Analog to analog conversion

TimothyMoulder · Oct 5, 2004

Here's a problem I'm sure we've all faced at some point, but I couldn't find an answer when I searched...

You got a +/- 10 VDC signal you want to measure. Your input will only do 0-10 VDC.

My solution is to use a converter to change the negative value to a positive one, and bring the converted value in on a separate input.

Does anybody know of an isolating signal convertor that will change -1 to -10 VDC into +1 to +10 VDC?

Thanks in advance!

TM

panic mode · Oct 5, 2004

If you cannot find it make it yourself. Just make simple
voltage divider (two 10k 1% resistors will do):
Connect midpoint of the resistors to your PLC input.
Connect one resistor to your +/-10V analog signal source.
Connect other resistor to +10V.
This will give you output signal 0-10V for input changing
from -10 to +10V.
To make +10VDC source out of 24V just use LM317L and two
resistors. The whole thing costs $3 and ca 10-15minutes
assembly.

TimothyMoulder · Oct 5, 2004

Thanks Panic

Thanks! Beats the heck out of the $250+ unit I was checking from Phoenix Contact.

I'm still interested in off-the-shelf solutions, if anybody knows of any cheaper ones.

Thanks again!

TM

panic mode · Oct 5, 2004

yep except it lacks isolation.
(which most of the time is not a problem)

TimothyMoulder · Oct 5, 2004

Is there a way to do this with op amps?

TM

jimbo3123 · Oct 5, 2004

My original thought was to do it a bit differently, I would have used a full-bridge rectifier. Of course, you would have to compensate for the .7V or so drop across the diodes. You would also have to figure out how to determine the polarity of the original signal, as the new one would always be positive.

The voltage divider solution is probably the better though.

bernie_carlton · Oct 5, 2004

Maybe more than you want to spend, but check out the OM7-31 at Omega

Mickey · Oct 5, 2004

Try here

http://www.miinet.com/products/sg_signal.shtml

randylud · Oct 5, 2004

Tim,
I have used this device:
MM4380 A
DC INPUT, FIELD RANGEABLE,
ISOLATED TRANSMITTER

You can find them through distributors all over under Wilkerson Instruments. In our area that is PEProducts but you may have a local one to your area.
Check it out. Click on products, then by manufacturer and so on till you get to the page with the spces. If you have difficulty, let me know and I can email them to you.

Mickey · Oct 5, 2004

Try this also

http://www.actionio.com/products/slimpak2/wv408.html

Analog to analog conversion

TimothyMoulder

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panic mode

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