dyno issue

i have an issue while running any car on the dyno ... during running the car the dyno puts an unexpectedly load at the middle of the run need to know what to do to be sure its ok

Your question lacks all of the needed basic information.

As Dom' said - you need to give something like, but not limited to, the specific make and model machine being used, the software, exactly what's happening, how it's being operated, etc.

Oh, would these be predominantly turbo-charged vehicles, if so that's perfectly natural operation because

a/ for eddy current or water brake dyno's the dyno' will be normally be set to a specific ramp rate - increase in rpm per second - and as the engines come on boost and their torque increases, the dyno' has to add load to balance that increase while maintaining the ramp.

b/ for inertial dyno's the more rapid rpm increase as the engine comes on boost will be displayed as a steep increase in torque.

thank you gord