Problems with converting a String to a float

Processing Electronics (Arduino, etc.)
8

Arduino code:

//

//    FILE: DS18B20_two_sensors.ino
//  AUTHOR: Rob Tillaart
// VERSION: 0.0.1
// PURPOSE: demo with two sensors (on two pins)
//
// HISTORY:
// 0.0.1 = 2017-07-25 initial version

#include <OneWire.h>
#include <DS18B20.h>

// numbers chosen to match pin numbers..
#define ONE_WIRE_BUS2   2
#define ONE_WIRE_BUS3   3
#define ONE_WIRE_BUS4   4

OneWire oneWire2(ONE_WIRE_BUS2);
OneWire oneWire3(ONE_WIRE_BUS3);
OneWire oneWire4(ONE_WIRE_BUS4);

DS18B20 sen1(&oneWire2);
DS18B20 sen2(&oneWire3);
DS18B20 sen3(&oneWire4); 


void setup(void)
{
  Serial.begin(9600);
  Serial.println(__FILE__);
  Serial.print("DS18B20 Library version: ");
  Serial.println(DS18B20_LIB_VERSION);

  sen1.begin();
  sen2.begin();
  sen3.begin();

  // different resolution shows nicely the async behavior
  sen1.setResolution(11);
  sen2.setResolution(11);
  sen3.setResolution(11);

  sen1.requestTemperatures();
  sen2.requestTemperatures();
  sen3.requestTemperatures();
}


void loop(void)
{
  // print the temperature when available and request a new reading
  if (sen1.isConversionComplete())
  {
    //Serial.print(" , ");
    Serial.print("sen1");
    Serial.print(",");
    Serial.println(sen1.getTempC(),1);//
    //Serial.print(","); 
    sen1.requestTemperatures();
    delay(500);

  }
  
  if (sen2.isConversionComplete())
  {
    //Serial.print(",");
    Serial.print("sen2");
    Serial.print(",");
    Serial.println(sen2.getTempC(),1);
    sen2.requestTemperatures();
    //Serial.print(" , ");
    delay(500);
  }
  
  if (sen3.isConversionComplete())
  {
   //Serial.print(" , ");
   Serial.print("sen3");
   Serial.print(",");
   Serial.println(sen3.getTempC(),1);
   //Serial.print(" , ");
   sen3.requestTemperatures();
   delay(500);  
   
  }
  delay(1000);
}