# Interview question



## keepdry (Jul 24, 2012)

Had an interview for a maintenance technician position. 
One question was how do you control the speed on an AC motor and how do you control the speed on a DC motor?
I said AC motor-frequency. 
DC motor-current. 
Is that correct?


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## MichielSanders (Mar 31, 2013)

Ac motor is correct
dc motor is voltage


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## keepdry (Jul 24, 2012)

I also did not know the answer to this one. 
What would cause a PLC to have a long scan time. 
I'm thinking now. Maybe a long program with complex subroutines. 
I am not knowing.


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## Aydin2011 (Apr 2, 2013)

Dc motor control with voltage. DC motor has dc motor drive unit . Usally 110v ac primary 90v dc secondary or 220 v ac primary 180v dc secondary depend on motor size. I hope best for you


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## wdestar (Jul 19, 2008)

AC Motor speed is controlled by frequency. DC Motor speed is controlled in 2 ways - amplitude of voltage or through pulse width modulation.


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## Peewee0413 (Oct 18, 2012)

keepdry said:


> I also did not know the answer to this one.
> What would cause a PLC to have a long scan time.
> I'm thinking now. Maybe a long program with complex subroutines.
> I am not knowing.


You could say that...


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## Peewee0413 (Oct 18, 2012)

Or simply say .....system overhead....it'll sound cool...


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## keepdry (Jul 24, 2012)

:thumbsup:


Peewee0413 said:


> Or simply say .....system overhead....it'll sound cool...


I will use that thanks!!:thumbsup:


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## wendon (Sep 27, 2010)

Aydin2011 said:


> Dc motor control with voltage. DC motor has dc motor drive unit . Usally 110v ac primary 90v dc secondary or 220 v ac primary 180v dc secondary depend on motor size. I hope best for you


Either powerstat on primary or rheostat on secondary correct?


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## Aydin2011 (Apr 2, 2013)

I had 20 dc motor in my work place they are all rheostat on secondary same drive unit.


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