Details on P/I converter- pressure to current converter

P/I converter or Pneumatic pressure-to-Current is a transducer. It converts pressure input to a current in mili-ampere range. P/I converter is a common instrument in automation system. Like a temperature senor or level sensor, it transmit data to other source like PLC, instrument to control systems only here the input is pressure.

let’s say we have to control a valve that is to open it, shut it, or control the openings by percentage that is we may choose it to be open for 70% to control a fuel flow or steam flow. The valve is in a hazardous place so we cannot reach it; we can only observe this in SCDA (supervisory control and data acquisition).

To control first thing first, we have to know its initial position. So how we may know it- the percentage openings? This can be done by a P/I converter. If we place it in the vicinity of valve, it can easily monitor the pressure of working liquid or steam, then convert this to current in mili-amps, which can be easily feed to PLC’s to avail an output pressure, valve openings etc. and can be feed to any other devices like SCDA etc.

Calculate pressure and current value in P/I converter

So P/I converter converts pressure to current, say if we set 0 to 6 bar for 4-20 mili-amps current, in case of 0 bar pressure there will be 4 mili-amps current in the P/I converter output and for 6 bar there will be 20 mili-amp current. Plus for 3 bar, we have to calculate the associated pressure as follows {X/(20-4)} mili-amps={3/(6-0)}=.5*16=8; As 0 bar is equals to 4 mili-amp current, then the final result will be 4+x=4+8+12 mili-amps for 3 bar pressure.

Calibration of P/I converter transmitter