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'[EE]: Looking for 4-20mA to digital converter'
2001\02\05@122002 by Jerome Knapp

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   I need to convert a 4-20mA signal to digital.  Does anyone know if a
 chip is available to do this?  If not, what is the best approach to take?
 Thanks,

--Jerome Knapp

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2001\02\05@123058 by Fred Bailey

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Generally the 4-20mA driver can tolerate an impedance up to about 1kohm. I use a
250 ohm resistor and get 1 to 5 volts from the current loop.  You can add a
divider network from V+ to V- to get 0-4 volts and then use an opamp to get 0-5
volts for the PIC input.

Best Regards, Fred

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2001\02\05@180501 by Olin Lathrop

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> Generally the 4-20mA driver can tolerate an impedance up to about 1kohm. I
use a
> 250 ohm resistor and get 1 to 5 volts from the current loop.  You can add
a
> divider network from V+ to V- to get 0-4 volts and then use an opamp to
get 0-5
> volts for the PIC input.

These current loops can usually go up to 20V for the whole loop.  Unless you
know for sure that you can tolerate 5V per device, I would use significantly
less than 250 ohms as the current sense resistor.  50 ohms still gives you a
minimum of 200mV, which is plenty for running into a comparator.


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Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, olinspamKILLspamembedinc.com, http://www.embedinc.com

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2001\02\05@180505 by Olin Lathrop

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>     I need to convert a 4-20mA signal to digital.  Does anyone know if a
>   chip is available to do this?  If not, what is the best approach to
take?
>   Thanks,

How about a small current sense resistor with a suitable comparator circuit.


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Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, EraseMEolinspam_OUTspamTakeThisOuTembedinc.com, http://www.embedinc.com

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2001\02\05@203736 by Spehro Pefhany

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At 03:17 PM 2/5/01 -0500, you wrote:

>How about a small current sense resistor with a suitable comparator circuit.

Or an op-amp to an A/D if you need more than on/off (one bit) digital.
You might need a R-R op-amp if the A/D is expecting 0-5V. And an analog
low-pass
preceding the A/D for anti aliasing and to keep spikes out.

Best regards,

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2001\02\06@062652 by Vasile Surducan

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On Mon, 5 Feb 2001, Olin Lathrop wrote:

> >     I need to convert a 4-20mA signal to digital.  Does anyone know if a
> >   chip is available to do this?  If not, what is the best approach to
> take?
> >   Thanks,
>
> How about a small current sense resistor with a suitable comparator circuit.
>
 Yapp! Or a cheap curent to frequency  converter using oldest 555 if you
haven't enough memory for trick's and computation.
Vasile

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2001\02\06@074248 by fernteix

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Hi

Perhaps you could search in Texas site for RCV420.
The output is 0-5V good to connect of any A/D or the A/D of one PIC.
Best Regards

Fernando


>    I need to convert a 4-20mA signal to digital.  Does anyone know if a
>  chip is available to do this?  If not, what is the best approach to take?
>  Thanks,
>
>--Jerome Knapp

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