Baxter Travenol Laboratories, Inc.

Cheng L Wang

Charles I Soodak

David A Lohr

Richard D Holmes

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.

Backup control circuit for kidney dialysis machine

The leakage current thermostat is utilized in an electric heater assembly including a housing, a heating element mounted in the housing, electrical supply lines to the heating element and an electrically insulating material in contact with at least a portion of the heating element. The material has a temperature-resistance relationship such that the leakage current therethrough is a steep function of temperature. A leakage current thermostat includes a thermostat control circuit which is coupled to the supply lines and which is operative to control the current to the heating element in response to changes in the leakage current. The heating element is preferably formed by printed circuit techniques on a ceramic material which is affixed in a layer to a metal (conductive) base layer and the leakage current from the printed circuit element to the base is measured by the control circuit.

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Silver Spring, MD, United States of America

Cheng L Wang