signal converter

Thread Starter

Ramasule

Joined Nov 6, 2004
12
Greetings, my problem is this.
I am interfacing a plc with a vfd. The problem I am having is that the vfd signal out is a 4-20ma loop and the plc card takes a 0-5 volt signal.

What could I use to convert a 4-20ma signal to a 0-5 volt one.
(I was thinking of a Fet and a battery and having the 4-20 control the voltage through put through the fet.)

Any suggestions welcome
Thank you,
Derek
 

Thread Starter

Ramasule

Joined Nov 6, 2004
12
Originally posted by Iodem_Asakura@Nov 6 2004, 10:41 PM
I think it easier and better for you to use an optocoupler.
[post=3394]Quoted post[/post]​
optocoupler hmm that sounds interesting, anything that i could use that you would find in basic electronics kit.
(also scematic if you can include one pls thanks)
 

Iodem_Asakura

Joined Sep 14, 2004
140
Well, here is a transistor optocoupler. Read it to see if it works for you.

If the on current is higher than 20 mA, you must build an amplifier so it amplifies the 20 mA to a level that can make the optocoupler to turn on, but that amplifies the 4 mA to a level below that, so the optocoupler remain turned off.

By the way, sorry for been late :p , i have been a little busy.
 

Thread Starter

Ramasule

Joined Nov 6, 2004
12
No problem, can u check the file again though im reading it as corrupted.
Thanks.
 

Wendy

Joined Mar 24, 2008
21,840
I'll make one in a bit. Basically an op amp current to voltage convertor along with a summer to set the 0 point.

Here is the starting point.

 

Wendy

Joined Mar 24, 2008
21,840
OK, this will do it, you can use variables potentiometers to replace the odd resistances.



Since most op amps do not go rail to rail you will need supply voltages that exceed your output range, as well as a plus and minus power supply.

Have you really looked at the dates of the original posts? You really should have started a new thread, those guys are long gone.
 
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