in current transmitter why we use 4-20ma ???

Question Posted / ravi kumar

2 Answers
5548 Views
IMCO, IOCL, I also Faced
E-Mail Answers

Answers were Sorted based on User's Feedback

in current transmitter why we use 4-20ma ???..

Answer / kinjalkumar chauhan

1) because output is linear in that region.
2) if communication wire brokeup then we come to know that.

Is This Answer Correct ?

5 Yes

1 No

in current transmitter why we use 4-20ma ???..

Answer / carl_ellis

1) A current signal has the same current in all parts of the loop, unlike a voltage that drop voltage over distance, which provides reliability that a voltage signal does not.

2) A current signal is more resistant to noise pickup than a voltage signal is.

3) A live zero at 4mA allows for '2 wire operation', where the power for the loop uses the same two loop wires as the signal, a critically important feature for geographically dispersed industries like oil & gas, steel, paper and mining. 2 wire loop powered transmitters use about 3.5 or 3.6mA of current to operate the transmitter.

4) A live zero is a diagnostic detection of an open circuit

5) 4-20mA is a low enough current with limited energy that transmitters can be designed to operate intrinsically safe in hazardous areas with the appropriate barrier protection from faults in the safe area.

6) The DC current signal is suitable for superimposing a modulated FSK signal used by HART for digital communications that allow for configuration, troubleshooting, diagnostics or multivariable data transmission, all while retaining an analog primary variable

7) 4-20mA drives considerable sized loads at fairly low DC voltages, allowing for a relatively long distance signal path (1-2km depending on wire size). 20mA has a relatively low IR drop.

Is This Answer Correct ?

6 Yes

2 No

Post New Answer

More Instrumentation Interview Questions

Identify the electrical variable that is either directly or inferentially used by various instruments to determine the value of a measured variable.

4 Answers

Please asked me How calculate DCS controller memory.

0 Answers Yokogawa,

what is the calibration procedure for transweigh make weigh feeder?

0 Answers Anjani Cements,

Whether the DI, DOs shields can be connected with Analog Input Shield Earthpit?