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,

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.

Answer / selvam

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,

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.

Answer / jay

4 - 20 ma is used because of Live Zero.

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.

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2 Answers