What is I to P converter? and why are they used?

 We all should've heard about control valves and the things they can do by now. To give an overview, they are just valves that open and close when the signal is given to them. Now that being said they can be operated in various ways such as,

  • Fully open
  • Fully closed
  • partial open/partial close( anywhere between 0 - 100 %)

Here is where the I to P converter plays the role. To control the movement of the valve, pressure has to be given. Now let's say we are controlling the valve using a PLC. The output signal of the PLC is voltage or current clearly they won't provide pressure to the valve. 

So, We are going to convert the current output from the analog output module of the PLC to Pressure. 
Hence, the name 'I' to 'P' converters.

Let us get into the working of the I to P converters,  It is a flapper nozzle mechanism that controls the output pressure signal ( 3 to 15 psi ) proportional to the input current signal ( 4 to 20 mA ). The output pressure will change according to the movement of the flapper.

The construction includes,

                A flapper nozzle arrangement to control the pressure and an electromagnet and two springs to stable the flapper.

We usually give the input current signal ( 4 to 20 mA ) and continuous air supply of 20 psi to the flapper nozzle arrangement. As we give the current signal, the electromagnet gets activated. 

The one end of the flapper is connected to the pivot so it can move up and down. The other end of the flapper is attached with the magnetic material and kept near the electromagnet.
If the current signal is 4 mA, the power of the electromagnet will be less and the gap between the flapper and the nozzle will be more, so some of the supplied pressure 20 psi will escape through that gap and the remaining pressure will come as output pressure ( 3 psi ).

If the current signal is high ( 20 mA ), the power of the electromagnet will be high, the flapper moves closer to the nozzle so the gap between the flapper and nozzle will be less. So less input pressure escapes through that gap and output pressure increases ( 20 mA ).