int set = 20;  //(4-20mA) It can be mapped with tank level
int err, actual, pv;
bool a = LOW;
int valve = 9;
int disp=0;
int step = 5;  //(Minimum Step value-low error and slow response)

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
}

void loop() {
  // put your main code here, to run repeatedly:
  int sensor = analogRead(A0);
  actual = map(sensor, 50, 950, 4, 20);  //Input current sensor output


  err = set - actual;

  if (a == LOW) {
    if (pv > 0)  //empty
    {
      pv = err * 20 / 4 + 20;
    } else  //partially filled
    {
      pv = 20;  // Should be equal to 4mA
    }
    a = HIGH;
  }

  if (err == 0) { pv = pv; }
  if (err > 0) {
    pv = pv + step;  //(Minimum Step value-low error and slow response)
    if (pv > 255) {
      pv = 255;  //SHould be equal to 20mA
    }
  }
  if (err < 0) {
    pv = pv - step;  //(Minimum Step value-low error and slow response)
    if (pv < 25) { pv = 20; }
  }
  analogWrite(valve, pv);
  disp++;
  
  if (disp > 10) //Display rate disp*delay
  {
    Serial.println("Sensor value");
    Serial.println(sensor);
    Serial.println("Actual value");
    Serial.println(actual);
    Serial.println("Error value");
    Serial.println(err);
    Serial.println("PV value");
    Serial.println(pv);
    disp = 0;
  }


  delay(100); //Response delay
}