why can't we use 5-20mA standard or some other instead of 4- 20mA?

Categories >> Engineering >> Instrumentation
Suggest New Category

why can't we use 5-20mA standard or some other instead of 4-
20mA?

Question Posted / s chittibabu sidagam

6 Answers
15199 Views
Emerson, I also Faced
E-Mail Answers

Answers were Sorted based on User's Feedback

why can't we use 5-20mA standard or some other instead of 4- 20mA?..

Answer / mohammed abbas

4 - 20 ma is used because one resion is that control system
like DCS AND PLC will accept (1 - 5vdc)only for that resion
by connection 250 ohm resistand accross with ( 4 - 20 ma)
we can get ( 1 to 5 vdc) (1vdc=4ma and 5vdc=20ma) this is
as per ohms law ,V=IR
IF V=4ma*250ohm=1vdc
20ma*250ohm=5vdc
(4 - 20)ma is linear with(0 -100%) and the output will get
linear from 4ma,

Is This Answer Correct ?

37 Yes

2 No

why can't we use 5-20mA standard or some other instead of 4- 20mA?..

Answer / sivasankar

The base range of the electronic transmitter out put is 0
to 16 mA. but during measuring through a series DC volt
connection (24VDC)the negative reading could not be
justified either the result is wrong polarity or the actual
negative reading below Zero value. So international
accridation has decided to elevate the zero value from 0 mA
to 4mA and straight way increased span value also from 16mA
to 20mA.(as an equal increment in 5 step 0%,25%,50%,75% and
100% of out put). Generally the electronic sensor base
output reading trimmed with 2.99 to 3.22 mA from
manufacturer. if the sensor is in good condition it will
show the base reading. 5 to 20 mA reading is not accepted
in industry so far.

Is This Answer Correct ?

20 Yes

14 No

why can't we use 5-20mA standard or some other instead of 4- 20mA?..

Answer / selvam

Is This Answer Correct ?

3 Yes

0 No

why can't we use 5-20mA standard or some other instead of 4- 20mA?..

Answer / sutharani.a

The electronic instrument using only dc power supply. so
using the standed value of 4-20mA, because 0-16mA is the
standared deviation elctronic meters. 0 value is not
pricise value so zero insted of four and 16 insted of 20.so
we are use to 4-20mA normal.

Is This Answer Correct ?

2 Yes

2 No

why can't we use 5-20mA standard or some other instead of 4- 20mA?..

Answer / jay

4 - 20 ma is used because of Live Zero.

Is This Answer Correct ?

3 Yes

3 No

why can't we use 5-20mA standard or some other instead of 4- 20mA?..

Answer / naveed ahmad

due to linearity, we can't use 5-20ma because in case of 5-
20mA our 25%,50% and 75% 'll not linear.

Is This Answer Correct ?

0 Yes

2 No

Post New Answer

More Instrumentation Interview Questions

What safety precautions you will adopt to work on Steam service control valve?

1 Answers QAFCO,

In case of Transmitter's(e.g.Ultrasonic Flow meter ) we have an normal practise of selction of upstream and downstream distance such as (20D and 5D ).can anyone please let me know whow to calculate "D" ?? i guess it refers to pipe thickness is t right ?

2 Answers

What is the difference between PLC and DCS?

4 Answers Honeywell,

Isometric drawings are generated during _________________ phase of a project

0 Answers

Can a pneumatic control valve work without positioner?

4 Answers SMC,

How to derive IO Count (AI, AO, DI and DO ) from a Field instrument (FI) Bill of Quantities (BOQ) given by client.

1 Answers

What is loop checking ?

10 Answers Kharafi National, Petrofac, Samsung,

What is Span Error