Speed control on PowerFlex 70

[danatomega]

Wow - I didn't think that through very well. Thanks to ASF for catching my blunderous post.

I am now thinking that if you are going to use a 24V supply you could series a 14.7K resistor with the 10k pot then the whole rig would equate to 24.7k ohms and the max value you will get out of the pot is 9.72 V.

I located a mouser resistors that would work:
http://www.mouser.com/ProductDetail/Vishay-Dale/CCF5514K7FKE36/?qs=sGAEpiMZZMu61qfTUdNhG3EzrPz99APhmwAUVwPC8VI%3d

 

[Lancie1]

Lancie1 the speed settings are two seperate tags in the program.

That little "two" is the part that is bugging me. I don't see why TWO tags would be needed IF your PowerFlex 70 is set up to use the Analog Input speed control option. That only needs and uses ONE tag.

Here are the speed reference options from the PowerFlex 70 manual. I think you must be set up now for the Preset Speed Parameter (which would use TWO PLC tags), but now you need to swap to the Analog Input option (1 PLC "Speed" tag). That would require some re-programming of the Powerflex parameters.

It is possible that one of your tags is simply a Run/Stop command for the drive. If so, then you are probably okay with your current plan.

Too bad you don't have a PowerFlex 700, which has direct-wired Pot input terminals.

 

[jrsnydley]

My potentiometer is working, I have a value range from 4-630. My input config is set to 0-10V. Now I am not sure how to write the code. I know I need to, in the end, convert my analog input into speed and move it to the vfd. So how do I do that? I am guessing I have to set up some sort of ratio so that, for example when my analog input value increses by 1 my speed changes .05 Hz or something like that? I should also add that we only want to go +/- 1Hz max with the adjustment on the pot because as Andybr previously mentioned, if you ramp up the speed too much on this system it will tear it apart.

 

[jrsnydley]

Lancie1, the drive is not running off of the analog input speed control option. It has a set speed for running and a set speed for stall speed. What I am trying to do is find a way to run my pot into my analog input module on the bus and convert that in a way that changes the running speed value that I send to the PowerFlex 70.

 

[Lancie1]

I know I need to, in the end, convert my analog input into speed and move it to the vfd. So how do I do that?

EDIT: Look at how the existing speed tag is scaled (range from 0 to ?) and scale your pot input to be in the same range using the SCL (Scale Date) instruction or the CPT (Compute) instruction. The existing Running Speed Tag then should be set equal to your new pot speed number. If the 2 tags are getting into the Powerflex now, then all you need to do is substitute your new pot speed number for the Running Speed tag.

 

[ASF]

I've attached an add-on instruction that can do scaling for you. You send it the input, then set your 0 and 100% for the input, and your 0 and 100% for the output, and you're away. Unzip and import it, and then you can either just drop it in and use it, or look at how it works and do it yourself. It's literally two rungs of code, and one of them is just to stop you doing something stupid and making the PLC divide by zero