Answer Posted / carl_ellis
@Marmkijani
The main reason for 4-20mA is that 2-wire field instruments need to use 3.5mA to power their own electronics in order to make a measurement and to control the regulated output.
4-20mA is also, as you pointed out, a range in which the energy in the circuit is low enough to qualify for Intrinsic Safety approval (when used installed properly with an approved DC power supply and I/S barrier).
The "live zero" is nice and convenient as a diagnostic for an open circuit fault, but it was not the main reason for 4-20mA; powering field instruments was the main reason.
| Is This Answer Correct ? | 0 Yes | 0 No |
Post New Answer View All Answers
How earthing can be checked????
HOW TO CHOOSE FREAQUENCY IN FMCW TYPE RADAR INSTRUMENTS. DESIGN BASIS OR DESIGN CALCULATONS ?
what is the imbustion control loop
what is use of communication wire in multipare cable(oil and gas field), why this communication wire not used in single pair cable?
how to check earthing,what is minum ohms for proper earthing
Why we are using reverse action in displacer types level transmitters on some Vessels?
What is cut off relay? And why use in PLC and DCS?
What is the use of double seated valve?
how to convert MA in to measuring values..and how mwasuring values into MA ?..plz ansr.i have intervw
why would you like to join our company
A PLC is programmed to drive three motors A, B and C as follows : After running motor A for an hour, motor B should get ON and motor A should get OFF. And after running motor B for an hour, motor C should get ON and motor B should get OFF. And after running motor C for an hour, motor A should get ON and motor C should get OFF. (That is, a cyclic repetition with time period one hour) Now, the second condition is: If any motor gone faulty and is tripped, the consecutive motor should get ON and the faulty (tripped) motor should be eliminated from cyclic repetition. The remaining two motors should bear the cyclic repetition of one hour each. (For healthy motor take logic as high and for tripped motor take logic as low) Now, the third condition is: When motor A load(Amps) exceeds 60% of its rated load, motor B should get ON in parallel to motor A. And when both motors A & B are running in parallel, and if their load exceeds 60% of their rated load, motor C should also start in parallel to A & B. [Here the cyclic repetition is eliminated, until their loads become normal(40%)] [Take logic high(1) for load at 60% and logic low(0) for load at 40%] Now draw a flow chart or a ladder diagram to fulfill the above condition.
What is profibus?
What is force balance principle? State some of its’ advantages.
What is the principle of capacitance type level transmitter?
describe flow nozzel principle?
