TCLab Temperature Sensor

Objective: Use the TMP36 sensor correlation for converting between voltage signal and temperature.

The two temperature sensors on the TCLab are TMP36GZ sensors that report an output voltage (mV) that is linearly proportional to temperature

$$T^oC = 0.1 \, mV-50$$

TMP36 sensor accuracy is `\pm 1^oC` at `25^oC` and `\pm 2^oC` over the range `-40^oC` to `150^oC`. The TMP36 is not a thermistor because it does not have a temperature sensitive resistor. The TMP36 uses the property of diodes that repeatedly change voltage with temperature. The sensor measures the small change and outputs an analog DC voltage between 0 and 1.75V.

  • What is the gain, zero, and span of the TMP36?
  • What mV signal corresponds to `25^oC`?
  • What mV signal corresponds `80^oC`?
  • What temperature corresponds to a `0.5V` signal?
  • What temperature corresponds to a `1.2V` signal?
  • Print the current temperature for `T_1` and `T_2` in Celsius and milliVolts.

Additional Information (Not Required)

The mV is read on the Arduino with a 10-bit Analog to Digital Converter (ADC). There are 210 discrete levels (DL) with a 10-bit ADC between 0 and 3300 mV. The Arduino reports a DL integer between 0 and 1023. This is converted to milliVolts with `mV=DL \frac{3300}{1024}`. The following is a code segment from the firmware (C code) that is loaded on the Arduino.

// Arduino code tclab.ino
const int pinT1   = 0;
const int pinT2   = 2;
float mV = 0.0;
float degC = 0.0;
for (int i = 0; i < n; i++) {
  mV = (float) analogRead(pinT1) * (3300.0/1024.0);
  degC = degC + (mV - 500.0)/10.0;
}
degC = degC / float(n);  
Serial.println(degC);
[$[Get Code]]

Temperature 1 (T1) is from pin 0 and temperature 2 (T2) is from pin 2 on the Arduino as shown in the instrumentation wiring schematic.

The temperature is read 10 times in rapid succession and then an average is reported over the serial interface. The temperature is reported over the serial (USB) connection when Python requests a value for T1.

import time
import tclab
lab = tclab.TCLab()
print(lab.T1)
lab.close()
[$[Get Code]]

Solution

def T(mV):
    return round(0.1*mV-50.0,1)

def mV(T):
    return round((T+50.0)*10.0,2)

print('mV signal at 25 degC: ' + str(mV(25)))
print('mV signal at 80 degC: ' + str(mV(80)))
print('T at 0.5V: ' + str(T(0.5*1000)))
print('T at 1.2V: ' + str(T(1.2*1000)))

print('Current temperature for T1 and T2 in Celsius and milliVolts')
import tclab
lab = tclab.TCLab()
T1 = lab.T1
T2 = lab.T2
T1mV = (T1+50.0)*10.0
T2mV = (T2+50.0)*10.0
print('T1: '+str(T1)+' degC')
print('T2: '+str(T2)+' degC')
print('T1: '+str(round(T1mV))+' mV')
print('T2: '+str(round(T2mV))+' mV')
lab.close()
[$[Get Code]]