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current source
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Rich Grise
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3971

PostPosted: Fri Jul 21, 2006 12:39 am    Post subject: Re: current source Reply with quote

On Wed, 19 Jul 2006 01:55:57 -0400, Paul E. Schoen wrote:
Quote:
"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
On Tue, 18 Jul 2006 16:10:41 -0700, the renowned Don Lancaster

And the problem with a resistor is...?

Process control & measurement circuits are designed to provide a quite
accurate constant current output over a wide range of load resistances
(depending on compliance and supply voltage). Obviously, this can only
be accomplished with an active circuit in the transmitter.

Also, these are generally loop powered, which is why there is at least 4 mA
flowing for a zero input (to provide power). Thus, the active circuitry can
have a high impedance for the 0-20 VDC input, and it essentially changes
its loop impedance to draw the 4-20 mA. You can just add a battery or other
power supply at one point in the loop, and a meter at another point,
without concern for wire voltage drop (as long as it is within the
compliance specification).


I read somewhere once, that in a 4-20 mA system, 4 mA means "zero" (of
whatever you're measuring, which is up to the system), and 0 mA means
"fault", which the first thing that springs to mind is an open. Anyway,
when your system detects 0 mA, it's supposed to manage the fault condition.

But designing a current source with an offset shouldn't be too hard -
should we take the thread to .basics?

Thanks!
Rich
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Jim Thompson
electronics forum Guru


Joined: 06 May 2005
Posts: 5440

PostPosted: Wed Jul 19, 2006 9:05 pm    Post subject: Re: current source Reply with quote

On 19 Jul 2006 13:21:20 -0700, "naser" <naser.yousofi@gmail.com>
wrote:

Quote:
Thank you very much jim
i think this is that i wana it .

Jim Thompson wrote:
[snip]
From 5 years ago...

http://analog-innovations.com/SED/SpehroLoopProtect2.pdf


Enjoy!

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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naser
electronics forum beginner


Joined: 17 Jul 2006
Posts: 5

PostPosted: Wed Jul 19, 2006 8:21 pm    Post subject: Re: current source Reply with quote

Thank you very much jim
i think this is that i wana it .

Jim Thompson wrote:
Quote:
On 17 Jul 2006 13:33:11 -0700, "naser" <naser.yousofi@gmail.com
wrote:

HI
i want to desighn a current source to convert 0-20v/dc to 4-20ma.
and i tried to do this by current miror circuits but i had a problem
with unstable
the current ...
can any one guide me?
how i can do this work?
thank you

From 5 years ago...

http://analog-innovations.com/SED/SpehroLoopProtect2.pdf

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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naser
electronics forum beginner


Joined: 17 Jul 2006
Posts: 5

PostPosted: Wed Jul 19, 2006 3:57 pm    Post subject: Re: current source Reply with quote

oh yes
excuse me rality
i had a wrong in warting....
i want a 4-20mA current source .
redbelly wrote:
Quote:
naser wrote:
YES i must to have a circuit to convert a 0v- 20v DC input to
4-20mA output.
that is ok i want to have 0mA for 0 volt input and 4 mA for 20volt
input.
the accuraccy is not so iportant for example 19,20 or21 mA not so
different.

Naser

Now that you have given two different specs, can you clarify which one
you really want?

Is it 4 to 20 mA, or 0 to 4 mA???

Mark
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redbelly
electronics forum Guru Wannabe


Joined: 29 May 2005
Posts: 210

PostPosted: Wed Jul 19, 2006 3:18 pm    Post subject: Re: current source Reply with quote

naser wrote:
Quote:
YES i must to have a circuit to convert a 0v- 20v DC input to
4-20mA output.
that is ok i want to have 0mA for 0 volt input and 4 mA for 20volt
input.
the accuraccy is not so iportant for example 19,20 or21 mA not so
different.

Naser

Now that you have given two different specs, can you clarify which one
you really want?

Is it 4 to 20 mA, or 0 to 4 mA???

Mark
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Paul E. Schoen
electronics forum Guru Wannabe


Joined: 01 Jul 2005
Posts: 171

PostPosted: Wed Jul 19, 2006 5:55 am    Post subject: Re: current source Reply with quote

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:7n0rb2ds1kgdvn8lnmdjfbqsa6in3bi5d1@4ax.com...
Quote:
On Tue, 18 Jul 2006 16:10:41 -0700, the renowned Don Lancaster
don@tinaja.com> wrote:


And the problem with a resistor is...?

Process control & measurement circuits are designed to provide a quite
accurate constant current output over a wide range of load resistances
(depending on compliance and supply voltage). Obviously, this can only
be accomplished with an active circuit in the transmitter.



Also, these are generally loop powered, which is why there is at least 4 mA
flowing for a zero input (to provide power). Thus, the active circuitry can
have a high impedance for the 0-20 VDC input, and it essentially changes
its loop impedance to draw the 4-20 mA. You can just add a battery or other
power supply at one point in the loop, and a meter at another point,
without concern for wire voltage drop (as long as it is within the
compliance specification).

Paul
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Spehro Pefhany
electronics forum Guru


Joined: 01 May 2005
Posts: 2326

PostPosted: Wed Jul 19, 2006 12:54 am    Post subject: Re: current source Reply with quote

On Tue, 18 Jul 2006 16:10:41 -0700, the renowned Don Lancaster
<don@tinaja.com> wrote:


Quote:
And the problem with a resistor is...?

Process control & measurement circuits are designed to provide a quite
accurate constant current output over a wide range of load resistances
(depending on compliance and supply voltage). Obviously, this can only
be accomplished with an active circuit in the transmitter.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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Jim Thompson
electronics forum Guru


Joined: 06 May 2005
Posts: 5440

PostPosted: Wed Jul 19, 2006 12:13 am    Post subject: Re: current source Reply with quote

On 17 Jul 2006 13:33:11 -0700, "naser" <naser.yousofi@gmail.com>
wrote:

Quote:
HI
i want to desighn a current source to convert 0-20v/dc to 4-20ma.
and i tried to do this by current miror circuits but i had a problem
with unstable
the current ...
can any one guide me?
how i can do this work?
thank you

From 5 years ago...

http://analog-innovations.com/SED/SpehroLoopProtect2.pdf

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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Don Lancaster
electronics forum Guru


Joined: 30 Apr 2005
Posts: 416

PostPosted: Tue Jul 18, 2006 11:10 pm    Post subject: Re: current source Reply with quote

naser wrote:
Quote:
YES i must to have a circuit to convert a 0v- 20v DC input to
4-20mA output.
that is ok i want to have 0mA for 0 volt input and 4 mA for 20volt
input.
the accuraccy is not so iportant for example 19,20 or21 mA not so
different.

Naser






RST Engineering (jw) wrote:

Are you trying to say that at 0 volts input you will have 4 mA output and at
20 volts input you will have 20 mA output? To what accuracy?

Jim




"naser" <naser.yousofi@gmail.com> wrote in message
news:1153168391.045620.220130@35g2000cwc.googlegroups.com...

HI
i want to desighn a current source to convert 0-20v/dc to 4-20ma.
and i tried to do this by current miror circuits but i had a problem
with unstable
the current ...
can any one guide me?
how i can do this work?
thank you



And the problem with a resistor is...?



--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: don@tinaja.com

Please visit my GURU's LAIR web site at http://www.tinaja.com
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naser
electronics forum beginner


Joined: 17 Jul 2006
Posts: 5

PostPosted: Tue Jul 18, 2006 8:44 pm    Post subject: Re: current source Reply with quote

YES i must to have a circuit to convert a 0v- 20v DC input to
4-20mA output.
that is ok i want to have 0mA for 0 volt input and 4 mA for 20volt
input.
the accuraccy is not so iportant for example 19,20 or21 mA not so
different.

Naser






RST Engineering (jw) wrote:
Quote:
Are you trying to say that at 0 volts input you will have 4 mA output and at
20 volts input you will have 20 mA output? To what accuracy?

Jim




"naser" <naser.yousofi@gmail.com> wrote in message
news:1153168391.045620.220130@35g2000cwc.googlegroups.com...
HI
i want to desighn a current source to convert 0-20v/dc to 4-20ma.
and i tried to do this by current miror circuits but i had a problem
with unstable
the current ...
can any one guide me?
how i can do this work?
thank you
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RST Engineering (jw)
electronics forum Guru


Joined: 24 Mar 2005
Posts: 313

PostPosted: Mon Jul 17, 2006 9:10 pm    Post subject: Re: current source Reply with quote

Are you trying to say that at 0 volts input you will have 4 mA output and at
20 volts input you will have 20 mA output? To what accuracy?

Jim




"naser" <naser.yousofi@gmail.com> wrote in message
news:1153168391.045620.220130@35g2000cwc.googlegroups.com...
Quote:
HI
i want to desighn a current source to convert 0-20v/dc to 4-20ma.
and i tried to do this by current miror circuits but i had a problem
with unstable
the current ...
can any one guide me?
how i can do this work?
thank you
Back to top
martin griffith
electronics forum Guru


Joined: 06 May 2005
Posts: 1098

PostPosted: Mon Jul 17, 2006 8:52 pm    Post subject: Re: current source Reply with quote

On 17 Jul 2006 13:33:11 -0700, in sci.electronics.design "naser"
<naser.yousofi@gmail.com> wrote:

Quote:
HI
i want to desighn a current source to convert 0-20v/dc to 4-20ma.
and i tried to do this by current miror circuits but i had a problem
with unstable
the current ...
can any one guide me?
how i can do this work?
thank you
Put the circuit you are using on a website, in pdf, gif or jpg format

and tell us the web address


martin
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naser
electronics forum beginner


Joined: 17 Jul 2006
Posts: 5

PostPosted: Mon Jul 17, 2006 8:33 pm    Post subject: current source Reply with quote

HI
i want to desighn a current source to convert 0-20v/dc to 4-20ma.
and i tried to do this by current miror circuits but i had a problem
with unstable
the current ...
can any one guide me?
how i can do this work?
thank you
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