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Controller

02/07/2012 12:40 PM

why we need 250ohms for controller? why v need connection with in parralell?

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#1

Re: controller

02/07/2012 12:43 PM

It's needed to convert 4-20mA into 1-5V.

http://cr4.globalspec.com/thread/75689/1-5VDC-Signal

[Déjà vu alarm just went off.]

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#2
In reply to #1

Re: controller

02/07/2012 7:13 PM

y resistance need to connect with parralel? y series cnot be?

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#4
In reply to #2

Re: controller

02/07/2012 10:29 PM

Because of Ohm's Law.

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#6
In reply to #2

Re: controller

02/14/2023 7:39 AM

Because 4-20mA flowing into 250Ω gives 1-5V.

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#7
In reply to #2

Re: controller

03/14/2023 7:54 AM

...and if it were not there, then the input would be over-range all the time. That's why it is a <...need...>.

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#3

Re: Controller

02/07/2012 7:51 PM

Grammar error and misspellings are expected from those who write in English as a 2nd language, but texting is not professional and does not belong on the forum.

If it isn't worth your effort to write out your question in English, why do you think it worth my time to reply?

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#5

Re: Controller

02/08/2012 6:26 AM

This is how a loop-powered transmitter is typically wired to a controller, with the controller requiring a 1-5 volt signal:

The controller's analog-to-digital converter requires a voltage signal, and the transmitter regulates current, so the solution requires that the transmitter's current go through a 250 ohm resistor and then the controller senses the voltage dropped across that resistor.

If you need more information on this, see the chapter in this book called "Analog Electronic Instrumentation":

http://www.openbookproject.net/books/socratic/sinst/book/liii.pdf

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