Method and apparatus for premixing dialysate

An apparatus for premixing fluids to form a dialysate for an extracorporeal blood treatment, comprising:

• at least a first feed portion for supplying at least a first fluid from at least a first fluid reservoir;
• at least a second feed portion for supplying at least a second fluid from at least a second fluid reservoir;
• a premixing portion which is configured to premix the first and second fluids supplied via the first and second feed portions in counter flow to form a fluid mixture;
• at least one drain portion for draining the fluid mixture premixed in the premixing portion as the dialysate;
• and
• at least one conductivity measuring device along the at least one drain portion for measuring the conductivity of the premixed fluid mixture and to generate a conductivity measuring signal,
• wherein the at least one conductivity measuring device comprises a digital filter adjustable on the basis of at least two state variables of the premixing process,
• wherein one of the at least two state variables is derived from a respective other one and the digital filter is configured to be at least two-phase comprising a first predictive phase in which a next system state is determined by way of measured values and a second corrective phase in which the preceding determining is corrected by way of previous values.