Flow sensor methods and apparatus

Abstract

Apparatus and methods of calibrating a microfluidic flow sensor, in which the flow of a fluid through a flow sensor is stopped and a first value is read from the flow sensor, then the fluid is pumped through the flow sensor sequentially at first and second selected rates, and readings from the flow sensor of the flow rate are taken for each of the rates. The readings are used in a polynomial equation to determine the actual flow rate, which is used to calibrate the sensor. The flow sensor can be connected to a computer programmed to perform the calibration method, determine the actual flow rate of the sensor, and make appropriate adjustments to the flow rate of a pump.

1 . A method of calibrating a microfluidic flow sensor comprising the steps of: 
 pumping a fluid through a microfluidic flow sensor;    stopping the flow of the fluid and determining a first value from the flow sensor for the rate of flow;    pumping the fluid through the sensor at a first preselected rate of flow and determining a second value output by the sensor corresponding to the first preselected rate of flow;    pumping the fluid through the sensor at a second preselected rate of flow and determining a third value output by the sensor corresponding to the second preselected rate of flow;    calculating the constants c, b, and a, respectively, in a quadratic equation y=ax 2 +bx+c based on the corresponding first, second, and third values; and    calibrating the sensor based on the calculated values for c, b, and a.    
   
   
       2 . The method according to  claim 1  wherein the flow sensor comprises a thermal anemomity sensor.  
   
   
       3 . The method according to  claim 1  wherein the fluid comprises one selected from a group consisting of the following: tetrahydrofuran, methanol, water, ethanol, dimethylsulfoxide, and acetonitrile.  
   
   
       4 . The method according to  claim 1  further comprising the steps of first rinsing a pump used for pumping the fluid.  
   
   
       5 . The method according to  claim 1  wherein the steps of pumping the fluid through the flow sensor further comprises pumping the fluid through a valve to a waste receptacle.  
   
   
       6 . The method according to  claim 1  further comprising the step of providing a pump with a known flow rate.  
   
   
       7 . The method according to  claim 1  further comprising the steps of transmitting the first, second, and third values from the sensor to a computer.  
   
   
       8 . The method according to  claim 7  wherein the calculating step is performed by the computer in accordance with a computer program.  
   
   
       9 . A method of calibrating a microfluidic flow sensor comprising the steps of: 
 rinsing a pump with a selected fluid;    pumping the fluid through a flow sensor with the pump;    stopping the pump;    transmitting to a computer a first value for fluid flow as determined by the sensor;    pumping the fluid through the flow sensor at a first selected flow rate;    transmitting to the computer a second value for fluid flow as determined by the sensor at the first flow rate;    pumping the fluid through the flow sensor at a second selected flow rate;    transmitting to the computer a third value for fluid flow as determined by the sensor at the second flow rate;    pumping the fluid through the flow sensor at a third selected flow rate;    transmitting to the computer a fourth value for fluid flow as determined by the sensor at the third flow rate;    calculating values for constants a, b, c, and d in an equation y=ax 3 +bx 2 +cx+d based on the first, second, third, and fourth values; and    determining the flow rate x according to the equation.    
   
   
       10 . The method according to  claim 9  wherein the first flow rate is between approximately −1000 microliters per minute or so and approximately +1000 microliters per minute or so.  
   
   
       11 . The method according to  claim 9  wherein the second flow rate is between about −5000 microliters per minute or so and about +5000 microliters per minute or so.  
   
   
       12 . An article of manufacture comprising: an electronic storage device comprising computer software having program instructions directing a computer running said instructions to receive and store in memory a first value for a first flow rate transmitted from a microfluidic flow sensor, receive and store in memory a second value for a second flow rate transmitted from said flow sensor, receive and store in memory a third value for a third flow rate transmitted from said flow sensor, and calculating values for constants a, b, and c corresponding to said first, second and third values for calibration of said flow sensor.  
   
   
       13 . The article according to  claim 12  wherein said article comprises a hard disk.  
   
   
       14 . The article according to  claim 12  wherein said article comprises a CDROM.  
   
   
       15 . The article according to  claim 12  wherein said article comprises a non-volatile computer memory device.  
   
   
       16 . The article according to  claim 12  wherein said program instructions further direct the computer to adjust the flow rate of a pump responsive to the flow rate calculated using the values calculated for constants a, b, and c.