Answer / ritheesh kumar.p

why not take 0-20mA the reason for this is when 0 is
considered as minimum value then we will get 0 as output
when no signal is coming,when the instrument is not working
or there is any fault in it we get 0.inorder to ensure that
the instrument works we choose 4-20mA as standard output
value.4 corresponds to no signal from the instrument. 20mA
is the maximum value because below 20mA we will be able to
avoid schocks and short circuits

Answer / vinoth s

If we use 0 to 20ma, then 0 will be the minimum value and 20
will be maximum value.. In case if there is any problem in
the transmitter or in the cables, we get the value 0 but we
think it as a minimum value..we cant able to know that
there is problem in transmitter.. In order to overcome these
constraints, we went for LIVE ZERO concept as 4ma.
0 ma will be consider as DEAD ZERO.

Answer / haridass (kwt)

Including the above answers the reason for selection of 4-
20mA for the transmitter signal is, the LINEARITY.

From 0-4mA the signal will not be much linear (in graph we
can come to know),

from 20+ mA is the indication to conclude that the
measuring signal is above to its range or loop fault.

Only from 4-20 the mA signal is with perfect slope.

Answer / guhan

AS PER OHMS LAW V=IR...WE R USING THE SIGNAL IN DCS 1 TO 5 VOLTAGE DC..SO WE KNOW THE RESISTANCE VALUE 250 OHMS...OK
VOLTAGE=1,2,3,4,5,V DC..RESISTANCE S 250 OHMS...FIRST STEP S VOL=1 V, R= 250, SO V=IR, 1=I*250,I=1VDC/250 OHMS...SO 1000MA/250 = 4 MA..( HERE 1 V DC S = 1000MA) ...SAME LIKE 2V S 8 MA,3 VOLS S 12 MA, 4 VOL 16 MA, 5 VOL 20 MA....THAT S WHY WE USE 4 TO 20 MA...

Answer / caarpus

ABOVE MENTION IS CORRECT ANSWER.AT SAME TIME NORMALLY WIRE
CAN GIVE 1 OR 2 mA WHEN CONNECT TO ANY SIGNALLING
CIRCUIT.WITHOUT ANY INPUT THEY WILL PRODUCE THE MILL VOLT IS
WRONG ONE.

Answer / dinesh regar

when a 0-20mA used therefore insturment is not working i am
not indetified.there insturment are faulty ya supply
problem not sure.
therefore we used the 4-20ma .when supply will coming &
insturment not working.

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