Dialysis machine having enhanced D/A resolution
First Claim
1. In a dialysis machine comprising:
- pump means for supplying dialysate to an artificial kidney at a rate proportional to an analog supply rate signal; and
flow rate control means for providing the analog supply rate signal to the pump means, the analog supply rate signal having a value proportional to the value of a digital flow rate signal, the digital flow rate signal having a first predetermined number of bits of resolution;
the improvement comprising;
resolution enhancement means, responsive to a digital flow rate control signal having a second predetermined number of bits of resolution at least one bit greater than said first predetermined number of bits of resolution, for varying the value of the least significant bit of said digital flow rate signal during a selected resolution period in proportion to the value of the least significant bit of said digital flow rate control signal.
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Abstract
A dialysis machine has control circuit which detects changes in input water temperature and compensates the water heater. The control circuit detects changes in the conductivity of the dialysate concentrate and compensates the concentrate pump. Changes in supply voltage are detected and the outputs of the several sensors and the inputs to the pumps and heater comensated. The control circuit periodically calibrates the blood leak detector. In each of the feedback loops which service the heater and each of the pumps, the control circuit varies both the loop response time and the loop gain to compensate for changes in the dialysate flow rate. The resolution of the D/A converters which drive the pumps are enhanced by the control circuit by time modulating the LSB of the respective digital drive value. If any of the several sensed operating conditions varies significantly from the expected value, the control circuit terminates dialysis.
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Citations
8 Claims
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1. In a dialysis machine comprising:
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pump means for supplying dialysate to an artificial kidney at a rate proportional to an analog supply rate signal; and flow rate control means for providing the analog supply rate signal to the pump means, the analog supply rate signal having a value proportional to the value of a digital flow rate signal, the digital flow rate signal having a first predetermined number of bits of resolution; the improvement comprising; resolution enhancement means, responsive to a digital flow rate control signal having a second predetermined number of bits of resolution at least one bit greater than said first predetermined number of bits of resolution, for varying the value of the least significant bit of said digital flow rate signal during a selected resolution period in proportion to the value of the least significant bit of said digital flow rate control signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification