zero speed detector

[buckrod]

I have a machine that has a cylinder which takes some time to stop once power has been removed. I would like to detect when that motor has stopped, but would like to do it without having to run more wire to, say , a zero speed switch or encoder.
Is there a device that I can hook to the bottom of the motor contactor and once power is removed, sense the voltage fed back from the motor as it winds down? Once that motor has stopped, I would use that to open a contact.

 

[nbucska]

Use a timer.

<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032

 

[buzzp]

There is such a device. I can not for the life of me remember the name. It is something along the lines of a backspin relay that worked by measuring the voltage generated from a disconnected motor. It was used in the oil fields and still is. Lot of hits returned on google searching for 'backspin relay'(some are timers some are not).
Of course, if the time to stop is always the same (same load) then a timer will work as well.

 

[jraef]

This is probably like the one buzzp was thinking of. I've used them, but they are a little tricky to set up if you want absolute zero speed detection reliably (in terms of repeatability without re-adjustment).

http://www.rke.com/zvrs.pdf

&quot;Venditori de oleum-vipera non vigere excordis populi&quot;