Backup control circuit for kidney dialysis machine

Abstract

The backup control circuit is used with a main control circuit for a kidney dialysis machine and is operable upon failure of the main control circuit to operate with a predetermined time period to cause closing of a dialysate operate valve and opening of a dialysate bypass valve and/or stopping of a blood pump when an aberrant condition in the dialysate conductivity, temperature, flow or negative pressure are sensed and/or when an aberrant condition of the arterial or venous blood pressure is sensed and/or excessive leakage of blood into the dialysate is sensed. The backup control circuit includes control circuitry for controlling operation of the back-up control circuit, the circuitry having input contacts coupled to sensor inputs to the main control circuit. A time delay circuit has an input coupled to the control circuitry and is operable to initiate a timing cycle for the predetermined time period upon receiving an error signal from the control circuitry. Energizing and de-energizing circuitry has an input coupled to an output of the time delay circuit and outputs coupled to points in the main control circuit associated with coils for the dialysate operate valve, the dialysate bypass valve and the blood pump. The energizing and de-energizing circuitry is operable upon receiving an operate signal, after said predetermined time period has occurred and the main control circuit has not functioned properly, to close the operate valve, open the bypass valve and stop the blood pump.