Answer / ashok bhatti

Current does not have any drop during transimission through
electrical wires however the voltage drops as the lengh of
elecrical wire used for transmission increases.
Thats why mA is preffered over mV etc.

Answer / ibrahim s

mA Signal :-

1. Current measures remain same in any point of the signal
transmission line(no loss).
2. Less noise interference.

mV Signal:-

1. Voltage droup occurs(loss).
2. Noise interference is high.


So that mA signal is preferred over mV signal

Answer / saravanan.m

MA IS PREFFERED THERE IS NO DROP IN CURRENT.SO ONLY MA
IS PREFFERED

Answer / kush kumar

as we know voltage is noise sensitive ..so if transmission
is in the form of voltage then ll loose the original signal
nd at the reciever side ll not get accurate reading ,,but
in d form of current ..its not affected by noise

Answer / r santhosh kumar

most probably mA signal is preffered in signal transmission
because the voltage in the cable may be affected by the
sidewise power cables which are running with this cable
(in the same cable tray).

Answer / shan

mA is the ideal analog signal to be used because it has no
voltage drop. The same current will be recieved even in
100m transmission line.
Voltage signal is much accurate than mA but it is good only
for short range application because of its characteristics.
Prone to noise and voltage drop.

Answer / nikhil desai

NOISE REDUCTON AND NO CURRENT DROP FOR LONG TRANSMISSION LINE.

Answer / daher

THE ELECTRICITY SPECIFIED AS HIGH VOLTAGE-MEDIUM VOLTAGE-
LOW V.-HIGH CURRENT -LOW CURRENT.mA is used in control
signals $communication ,computers......,

Answer / deepak

ma signal is preffered because current signal does not drop
during transmission through sigal cable as comapred to
volatage signal but sometimes it gets affected by the stray
pickups that can e eliminated by connecting the shielding
at one end.

Answer / vipul joshi mfl

The voltage will drop at the length of the cable but in the
case of mA the current will not drop at the receiver end so
we preferred the current as a signal transmission and for
4-20 mA it is preferred cause the 4 mA is a signal we use as
a zero value if we use 0-12 or 0-20 mA then if any break in
cable was there, we cannot judge.

what is the difference between plant earth and instrument earth? and what type of cable( cable size ) used for both? and why ?

0 Answers  

A temperature sensor (RTD) connected via a temperature transmitter is adjusted to give an output of 4ma at 60 deg and 20 ma at 600 deg. This output (4-20ma) from the transmitter is connected to an IGBT-inverter to control a high speed (-12,000 to +12,000 RPM) DC motor. And in the inverter it is programmed as, for 4ma the motor speed will be -3,000 RPM and for 20ma the motor speed will be +10,000 RPM. The question is : If the motor speed is +5,500 (RPM), what will be the temperature? (-sign indicates that the motion is in reverse direction).

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1. What means HART communicator / where it is used / how to use it? 2. Types of Thermocouples and its temperature ranges / output of thermocouple? 3. Types of RTDs and its temperature ranges / output of RTD? 4. Idea about Temperature Transmitters? 5. Difference between Analog and Digital signals? 6. Difference between “2 wire” and “4 wire” system / instruments? 7. Difference between “Potential” and “Potential free” contact? 8. Types of flow meters / transmitters? 9. Types of level transmitters? 10. Difference between “Power/Control” cable and “Instrument” cable? 11. What means “shield” and “screen” in cables / how it is useful? 12. Draw a schematic of closed loop circuit of flow / level / pressure / temperature? 13. Idea about calibration of Control valve / positioned / I/P? 14. How to bypass a digital/analog signal in PLC/DCS by hardwire and software?

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