Convering from 4-20 ma to 0-10 v

aradhonline

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Nov 2009
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Dubai
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May be another stupid question

On a site i have seen 4-20 ma converted to 0-10 V using a Double decker TB putting some 500 ohm resistance and all ..it's also amazing to see that only one wire to card for an anlog input channel ( neutral looped ). What is actually the basic reason to convert to 0-10 V. Is this to reduce the quantity of wires ...I may ask PROS AND CONS..
 
This is usually done because the particular input card only accepts a voltage signal, not a mA signal. Voltage analog inputs are often less expensive than current inputs.

For some reason voltage signals for transmitters are more common in Europe, and 4-20 mA current transmitters are more common in North America.

Wiring complexity isn't really reduced. You can get single ended current inputs that share a common on the input card. Further, current transmitters are very often two-wire loop powered. The voltage output transmitters that I'm familiar with are four wire, with two wires for power and two for the output signal.
 
Even analog input cards that are designated as "current input" with typical 0-20mA or 4-20mA ranges are really voltage input cards. All the current input cards look at the voltage drop across a precision resistor as the input signal. Sometimes the resistor is external, sometimes it's buried on the card somewhere. But it's there.

I'm not sure what 'neutral looping' is. What is neutral looping?
 
@Micky

We are using 1794-if8 which i think accepts both 4-20 and 0-10.

@Tom,

Hi Tom How you beeen ..

May be you are right.The situation here is we have i/o card redundancy.So One Terminal Block to 2 cards . I thought for analog inputs when current is giving as inputs it splits in a 2 way path.Is that right ?.4 wire and 2 wire option availabe .


@danw

I just ment DC common looping (0 vdc).For analog cards .Sorry
 
If connecting the two cards with current you connect them in series.
If connecting them with voltage you connect them in parallel.

I would use an isolator to split the signal.
 
I have done many startups on remote applications that are not connected to the power grid and rely on solar power panels. In some of these installations actually getting to the physical location of the equipment can be very challenging. IE Swamp, Sand, very remote etc. In these setups they choose to do 0-5v / 0-10v rather than current as it consumes less power than regulating the current.

Just another reason as to why some people use voltage rather than current.
 
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