Convert 4-20mA into 0-20mA or scale?

Serhioromano

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Sep 2015
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I have frequency inverter. In has Analog input but it is 0-20mA. I also hase pressure indicator/transmitter but it is 4-20mA.

1. Is it possible connect them in signal scale adjust it? If yes how to calculate? Let/s say my low signal is -125Pa and high signal is +125Pa.

2. If 1 is not possible, is there any simple scheme to convert the signal?
 
I have frequency inverter. In has Analog input but it is 0-20mA. I also hase pressure indicator/transmitter but it is 4-20mA.

1. Is it possible connect them in signal scale adjust it? If yes how to calculate? Let/s say my low signal is -125Pa and high signal is +125Pa.

2. If 1 is not possible, is there any simple scheme to convert the signal?

Just use a signal conditioner, something like these:

http://www.axiomatic.com/converter.pdf

http://www.omega.co.uk/pptst/DRG-SC.html

http://www.pepperl-fuchs.com/global/en/classid_1827.htm
 
£200 each? That is why I am asking. I need simple solution.

Simple solution ? That would be you specifying your equipment correctly in the first place....

I am sure there is another way to do it with a few bits of dodgy electronics but if you want a solution that works then signal conditioner is the way to go. Either that or read into a PLC and push out again but i am guessing you don't have a PLC either

I am not quite sure why you would want to connect a pressure sensor directly to the VSD anyway, surely you will need to do some preprocessing on it first ?
 
What VFD are you using?
Many have parameters that can adjust the input/output.
Also many can perform PID on the pressure to control from within the VFD.
I have 4 400 hp vfds to control industrial water pressure and 3 200 hp to control spray water pressure.
All independent of the PLC so that as long as we have 480 VAC we have pressure.
They work quite well.
We are using Altivar Schneider VFDs setup for PID control with the 4 - 20 ma from dedicated pressure transmitters as feedback.
 
Configure the drive so the 0-20mA input range represents -187.5Pa to +125Pa and the 4-20mA signal will have be represented as -125Pa to + 125Pa.
 
What VFD are you using?
Many have parameters that can adjust the input/output.
I checked. There is no 4-20mA. theer is 2 options 0-10V and 0-20mA.


I am not quite sure why you would want to connect a pressure sensor directly to the VSD anyway, surely you will need to do some preprocessing on it first ?

I think that if sensor and МЫВ are both 4-20mA I can connect directly. Isn't it?
 

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