# VFD Digital input ref.



## JRaef (Mar 23, 2009)

Wireman191 said:


> Is there a voltage present on it?
> I need to hook up a sensor that needs a small amount of voltage in series to stop the pump if the water gets to low. Didn't have a time to try yesterday so I just want to be ready Monday so I can get this wrapped up. Thanks!


Don't do it. There is usually about 10VDC on the digital inputs from a common source, but the power capacity is in mA, and if something goes wrong in your sensor, it takes out the entire interface board of the VFD. Some drives have a small isolated power supply for 24VDC loop powered devices though.


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## Wireman191 (Aug 28, 2011)

Thanks for the heads up. Ill figure out a better way to do it. 
Were getting some pressure pads that will control the speed of the VFD and Im sure they will be able to stop it if the tank goes dry, but I dont think we will have them in time to run the pump.


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## Big John (May 23, 2010)

JRaef said:


> Don't do it. There is usually about 10VDC on the digital inputs from a common source, but the power capacity is in mA, and if something goes wrong in your sensor, it takes out the entire interface board of the VFD....


 Besides a back-feed from some other source or a ground-fault, is there any other mode of failure for these digital inputs? I'm just wondering what the sensor could do.

-John


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## John Valdes (May 17, 2007)

Big John said:


> Besides a back-feed from some other source or a ground-fault, is there any other mode of failure for these digital inputs? I'm just wondering what the sensor could do.
> 
> -John


 A digital input is nothing more than a contact.
A sensor would be an analog input.

Now we can use digital inputs to change speed and this is done with pre-set speeds. 
Contact closure initiates speed change.
What are we talking about here?
Reference signals, digital inputs or sensors.


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## DriveGuru (Jul 29, 2012)

Hmmm... John ...some drives will take a digital reference such as a square wave or a quadrature encoder


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## MDShunk (Jan 7, 2007)

DriveGuru said:


> Hmmm... John ...some drives will take a digital reference such as a square wave or a quadrature encoder


Which is damned handy to sync another drive for something like a big conveyor pony drive or similar master-slave arrangement.


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