Answer / g pravin

at 4-20ma with +24V power supply, no spark will be
generated.& 1 VDC at 4 mA of loop current and 5 VDC at 20
mA of loop current as per standard of analog i/o cards.
if we use 0 to 20ma instead of 4 to 20 ma then we can not
find actual position zero reference output, for example if
we have a motorized valve, it's full close at that time we
get 0ma (0%) reference and at fully open position we get
20ma (100%) reference, in this condition if power supply of
is off then we also get 0ma reference, so here in this kind
of
Condition we can't get actual result like that gate is
actually close or any other problems as per explanation of
above

Answer / venbha123

The 4 mA current has been selected for zero, so that we can distinguish the process zero condition from the supply failure condition. it is called the LIVE ZERO. If the process is zero then output will be 4 ma. If the instrument power is not available then it will give 0 ma. We can ensure the online  availability of the instrument for measurement.

The noise pick up in the signal cables may be in the order of say 3.5 mA and so 4 mA has been fixed as zero. As a convention the span to zero ratio is fixed as 5, so that the span output signal comes to 20 mA. (3 to 15 psi, 1 to 5 Volts,0.2 to 1.0 bar etc.)

For remote signal transmission the cureent signal is preferred to voltage because of the drop in the signal cable. The supply voltage is 24 V will make up for the loss in case of current signal transmission.  

Answer / shijith c

only at 4-20ma output, we are getting linearity. Also, at 4-20ma with +24V power supply, no spark will be generated. for these reasons only 4-20 ma is selected.

Hi, I am Newely Joined in Construction company instrument engineer? Any one can Plz tell me How can I advanced preparation for Releated Engineering and construction Documents?

0 Answers  

---

How to convert Differential pressure to flow in TPH

0 Answers   Chettinad, ELCO,

---

can we use flow transmitter instead of level transmitter?

7 Answers  

---

Why we used cage in control valve?

8 Answers  

---

What is meant by cold float of compressor shaft.

1 Answers   Sabic,

---

I am working in a process industry, in that there are several sections devided in the SCADA screens and individual sections may START independently. But sometimes i am facing problem i.e, if section 2 Stopped by the operator immediately Section 1 or Section 3 or Section 4 is getting stopped can you expain the reason behind this?

5 Answers  

---

Generally in which location ( JB or IO card or DCS) the thermocouple compensation is done.Also where they measure the atmosphere temp ( for compensation) in JB OR DCS panel? How they compensating that atmosphere temp? is any circuit for that ( like in rtd wheatstone bridge)?

3 Answers  

---

What denotes the 5/8mm in the 3300XL 5/8mm proximitor probe?

0 Answers  

---

DEAR SIR/MADAM MY NAME IS ARKAPROVA BHATTACHARYYA.I AM A FRESHER INSTRUMENTATION ENGINEER.CAN YOU PLEASE SEND SOME QUESTION PAPERS OF GRADUATE ENGINEER TRAINEE EXAM OF DVC(DAMODAR VALLY CORPORATION).MY EMAIL IDs ARE arka_aec@rediffmail.com.

0 Answers  

---

I have transmitter of range -20 to -5 kpa.if it is possible to zero trim with atmospheric pressure,means HP and lp having no pressure...what will get after zero trim and it is the right way.....plz give me reply ....

3 Answers   KOC,

---

What is the Difference between CNC and PLC

1 Answers  

---

I want to measure bidirectional steam flow? Kindly suggest me a suitable flow meter. steam is superheated at 41kg/cm2, 350°C

2 Answers  

---