Help needed in 4-20ma to 0-5v conversion

Gsi · Oct 2, 2003

Hello!

I could realy use some help.

I tried a sujestion that someone post here about converting 4-20ma to 0-5V. Everithing look OK and I tested with the multimeter, but when I connect my terminal board to the board in the PC that as the AD converter, the value of the tension starts floating.

Tkx in advance

Xion · Oct 2, 2003

I probably won't be able to help much BUT before anyone can try to help tell us exactly what you are doing. What are you doing to convert the current to voltage? What type of AD have you got? etc etc.

GSI · Oct 2, 2003

more information

Im using a 250 Ohm resistence in the current loop and im mesuring the voltage drop. My board for PC is a Advantech PCL 711S and im using-5/+5 sigle ended 12 Bit AD. Hope with this I can explain, because my english is not so good. Tks

Fritz_frederix · Oct 2, 2003

Hi,

Instead of building it yourself it's also possible to buy it. I think that Phoenix-Contact and/or Pepperl&****s sell that kind of convertors.

Rudi

randylud · Oct 2, 2003

Getting it figured out

If you are going to use a 4-20ma signal and a 250 ohm resistor to convert the current signal to voltage you will end up with a 1-5V signal and not 0-5V. Ohm's law clearly states that E=I x R so do the math. Now, if you have a 1-5Volt signal and you can live with that, then you might be able to do some scaling once you have the data digitized in your system. Good old Ohm's law is hard to beat.

The Dark Knight · Oct 2, 2003

Use a signal conditioner / signal isolator. ActionPak, Phoenix Contact, etc....

Thomas · Oct 2, 2003

is the common common enough?

Is your signal common properly tied in. If the voltage is floating it sounds like a problem with the common reference point. Or perhaps even chassis ground on the PC...

Regards,

Thomas

GSI · Oct 2, 2003

Re: is the common common enough?

Thomas said:
Is your signal common properly tied in. If the voltage is floating it sounds like a problem with the common reference point. Or perhaps even chassis ground on the PC...

Regards,

Thomas

What do you mean tied in??. I've conected the Analigic ground from my PC board to the groud of the 4-20ma Transmiter, Isn't this rigth?

Thomas · Oct 2, 2003

It should be the alright that way.... but if you are still having problems you may want to use a signal isolator as suggested by Dark Knight. What kind of analog PC board are you using?

GSI · Oct 3, 2003

Thomas said:
It should be the alright that way.... but if you are still having problems you may want to use a signal isolator as suggested by Dark Knight. What kind of analog PC board are you using?

12Bit Silgle Ended AD.
The board is an from Advantech model PCL 711S

ArikBY · Oct 3, 2003

Who the manufacture og this unit?

Arik

fmichael · Oct 4, 2003

I agree with Randylud.

rogerhollingsworth · Oct 4, 2003

Hi

If you are using multiple signal power supplies in your system and have a number of single ended signals coming back to your PLC or what ever, you must have all the signal transformer commons tied together. Otherwise you will get some very strange signals doing some very strange things. If you are using a PLC then 1-5 volts should not be a problem, condition the signal to what you can use.

Roger

Help needed in 4-20ma to 0-5v conversion

Gsi

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Xion

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GSI

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Fritz_frederix

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randylud

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The Dark Knight

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Thomas

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GSI

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Thomas

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GSI

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ArikBY

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fmichael

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rogerhollingsworth

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