The load meter just reads the output amps scaled as a percentage of the motor rated amps, normally in the range of 0 to 150% In SLV mode the VFD will try to keep the motor at the set RPM by increasing the current to the motor up to the upper set limit, at which time the VFD trips out. In SLV mode, the VFD will try to produce maximum torque, if needed, at any RPM below the base RPM (normally 1800) (constant torque) and above the base RPM will try to produce maximum HP (constant HP) by varying the torque (current) as needed to maintain the set RPM without overloading the motor.
To put this another way, let's take the case of a lawnmower engine. These are governed to about 3600 RPM at max throttle. So when running unloaded, the governor is opening the carb butterfly only enough to produce enough torque to maintain the engine speed. But when you start cutting grass, the governor is adjusting the butterfly to try to maintain the set RPM based on the load, producing only enough torque to maintain the RPM. When you hit that heavy patch of grass, the butterfly opens all the way to try to maintain RPM, this is the max torque that the engine can produce. If the torque required is greater than the engine can produce then it stalls.
You're wanting to torture the load meter into being a HP meter.
RPM doesn't enter into the math. The _TT command doesn't give you RPM, but rather the ''throttle position'', and the load output from the VFD gives you the ''torque'' (current draw) value as a percentage of the maximum available torque. You can calculate the HP, but this would require an encoder or tach input to the Galil.
Or another way using the formula (V * I * Eff)/746=HP, determine your electric motor's horsepower. Multiply the voltage, the current, and the efficiency, then divide the result by 746. For example, the horsepower of a 230v motor pulling 4 amps and having 82% efficiency would equal 1 horsepower. This would be difficult to implement because there is no easy way to read the instantaneous output voltage to the motor.
Bottom line is the load meter should just read the load output from the VFD, scaled as 150%=10V or ANin * the scale factor (1/(150/10)) = 0.066
I hope this makes sense.