# using a rheostat for speed reference



## dronai (Apr 11, 2011)

Read the instructions. AB shows right on there.


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## JRaef (Mar 23, 2009)

The drive should have it built-in, should be a +10VDC terminal. But is it a rheostat, or a potentiometer? Most drives will be looking for a potentiometer input. The difference is that a rheostat doesn't have a center reference point for the wiper, so when you find the wiring instructions for a remote pot, you will have to adapt it to a rheostat.

Also, check the drive specs for the resistance value compared to your rheostat. Most VFDs will be looking for a 10kohm pot.


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## deravator (May 11, 2015)

sorry meant potentiometer I often (incorrectly) use the terms synonymously.
I will check the Allen-Bradley for comparison though this is ABB


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## JRaef (Mar 23, 2009)

OK, I'm at a different PC now. I don't have an ACS355 manual, but I have an ACS350, should be the same wiring. They don't make it clear, so you get a "bye" on not being able to figure it out. They never use the term "potentiometer" or even "rheostat", they refer to it as a "Unipolar voltage" input... yeah, clear as mud.

So on your 10kohm pot (confirmed), one end of the pot goes to terminal 2, the other end to terminal 4, the wiper goes to terminal 3 and the screen (shield) goes to terminal 1. That's just the wiring though, you'll have to go into programming to set it up to respond to that pot, and with my manual being different, I can't help you there. You also may need to check if there is a DIP switch next to the terminal block (it shows in mine). That tells the drive if the speed command signal is voltage (0-10VDC) or current (4-20mA). You need it to be voltage, which on my version is down.


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## erics37 (May 7, 2009)

If you're using the ACS355 that doesn't have a potentiometer built in then it's easy to wire & program a 10k pot in there. Default I/O connection on the Standard macro is AI1. Here's the diagram from the 355 manual:










That's handy for a remote potentiometer. You can also get ones that just mount directly to the drive. ABB part number is MPOT-01


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