Interested to Buy Any Domain ? << Click Here >> for more details...
Answer Posted / marmikjani
Why we use 4-20mA signal?? Not start from 0-03mA? & 20mA??
· We can not use 0-20 mA signal cos then it becomes very difficult to distinguish between "zero" signal and "instrument fail" signal.
· Where as if we use 4-20 mA. its very easy like when we get 4mA means the signal is at low level and if it is below 4mA it shows us that the instrument is not working or it is failed
•That may have been one of those arbitrary decisions that is sometimes made when a standard is developed. In addition to providing a non-zero minimum to allow detecting signal loss, the minimum signal voltage provides for a margin between the minimum signal and any noise that might be present. Perhaps someone determined that 4ma was large enough to help with noise and thought that the numbers worked out conveniently. A 16 volt difference between min and max, difference = 4 X min, range of 20% to 100%, perhaps seemed easier to work with than 17 volts, 5.67 X min and 15% to 100% or 18V, 9 X & 10% to 100%
•This 20 mA signal is not enough to trigger a spark and therefore we can limit fire hazards in plant area
•As there is a leakage current so 0 to 3 MA, so we consider as 4-20MA. But in some cases we will find some transmitters 0-20MA which are more costly than 4-20mA
| Is This Answer Correct ? | 1 Yes | 0 No |
Post New Answer View All Answers
What is the formula of vabration sesore. i mean how to covert mils to volt plz share if any body knows very argent : my mai is merajalam143545@yahoo.com
What is difference between ESD and PLC please Explain me clearly.
how can we tune a PID. If it is by zeiger nichols method..please explain briefly with help of an example.
Please tell me details about Sox,Nox,SWAS analyser????
what is thermo coupler and how it works
i want to know the interview format fot gail, instrumentation. pls answer me in habib.sami1003@gmail.com
control panel design guidelines
i have been asked by QAFCO to appear for interview for thy post of Instrument Designer(INTOOLS)..i m engineering graduate with 5 years exp. in design engineering.Will this job profile suit me??i need all ur help n suggestions for thy same?
Explain the key components of control loop?
applications of plc in printing and packaging?
May I have a brief note above the voltage barriers? Whats is the purpose? Please mail me if you've operational details, mail id: rajkumar.diice@gmail.com
What is compensation for flow ? Why we use compensation ? What are the factors of different compensation ? We not use then what problems may happen ?
What is Alpha & Beta fctors related to Orifice Plate & its relation with flow?
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
protection relay watchdog contact operation?
