University of Montenegro

Faculty of Electrical Engineering

Course: Industrial Electronics

Theme: Surface Temperature Measurement Using a Type K

Thermocouple

Mentor: Prof. dr Radovan Stojanović

Students:

Golubović Tina 41/19

Djurković Jovan 6/19 Vojinović Ivan 43/19

Date and Place: March 2020, Podgorica

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Contents Problem description ................................................................................................................................ 3

Connection scheme................................................................................................................................. 3

Program................................................................................................................................................... 5

Experimental Results and Diagrams ....................................................................................................... 8

Conclusion ............................................................................................................................................. 10

Literature .............................................................................................................................................. 10

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Problem description

This is a lab project, made in ADEG electronics lab at the University of Montenegro, with

mentoring of prof. dr. Radovan Stojanovic. The task of this project is to demonstrate

sampling process of a VERNIER type K thermocouple sensor at time interrupt levels with the

possibility of setting the START / STOP function and sampling frequency at 5Hz, 2Hz and

1Hz.In our case, this set of commands defines the sampling rate of the sensor. Samples can

be taken every 0.2sec, 0.5sec and 1sec.

Connection scheme

The Surface Temperature Sensor has an exposed thermistor that results in an extremely rapid

response time. This design allows for use in air and water. For temperature measurements in

harsher environments, a more durable probe is required. The sensor is connected on Arduino

Uno board through BAT-ELV Vernier, where SIG1 is connected to Arduino analog pin A0,

5V and GND is from Arduino board.

Figure 1 – Arduino Uno board Figure 2 – analog protoboard adapter

Figure 3 – Experimental setup

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Here are some specifications of the sensor:

Temperature range: –25 to 125°C (–13 to 257°F)

Maximum temperature that the sensor can tolerate without damage: 150°C

Typical Resolution:

0.08°C (–25 to 0°C)

0.03°C (0 to 40°C)

0.1°C (40 to 100°C)

0.25°C (100 to 125°C)

Temperature sensor: 20 kΩ NTC Thermistor

Accuracy: ±0.2°C at 0°C, ±0.5°C at 100°C

Response time (time for 90% change in reading)

50 seconds (in still air)

20 seconds (in moving air)

Probe dimensions: Probe length (handle plus body) 15.5 cm

Typical uses for the Surface Temperature Sensor include the following:

Skin temperature measurements

Human respiration studies

Specific heat experiments

Heat transfer experiments

Friction and energy studies

Figure 4 – Running the experiment

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Program

The code shown below uses arduino timer interrupts, which allows us to briefly pause the

normal sequence of events taking place in the loop() function at precisely timed intervals,

while we execute a separate set of commands. Once these commands are done,

the Arduino picks up again where it was in the loop(). We also used EEPROM memory

which stands for electrically erasable programmable read-only memory. It is a non-volatile

flash memory device, that is, stored information is retained when the power is removed. The

information saved in an EEPROM chip is not lost even when power is turned off.

Arduino code:

#include <EEPROM.h> // nedded to access EEPROM memory

#include <MATH.h> // nedded to calculate log

float voltage = 0;

double R = 0;

double Rlog = 0;

double T = 0;

const double K0 = 1.02119e-3;

const double K1 = 2.22468e-4;

const double K2 = 1.33342e-7;

char inChar = 'A';

int sensorValue = 0;

unsigned int Nt = 53036;

boolean reading = false;

unsigned int NtEeprom=0;

void setup()

Serial.begin(57600);

NtEeprom = ((((EEPROM.read(4))*10 + EEPROM.read(3))*10 +

EEPROM.read(2))*10 + EEPROM.read(1))*10 + EEPROM.read(0);

Nt = NtEeprom;

noInterrupts(); // disable all interrupts

TCCR1A = 0;

TCCR1B = 0;

TCNT1 = Nt; // preload timer 65536-16MHz/256/5Hz

TCCR1B |= (1 << CS12); // 256 prescaler 64us

TIMSK1 |= (1 << TOIE1); // enable timer overflow interrupt

interrupts(); // enable all interrupts

void loop()

if(reading && inChar == 'a') //If A/D read

Serial.println(T); //Print value

reading = false; //enable A/D read again

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if(reading && inChar == 'b') //If A/D read

Nt = 53036; // T=0.2s

EEPROM.write(0, 6); // write 53036 in EEPROM

EEPROM.write(1, 3);

EEPROM.write(2, 0);

EEPROM.write(3, 3);

EEPROM.write(4, 5);

Serial.println(T); //Print value

Reading = false; //enable A/D read again

if(reading && inChar == 'c') //If A/D read

Nt = 34286; // T=0.5s

EEPROM.write(0, 6); // write 34286 in EEPROM

EEPROM.write(1, 8);

EEPROM.write(2, 2);

EEPROM.write(3, 4);

EEPROM.write(4, 3);

Serial.println(T); //Print value

reading = false; //enable A/D read again

if(reading && inChar == 'd') //If A/D read

Nt = 3036; // T = 1s

EEPROM.write(0, 6); // 3036 in EEPROM

EEPROM.write(1, 3);

EEPROM.write(2, 0);

EEPROM.write(3, 3);

EEPROM.write(4, 0);

Serial.println(T); //Print value

reading = false; //enable A/D read again

if(reading = false && inChar == 'e') //If A/D read

Serial.println(T); //Print value

reading = true; //enable A/D read again

void serialEvent()

while(Serial.available())

inChar = (char)Serial.read();

ISR(TIMER1_OVF_vect)

TCNT1 = Nt; // preload timer

sensorValue = analogRead(A0); //read A/D

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voltage = float(sensorValue)*5/1024;

R = (15000*voltage) / (5 - voltage);

Rlog = log(R);

T = 1/(K0 + K1*Rlog + K2*Rlog*Rlog*Rlog) - 273.15;

reading = true; //A/D read

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Experimental Results and Diagrams

This probe uses the 20 kΩ NTC Thermistor, which is a variable resistor. When the

temperature increases, the resistance decreases non-linearly. The best-fit approximation to

this nonlinear characteristic is the Steinhart-Hart equation. At 25°C, the resistance is

approximately 4.3% per °C. The interface measures the resistance value, R, at a particular

temperature and converts the resistance using the Steinhart-Hart equation:

T=[K0+K1(ln 1000R) + K2(ln 1000R)3]-1

–273.15,

Where T is temperature (°C), R is the measured resistance in kΩ, K0=1.02119×10-3

,

K1=2.22468×10-4

and K2=1.33342×10-7

. Our program performs this conversion and provides

readings in °C.

Figure 5 – Matlab plotter for thermistor function

Two experiments were done. First one is with ice water and the second with boiling water.

We have compared our results with results from software Logger Lite 1.9.4 from VERNIR

web site as a proof that our sensor is working correctly.

For the first experiment the Figure 6 shows results from Arduino Serial Plotter and Figure 7

shows corresponding measurement from Logger Lite software. Similar for the second

experiment, results are shown in Figure 8 and Figure 9.

As it can be seen, the sensor does not need to be calibrated, which indicates that our code is

valid and sensor does work correctly.

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Figure 6 – Arduino Serial Plotter results of ice water

Figure 7 – Software Logger Lite and Lab Quest results of ice water

Figure 8 – Arduino Serial Plotter results of boiling water

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Figure 9 – Software Logger Lite and Lab Quest results of boiling water

Conclusion

Surface temperature sensor is used for temperature measurements and it is useful in medicine,

industry and commercial purposes. The maximum allowed variation in accuracy is ±0.2°C at 0°C, ±0.5°C at 100°C.

As a software solution we used Arduino. For the code written above, the temperature changes

on the type K thermocouple can be seen in Arduino/Serial Monitor for specified entered

character which determines the speed of printed readings (sampling frequency), or releasing

and interrupting this series of samples. Graphic interpretation is obtained through

Arduino/Serial Plotter. For higher sampling frequency we get more detailed graph.

Literature 1. http://apeg.ac.me/nastava/VJEZBA3%20Timer%20interrupt.pdf

2. https://www.instructables.com/id/Arduino-Timer-Interrupts/

2. https://www.vernier.com/product/surface-temperature-sensor/

3. https://www.vernier.com/files/manuals/sts-bta/sts-bta.pdf