4 -20 mA converter

[Jurie]

I am looking for a 4 to 20 mA to 0 to 5 Volt converter circuit to connect industrial sensors to PIC micros.

I have some circuits but it requires negative supply which I do not have.

Any ideas will be appreciated.

Regards

Jurie

 

[asena]

Look around for ICs that are specialy made for that purpose.

I remember that Burr-Brown had plenty. And im shure there are many more.


If you dont want to use those chips, you can always use an ampop to convert the current to voltage.
That way, youre able to ADC the voltages.


asena

 

[Jurie]

Thanks Asena

I am using the XTR115 (ex Burr Brown now Texas) already to provide 4 - 20 mA loop supply to sensors but they no longer do a cost effective I/V. Like I said, my problem is with the dual supply opamp ciruits - I do not have a negative supply and cannot find single supply opamp examples.

Regards

Jurie

 

[asena]

Well, in that case i cant help much, for i dont have any circuits.

I design my circuits for the needs i have. THat way, each project is different.

If youre looking for single supply opamps, one is quad LM324. And im sure youll find plenty of more, single or dual.

I hope it helps

asena

 

[Nigel Goodwin]

I am using the XTR115 (ex Burr Brown now Texas) already to provide 4 - 20 mA loop supply to sensors but they no longer do a cost effective I/V. Like I said, my problem is with the dual supply opamp ciruits - I do not have a negative supply and cannot find single supply opamp examples.

You could use another opamp to generate a midpoint to give a simulated split supply, or use a 7660 IC to generate an actual spilt supply.

 

[stevez]

Note that 4 to 20 ma thru a 250 ohm resistor will give 1 to 5 volts drop.

 

[Russlk]

Here is a circuit. I know that I designed this circuit before, but can never remember where I stashed it.

The easiest way to adjust this circuit is to adjust R1 for a 5 volt swing at the output, then adjust R2 for zero at 4mA in or 5V at 20 mA in.

 

[Roff]

What supply voltage(s) do you have available? How about a reference voltage, such as for your A/D converter?

 

[Jurie]

Thanks Ron

I have 5 volt and 24 volt available.

Regards

Jurie

 

[Roff]

Thanks Ron

I have 5 volt and 24 volt available.

Regards

Jurie

Do you have a reference voltage?

 

[Jurie]

No Ron, I do not have a reference voltage.

Jurie

 

[laroche73]

4-20mA converter

Russlk's circuit should do the trick. To go along with the theme of this thread, here's another circuit that might be of interest. It performs the opposite function (converts an 0-1V input voltage to a 4-20mA current using a single supply).

**broken link removed**

 

[Sebi]

Just for opamp need + and -15V....

 

[Jurie]

I have now tested the attached circuit and it seems to work fine. Can you please tell me if there are some issues that I need to consider.

Regards

Jurie

 

[Russlk]

The LM324 output will not go all the way to ground unless there is a resistor to ground (about 1K).