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
33374 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

Explain bernoulli’s theorem. State its application.

0 Answers

If i have 4 Allen Bradely make RS logix 5000 PLC and for viewing that we are using 4 RS view SCADA for 4 different packages. Now, I will want to view two packages on only one SCADA. Then how i will do it?

0 Answers Essar, Reliance,

What are the uses of orifice plates?

0 Answers

HOW WE MEASURE A DRUM LEVEL BY DP TRANSMITTER ? WHAT IS ITS FORMULA ?

2 Answers Thermax,

WHAT REASEAN USE TRANSMETER TWO WIRE & FOUR WIRE

5 Answers Kentz,

How many loops are there in the power plant? how many closed & open loop in the power plant ? Please give me the exact clarification?

2 Answers Lanco, Reliance,

What is the purpose of RS Networks

2 Answers

why is negative range given to measure the steam drum level

2 Answers Jindal,

What is the use of temperature compensation?

0 Answers

Why capacitive banks ar5e important?

5 Answers Siemens,

While preparing the graphic diagrams trend display, 3 types of trends are prepared by Yokogawa system vender. These are for process variable, manipulated variable & set point variable. Why these 3 trends are required? Explain the purpose of these 3 trends.

1 Answers

How it the difference between force balance system and dispalacement balance system?

0 Answers

For more Instrumentation Interview Questions Click Here