producing an output when the output of the sensor departs from said predetermined value;
• and
• (ii) timing means coupled to said dispensing means and to said comparator means for controlling the duty cycle to said dispensing means such that when actuated by the output of said comparator means, the duty cycle of said dispensing means may be selectively limited, the timing means comprising means for generating a cyclic waveform, regulating means for regulating the timing means to provide a dispensing time period from only a small fraction of the duty cycle to substantially the entire duty cycle comprising means for clipping the cyclic waveform produced by said generator means, means for applying the clipped cyclic waveform to the dispensing means in such a manner that when the comparator means produces an output, it causes the dispensing means to dispense for only a portion of the cyclic waveform.