why we use 4-20 mA to do calibration of the instruments.why
we cant use 0-20 mA?
- 8 Answers
- 21500 Views
- Emerson, IEM, I also Faced
- E-Mail Answers
Answer Posted / zainuddin
1.We use 4-20mA is enough weak to ignite spark to prevent
fire. so these method is designed for safety.
2.There are several types to send the signal that
standardized in current(4-20mA), voltage(1-5v) and in
pneumatic (3-15psi 0r 0.2-1 bar). That means, u determine
how u were sending the signal to operate your process. but
here the best to sent the signal is in current(4-20mA).
3.24V is min. supply that transmitter to operate. if u put
supply more than that as long as not over the transmitter
supply range, u still get the same output 4-20mA, but the
voltage is changed. the change of voltage not effect your
process because you used current signal to operate your
process. Usually engineering will use current
rather than voltage because current not reduce at the long
distance to sent the signal. if u use voltage (1-5v) you
are facing with reducing signal(voltage) in certain
distance. however voltage that better to use is only 1-
5v(enough weak to ignite spark).
so here u should have a calculation how to produce signal
1-5V.(calculation can see at previous answers).
it more complicated than current not depend to supply(
either 24V 30V or 40V) & resistance( either 250ohm, 500ohm
or 700ohm) as long as you not reach over than transmitter
manufacturer range, because the transmitter is converter,
that convert standard signal to 4-20mA.
4.so why transmitter has supply range? this is because when
surging happens that the supply is going to transmitter
is still under transmitter supply range to reduce or
minimize transmitter going burned. so that means,
transmitter can operate at any supply voltage as long as
under supply range. it also can protect your process
immediately going shutdown.
| Is This Answer Correct ? | 16 Yes | 7 No |
Post New Answer View All Answers
I have a Control VAlve having size of 2 ".Only the known parameter is Pressure drop . Its 2 Kg. Then How to calculate control valve sizing means Cv.
for oil & gas industries which zone is normally preferred? why? give its example?
Q- Control problem are mainly classified in _____ types. a-)4 b-)3 c-)6 d-)nono of these Few of them i know is 1- regulator type problem (eg- Air conditioner) 2- tracking problem (eg missile trcking problem) 3- sybernatics 4- optimal control problem
what is Best Among SINK Or SOURCE Type Design In Digital Signal, Either Iput Or Output? WHY?Can any one..
what is the procedure of belt scale calibration?
what is the process to make control schematic ?
Why rdt and thermocouple both give different output .and one things more, how to generate ohm or mili volt plz mail me merajalam143545@yahoo.com
What types of Instrumentation Related Questions can an Interviewer ask in a Telephonic Interview ?
To become an Instrument DESIGN engineer, is there any softwares or training to become Instrument Design engineer, plz suggest me, Iam very much interested in designing.
how do we commission inergen system?
what is orfics working in main steam line. is it increase pressure, velocity of steam flow and dicrease steam flow rate. or any other
Define the terms Accuracy, precission, Spam, process tolerance while doing calibration of an instrument? Explaini with an example?
what is output of FOUNDATION FIELD BUS transmitter
how to work MIL contol valve posistioner ?
Hi my friends Is any one who can assist me in knowing the typical interview questions for system engineer at General Electric pty Ltd
