Component selection and solutions in dialysis equipment

Dialyzers are artificial kidneys used to treat patients with blood disorders or renal insufficiency. Dialyzers are several pieces of processor-based equipment containing an electromechanically controlled extracorporeal blood path that uses a pump and a semipermeable membrane to filter the patient's blood. From an operational perspective, dialysis equipment needs to meet specific safety conditions, one of which is single fault tolerance. This means that a single point of failure in the pump, motor, tubing or electronics will not endanger the patient or expose them to a dangerous environment. This means that several redundant components and circuits are required in the system as well as separation mechanisms managed by "watchdogs". These devices may include passive and active components such as control devices, sensors, motors, heaters, pumps and valve drivers. Typically, the "safe mode" of operation means that the arterial blood pump will be disabled and the venous line will be clamped to prevent unsafe blood from flowing into the patient.

Typical circuits in a dialyzer include:

Sensor control board: Contains analog-to-digital converters, precision references, clocks and VCOs, and instrumentation or op amps. While these circuits need to respond quickly, the devices included here are generally skewed more toward high accuracy than the high speeds considered today. Some of this is also driven by the need to validate measurements or alarm signals and coordinate responses across the entire system, rather than just reacting to random stimuli. The A/D used here will provide high reliability, good noise immunity (note that motors and pumps are included in the system), and high accuracy.

Arterial and venous control cards: These parts of the system may include functions such as arterial and venous pressure sensors, blood pumps, tube clamps, liquid level sensors, blood test sensors and various other monitoring and control functions. Since TI C2xxx DSPs are targeted at motor drive and industrial sensor applications, they have become an ideal microcontroller choice for these areas. It not only provides drive and diagnostic functions, but also implements RPM and motor coil current sensing and reads pressure transmitter data. At the same time, it can also support the redundancy required in the system with minimal cost impact.

Motor/Pump Drivers: The dialyzer contains many motors, pumps, valves, and heaters. Each component may require specific drive circuitry, some of which can be driven directly by the C2xxx controllers. Selecting the appropriate D/A converter and driver amplifier is very important for the control of the motor/pump and the expected life of the motor/pump. Any value or difficulty in driving the motor and high signal noise will cause them to heat up quickly and degrade performance, and will affect the overall comfort of the patient connected to the machine.

From TI's C2xxx family of high-performance 32-bit controllers to its precision analog family of amplifiers and data converters to a range of power management solutions, TI has the right components and support.

Dialyzer system block diagram