Answer / marmikjani

Why we use 4-20mA signal?? Not start from 0-03mA? & 20mA??





· We can not use 0-20 mA signal cos then it becomes very difficult to distinguish between "zero" signal and "instrument fail" signal.



· Where as if we use 4-20 mA. its very easy like when we get 4mA means the signal is at low level and if it is below 4mA it shows us that the instrument is not working or it is failed




•That may have been one of those arbitrary decisions that is sometimes made when a standard is developed. In addition to providing a non-zero minimum to allow detecting signal loss, the minimum signal voltage provides for a margin between the minimum signal and any noise that might be present. Perhaps someone determined that 4ma was large enough to help with noise and thought that the numbers worked out conveniently. A 16 volt difference between min and max, difference = 4 X min, range of 20% to 100%, perhaps seemed easier to work with than 17 volts, 5.67 X min and 15% to 100% or 18V, 9 X & 10% to 100%


•This 20 mA signal is not enough to trigger a spark and therefore we can limit fire hazards in plant area


•As there is a leakage current so 0 to 3 MA, so we consider as 4-20MA. But in some cases we will find some transmitters 0-20MA which are more costly than 4-20mA

Answer / osagie

The 4mA is called a live Zero.

It make it possible for fault detection.


OSAGIE.

what is the difference between 2 wire and 3 wire RTD- application wise,cost effectivity?

2 Answers  

---

how i can copy paste the program of smart transmitter to another smart one with hart communicator?

2 Answers   KOC,

---

What is the use of gauge?

0 Answers  

---

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

0 Answers  

---

State some of balance principle’ advantages?

0 Answers  

---

What happen if I install my pressure transmitter below the elevation of pipe in natural gas service?

0 Answers  

---

What is surge and how is it prevented.

1 Answers   ADMA OPCO,

---

what is the imbustion control loop

0 Answers   Manali Sugars,

---

There are two chlorination tonners both are connected to two pressure swithes and the pressure switch is connected to SOV which operates the valve to changeover the tonner selection i.e if pressure one tonner goes low the other tonner should come in line if it is inautomatic selection design a circuit using relays ?

0 Answers  

---

Speedtronic system .

0 Answers   CCIE,

---

how to tune siemens sipart electro pneumatic positioner..plz tel me..

0 Answers  

---

what is the process for double acting cylinder pneumatic for 32' v/v

0 Answers  

---