dB vs Frequency (torque )

Hi automation gurus,

I have a question regarding about defining a torque & period graph in terms of frequency.
The blue is periodicity, and red is torque.

http://www.2shared.com/file/7864636/c4fd6b77/torque.html

At 347Hz, the torque dB increases. What does this means in terms of a motor running ?

hope to hear from everybody.

I am not sure why you are recording period if it is period of your AC signal in essance you already have it from the frequency. If it is period of some part of the machine that is another matter. More explanation of what you are measuring and what the machine does would help.

I also have difficulty seeing why you are converting torque to dB.

For why at 347 the torque went up I just dont see where there is enough data to make a conclusion. The short spike indicates to me a "random event" ?? that will never be understood - could even be instrument error or just simply somebody dropped a wrench in the machine increasing torque while machine chewed up wrench.

Dan Bentler

Dan, what he has there is a plot of the relative energy content of a given frequency in a measured signal. In his graph a pure 60Hz AC wave would show as a single spike at 60Hz with nothing else showing anywhere.

AmazingTrans, at a frequency of 347 Hz my first question is what are you using to measure this? If it is an analog torque sensor it may be real. If it is drive feedback I may be a bit suspect. You don't tell us how fast the motor is going. If it is at standstill it is possibly a loop closure artifact that may or may not require tuning. If it is at some speed it may be magnet passing frequency (in a PM motor), it may be a drivetrain induced harmonic, it may be a control loop response triggered by a vibration on the machine or it could be none of these. As Dan said, you are a bit light on information.

Keith