Patent ID: 8198837

Claim:
A device for controlling the speed of a DC motor, wherein the speed of the DC motor is calculated in the device using determinations of motor field flux and armature voltage in the motor, the device comprising: a control module having one or more control inputs and one or more control outputs; at least one control input is configured to receive data representing field current measured in the DC motor; the control module includes flux curve logic that is responsive to measurements of motor field current to calculate a field flux in the motor, the flux curve logic using a flux curve stored in the control module, the flux curve representing a functional relationship between field current and field flux in the motor; wherein the flux curve is defined by a plurality of flux curve data points corresponding to a plurality of motor field currents within a lower current range and within an upper current range; and wherein the flux curve is further defined by at least a first flux curve line positioned within the lower current range and a second flux curve line positioned within the upper current range.