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Commentator

Join Date: Sep 2009
Posts: 59

Heavily-Loaded Loop

09/18/2009 1:28 PM

I have a ultra sonic in the field and it has to run to 3 digital level indicators on 3 separate VFDs before it goes back to the PLC.

According to the VFD submittal each level indicator is 4.75 Kohm, which will kill my Hydro-Ranger 200 loop. Ultra Sonic can only handle 750 ohms max.

What is the resolultion to this issue? Some people say a booster, but I have no idea what it does or where it goes.

Can some one shine some light?

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Join Date: Aug 2007
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Posts: 2143
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#1

Re: Loop Heavily Loaded

09/18/2009 2:06 PM

Read the manuals.

750 ohm impedance is pretty standard for a 4-20ma loop. Your PLC typically has a 250 ohm resistor that the current flows through to develop 1-5VDC.

4.75K ohms tells me that the level indicators are voltage, not current. Look at the analog input specifications in the manual for the level indicators. That will spell out whether the inputs are 0-5,1-5VDC or 0-10,2-10VDC.

Your best bet is to get an isolated current to voltage transducer. Hook the current input in series with your PLC input, and the voltage output in parallel with your 3 level indicators.

Read the manuals.

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