Improvements in fluid volume measurement systems are disclosed for a pneumatically actuated diaphragm pump in general, and a peritoneal dialysis cycler using a pump cassette in particular. Pump fluid volume measurements are based on pressure measurements in a pump control chamber and a reference chamber in a two-chamber model, with different sections of the apparatus being modeled using a combination of adiabatic, isothermal and polytropic processes. Real time or instantaneous fluid flow measurements in a pump chamber of a diaphragm pump are also disclosed, in this case using a one-chamber ideal gas model and using a high speed processor to obtain and process pump control chamber pressures during fluid flow into or out of the pump chamber. Improved heater control circuitry is also disclosed, to provide added or redundant safety measures, or to reduce current leakage from a heater element during pulse width modulation control of the heater. Improvements are also disclosed in the application of negative pressure during a drain phase in peritoneal dialysis therapy, and to control the amount of intraperitoneal fluid accumulation during a therapy. Improvements in efficiency are also disclosed in the movement of fluid into and out of a two-pump cassette and heater bag of a peritoneal dialysis cycler, and in the synchronization of the operation of two or more pumps in a peritoneal dialysis cycler or other fluid handling devices using a multi-pump arrangement.L'invention concerne des améliorations apportées à des systèmes de mesure de volume de fluide pour une pompe à diaphragme actionnée par voie pneumatique en général et un cycleur de dialyse péritonéale utilisant une cassette de pompage en particulier. Les mesures de volume de fluide de la pompe se basent sur des mesures de pression dans une chambre de régulation de pompe et une chambre de référence dans un modèle à deux chambres, différentes sections de l'appareil étant modélisées à l'aide d'une combinaison de processus
