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Anonymous Poster

4-20ma

08/31/2008 2:22 PM

hi all

what is 4-20ma mean? is it fixed voltage supplied to the sensor and the change in sensor resistance will change the MA?

is it like this: sensor which i should give it fixed voltage to give me changable MA with the change of temprature or pressure ...etc?

will be great full for any info you could supply.

many thanks
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k.dhana
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Join Date: Aug 2008
Location: TN, India.
Posts: 35
Good Answers: 2
#1

Re: 4-20ma

08/31/2008 8:25 PM

Exactly, what you are thinking is correct. as a common 24 v dc applied at the transmitters cable, then a transducer changes its resistance according to the process variable. The 4-20 mA is measured at the suuply side.

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PWSlack
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United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
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#2

Re: 4-20ma

09/01/2008 10:30 AM

The principle is as follows:

  • the transmitter modulates its output between 4 and 20mA according to the process variable
  • all the measurement and display devices are wired in series with the transmitter output signal, up to a maximum resistance on the loop; the maximum permissible resistance varies with the power supply voltage
  • All the items in the loop, being in series, 'see' exactly the same current.
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Anonymous Poster
#3
In reply to #2

Re: 4-20ma

09/02/2008 12:28 AM

Hi,

And the application for 4-20mA is to send Signals for SCADA equipments.

Regards,

N.Suresh
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