4-20ma transducer

[lewlec]

Evening all

any one know if I can use 1x 4-20ma transducer controlling 3 vsd's.... Paralleling them up???
greatfull for any info.

regards
gary

 

[johnboy6083]

Yes you can, we use them for that purpose, but we use the PLC to give three seperate outputs to the VSDs.

 

[snowhead]

Input to 1st
Output from 1st to control 2nd
Output from 2nd to control 3rd.

 

[johnboy6083]

You can buy splitters if you want to send the signal to more than one place, without using a PLC

 

[johnboy6083]

Input to 1st
Output from 1st to control 2nd
Output from 2nd to control 3rd.

This will work fine until drive one or two develop a fault. Using a splitter, or a PLC to duplicate the signal will mean that you have redundancy.
Am I correct that this is for pumps, maybe a booster set?

 

[lewlec]

Hi john
ye it's for a milking parlour, vacuum on demand. Three vsd's controlling three motors with one transducer. Any recommendations on transducers?

 

[johnboy6083]

We use GE/ druck and they are good, no problems.

 

[lewlec]

We use GE/ druck and they are good, no problems.

Thanks for info, with using a plc would I need one analogue output or three?

 

[johnboy6083]

I think you would need three AO's. I take it your using integral control to control the pressure?

 

[lewlec]

I think you would need three AO's. I take it your using integral control to control the pressure?

Ye going to use pid control and probably use a macro on the drive

 

[silva.foxx]

Some light reading explains a lot

How to send a 4-20 mA current loop to multiple loads | Laurels Electronics Blog

Which VSDs are you inputting to?
What voltage range is your transducer and is it two/three/four-wire?
What voltage is your transducer supply, is it variable?

If you lost 4-20mA signal to one of the VSD, what would you want to happen?


And further info to confuse http://www.plctalk.net/qanda/showthread.php?t=46780

 

[Sparkattack]

You can use 3x signal isolators and loop the transducer 4-20mA signal through the inputs of each unit, then you can have an isolated output to each drive.