why we take 4 to 20 mA as out put of every instrument like
pressure transmittre ?why we cant take 0 to 20mA as output?
Answers were Sorted based on User's Feedback
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
|Is This Answer Correct ?||32 Yes||2 No|
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.
|Is This Answer Correct ?||24 Yes||0 No|
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.
|Is This Answer Correct ?||4 Yes||1 No|
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...
|Is This Answer Correct ?||3 Yes||0 No|
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
|Is This Answer Correct ?||1 Yes||1 No|
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.
|Is This Answer Correct ?||0 Yes||0 No|
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