Q:

Will torque and power data reported from an air-cooled eddy current dynamometer become less “accurate” or “repeatable” as brake temperature increases?

  A:

No. The amount of torque reported from an absorption chassis dynamometer is a product of steady state (also known as “static-torque”), acceleration, and parasitic based torque values.  As the brake heats up, it requires more electric current in order to achieve the same absorption effect, but this has no bearing on the actual torque numbers recorded: only the dynamometer’s ability to hold the vehicle at the predefined speed.  If the vehicle exceeds the pre-defined speed, the torque that would have been absorbed and reported as steady state torque is instead reported as acceleration torque – total torque remains unaffected.  The eddy current brake is only used to impose load, and has no direct kinship to the accuracy of the reported data. 

To avoid circumstances whereby a brake is “undersized”, and as a result unable to sustain proper load, one should consult the manufacturer when attempting to size the dynamometer itself.