Patent ID: 8346507

Claim:
An apparatus for detecting a condition in a fluid delivery system, said apparatus comprising: a motor control configured to provide electric power to an electric motor; a logic circuit in communication with the motor control; and a memory in communication with the logic circuit, wherein the memory is configured to store a first rate threshold associated with a first system condition and a second rate threshold associated with a second system condition, wherein the second rate threshold is less than the first rate threshold; wherein the logic circuit is configured to (1) determine a motor parameter at a first time within a time period and store, in the memory, a value indicative of the motor parameter at the first time associated with a value indicative of the first time and at a second time in the time period, (2) compute a change in the motor parameter within the time period as the difference between the motor parameter at the first time and the motor parameter at the second time, (3) compute an elapsed time as the difference between the second time and the first time, (4) compute a rate of change in the motor parameter within the time period as the computed change divided by the computed elapsed time, (5) store the computed rate of change in the memory, (6) compare the computed rate of change to the first rate threshold and if the computed rate of change is greater than the first rate threshold, determine that the first system condition has been detected, and (7) compare the computed rate of change to the second rate threshold and if the computed rate of change is greater than the second rate threshold but less than the first rate threshold, determine that the second system condition has been detected; wherein the motor parameter is selected from the group consisting of system current, system power, system efficiency, motor current, motor power, and motor efficiency; and wherein the first system condition corresponds to a register condition, and the second system condition corresponds to a frozen coil condition.