canu tell me why 4-20 ma and why not this 3-25ma?please
give reason of this value.
Answers were Sorted based on User's Feedback
Answer / jose
Instruments have a nominal resistance of 250 ohms. With
that, the usual output of field instruments is 1-5 volts or
4-20 mA. If you put a 250 ohm resistor on a 1 volt output
the the result will be .004 amps or 4 mA. The same holds
true if you put a 250 ohm resistor accross a 5 volt output
you will get .020 amps or 20 mA.
Is This Answer Correct ? | 32 Yes | 9 No |
Answer / vijay
usually there exsist linear relationship between this range
when you plot pressuer verses current graph. so depending
on application we can select o/p as 4-20mA or 3-15 psig.
also
for long distance transmission 4-20mA is good
Is This Answer Correct ? | 11 Yes | 2 No |
Answer / rajesh mistry
1> Liner Scale
2> Live Zero as a electronics
3> Active signal for pneumatic equipment.
Is This Answer Correct ? | 8 Yes | 1 No |
Answer / karthik
The Electronic circuits employed in all Instruments require
atleast 3 mA for its actuation so the lowest range is
limited to 4mA & the rest as said by JOSE is exactly correct
Is This Answer Correct ? | 1 Yes | 1 No |
After observation of current functioning engineers finalized
that at 4-20ma the current is having linear and constant
properties. Below 3ma and above 25ma the current properties
are different.
Is This Answer Correct ? | 1 Yes | 2 No |
Answer / s
there are two reason live zero and other is linearity..
if we divide the 4-20ma in four part it will show more
linearity than 3-15ma
Is This Answer Correct ? | 0 Yes | 2 No |
for oil & gas industries which zone is normally preferred? why? give its example?
how to calibrate control valves & power cylinders & ultra sonic level transmitters
what are the following documents comes under loopchecking
What is the calibration procedure of Drum level transmitter if range is 0 to -400 mmh2o in lab?
how to change 4 wire rtd transmitter into a 3 wire rtd transmitter? as our transmitter is working for 4 wire rtd, what should do for working on 3 wire rtd transmitter
generally transmitter power supply having some range(12v to 35v) but the out put(4-20 mA) must same for given input.If we vary the power supply voltage then output mA also to be change according to V=IR. Is there any voltage regulator in the transmitter ?
how flame detectors sense the flame.
square root calculation for dp flow transmitter? give me a explanation with example
what is difference between wheatstone bridge, pirani gauge and strain gauge ??? explain its principle and working
what is the difference between AUTOMATION AND INSTRUMENTATION?
There are two chlorination tonners both are connected to two pressure swithes and the pressure switch is connected to SOV which operates the valve to changeover the tonner selection i.e if pressure one tonner goes low the other tonner should come in line if it is inautomatic selection design a circuit using relays ?
Speedtronic system .