Means and method for detecting free flow in an infusion line

1. An infusion pump, comprising:

a pump chassis;

a pump mechanism controller supported by the pump chassis and including a processor and a memory;

a pump mechanism mounted on the pump chassis and including a plunger controlled by the pump mechanism controller;

a loader assembly including a carriage movably mounted to the pump chassis, the carriage having an opening formed thereon for receiving an administration set removably installable in the opening by a user, the administration set including a flexible membrane covering a portion of the administration set and a normally closed pivotable flow stop adjacent to the membrane covered portion, the carriage of the loader assembly being movable from 1) a fully open position wherein the user can remove the administration set with clearance between the flow stop and the plunger, and 2) a fully closed position wherein the membrane is engaged by the plunger to pump fluid through the administration set and the plunger is free from contact with the flow stop;

a plunger force sensor connected to the plunger for sending plunger force signals to the pump mechanism controller;

the memory including program code stored therein, the program code being executed by the processor to:

a) sample force signals from the plunger force sensor at a predetermined frequency;

b) store each of the sampled force signals in a four point circular buffer;

c) calculate a derivative dF/dt based on the two most recent samples;

d) repeat step c) and when the most recently calculated derivative dF/dt exceeds a first predetermined threshold, then calculate a four point moving average of the derivatives dF/dt;

e) when the four point moving average exceeds a second predetermined threshold, generate a user perceptible alarm to alert the user that a plunger hit/flow stop open condition may have occurred; and

wherein the program code is executed by the processor while the carriage of the loader assembly is moving between the fully closed position and the fully open position.

2. The infusion pump of claim 1 wherein the user perceptible alarm is generated on a display screen on the pump.

3. A method of detecting and alerting for a possible unintended free flow condition in an administration set for intravenous medical fluids while the administration set is being removed from an infusion pump, the method comprising the steps of:

a. sampling force signals from a force sensor of the pump at a predetermined frequency;

b. storing each of the sampled force signals in a four point circular buffer;

c. calculating a derivative dF/dt based on the two most recent samples;

d. repeating step c) and when the most recently calculated derivative dF/dt exceeds a first predetermined threshold, then calculating a four point moving average of the derivatives dF/dt;

e. when the four point moving average exceeds a second predetermined threshold, generating a user perceptible alarm to alert the user that a flow stop open condition may have occurred;

wherein the steps start after an administration set receiving carriage of an automated loader assembly of the infusion pump begins to move away from a fully closed position and are completed before arrival of the carriage of the automated loader assembly at a fully open position.