Air sampler with closed loop flow control system
A battery powered, personal air sampler is described which uses a closed loop control circuit to adjust the power that is delivered to an internal pump such that a stable and accurate flow rate is maintained independent of changes in inlet pressure due to filter loading. Furthermore, the described personal air sampler provides improved efficiency to the entire electronic and flow pumping system which, in turn functions to optimize the available battery run time of the device.
1. A personal air sampler, comprising:
a housing having an air flow passage defined between an air inlet and an air outlet;
a pump disposed in the air flow passage for moving air through the air flow passage at an air flow rate;
a pressure sensing sub-system for generating a signal indicative of the air flow rate;
a coreless DC motor for driving the pump;
a battery for providing a voltage to the DC coreless motor;
a regulator sub-system, having a switch and an inductor, wherein the switch is electrically coupled to and disposed between the battery and the inductor and the inductor is electrically coupled to and disposed between the switch and the coreless DC motor;
a processing device coupled to the regulator sub-system; and
a memory associated with the processing device having stored therein a look-up table for use in implementing a proportional-integrated-derivative closed loop air flow control process;
wherein the processing device switches on and off the switch of the regulator sub-system as a function of the signal indicative of the air flow rate and data contained within the look-up table to thereby adjust the voltage that is provided from the battery to the coreless DC motor via the inductor in accordance with the proportional-integrated-derivative closed loop air flow control process whereupon a driving of the pump by the coreless DC motor is controlled for the purpose of having the air flow rate attain a target set point level.
2. The personal air sampler as recited in claim 1 , wherein the regulator sub-system is arranged to step-up the voltage that is provided from the battery to the DC coreless motor.
3. The personal air sampler as recited in claim 2 , wherein the inductor of the regulator sub-system is arranged between the battery and the switch.
4. The personal air sampler as recited in claim 1 , wherein the regulator sub-system is arranged to step-down the voltage that is provided from the battery to the DC coreless motor.
5. The personal air sampler as recited in claim 4 , wherein the inductor of the regulator sub-system is arranged between the switch and the motor.
6. The personal air sampler as recited in claim 1 , wherein the pressure sensing sub-system comprises a flow element for generating a pressure signal proportional to the flow rate and a pressure sensor which uses the pressure signal to generate the signal indicative of the air flow rate.
7. The personal air sampler as recited in claim 1 , wherein the pump comprises a rotary diaphragm pump.
8. The personal air sampler as recited in claim 1 , wherein the processing device uses a pulse-width-modulated signal to switch on and off the regulator sub-system.
9. A method for controlling an air flow rate through an air flow passage defined between an air inlet and an air outlet of a housing of a personal air sampler, the method comprising:
generating with a pressure sensing sub-system a signal indicative of a current air flow rate through the air flow passage;
using the signal indicative of the current air low rate through the air flow passage and data for use in implementing a proportional-integrated-derivative closed loop air flow control process as stored within a look-up table to control a regulator sub-system, having a switch and an inductor, wherein the switch is electrically coupled to and disposed between a battery and the inductor and the inductor is electrically coupled to and disposed between the switch and a coreless DC motor, whereby the switch is controlled to turn on and off to thereby adjust a voltage that is provided from the battery to the coreless DC motor via the inductor in accordance with the a proportional-integrated-derivative closed loop air flow control process whereupon a driving of a pump disposed in the air flow passage by the coreless DC motor is controlled for the purpose of having the current air flow rate attain a target set point level.
10. The method as recited in claim 9 , comprising using the regulator sub-system to step-up the voltage that is provided from the battery to the coreless DC motor.
11. The method as recited in claim 9 , comprising using the regulator sub-system to step-down the voltage that is provided from the battery to the coreless DC motor.
12. The method as recited in claim 9 , comprising using a pulse-width-modulated signal turn on and off the switch of the regulator sub-system.