Answer / nisarg mehta

4-20ma response is linear and we can break it into several
groups e.g '4-20' is 16 means 0 = 4ma and full = 20 ma.
half of that is 8 and quater of that is 4 again half of
the quater is 2 and so on . so we can easily calculate all
the neccessary details relating to the signal supply ,...

now why we r not using the 4 -40 ma -- cause difference is
36 here so the quater part of it , is 4.5 and half of the
quater is 2.something so the calculation is complex in such
a case .... also it ll not shows linear responce....

Answer / jobby johnson

4-20ma and 3-15psi are the international standards following every where.clearly the range 0-4ma and 0 to 3psi are called live zero. hence we are not using it in signal transmission

y mainly 4-20ma. this is because all the electrical signals from a controller(electronic) should go to a final control element.most probably in process industries it will be a control valve, which accepts 3-15psi. so it is very easy to calibrate a 4-20ma current signal into 3-15psi with the help of i/p converter..moreover 4-20ma range possess good linearity

Answer / alfred t jose

4-20ma is the standard value,because any small changes
occurs we can simply identify when we use 4-20ma. if any
zero error occur we can identify it by using 4-20ma.
according to pneumatic 3-15psi is used.same reson for that.
when 4ma applied corresponding 3psi optain and 20ma is
applied then we get 15psi.

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