Personal air sampling system and pump for use therein

Abstract

An improved personal sampling pump design makes use of non-circular diaphragms within the pump assembly to provide a compact, space saving design. Both upstream and downstream dampers are employed to reduce pulsation in the airflow. Flow control is achieved by monitoring the back pressure created by a flow restriction or adjustable valve located at the sampler's outlet. The created pressure is monitored by a pressure sensor and is directly related to inlet flow rate. The use of an adjustable restriction on the outlet provides increased dynamic range of the flow measurement system without excessive loading to the pump. A signal conditioning circuit takes the signal from the pressure sensor and feeds it to an analogue to digital converter which in turn feeds it to a microprocessor. The microprocessor controls the pump drive circuitry such that a constant inlet flow rate is maintained.

1 . A displacement pump for an air sampling system comprising a pumping chamber having a displaceable wall, a motor and a drive operated by the motor for reciprocating the wall, the wall having a major dimension and a minor dimension, and being disposed with its major dimension substantially parallel to a major dimension of the motor.  
     
     
         2 . A pump as claimed in  claim 1  wherein the major dimension of the motor is parallel to an axis of rotation thereof.  
     
     
         3 . A pump as claimed in  claim 1  wherein there are two pumping chambers, each with a displaceable wall disposed on opposite sides of the motor.  
     
     
         4 . A pump as claimed in  claim 1  wherein the drive comprises an eccentric mounted on a shaft of the motor.  
     
     
         5 . A pump as claimed in  claim 1  where the wall has substantially semicircular ends joined by straight sides.  
     
     
         6 . A pump as claimed in  claim 1  wherein the wall is a diaphragm.  
     
     
         7 . A displacement pump comprising a pumping chamber having a displaceable diaphragm, a motor and a drive operated by the motor for reciprocating the diaphragm, the diaphragm having a major dimension and a minor dimension, and being disposed with its major dimension substantially parallel to a major dimension of the motor.  
     
     
         8 . An air sampling system comprising a pump for drawing air through a sampling device, a local flow restriction downstream of the pump, a transducer for measuring a pressure drop across the restriction and for producing a signal indicative thereof, and a controller containing a correlation between the pressure drop and the volumetric flow rate of air through the restriction, the controller being configured to control the pump to produce a said pressure drop corresponding to a desired flow rate.  
     
     
         9 . A system as claimed in  claim 8  wherein the local flow restriction is adjustable.  
     
     
         10 . A system as claimed in  claim 9  wherein the local flow restriction is a needle valve.  
     
     
         11 . A system as claimed in  claim 8  comprising a temperature sensor for sensing the temperature of the air passing through the restriction, the controller adjusting the said correlation according to the sensed temperature.  
     
     
         12 . A system as claimed in  claim 8  comprising a pulsation damper downstream of the pump.  
     
     
         13 . A system as claimed in  claim 8  comprising a pulsation damper upstream of the pump.  
     
     
         14 . A system as claimed in  claim 11  comprising a pulsation damper downstream of the pump, the temperature sensor being located in the pulsation damper.  
     
     
         15 . A system as claimed in  claim 8 , the pump comprises a pumping chamber having a displaceable wall, a motor and a drive operated by the motor for reciprocating the wall, the wall having a major dimension and a minor dimension, and being disposed with its major dimension substantially parallel to a major dimension of the motor.