Answer / priyabeet das

1st of all this is a live zero concept. now what is live zero? suppose the range is 0-20ma.so the Tx will indicate0ma as lower value.but when there is no i/p or there is some fault in process then also Tx will show 0ma as reading. so , seeing 0ma we cant decide whether it is for any i/p or not. that is why the lower LRV is chosen as 4ma.

Answer / suresh

This is Live zero concept. In case of airsupply failure or
Current loop failure the Control equipment (DCS/PLC) senses
below 3.5mA, considered as Loop Open circuit.

Answer / sudipta,iter

bcz 4 ma is the amount of current that occurs when there is
no input to the transmistter and coresponding pressure is
3psi.this is called as live zero concept.so by using thus
we can detect error easily .thats why we usese this value.

Answer / saravanan.m

FOR LIVE ZERO & ITS THE CORRECT LINERITY

Answer / oza paritosh m.

It is also useful for instrumentation guy to differentiate
between process zero and instrument zero.

Answer / abu maryam

For 4 mA & 3 Psi it is virtual zero to differ with actual zero (0 mA & 0 psi) to define if actual signal (mA & air )is found or not.
For 4: 20 mA
In my opinion the reason for use these values is most electronic cards work from 1: 5 volt and resistance (hart ) is 250 ohm
then V=I * R
R= 250 ohm and V= 1 volt so I= 1/250=,004 A= 4 mA
R= 250 ohm and V= 5 volt so I= 4/250=,02 A= 20 mA

Answer / dr

Why not more than 20ma??
More than 20ma continuously for 20Sec will make your heart
to malfunction.

Answer / prashant jadhav

If we look at Hazardous and power consumption point, 4-20 mA is the perfect range qualifying both points...Not able to produce large sparks and consumes least power...So it is made as a Standard signal..

Answer / rajesh j

4-20mA is because the least power consumption range with
linearity and to detect even when signal line opens

3-15psi is because of the minimum linear range for which
the control valve will respond to pneumatic signal

Answer / rafiq

these are standared things. its nothing but a i to p
converter. for 4 ma it will convert 3 psi and for 20 ma it
has 15 psi.

What is megering????

2 Answers  

How does temperature bath work? How does coil gets heated only by applying some current?

0 Answers   Process Control Technologies,

i want to make project on process control using plc.please give me idea about this.

2 Answers  

I am teja. I am studying Msc(tech) Electronics and Instrumentation (3years course) in Andhra university. But my course is not recognised by UGC and AICTE. Please tell me the job opportunities after this course. And i fineshed PLC course in IGIAT ,Vizag.Also complted my short term coure in SCADA, Seimans WinCC in ATI,Hyd.After Msc can i join Mtech for good job? or phd. How i can get good job in INdustrial Automation Side. Please give replay.Because this is my life matter.

0 Answers  

What is protocol ?

3 Answers  

Steve said that "An eddy-current probe works by passing an alternating current through a coil of wire and measuring the coil’s impedance" while we are using -24 Volt DC , So I am confused about DC and AC. Plz .

2 Answers   Jindal, Sadara Chemicals,

What is hp & mp seperator .& what is its working principle ?

0 Answers   Chevron,

How to Calibrate Vortex Flow transmitter in field

0 Answers  

What is the difference between a PLC (Programmable logic controller) and DCS (distributed control system)?

7 Answers  

which type of filter gives the constant phase characteristics?

0 Answers  

If range of 3-15 psi, a multiplying relay with a 1:2 ratio would give what output pressure for 6 psi input?

1 Answers  

what is difference between 1/2"NPT & M20 x 1.5 cable gland?

8 Answers