can any one help me on an electronic circuit on how to switch a relay at a speed just a few revs above synchronous speed, switches off at synchronous speed and also switches off at high revs which the motor does not resist and apply breaks to it. does the LM2907 help??

 

How are you measuring your motor speed?

 

by means of a sensor and the frequency is determined by the output voltage from the LM2907

 

It is possible, but you will need an optical encoder mounted on the motor shaft. Encoder will supply the speed dependent frequency to your LM2907 and the analog out must be compared with a fix value. The comparator output will be the signal you could use to activate your realy (with a proper amplifier).

Alberto

 

thanks for your help. i found it very helpful. thanks again!!!