Value of an sensitive Analogsensor changes heavy with other power sup. than USB

Hi,

THAT'S IMPOSSIBLE BECAUSE THE ARDUINO CAN ONLY MEASURE VOLTAGE NOT RESISTANCE SO YOUR STATEMENT
MAKES NO SENSE WHATSOEVER

I plug in all 3 pins (Vcc,GND and Signal) in the Arduino, then I measure with my multimeter the resistance between the 2 Pins of the sensor and get 300 OHM its not impossible, its the truth.

When the signal pin is not connected I measure 1 MOHM what I think is not correct.(Vcc and GND are connected to the Arduino all the time but this cant be the problem or?)

When I take out the Vcc Pin and measure then with my multimeter , the resistance is 1 MOHM but maybe its influenced by the 1 MOHM resistor soldered to the sensor or the Arduino (which is still pluggerd in with GND and Signal)or the cables or the shield or something ?
Because I think the resistance with no load and no connection on the sensor was much higher then 1 MOHM .

You measured it because the ONLY WAY YOU CAN CONVERT THE VALUE MEASURED IS BY KNOWING THE RESISTANCE IN THE CIRCUIT. You are trying to measure a physical parameter. Your code has to convert the value measured in analog counts to the physical parameter units you are trying to measure. (torque)

Sure, but i have the suspicion that my measurement of the 1 MOHM resistance with no load is wrong!
It was much higher and all documentation says the same : resistance at no load 5-10 MOHM.

POST YOUR CODE

void setup() 
{
  // Start serial at 9600 baud
  Serial.begin(9600); 
}

    void loop() 
{
  // Read the input on analog pin 0:
  int sensorValue = analogRead(A0);
 
  
  // Print out the value you read:
  Serial.println(sensorValue);
  
  // Wait 100 milliseconds
  delay(100);
}

Thanks for your help.

Ralf