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gauchosuizo
Joined: 14 Jul 2004
Posts: 28
Location: Switzerland
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 05 Oct 2004 7:48 How design a isolated current loop 0/4..20mA?? |
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hi guys
I'm looking for a current loop 0/4..20mA. I've a PIC with a PWM output and I want to need this to control the current loop. My idea is the following:
With a Filter (LPF) I can convert the PWM into a DC Voltage and with them I can drive a VCO. The generated Signal from VCO will be connected to a transformator. On the secondary side of this I get a voltage, wich I can rectifier and need as a current output. What do you think about this?
If you have an other Idea, it's welcome. Maybe has anyone a circuit? other a link?
Thank you very much and aloha
Pablo
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Mr_Programmer
Joined: 21 Feb 2002
Posts: 153
Helped: 4
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| 05 Oct 2004 10:38 Re: How design a isolated current loop 0/4..20mA?? |
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| I've seen a lot of application notes from Analog Devices concerning current loops. Just as a option for you to look for.
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gauchosuizo
Joined: 14 Jul 2004
Posts: 28
Location: Switzerland
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| 05 Oct 2004 10:41 Re: How design a isolated current loop 0/4..20mA?? |
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hi Mr_Programmer
thank you for your answer. I will check the homepage from AD.
Aloha Pablo
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koky
Joined: 12 May 2001
Posts: 157
Helped: 3
Location: Italy
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| 05 Oct 2004 10:50 Re: How design a isolated current loop 0/4..20mA?? |
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| see dac8512 data sheet, there are an example, you can change 8512 with dac
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gauchosuizo
Joined: 14 Jul 2004
Posts: 28
Location: Switzerland
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| 05 Oct 2004 10:58 Re: How design a isolated current loop 0/4..20mA?? |
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hi
I've checked the page from AD and I've found nothing. I don't know where you saw it. Please if you have some link about this, I will be very happy.
You must see: the current loop must be not expensive and as simply as possible.
Thanks
Pablo
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Mr_Programmer
Joined: 21 Feb 2002
Posts: 153
Helped: 4
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| 05 Oct 2004 11:33 Re: How design a isolated current loop 0/4..20mA?? |
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Pablo,
I'm sorry, I was wrong. I saw app notes in a Burr Brown Application book, but TI bought Burr Brown not AD. Again, I'm sorry.
I make a search at TI web site for "current loop" and got 500+ hits.
Under the first 25 hits is the following:
http://focus.ti.com/lit/an/sboa025/sboa025.pdf
In this app note you can also see the internals of a XTR1xx, I hope this will help you.
Regards...
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gauchosuizo
Joined: 14 Jul 2004
Posts: 28
Location: Switzerland
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| 05 Oct 2004 12:14 Re: How design a isolated current loop 0/4..20mA?? |
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hi Mr_Programmer
I know this application note and the IC line XTR... My problem is, that the current loop must be isolated. Now how can I isolate the current loop? With a transformator or maybe with optocouplers?
You see my problem?
Thanks and regards from Switzerland.
Pablo
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papyaki
Joined: 13 Apr 2002
Posts: 564
Helped: 19
Location: A small village somewhere in Gaul
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| 05 Oct 2004 13:00 Re: How design a isolated current loop 0/4..20mA?? |
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Hi,
Here are some links :
h**p://www.bb-europe.com/bb-euro/literature/curentlp.pdf
h**p://www.discovercircuits.com/C/cur-loop.htm
* = t
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Mr_Programmer
Joined: 21 Feb 2002
Posts: 153
Helped: 4
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| 05 Oct 2004 13:06 Re: How design a isolated current loop 0/4..20mA?? |
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@Pablo:
Well ... I see...
I found this circuit, it works with optocouplers:
http://www.elecdesign.com/Files/29/4950/Figure_01.gif
Regards from Germany
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koky
Joined: 12 May 2001
Posts: 157
Helped: 3
Location: Italy
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| 05 Oct 2004 13:14 Re: How design a isolated current loop 0/4..20mA?? |
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see at pag 17
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gauchosuizo
Joined: 14 Jul 2004
Posts: 28
Location: Switzerland
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| 05 Oct 2004 13:58 Re: How design a isolated current loop 0/4..20mA?? |
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hi guys
thanks for your answers.
@koky
I've checked the circuit. It's not what I'm looking for, you know? I don't want to need to much components on the isolated side. Therefor I thought at a transformator to isolate the current loop.
@Mr_Programmer
thanks again for your answer. I know this design. First I want to try with a transformator.
@papyaki
Thanks for the links. I will see it.
Regards and aloha
Pablo
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