Answer / sam

The hardware electronic controller you are using has a 1-5
Volt input but the transmitter you use in the field, is a 4
to 20 mA transmitter. So in order for the hardware
controller to accept this input, you install a 250 Ohm
resistor on the controller's input which will convert it to
a 4 to 20mA input.

Weather you need a I/P converter on the control valve
depends on the positioner you will use. The hardware
electronic controller will give a 4 to 20mA signal to the
control valve, so if you want to use a full pneumatic
positioner on the valve, you need to install a I/P converter
and calibrate it for a 4 to 20mA input and a 20 to 100 Kpa
pressure output. You then need to calibrate the pneumatic
positioner for a 20 to 100 Kpa = 0 to 100% stroke.
If you want to use any other type of positioner a I/P will
not be necessary, since in electromechanical positioners the
I/P is already part of the positioner and obviously in SMART
positioners, the input to the positioner is 4 to 20 mA.
Good luck

Answer / vishal sharma

we need 250 ohm resistane because when we need to opearte
any loop eg.line pressure control loop er need to instal
pressure transmitter in line after control valve on that
time if we instal 250 ohm resistane in controller we dont
have to need another SMPS install for 24v signl to pressure
trasmitter for 2-wire system after install 250 ohm
resistance we recive 24v output trrough controller.

Answer / rohit

A electronics controller needs 4-20mA current and we have
230v or more voltage in industry so to maintain flow of
current 250 ohm resistance is vital.
I=V/R

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