Dialysate preparation apparatus with improved control

Claim 1

Dialysate preparation apparatus for mixing dialysate concentrate with water, said apparatus comprising a main flow line having one end connected to a source of water and another end for connecting to a dialyzer for providing dialysate to said dialyzer, a concentrate flow line having one end for connection to a source of dialysate concentrate and another end connected to a junction on said main flow line for adding concentrate to water in said main flow line, a volumetric pump having a fixed discharge volume per stroke on said concentrate line so as to pump said concentrate to said main flow line, a concentrate sensor means on said main flow line downstream of said junction providing concentration signals indicating concentration of liquid flowing through said concentrate sensor means, and a controller means connected to said sensor means for receiving said concentration signals and connected to said pump for providing pump stroke rate control signals to said pump to control the stroke rate of said pump, means including said controller means providing with said sensor means and pump a feedback loop in which said pump stroke rate control signals are adjusted so as to achieve a desired concentration corresponding to a desired concentration signal, said controller means including a comparator connected to compare a signal indicating commanded stroke rate provided by said controller means with a limit signal indicating desired operating stroke rate range and means to provide an alarm when said signal indicating commanded stroke rate exceeds said limit signal, thereby avoiding pumping of said volumetric pump beyond said desired operating stroke rate range even though commanded to do so based upon said feedback loop.