Why we use 4 to 20 mA, (This is International Standard) instaed of this can we

Categories >> Engineering >> Instrumentation
Suggest New Category

Why we use 4 to 20 mA, (This is International Standard)
instaed of this can we use 4-16, or 4-24 or 3- 15 or any
other range

Question Posted / abi.inst

13 Answers
33517 Views
ONGC, I also Faced
E-Mail Answers

Answers were Sorted based on User's Feedback

Why we use 4 to 20 mA, (This is International Standard) instaed of this can we use 4-16, or 4-24 o..

Answer / nagarajan.p

First the question is why can't we use 3~15mA or other
range, here also we can check live zero and also we can go
step current like 3,6,9,12,15(i.e 0%,25%,50%,75%,100%).ok
The reason is the transmitter voltage is 24Vdc , here we
can load max of 600 ohms, for this voltage & load better
range is 4~20.
Why 4 ~ 20 is better since we can convert easily 1~5Vdc by
put 250 ohms.All the controllers and DCS , PLCs are operated
by the input of 1~5Vdc (external or Internal convertion)

Is This Answer Correct ?

47 Yes

5 No

Why we use 4 to 20 mA, (This is International Standard) instaed of this can we use 4-16, or 4-24 o..

Answer / nilesh upadhyay

There are basically 2 reasons of using 4-20ma
1. we can know whether the instrument is working properly
or not. we can distinguish "live zero" and "dead band". if
there is problem in instrument then also it is going to
show zero and if there is no supply then also it will show
zero so we can differentiate this two.
2. 4-20ma is linear with 3-15psi .

Nilesh Upadhyay...

Is This Answer Correct ?

23 Yes

12 No

Why we use 4 to 20 mA, (This is International Standard) instaed of this can we use 4-16, or 4-24 o..

Answer / richard marks

the 4mA zero is termed a "live zero". If 0mA was the zero
point there would be no way of telling if the transducer
was reading zero or in a fault condition eg. an open loop.
with a 4mA zero an open loop would drive the indicator eg.
a recorder into a minus figure (-25%). The 4 - 20mA scale
is to give a calibration points for 0-25-50-75-100%.
Because the start point is 4 the steps are 4mA.

Is This Answer Correct ?

14 Yes

6 No

Why we use 4 to 20 mA, (This is International Standard) instaed of this can we use 4-16, or 4-24 o..

Answer / samrat kar

Answers 5 & 6 are totally correct.. just adding another point.
20 mA as upper value is used to keep electrical components
intrinsically safe at hazardous area.

Is This Answer Correct ?

8 Yes

3 No

Why we use 4 to 20 mA, (This is International Standard) instaed of this can we use 4-16, or 4-24 o..

Answer / dhaval joshi

for any active ckt make it standard 1 volt dc

actually formula is 20-4= 16 then

16/1000*250=4 ma
32/1000*250=8 ma
48/1000*250=12 ma
64/1000*250=16 ma
80/1000*250=20 ma
by using 250 ohm resistance and standard 1000 ma it give
standard voltage.

Is This Answer Correct ?

5 Yes

3 No

Why we use 4 to 20 mA, (This is International Standard) instaed of this can we use 4-16, or 4-24 o..

Answer / rajesh.a

STANDARD VOLTAGE IS 1-5V DC,250OHM RESISTANCE

AT V=I*R
AT 1V=I*250OHM = 4MA
AT 5V=I*250 OHM = 20MA

SIMPLE CALCULATION

Is This Answer Correct ?

3 Yes

1 No

Why we use 4 to 20 mA, (This is International Standard) instaed of this can we use 4-16, or 4-24 o..

Answer / anup ramteke

Answers 5, 6 & 7 are correct. just want 2 add that why cant
we use 3 mA current as lower value. The reason is that there
are many small noise signals that can be picked up by our
signal wire which has the potential of providing upto 3 mA
current. So to be on the safe side to distinguish between
our proper field signal and the noise pick-ups we use 4 mA
as our lower value

Is This Answer Correct ?

6 Yes

5 No

Why we use 4 to 20 mA, (This is International Standard) instaed of this can we use 4-16, or 4-24 o..

Answer / gopi

the 6th answer is very pakka

Is This Answer Correct ?

1 Yes

2 No

Why we use 4 to 20 mA, (This is International Standard) instaed of this can we use 4-16, or 4-24 o..

Answer / abdus sattar mollah

ALL ANSWERS ARE WRONG.....
4-20 is a standard because transistor which is the basic building block of any transmitter has a linear output charecteristics in 4-20ma range.

Is This Answer Correct ?

4 Yes

8 No

Why we use 4 to 20 mA, (This is International Standard) instaed of this can we use 4-16, or 4-24 o..

Answer / mayur

ans. 5,6,7 & 8 r correct.only two points add.
1.in ancient time,niddle type galvanometers are used,only if
we pass 4mA current it shows deflection.therefore 4mA.
2.if 21mA current will pass through our body,man can goes
dead.therefore 20mA. & 4-20 mA can divided into 5 equal %.

Is This Answer Correct ?

4 Yes

12 No

Post New Answer

More Instrumentation Interview Questions

What is frequency factor in massflow meter? When using frequency output?

0 Answers PCMIL,

what is function of SCADA , and how is it work, explain with difination

0 Answers Bapco Bahrain Petroleum Company,

If an Instrument has 550 ohm internal resistance and the cable used for that instrument is 0.5 ohm per meter resistance. If the voltage is 12volt.How much length cable can be used?

2 Answers

Can anybody tell me how to select the size of earthing cable for DCS & PLC system.Please tell me any relevant answer here or mail it to me.

0 Answers Essar, Sail,

Working principle of vibration sensor?, Type of vibration sensor? , Can we use vertical instead of horizental or vice versa?, if not Reasons?

2 Answers

Please any one can provide latest aptitude test,technical test and interview questions for tata consulting engineering (TCE) i need it asap thanks in advance

0 Answers TCE,

WHAT IS AN INTERLOCK SYSTEM ?? HOW THEY WORKs ?? WHERE IT IS USED ??? MAINLY ??

2 Answers TATA, Tata Steel Limited,

why 4 to 20 ma used at 0 set

2 Answers Borouge, Yokogawa,

1. Pl. send details about different types Gas Analyser, like Co2, O2, SOX/NOX, etc. with calibration procedure. 2. How to calibrate H2S gas detector in field?

1 Answers HPCL, Napesco,

one rtd sensor which is connected at middle of distillation column where actual temp. is 100deg but when we tight this sensor at thermowell end it goes down to 90 deg & when remove from the thermowell(but sensor end dipped in well) showing actual reading, what is reason?

3 Answers

Tell about your IFFCO plant visit.

0 Answers L&T,

what is the imbustion control loop

0 Answers Manali Sugars,

For more Instrumentation Interview Questions Click Here