Pump control for low flow volumes

Abstract

A method for controlling a gas flow of a pump for high flow rates at a low average flow rate by changing the gas pressure inside a cavity in said pump. The method includes decreasing the gas pressure in said cavity during a first predetermined time period, increasing the gas pressure in said cavity during a second predetermined time period, and stopping the active change of gas pressure during at least a third predetermined time period. Additionally, a pump assembly for high flow rates operated at a low average flow rate is disclosed that includes a number of pumps, a pump motor with a number of stator windings adapted to drive said pumps, and a control unit adapted to control said pump motor. In one embodiment the number of pumps is equal to said number of stator windings. The motor can momentarily increase its force on the pumps.

1 . A method for controlling a gas flow of a pump for high flow rates at a low average flow rate by changing the gas pressure inside a cavity in said pump, said method comprising the steps of:
 decreasing the gas pressure in said cavity, during a first predetermined time period;   increasing the gas pressure in said cavity during a second predetermined time period;   stopping the active change of gas pressure during at least a third predetermined time period; and   wherein the decreased gas pressure and the increased gas pressure are predefined to overcome an opening resistance of an inlet valve and an outlet valve, respectively.   
     
     
         2 . The method of  claim 1 , wherein said first predetermined time period is substantially equal to said second predetermined time period. 
     
     
         3 . The method of  claim 1 , wherein said first predetermined time period and said second predetermined time period correspond to a part of a pump cycle of said pump. 
     
     
         4 . The method of  claim 1 , wherein said pump is connected to a control unit, said method including controlling with said control unit said gas pressure decrease and said gas pressure increase; and
 said first predetermined time period and said second predetermined time period.   
     
     
         5 . The method of  claim 1 , wherein said pump is a membrane pump. 
     
     
         6 . The method of  claim 4 , wherein said control unit controls two or more membrane pumps, said pumps having individual pump cycles that are maximally phase shifted in relation to each other. 
     
     
         7 . The method of  claim 5 , further comprising the step of: controlling the main gas flow of the pump by repeatedly introducing a short interrupt of flow between one or several pump cycles of said membrane pump for reducing the average gas flow over time. 
     
     
         8 . The method of  claim 1 , wherein said gas is air. 
     
     
         9 . The method of  claim 1 , wherein said pump is adapted to be used in connection with a sampling device for measuring air quality. 
     
     
         10 . The method of  claim 4 , wherein said pump includes a pump motor,
 said pump motor is an electrical motors and   said method includes controlling the increase of gas pressure and said decrease of gas pressure by said control unit based on a voltage provided to a pump motor of said pump or pumps.   
     
     
         11 . The method of  claim 10 , further including momentarily increasing said voltage provided to said pump motor of said pump or pumps to a voltage substantially higher than a specified input voltage for said pump motor. 
     
     
         12 . The method of  claim 10 , wherein said pump motor includes a rotor, the method further comprising the steps of:
 detecting an angle of the rotor in said pump motor;   comparing said angle with the positions of said pump or pumps; and   providing a higher voltage to the electrical motor to increase angular velocity in order to increase or decrease said gas pressure inside the pump chamber sufficiently fast to let said inlet valve and outlet valve operate.   
     
     
         13 . The method of  claim 12 , further comprising the step of
 monitoring output gas flow during one revolution or a part of a revolution of the pump motor for detecting possible pump failure of any one of said pump or pumps.   
     
     
         14 . A pump assembly for high flow rates operated at a low average flow rate comprising:
 a plurality of pumps;   a pump motor with a number of stator windings adapted to drive a rotor, said rotor driving the crank shafts of said plurality pumps;   a control unit adapted to control said pump motor;   wherein said number of pumps is equal to said number of windings.   
     
     
         15 . The pump assembly according to  claim 14 ,
 wherein said stator windings are positioned relative to said pumps with such an angle that the maximum torque by said rotor and windings is exerted at an angle of said rotor where most force is required to operate said pumps.