Automatic constant air flow rate pump unit for sampling air

An air sampling device comprising:

• a) an air pump assembly including a pump having at least a cylinder including glass material and a piston including graphite material and a motor operably associated with said pump, the air flow rate of said assembly being substantially characterized by a function having a plurality of measurable variables;
• b) means for operator input of a desired air flow rate;
• c) means for continuously automatically monitoring the variables;
• d) programmable computer means operably associated with the means for operator input and with monitoring means for continuously estimating the instantaneous air flow rate of said pump from the function and the monitored variables and for comparing the calculated instantaneous air flow rate with the desired flow rate;
• e) means operably associated with said computer means for automatically regulating one of the variables in response to said computer means for modulating the motor speed to thereby cause the instantaneous air flow rate of said pump to approach the desired air flow rate.

A method for operating at a predetermined desired flow rate a pump assembly including a motor, the method comprising the steps of:

• a) characterizing the instantaneous flow rate of the pump assembly as a polynomial function of measurable variables by selecting the input voltage, current draw and motor speed as the variables;
• running the pump under various suction pressures and motor speeds;
• recording the input voltage, current draw, motor speed and flow data rate;
• and performing a regression analysis to obtain a best fit equation for relating flow rate as a function of the selected variables;
• b) measuring the variables;
• c) calculating the estimated instantaneous flow rate from the characteristic polynomial function;
• d) comparing the calculated instantaneous flow rate with the desired flow rate;
• e) adjusting one of the variables to decrease any variance between the calculated instantaneous flow rate and the desired flow rate;
• and
• f) repeating periodically the steps of calculating, comparing and adjusting.

An air sampling device, comprising:

• a) an air pump assembly including a pump and a motor operably associated with said pump, the air flow rate of said assembly being substantially characterized by a function having a plurality of measurable variables;
• b) means for operator input of a desired air flow rate;
• c) means for continuously automatically monitoring the variables including means for comparing each of the monitored variables with a reference, thereby permitting measurement of the monitored variables;
• d) programmable computer means operably associated with the means for operator input and with monitoring means for continuously estimating the instantaneous air flow rate of said pump from the function and the monitored variables and for comparing the calculated instantaneous air flow rate with the desired flow rate;
• e) means operably associated with said computer means for automatically regulating one of the variables in response to said computer means for modulating the motor speed to thereby cause the instantaneous air flow rate of said pump to approach the desired air flow rate;
• and
• wherein said comparing means includes a voltage comparator and a ramp generator operably associated with said computer means, the input of said comparator including one of said monitored variables and the output of said ramp generator and the output of said comparator being operably associated with said computer means.

An air sampling device, comprising:

• a) an air pump assembly including a pump and a motor operably associated with said pump, the air flow rate of said assembly being substantially characterized by a sixth order polynomial function having measurable variables of input voltage, current draw and motor speed and the suction pressure of said assembly being substantially characterized by an equation dependent on the air flow rate of said pump assembly and motor speed;
• b) means for operator input of a desired air flow rate;
• c) a constant pressure intake manifold assembly operably associated with said pump assembly;
• d) means for periodically automatically monitoring the input voltage, current draw and motor speed;
• e) programmable computer means operably associated with the means for operator input and with said monitoring means for periodically estimating the instantaneous suction pressure of said pump from the air flow rate function, the suction pressure equation and the monitored variables and for comparing the calculated instantaneous suction pressure with a desired suction pressure;
• and
• f) means operably associated with said computer means for automatically regulating the input voltage to said motor in response to said computer means for modulating the speed of said motor, thereby causing the instantaneous suction pressure of said pump to approach the desired suction pressure.