This is less a question about PT1000 and more about the capabilities of TIVA-C ADC and correctness of my circuit.
Board: TIVA-C Launchpad TM4C123GXL
Sensor: PT1000 RTD, which has a resistance of 1000 Ohms at 0 degrees and increases by about 40 Ohms for a rise of 10 degrees, although not linearly and a lookup table is to be used to converting the resistance to temperature. Sensor is brand-new and is considered to be quite precise and durable with a stated accuracy of +/- 0.3 deg C and resolution of 0.1 Deg C.
Now, trying to solve it simply (more complicated solution here), I am using a voltage divider with a 120 Ohm resistance in series. I am using the 3.3V output from board across the ends of this series and reading the voltage across the PT1000 sensor leads into the ADC pin with common grounds.
Images of my setup at the end of the post.
My code (written in Energia)
// the setup routine runs once when you press reset:
void setup() {
// initialize serial communication at 9600 bits per second:
Serial.begin(9600); // msp430g2231 must use 4800
}
// the loop routine runs over and over again forever:
void loop() {
// read the input on analog pin A3:
int sensorValue = analogRead(A0);
// print out the value you read:
// The ADC Value
Serial.println(sensorValue);
// The voltage
Serial.println(sensorValue*3.3*1000/4096);
// The resistance of RTD
Serial.println((sensorValue*3.3/4096)*120/(3.3 - (sensorValue*3.3/4096)));
delay(1000); // delay in between reads for stability
}
And the output that I get, for small duration of time :
R = 1111.88 ADC = 3702 Voltage *1000 = 2982.57 ...
R = 1127.51 ADC = 3701 Voltage * 1000 = 2981.76 1124.35 3695 2976.93 1105.74 3701 2981.76 1124.35 3699
As can be seen the value from the ADC, which should for the 12-bit TIVA-C ADC vary between 0-4095 fluctuates quite a bit (for not so much change in temperature). The voltage was multiplied by 1000 so that the fluctuations become more apparent. As a result the resistance varies by around 20 ohms, resulting in an overall accuracy of around 5 Degrees C.
Is this is the best possible output accuracy using the current circuit ? What factors can be leading to these fluctuations?
My board is being powered from my dell-laptop USB port using the provided cable.
