Answer / vimal

Whether our instrument is in good condition or not, in order
to check that we are using 4ma as a low value. If we use 0
ma, We can't say that whether the problem is in instrument
or in supply panel.Normally, when we not give supply to the
instrument it will show 0 ma. for that, we use 4 ma as a low
value. Moreover we use 4 to 20 ma as a standard output
because to get linear graph. So, we prefer 4 to 20 ma
instead of 0 to 16 ma..

Answer / ninad gaikwad

Please give you attention below:

4 mA 0 %
8 mA 25 %
12 mA 50 %
16 mA 75 %
20 mA 100 %

at the time of no voltage (zero voltage) we get 0 mA
at the time of 24v dc supply we get 4 mA.
IF we keep the range starting from 0 mA we will get 0 mA at
the time of zero voltage & 24 V dc voltage supply which is
technically not good.
If your observation is too good that time you will
find that from above every gap between each other of 'mA'
& '%' the differrences are equally same.
see for mA : 0-4-8-12-16-20 (gap of 4 mA equally)
and see for % : 0-25-50-75-100 (gap of 25 % equally)
This things easily helpful to sort out the problems.

Therfore this STANDARDISATION is Universal.

Answer / faiyaz ahmad

4 to 20 mA is a analog signal and its continuous signal its allow to 1 to 5 volts in this signal because its drop of voltage its not drop of current that's why its called standard signal its electrical out put of the transmitter.
4 mA is zero
20 mA is hundred

Answer / farooq ahmad

Because we want to check the tx is damaged or not.If it
will be normal & no process variable applied then we can
get o/p 4mA...if it will damaged then o/p will not show 4
or near about..

Answer / sandeep varma

the instruments starts responding from 4mA

What is ALSPA 370 control system

1 Answers   DUBAL-Dubai Aluminium,

what is solenoid valve?

1 Answers  

i want to measure temp of hot sand(welding flux) in closed chamber(around 150 deg C).Which is better thermocouple or thermometer?

1 Answers  

which one is best profibus or RS485 for communication?

2 Answers   Honeywell,

Please explain the difference between instrument range and calibration range in terms of pressure transmitter? line design pressure: 93 bar operating pressure : 82 bar press Transmitter Range? calibration range ?

3 Answers   L&T,

I need circuit for RTD senser?

0 Answers  

what are the different types of terminal lugs used for wiring termination?

5 Answers   Yokogawa,

What is the input impedence of an OPAMP as an ideal device.

1 Answers   CCIE,

In case of Transmitter's(e.g.Ultrasonic Flow meter ) we have an normal practise of selction of upstream and downstream distance such as (20D and 5D ).can anyone please let me know whow to calculate "D" ?? i guess it refers to pipe thickness is t right ?

2 Answers  

open tank and close tank leavel transmiter about range and calibration

0 Answers  

what is the difference between cold loop and hot loop

2 Answers  

what does ip65 signify??what is its NEMA equivalent???

1 Answers