Why we are using 4-20 mA as Analog signal transmission
other than 3 to 19 or 2 to 18 or 6 to 22 like wise ? What
is the reason behind using 4 & 20 mA? Can anyone give
proper technical reply ?
Answers were Sorted based on User's Feedback
the destination of any signal will be a Controller.
Take DCS, its input supply will be 1-5V.
from instruments, across a 250ohm resistor, the value will
reach DCS as desired 1-5V.
expl:
say 4ma is the output of transmitter.
V=IR,
V=4ma * 250 ohm
V= 1V,
say 20ma,
V=20ma*250ohm
V=5V.
Is This Answer Correct ? | 10 Yes | 1 No |
Answer / dhanabalan
It is where the linearity is maintained (4-20 mA Signal).
Is This Answer Correct ? | 9 Yes | 1 No |
Answer / t.naveen babu
The reasons for the 4-20 mA standard (and, before it, the
10-50 mA standard) have a lot to do with the original 3-15
psi/20-100 kPa air
signal. The origin of the suppressed or "live" zero in the
pneumatic system was two-fold - if you want to reduce a
passive pneumatic signal quickly, you need to maintain some
differential between the pressure and the "sink" - in this
case, atmospheric air. The basic characteristic of a
flapper-nozzle assembly also has a bit to do with it -
the "linear" range of the flapper pressure is about 3 - 15
psi for a 20 psi supply. Next question - why a 20psi
supply? Anyone else remember 6-30 psi equipment for
final actuators needing a bit more grunt??
The original electronic instruments were direct imitations
of the pneumatic systems with bellows replaced by magnet-
coil assemblies. The first I came across were used in a
geothermal power project (1958 vintage)where the pressure
at the power station was controlled by manipulating valves
in the steam field 1 1/2 miles or so away. The flapper-
nozzle was replaced by a
contact moving between positive and negative terminals - I
guess a bity of mains hum in the amplifier kept it
jittering. In the mid-70's Foxboro produced a range of
pressure transmitters using the magnetic principle which
used the same basic mechanism as their pneumatic equipment -
but the size of the coils made the assemblies a lot
bigger ...
Is This Answer Correct ? | 3 Yes | 3 No |
Answer / abhishek
this 3-15 psi later used in electronic signal as 4-20mA. 4mA
used as live Zero , & 20mA is current so
20mA*24V=480mWatt. this power if we increase any signal
wire can cause such type of arc that can cause Fire.
Is This Answer Correct ? | 4 Yes | 4 No |
Answer / ahmad
1- Any electronic circuit having its error, here Ico=3.85 ma(aprox=4 ma). that is why we do start from 4 ma.
2- it is also convertable to 1-5 volt, with precision resistance of 250 ohms.
Is This Answer Correct ? | 0 Yes | 0 No |
SOME OF YOUR QUESTIONS ARE NOT MAKING ANY SENSE SO TRY AND PUT IN A LITTLE BIT MORE EFFORT BEFORE YOU POST A QUESTION. WE WILL ONLY HELP THOSE WHO WE CAN SEE ARE TRYING TO HELP THEMSELVES.
what is hall effect?where it is use in power plant?
What is the meaning of slope in PH transmeter?
basic connection and principle of axial shift sensor n differential sensors in tubine describes n draw......
why to use 3 wire at RTD ? what's the reason for common wire ?
What are the type of bonnets in the control valves?
can we use a control valve without positioner
What is the potential contact / output??
1 Answers Vasava Engineering Private Limited,
wht is Zero Elevation and Zero Suppression?
what is positive displacement meter.
Need Intergraph softwares like SPI(INTOOLS),sp3d,PV ELITE, SP P&ID. CONTACT : logu.2211@gmail.com (8867825756)
what is positive feedback and negative feedback?