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.

What is Integral and Derivative control?

5 Answers   Qatar Petroleums,

---

Can any body tell me about SAP MAINTINANCE MODULE. WHAT IS its function and application. And study material Source about it. I shall be very thankful.

0 Answers  

---

Why we are using PLC instand of DCS in ESD System? can u explain any one?

2 Answers  

---

How EMF is generated in Thermocouple

3 Answers  

---

What is protocol ?

3 Answers  

---

why 8bit microprocessor referred as 2^16?

2 Answers  

---

What is the purpose of LO overhead tank in turbines.

1 Answers   ADMA OPCO,

---

What is the difference between precision and repeatability of any instrument. Why it is measured always in percentage

2 Answers  

---

1- Explain about HPM 2- What is the FSC and explain the configuration of FSC 3- explain the complete loop of vibration, how it works (field to control room) 4- What is the use of proxymitter? 5- During job your partner effected with H2S then what you have to do. 6- what type of gland packing uses when valve glind is leaking.

0 Answers  

---

why we use 24v dc in instrument rahter than 230vac????

4 Answers  

---

WHAT REASEAN USE TRANSMETER TWO WIRE & FOUR WIRE

5 Answers   Kentz,

---

what is Potential free contact? where it is used?

3 Answers   Engineers India Limited,

---