Y to use 4 to 20ma instead of 0-10v
Answers were Sorted based on User's Feedback
Answer / ravinder
Because Voltage drops as resistance of cable conductor
increases but current will be same at any point of the
loop.4mA is called Live Zero,shows liveliness of the loop
when process variable is zero.
Is This Answer Correct ? | 27 Yes | 4 No |
Answer / jaldeep
For signal transmission we are using 4 to 20 mA, because of
following reasons.
1. If you are using 0 to 10 for long distance then
signal will be dropped due to cable resistance you will not
get correct feedback
2. 4 to 20 mA will give correct feedback even for
long distance. It will not drop according to cable
resistance. Only you have to keep loop impedance as per
your field instrument.
3. Open loop, you can easily detect in 4 to 20 mA.
You can program if mA is less than 4 then you can define it
as open loop.
4. For 0 to 10 v input if cable is open then it will
be difficult to identify that cable is open or input is 0
volt.
Is This Answer Correct ? | 17 Yes | 0 No |
Answer / himanshu
beacause total loop resistence is 250ohms.
so 24VDC supplied loop 1v corresponds to 4mA
and 5v corresponds to 20mA.
HART PC communicates to 1-5VDC only.
As explained in above answer 4mA is LIVE ZERo.
for 20mA reason is above 20mA current can be hazareous for
fieled.(fire).like HC and Refineries
thats why 20mA signal is used.
Is This Answer Correct ? | 9 Yes | 4 No |
Answer / ecxlsync
current signal is used because as explained
it will not change even the loop resistance is changed
due to transmission lines resistance. it is stated in the KCL that current entering in the circuit will be equal to the
current leaving no matter if the circuit resistance is changed.
Voltage signal is greatly affected by the circuit resistance.
long distance transmission has large wire resistance that
will cause large voltage drop.
Is This Answer Correct ? | 1 Yes | 0 No |
Answer / kalpesh
Because if we use 0-10V signal and if there is a break in
cable loop then it will show 0V which is the low level of
the measured signal but in reality it is a signal failure
from transmitter.
Is This Answer Correct ? | 4 Yes | 4 No |
I WANT SECURITY PAPER MILL, HOSHANGABAD TEST PAPER.KINDLY SEND TO MY MAIL ID
how pressure reduce through pressure control valve? suppose we have to reduce 20 kg pressure to 10 kg pressure , then what we do ? open the valve or close the valve , initially it is 20 % is upon ( for ur knowledge ).
I want to know about DDCMIS in detail ? please explain it. Also give name of reference books in which it is explained in detail in very simple manner.
How to calibrate electronic type level switch low?
Can please tell mi about SIOS, PRM, SERVER, and what is the diference between PIN LAN, PCS LAN,APC Server, and please send the Doc if possible for referance,mail id patil_amit17@yahoo.com
what is meant by nuclear collector?
as an instrumentation engineer which are the things we have to know / or we must have idea about that....
What FLOW METER generally used in Gas plant?
how to rectify the problem ,if we erected the DPT instrument wrongly of hp on lp side and lp on hp side?
How process line mpm calculation is done?
what is the difference between single and double compression cable gland
i have one tank of 500mm height, which is in under vacuum of 735 mmHg, I want measure level of the same using DPT , SO WHAT WILL BE THE URV & LRV, DENSITY OF THE TANK FLUID IS 0.95. is there necessary to fill the LP side with fluid.