I am currently working on a positioner and have basic knowledge of the functioning. My clarification are how the power for controller is drawn from the 4-20mA current loop.

I understand that the 4-20 mA current loop is being used for both signal as well as power.My clarification is

a. How the power is drawn from the current loop even though the current varies 4mA - 20 mA?

b. How the 4-20 mA current signal is converted into voltage signal?

 

lets simplify:
If you put a 5V Zener diode in series with the loop it would always have 5 V across it. And it you connected a load across the diode, as long as it draws less than 4 ma, it would see 5V as well.

The signal conversion can use a resistor. 4-20 ma across a 250 Ohm resistor gives 1-4 V.

In the real world it's fairly simple to craft a circuit that does both these things with active components. But, many PLC inputs are simply a voltage input with a 250 Ohm resistor. Loop powered devices are only a bit more clever.

Regards
cww

 

Currently we are supporting a Academic research for developing a PID algorithm for valve.

we wanted to know what are the main criteria we have to inhibit in our development for getting a accuracy and with no shootups

Our goal for the development is: manually control the inlet, outlet valve control though PWM on POT value

regards,
NS
skype id -emfocus.sivaa

 

Hi,

Implement Fuzzy logic or Neural Network in your algorithm.