Flow meter for a positive displacement pump

Apparatus for injecting relatively small metered quantities of fluid over relatively long periods of time, comprising:

• a fluid source;
• a chamber defining a preselected volume between upper and lower fluid levels associated therewith;
• a first sensor for sensing the presence of a fluid boundary of a fluid column at the lower level in said chamber and for sending a signal indicative thereof;
• a second sensor for sensing the presence of a fluid boundary at the upper level in said chamber and for sending a signal indicative thereof;
• discharge means downstream of said chamber having an outlet and an inlet coupled to said chamber and to said fluid source;
• remotely actuable valve means upstream of said chamber, between said fluid source and said chamber, said valve means having an outlet and an inlet coupled to the fluid source and further including means for opening and closing the valve in response to signals received from a computer control means;
• fluid coupling means coupling the chamber and the discharge means to the valve outlet;
• computer control means coupled to said first and said second sensors and said valve means, for receiving a signal from said first sensor indicating the presence of a fluid boundary at the lower level in said chamber and for sending an opening signal to said valve means in response thereto so as to initiate filling of said chamber above said lower level;
• operating cycle timer means responsive to said opening signal and said first sensor signal for measuring an operating time interval beginning at the opening of said valve and ending upon an ending signal from said first sensor responding to a fall of fluid level in said chamber, and said operating cycle timer means including means for sending a signal corresponding to the operating time interval to said computer control means;
• said computer control means including means responsive to said second sensor signal indicating the presence of a fluid boundary at the upper level in said chamber so as to issue a closing command to the valve, whereupon fluid in said chamber is evacuated, flowing to said discharge means;
• evacuation timer means responsive to said first and said second sensor signals for measuring a time interval for evacuating said chamber during which the fluid level in said chamber falls from said upper level to said lower level and said evacuation timer means further including means for sending a signal corresponding to the evacuation time interval;
• and
• said computer control means including first input means for inputting the preselected volume of the chamber, second input means coupled to the operating cycle timer means for receiving a signal corresponding to the operating cycle time interval, third input means coupled to the evacuation timer means for receiving a signal corresponding to evacuation time interval, means for calculating a flow rate from the preselected volume of the chamber and the evacuation time interval and means for calculating the total volume of the fluid inputted to said pump from the calculated flow rate and the operating cycle time interval.