I have monitored my temperature sensor. In the attachment you can see the values.
My question is how precise are this measurements. The time interval is 1 second and there is a big change at some times. The measurements are done with the 5V output from my arduino uno and A0 is reading the values. The sensor is a TMP36.
The TMP36 is not very inaccurate, but once it is connected to an Arduino, any accuracy is gone.
It has to do with the reference voltage of the Arduino.
The Arduino uses the 5V as default reference. If that 5V is lowered, then the Arduino thinks that the temperature rises (because the output voltage of the TMP36 stays the same, but the reference of the Arduino got lower). Changes of a few degrees is common with a few RGB leds or something else that uses current and lowers the 5V.
Do as we all do. Test a TMP36, and it works. That was fun. Then move forward to something that is actually useable. For example the DS18B20.
A DS18B20 is ±0.5 °C accurate.
There are other sensors that are 0.1 °C accurate.
Koepel:
The TMP36 is not very inaccurate, but once it is connected to an Arduino, any accuracy is gone.
It has to do with the reference voltage of the Arduino.
The Arduino uses the 5V as default reference. If that 5V is lowered, then the Arduino thinks that the temperature rises (because the output voltage of the TMP36 stays the same, but the reference of the Arduino got lower). Changes of a few degrees is common with a few RGB leds or something else that uses current and lowers the 5V.Do as we all do. Test a TMP36, and it works. That was fun. Then move forward to something that is actually useable. For example the DS18B20.
A DS18B20 is ±0.5 °C accurate.There are other sensors that are 0.1 °C accurate.
Thanks for your explanation!
Your Temperature sensor:
"It provides a voltage output that is linearly proportional to the Celsius temperature. It also doesn't require any external calibration to provide typical accuracies of ±1°C at +25°C and ±2°C over the −40°C to +125°C temperature range".
This is the data sheet for your temperature sensor:
The TMP35/ TMP36/TMP37 do not require any external
calibration to provide typical accuracies of ±1°C at +25°C
and ±2°C over the −40°C to +125°C temperature range.
With that in mind you can read the specifications. We buy a temperature sensor based on its intended application. If I want to read 120 Degrees C to an uncertainty of +/- 1.0 Degree C then the TMP36 would be a poor choice because its specifications don't meet that uncertainty.
The only way to know actually how accurate a temperature sensor actually is would be to compare it to a known standard of accuracy which is much greater in accuracy than my unit under test. There is quite a bit involved in the process but you should get the idea. Anyway the only way to know the uncertainty of a temperature sensor is to compare it to a known.
Ron
Temp depends on sensor output voltage AND reference voltage of the A/D.
Default reference of an Arduino is it's supply, which is potentially unstable, which could make temps also unstable.
Better to use the more stable build-in reference of the Arduino.
With aTMP36, a 10-bit A/D, and default Aref, you get ~204 A/D values over a span of 100 degrees C.
Jumps of ~0.5C, so a display of 1 degree C is fine, but two or even one decimal place is wishful thinking.
Lower Aref to ~1volt, and you get ~1000 A/D values per 100 degrees C. One decimal place is now possible.
Try this sketch.
Power the TMP36 from the 3.3volt pin (cleaner), and don't share TMP36 ground (not the breadboard ground rail).
Leo..
// TMP36 temp
// works on 5volt and 3.3volt Arduinos
// connect TPM36 to 3.3volt A0 and not_shared ground
// calibrate temp by changing the last digit(s) of "0.1039"
const byte tempPin = A0;
float calibration = 0.1039;
float tempC; // Celcius
void setup() {
Serial.begin(9600);
analogReference(INTERNAL); // use internal 1.1volt Aref
}
void loop() {
tempC = (analogRead(tempPin) * calibration) - 50.0;
Serial.print("Temperature: ");
Serial.print(tempC, 1); // one decimal place is all you get
Serial.println(" Celcius");
delay(1000); // use a non-blocking delay when combined with other code
}
Your topic title says:
How accurate is my temperature sensor
The body of the topic says your actual:
FransdeHaan:
question is how precise are this measurements.
Accuracy and precision aren't the same thing.