198 lines
5.9 KiB
C++
198 lines
5.9 KiB
C++
/* Test program for reading of thermistor, thermocouple and LVDT.
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K-type thermocouple functions written by Arthur Jones using
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official NIST polynomial data from
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https://srdata.nist.gov/its90/download/type_k.tab */
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#include <math.h> /* needed for exp() and pow() */
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/* It is good practice to define things like pins used at the start
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so that you avoid hard-coded values (magic numbers) in code */
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#define TCpin A0
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#define ThermistorPin A1
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/* Similarly, define any constant values e.g. Vref, B, R0 here to avoid
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need for "magic numbers" in code */
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#define V_REF 5
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float adc_to_voltage(int n_adc);
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float kelvin_to_c(float k);
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float resistance_to_temperature(float r);
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float voltage_to_thermistor_resistance(float v);
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float voltage_to_erc(float v);
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void setup()
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{
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Serial.begin(9600);
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}
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void loop()
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{
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float e_rc, e_comp, thermistor_temp, thermocouple_temp;
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int thermistor_val, thermocouple_val;
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/* Put your code here to read ADCs and convert ADC voltages to
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temperatures */
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thermistor_val = analogRead(ThermistorPin);
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thermocouple_val = analogRead(TCpin);
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// Calculate thermistor temperature in degrees C ( Part b, i,ii,iii & v)
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thermistor_temp = kelvin_to_c(resistance_to_thermistor_temperature(voltage_to_thermistor_resistance(adc_to_voltage(thermistor_val))));
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// Calculate thermocouple temperature in degrees C ( Part c, i - iv)
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e_rc = 1000*voltage_to_erc(adc_to_voltage(thermocouple_val)); // convert to millivolts
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e_comp = NISTdegCtoMilliVoltsKtype(thermistor_temp); // eqn (6) lab prep sheet
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thermocouple_temp = NISTmilliVoltsToDegCKtype(e_rc + e_comp); // eqn (7) lab prep sheet
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/* Display results. Don't use printf or formatting etc., they don't work on the Arduino. Just use
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the serial print statements given here, inserting your own code as needed */
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Serial.print("Thermistor temperature (deg C): ");
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Serial.println(thermistor_temp);
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Serial.print("Thermocouple temperature with CJC (deg C): ");
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Serial.println(thermocouple_temp);
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Serial.println("\n");
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delay(1000);
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}
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/* Write a function to convert ADC value to
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voltage: put it here and use it in your code above*/
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float adc_to_voltage(int n_adc) {
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return (float)n_adc*V_REF/1024.0; // eqn (1) lab prep sheet
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}
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/* Write a function to convert degrees K to degrees C
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Call it from the main() function above */
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float kelvin_to_c(float k) {
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return k-273.15;
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}
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// Convert Resistance (Ohms) to Temperature (Kelvin) (for thermistor)
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float resistance_to_thermistor_temperature(float r) {
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// Define Thermistor constants
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float t_0 = 298.15; // Kelvin
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float r_0 = 10000; // Ohms
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float b = 3975; // Kelvin
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return 1.0 / ( (1.0/t_0) + (1.0/b)*log(r/r_0)); // eqn (3) lab prep sheet
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}
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// Convert Voltage (Volts) to Resistance (Ohms)
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float voltage_to_thermistor_resistance(float v) {
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float pull_down_resistance = 10; // kOhms
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float v_hi = 3.3; // Volts
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return 1000*((pull_down_resistance*v_hi/v)-10.0); // eqn (4) lab prep sheet
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}
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// Convert Voltage to E_RC
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float voltage_to_erc(float v) {
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return (v-0.35)/54.4; // eqn (5) lab prep sheet
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}
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/* Under no circumstances change any of the following code, it is fine as it is */
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float NISTdegCtoMilliVoltsKtype(float tempDegC)
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/* returns EMF in millivolts */
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{
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int i;
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float milliVolts = 0;
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if(tempDegC >= -170 && tempDegC < 0)
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{
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const float coeffs[11] =
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{
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0.000000000000E+00,
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0.394501280250E-01,
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0.236223735980E-04,
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-0.328589067840E-06,
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-0.499048287770E-08,
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-0.675090591730E-10,
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-0.574103274280E-12,
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-0.310888728940E-14,
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-0.104516093650E-16,
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-0.198892668780E-19,
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-0.163226974860E-22
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};
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for (i=0; i<=10; i++)
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{
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milliVolts += coeffs[i] * pow(tempDegC,i);
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}
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}
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else if(tempDegC >= 0 && tempDegC <= 1372)
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{
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const float coeffs[10] =
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{
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-0.176004136860E-01,
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0.389212049750E-01,
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0.185587700320E-04,
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-0.994575928740E-07,
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0.318409457190E-09,
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-0.560728448890E-12,
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0.560750590590E-15,
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-0.320207200030E-18,
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0.971511471520E-22,
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-0.121047212750E-25
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};
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const float a0 = 0.118597600000E+00;
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const float a1 = -0.118343200000E-03;
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const float a2 = 0.126968600000E+03;
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for (i=0; i<=9; i++)
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{
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milliVolts += coeffs[i] * pow(tempDegC,i);
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}
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milliVolts += a0*exp(a1*(tempDegC - a2)*(tempDegC - a2));
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}
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else
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{
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milliVolts = 99E9;
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}
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return milliVolts;
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}
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float NISTmilliVoltsToDegCKtype(float tcEMFmV)
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// returns temperature in deg C.
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{
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int i, j;
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float tempDegC = 0;
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const float coeffs[11][3] =
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{
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{0.0000000E+00, 0.000000E+00, -1.318058E+02},
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{2.5173462E+01, 2.508355E+01, 4.830222E+01},
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{-1.1662878E+00, 7.860106E-02, -1.646031E+00},
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{-1.0833638E+00, -2.503131E-01, 5.464731E-02},
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{-8.9773540E-01, 8.315270E-02, -9.650715E-04},
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{-3.7342377E-01, -1.228034E-02, 8.802193E-06},
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{-8.6632643E-02, 9.804036E-04, -3.110810E-08},
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{-1.0450598E-02, -4.413030E-05, 0.000000E+00},
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{-5.1920577E-04, 1.057734E-06, 0.000000E+00},
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{0.0000000E+00, -1.052755E-08, 0.000000E+00}
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};
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if(tcEMFmV >=-5.891 && tcEMFmV <=0 )
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{
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j=0;
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}
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else if (tcEMFmV > 0 && tcEMFmV <=20.644 )
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{
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j=1;
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}
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else if (tcEMFmV > 20.644 && tcEMFmV <=54.886 )
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{
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j=2;
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}
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else
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{
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return 99E9;
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}
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for (i=0; i<=9; i++)
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{
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tempDegC += coeffs[i][j] * pow(tcEMFmV,i);
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}
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return tempDegC;
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}
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