Patent ID: 7547196

Claim:
In a rod pumping arrangement including a motor ( 12 ) coupled by a mechanical linkage to a polished rod ( 32 ), rod string ( 36 ), subsurface pump ( 44 ) assembly, wherein said motor and mechanical linkage cause said assembly to reciprocate in a borehole, and a variable frequency drive ( 8 ) coupled to said motor ( 12 ) for controlling speed of rotation of said motor, a method for mitigating rod float comprising the steps of, providing a controller ( 52 ) with software and data memory and with a signal path ( 9 ) provided between the controller ( 52 ) and said variable frequency drive ( 8 ), producing an operating load level representative of polished rod ( 32 ) load during assembly downstroke while said assembly is reciprocating in said borehole, operating said software in said controller to compare said operating load level with a predetermined load limit indicative of a rod float condition stored in said data memory and generating a low load signal only while said operating load level is below said predetermined load limit, applying said low load signal via a signal path ( 9 ) to said variable frequency drive ( 8 ), and controlling the speed of said motor ( 12 ) with said variable speed drive as long as said low load signal is applied.