Microcontroller based Digital Heater Control of a Catalytic Gas Sensor

Mikrosensoren, -aktoren und -systeme (IMSAS) Prof. Dr.-Ing. Walter Lang

Microcontroller based Digital Heater Control of a Catalytic Gas Sensor by Md. Eshrat E Alahi Matriculation Nr. 2279081 30th January,2012

Supervisors: Prof. Dr.-Ing. W. Lang Prof. Dr.-Ing. Michels Tutor

: Dipl.-Ing. Eike Brauns

Master Thesis for the partial fulfillment of the degree of Master of Science in Information and Automation Engineering (IAE)

Declaration

I certify that I have conducted this work on my own and no other supporting material has been used other than those which are listed as references.

_____________________________ Bremen,30th January,2012. Md. Eshrat E Alahi

i

ACKNOWLEDGEMENT First I am very grateful to Prof.Dr.-Ing W. Lang,Director ,IMSAS,University of Bremen for his patronage and then my tutor,Mr. Eike Brauns, who gave me constant support throughout the work. He assists me with lot of engineering advice and accompanied me with practical implementation of the work. In addition,I would like to thank many staffs from IMSAS who gave valuable support inside laboratory. Special thanks to Mr.Nils from ITEM (Institute für Theoretische Electrotechnik und Mikroelektronik)who gave me lot of advices during the coding. My special thanks to my parents who supported me throughout the work. I can not forget the support of a special person,Fahmida Wazed Tina, who inspired me all the time to finish the work successfully. Finally,I would like to thank God to keep me in good health and mental peace in all through this period.

ii

ABSTRACT A digital control system has been developed to control the temperature of a catalytic gas sensor. During the sensing of gases, such as ,hydrogen, a chemical reaction happens with the environmental air and the heater temperature crosses the accepted limit of the sensing element. So the delamination occurs and to prevent the sensor from this delamination , this control system has been developed where it keeps the temperature in a constant level. Operational amplifier has been used as impedance converter, subtractor to precisely control the voltage of the heater. A shunt resistor is used to measure the current which is flowing through the heater. The microcontroller is measuring the error of the actual and reference resistance, and proportional power according to the error is transferring through the PWM(Pulse Width Modulation) signal with a low pass filter and a npn transistor. A sine wave reference is generating with the same system. Whole code is written in C and the Software is IAR Embedded Workbench from Texus Instrument.

iii

CONTENTS 1. Introduction ......................................................................................................................................... 1 1.1 Gas Sensor ..................................................................................................................................... 1 1.2 Measurements ............................................................................................................................... 2 1.3 Task of this Project ....................................................................................................................... 3 1.4 Choosing of Digital control over Analog control ...................................................................... 4 2. Developing of the Prototype .............................................................................................................. 5 2.1 Design Hypothesis ......................................................................................................................... 6 2.2 Hardware Development ............................................................................................................... 6 2.2.1 Sensor’s Heater ....................................................................................................................... 7 2.2.2 Driver ...................................................................................................................................... 7 2.2.3 Shunt Resistor ........................................................................................................................ 7 2.2.4 Voltage Follower and Differentiator .................................................................................. 8 2.2.5 Microcontroller ..................................................................................................................... 8 2.2.6 Design Hypothesis ................................................................................................................ 8 2.2.7 Reason of Using PWM Signal ............................................................................................. 9 2.2.8 Reason of Using Proportional Controller ......................................................................... 11 2.3 Software Development .............................................................................................................. 11 3. Designed System .............................................................................................................................. 12 3.1 Heater .......................................................................................................................................... 12 3.2 Shunt resistor ............................................................................................................................... 12 3.3 Impedance Converter ................................................................................................................. 12 3.4 Subtract /Differential Amplifier ................................................................................................ 13 3.5 NPN Transistor and PWM Signal ............................................................................................. 14 3.6 Microcontroller ........................................................................................................................... 15 3.7 Design Procedure ........................................................................................................................ 17 3.8 PCB Design ................................................................................................................................. 17 3.9 Software Design ......................................................................................................................... 19 3.9.1 MSP430f149 ........................................................................................................................ 19 iv

3.9.2 CPU ....................................................................................................................................... 20 3.9.3 Operating modes .................................................................................................................. 21 3.9.4 Watchdog Timer .................................................................................................................. 21 3.9.5 Timer_A3 ............................................................................................................................ 22 3.9.6 ADC12………………………………………………………………………………. 24 3.10 Software flow technique .......................................................................................................... 28 3.11 Procedure of Calculation ......................................................................................................... 31 3.11.1 Constant temperature ....................................................................................................... 32 3.11.2 Sine Wave Generator ....................................................................................................... 36 4. Result Analysis ................................................................................................................................. 43 4.1 Constant Temperature ............................................................................................................... 43 4.2 Sine Wave ................................................................................................................................... 47 5. Conclusion ........................................................................................................................................ 50 6. Future Work ..................................................................................................................................... 50 7. References ............................................................................................................................... 51 Appendix ..........................................................................................................................................4

v

List of Figures 1

Catalytic gas sensor design with two separated membranes to decrease interaction

between reference and catalyst. Thermopiles measure temperature between substrate and membrane. Gold (Au) is used as adhesion layer for platinum nanoparticles……………………2

2

Measurement setup for catalytic gas sensor of different gas concentrations…….......3

3

Schematic of the heater control system……………………………………………….7

4

Block diagram of a temperature control algorithm…………………………………..9

5

The wave form of PWM signal……………………………………………………….10

6

Configuration of Impedance Converter………………………………………………13

7

Configuration of subtractor……………………………………………………….....14

8

Configuration of NPN Transistor…………………………………………………….14

9

Schematic of the Temperature Control System………………………………………15

10

Top and bottom layers in EAGLE……………………………………………………18

11

The Actual Circuit and surrounding system………………………………………….18

12

The Sensor’s holder and board……………………………………………………….19

13

Functional Block Diagram of MSP430f149………………………………………….20

14

Timer_A configuration……………………………………………………………….23

15

12 bit ADC configurations……………………………………………………………25

16

Image of MSP430F149 from Texus Instrument……………………………………..26

17

Image of the MSP-FET430UIF………………………………………………………26

18

Image of MSP-TS430PM64………………………………………………………….26

19

Software flow chart…………………………………………………………………..28

20

A sine wave with 5 points…………………………………………………………….37

21

Software flow of sine wave generation………………………………………………38

22

Heater Temperature(°C) vs Time(s) in 0.1% Hydrogen Gas concentration…………43

23

Heater Temperature(°C) vs Time(s) in different Hydrogen Gas concentration……44

24

Voltage Difference (mV) vs Time(s)………………………………………………..45

25

Heater temperature(°C) vs Time(s)………………………………………………….46 vi

26

Voltage Difference of thermopiles(mV) vs Time(s)………………………………..46

27

Heater Temperature(°C) vs Time(ms)………………………………………………47

28

Voltage difference of thermopiles(mV) vs Time(ms)……………………………47

29

Heater Voltage(V) vs Time(ms)……………………………………………………48

30

FFT analysis of Difference Voltage………………………………………………..48

List of Table

1

Terminal Functions………………………………………………………………..27

2

The list of used registers……………………………………………………………29

3

Gas Concentration and Temperature……………………………………………..45

vii

1. Introduction The embedded systems become very popular day by day to the scientific and engineering communities. It is encouraging to the engineers and the researchers to develop new applications. It plays a major role and brings a lot comfort to the consumer electronics and mass people.

The detection of hazardous gases has always been a difficult task, making the choice of an appropriate gas sensor is a difficult task for different applications. Depending on the applications, there are different sensing methods used for these gas sensors. Gas sensors have been used for several applications, such as environmental control, security at closed places and home, military applications, air -quality monitoring to automotive and industrial control.

In this work, a Catalytic Gas sensor is using for application which has been developed in IMSAS.This is a thermally based integrated sensor and like all the other thermally based integrated sensors, it is important to maintain the constant heating power for the proper operation. The developed sensor is used for hydrogen gas detection.

1.1 Gas Sensor Catalytic gas sensors are thermal devices to measure the combustible gas in the air. In principle, a catalytic layer is heated by an external heating source and the power of the heating source or temperature of the catalytic layer is measured. When certain amounts of combustible gases,e.g. Hydrogen, ethanol or isopropanol, are added to the environmental air, the gases will react with oxygen. The heat of reaction leads to a temperature change in the catalytic layer which can be measured directly or indirectly by a change of the heating power [1].

Structures are realized on two separate membranes for both catalyst and reference to get less interaction. A heater, placed over both membranes, heats the catalyst up to the operating temperature. Thermopiles are placed on both membranes (Fig. 1.). Reaction of hydrogen leads to higher temperatures at the catalytic layer. The difference can be interpreted as a gas 1

concentration. A selective heat controlling prevents the catalyst‟s temperature from increasing and damaging the catalyst. To protect the functional layers from influences of higher temperatures, the sensor is passivated with a layer of silicon nitride. A diffusion barrier avoids diffusion effects. Ligand capped nanoparticles, deposited by ink-jet-method, are more stable toward the given influences. A modified gold (Au) surface is used to obtain high adhesion of the nanoparticles.

Heater

Membrane with catalyst

Membrane with reference Thermopiles Adhesion Layer (Au) for Nanoparticles

Fig. 1: Catalytic gas sensor design with two separated membranes to decrease interaction between reference and catalyst. Thermopiles measure temperature between substrate and membrane. Gold (Au) is used as adhesion layer for platinum nanoparticles.

1.2 Measurements A measurement setup for developed catalytic gas sensor can be seen in Fig. 2.Lower heater temperatures lead to a reduced sensitivity, but it is observed that temperatures needs to be CCTL1 = OUTMOD_7; // CCR1 reset/set mode CCR1 =pwm_duty; TACTL = TASSEL_2 + MC_1; __delay_cycles(100); ADC_init(); while(1) { //////////////////////////////////////////////////////////////////////////////// //-------------------------------calculation------------------------------////// //////////////////////////////////////////////////////////////////////////////// resolution=VCC/4096; U_INPUT_H=( UH*resolution); U_INPUT_S=(US*resolution); U_H=(R1H/R3H)*U_INPUT_H; //voltage drop across heater U_S=(R1S/R3S)*U_INPUT_S; //voltage drop across shunt IH=U_S/RS; //Heater current RH=(U_H/IH); //actual Heater Resistance e=(RHT-RH); //variation of Heater Resistance y=(Kp*e); temp=pwm_duty_float+y; pwm_duty_float=temp; #define round(temp) ((temp)>=0?(long)((temp)+0.5):(long)((temp)-0.5)) pwm_duty=round(temp);

34

//////////////////////////////////////////////////////////////////////////////// //----------Updated PWM SIgnal-----------------------------------------------/// //////////////////////////////////////////////////////////////////////////////// CCTL1 = OUTMOD_7; // CCR1 reset/se CCR1 = pwm_duty ; //corrected duty cycle of PWM signal TACTL = TASSEL_2 + MC_1; } } void ADC_init(void) { //////////////////////////////////////////////////////////////////////////////// //-------------------initialization of the ADC---------------------------------//////////////////////////////////////////////////////////////////////////////// P6SEL = 0x0F; // Enable A/D channel inputs ADC12CTL0 = ADC12ON+MSC+SHT0_4+SHT1_4; // Turn on ADC12, extend sampling time // to avoid overflow of results,Reference Voltage=0V~3.3V ADC12CTL1 = ADC12SSEL_3+SHP+CONSEQ_3; // Use sampling timer,repeated sequence ADC12MCTL0 = INCH_0; ADC12MCTL1 = INCH_1+EOS; seq. ADC12IE = 0x01; ADC12IE = 0x02; ADC12CTL0 |= ENC; __delay_cycles(50000);

// ref+=AVcc, channel = A0 // ref+=AVcc, channel = A1, end

// Enable ADC12IFG.0 for channel 0 // Enable ADC12IFG.1 for channel 1 // Enable conversions

ADC12CTL0 |= ADC12SC; // Start conversion _BIS_SR(GIE); // Enable interrupts

}

35

//////////////////////////////////////////////////////////////////////////////// //-------------------- ADC12 Interrupt Service Routine-------------------------//////////////////////////////////////////////////////////////////////////////// #pragma vector=ADC12_VECTOR __interrupt void ADC12ISR (void) { US= ADC12MEM0; // Move US results, IFG is cleared UH= ADC12MEM1; // Move UH results, IFG is cleared //////////////////////////////////////////////////////////////////////////////// //-------Over Voltage indication of Microcontroller--------------------//////////// //////////////////////////////////////////////////////////////////////////////// if ( US < MAX_VOL_IN_DECIMAL ) P1OUT |= SAFETY_LED; // Set safety led ON else P1OUT &= ~SAFETY_LED; // Set LED off if ( US > MAX_VOL_IN_DECIMAL ) P1OUT |= ERROR_LED; else P1OUT &= ~ERROR_LED; }

// Set ERROR led ON

3.11.2 Sine Wave Generator The reference heater resistance is not constant rather it is a continuous sine function. Fig. 20 is showing a sine wave with 5 different points. The points are indicating at 0,

, ,

,

with

1,2,3,4 and 5 respectively. At point 1,3 and 5,the resistance is same when the temperature is 90°C. At point 2,the temperature is 100°C and at point 4 ,the temperature is 80°C.

36

2

1

3

5

4

Fig. 20: A sine wave with 5 points

In digital circuit, the response is always slow. The slowness of grabbing these 5 points makes the response to a continuous sinusoidal which has a good shape to analyze. It is also tried with more than 5 points. But it decreases the expected frequency. The software operation is same as discussed in constant temperature part. But some modification is needed which is shown in fig. 21.

Every time the reference resistance is changing and running the loop for 4 times. The loop running time depends on the shape of the sine wave So the response of heater voltage,voltage difference of thermopiles and temperature curve are also a sine shape. It does not need to change a lot in the coding part.

37

Begin

Stop watchdog Timer and Storing references

Initialize I/O Ports, Timer_A3 & Generating PWM Signal

Initialize A/D

Interrupt Service Routine for ADC12

Calculating the error for 90°C and updating PWM Duty cycle

Updating Channels

the

A/D

Calculating the error for 90°C and updating PWM Duty cycle Calculating the error for 90°C and updating PWM Duty cycle

Calculating the error for 100°C and updating PWM Duty cycle

Calculating the error for 80°C and updating PWM Duty cycle

Fig. 21: Software flow of sine wave generation 38

The codes are given below:

for(;;) { volatile unsigned int i=4,j=4,k=4,l=4,m=4;

//////////////////////////////////////////////////////////////////////////////// //-------------------------------calculation------------------------------////// ////////////////////////////////////////////////////////////////////////////////

//i=10; do {resolution=VCC/4096; U_INPUT_H=( UH*resolution); U_INPUT_S=(US*resolution); U_H=(R1H/R3H)*U_INPUT_H;

//voltage

drop across heater U_S=(R1S/R3S)*U_INPUT_S;

//voltage

drop across shunt IH=U_S/RS; RH=(U_H/IH);

//Heater current //actual Heater

Resistance e=(RHT_90-RH);

//variation of

Heater Resistance y=(Kp*e); temp=pwm_duty_float+y; pwm_duty_float=temp; #define round(temp) ((temp)>=0?(long)((temp)+0.5):(long)((temp)-0.5)) pwm_duty=round(temp); //////////////////////////////////////////////////////////////////////////////// //----------Updated PWM SIgnal-----------------------------------------------/// //////////////////////////////////////////////////////////////////////////////// CCTL1 = OUTMOD_7; reset/se

39

// CCR1

CCR1 = pwm_duty ;

//corrected duty

cycle of PWM signal TACTL = TASSEL_2 + MC_1; i--; } while(i!=0);

// j=10; do {resolution=VCC/4096; U_INPUT_H=( UH*resolution); U_INPUT_S=(US*resolution); U_H=(R1H/R3H)*U_INPUT_H;

//voltage

drop across heater U_S=(R1S/R3S)*U_INPUT_S;

//voltage

drop across shunt IH=U_S/RS; RH=(U_H/IH);

//Heater current //actual Heater

Resistance e=(RHT_100-RH);

//variation of

Heater Resistance y=(Kp*e); temp=pwm_duty_float+y; pwm_duty_float=temp; #define round(temp) ((temp)>=0?(long)((temp)+0.5):(long)((temp)-0.5)) pwm_duty=round(temp); //////////////////////////////////////////////////////////////////////////////// //----------Updated PWM SIgnal-----------------------------------------------/// //////////////////////////////////////////////////////////////////////////////// CCTL1 = OUTMOD_7;

// CCR1

reset/se CCR1 = pwm_duty ; cycle of PWM signal

//corrected duty 40

TACTL = TASSEL_2 + MC_1; j--;} while(j!=0);

// k=10; do {resolution=VCC/4096; U_INPUT_H=( UH*resolution); U_INPUT_S=(US*resolution); U_H=(R1H/R3H)*U_INPUT_H;

//voltage

drop across heater U_S=(R1S/R3S)*U_INPUT_S;

//voltage

drop across shunt IH=U_S/RS; RH=(U_H/IH);

//Heater current //actual Heater

Resistance e=(RHT_90-RH);

//variation of

Heater Resistance y=(Kp*e); temp=pwm_duty_float+y; pwm_duty_float=temp; #define round(temp) ((temp)>=0?(long)((temp)+0.5):(long)((temp)-0.5)) pwm_duty=round(temp); //////////////////////////////////////////////////////////////////////////////// //----------Updated PWM SIgnal-----------------------------------------------/// //////////////////////////////////////////////////////////////////////////////// CCTL1 = OUTMOD_7;

// CCR1

reset/set CCR1 = pwm_duty ;

//corrected duty

cycle of PWM signal TACTL = TASSEL_2 + MC_1; k--;} while(k!=0);

41

//l=10; do {resolution=VCC/4096; U_INPUT_H=( UH*resolution); U_INPUT_S=(US*resolution); U_H=(R1H/R3H)*U_INPUT_H;

//voltage

drop across heater U_S=(R1S/R3S)*U_INPUT_S;

//voltage

drop across shunt IH=U_S/RS; RH=(U_H/IH);

//Heater current //actual Heater

Resistance e=(RHT_80-RH);

//variation of

Heater Resistance y=(Kp*e); temp=pwm_duty_float+y; pwm_duty_float=temp; #define round(temp) ((temp)>=0?(long)((temp)+0.5):(long)((temp)-0.5)) pwm_duty=round(temp); //////////////////////////////////////////////////////////////////////////////// //----------Updated PWM SIgnal-----------------------------------------------/// //////////////////////////////////////////////////////////////////////////////// CCTL1 = OUTMOD_7;

// CCR1

reset/se CCR1 = pwm_duty ;

//corrected duty

cycle of PWM signal TACTL = TASSEL_2 + MC_1; l--;} while(l!=0); } 42

4. Result Analysis The meausrement is simulated in the lab where the hydrogen gas was flowing with different gas concentration. The measurement setup is same for all the experiment. Only the concentration of gas varied to get the simulated result. The data is collected through LABVIEW software. So that, it was possible to collect the measurement data precisely.

4.1 Constant Temperature In constant temperature mode,the temperature remains constant at different gas concentration. The whole simulation duration was 1 hour.After every 10 minutes , the concentration of gas has been increasing from 0% to 0.5%. Fig. 22 shows the heater temperature of 0.1% gas concentration. The average temperature is 97.45°C and most of the time the temperature remains at that constant level.

Fig. 22: Heater Temperature(°C) vs Time(s) in 0.1% Hydrogen Gas concentration

43

Fig. 2 shows the heater temperature in different gas concentration. When the gas concentration increase, the thermopiles get more gas to react. So temperature increases and if it crosses the maximum teximum, the delamination occurs. But from fig 23, it is shown that the control device keeps the temperature in certain limit. Gas concentration is also indicating in the same figure.

Fig. 23: Heater Temperature(°C) vs Time(s) in different Hydrogen Gas concentration

In the following table 3, the average temperature is showing where all are nearly constant. The code is written to keep the temperature at nearly 100°C, but from the table, it is seen that the temperature is approximately 97.5°C for different gas concentration. In our calculation part (3.11), it is already shown that the microcontroller is using the direct formula for subtractor from heater and shunt resistor. There is some delay occurring during the ADC conversion. When the loop is running inside a microcontroller, each instruction needs some execution time to perform. So considering these all disturbance, the output temperature has some error compare to the constant temperature which has been seen in table 3.

44

Table 3: Gas Concentration and Temperature

H2 Gas Concentration

Avg Temperature(°C)

0%

97.56

0.1%

97.45

0.2%

97.30

0.3%

97.40

0.4%

97.34

0.5%

97.30

Fig. 24: Voltage Difference (mV) vs Time(s) Fig. 24 shows the voltage difference of thermopiles in different gas concentration. When the concentration is 0.5%, the voltage difference of the thermopiles is higher than the other concentration.

In another simulation, the gas concentration has been changed as 0%, 0.5% and 1%. The measurement duration is only 1 minute for one concentration. Fig 25 shows the simulation result where the temperature is not stable as Fig 22.The average temperature is 97.28 °C which is very similar to the first simulation result. Only difference is that the gas flow duration is limited

45

compare with the other simulation. Fig 26 shows the voltage difference of thermopiles in different gas concentration. When the gas is increasing, the thermopiles difference is also increasing. The difference is increasing because the catalysts‟ temperature is increasing - this leads to a higher temperature which will be controlled to the volitional temperature by the controller. Because the controller is controlling the whole heaters mean value, the catalysts part of the heater is hotter than the reference thermopiles.

Fig 25 : Heater temperature(°C) vs Time(s) 1% Concentration O.5% Concentration O% Concentration

Fig. 26 : Voltage Difference of thermopiles(mV) vs Time(s) 46

4.2 Sine Wave The purpose of this simulation is to get a good sine wave to differentiate the different concentration of gas. Fig. 27 shows the heater temperature of different gas concentration. 0%,0.5% and 1% are indicating the gas concentration. The sine shapes are nice to analyze.

0.5%

1%

0%

Fig. 27.Heater Temperature(°C) vs Time(ms)

Fig. 28 shows voltage difference of thermopiles and the concentration and measurement time is same as fig. 27. These shapes are also very nice. This graph is main interest for FFT analysis. Another graph is showing in fig. 29 which is heater voltage vs time. 0.5% 1% 0%

Fig. 28: Voltage difference of thermopiles(mV) vs Time(ms)

47

Fig. 29: Heater Voltage(V) vs Time(ms)

1500

0%

1000

500

Amplitude

0

0

5

10

15

20

25

30

35

40

45

1000

0.5% 500

0

0

5

10

15

20

25

30

35

40

800

1%

600 400 200 0

0

5

10

15

20

25

30

35

Frequency (Hz)

Fig. 30: FFT analysis of Difference Voltage 48

Fig. 30 shows the FFT analysis of the different gas concentration. It is just shown the result after doing the FFT in MATLAB. It is clearly seen from the figure that frequency spectrum is different gas concentration. As it is discussed earlier, that the sine shape is different for different gas concentration. We are not interpreting any result from here. It will be helpful for the reader to understand about the generation of the sine wave with the same system.

49

5. Conclusion A temperature control of the system has been designed. The system is controlling the temperature by directly measuring the heater resistance. A simple proportional algorithm is used to avoid system delays. The sine wave generation is another successful implementation. Only software modification can shift the experiment from one to another.

6. Future Work The PID controller can be implemented without changing the hardware design. The system has unexpected delays which can be reduce in future. The system could be robust for any gas sensor in the same family if considering the temperature control. It needs to analyze the FFT and interpret the result for different gas concentration, gas quality or name of the gas.

50

7. References 1. H. Sturm, E. Brauns,T. Seemann, V. Zoellmer,W. Lang,“A Highly Sensitive Catalytic Gas sensor for Hydrozen Detection Based on Sputtered Nanoporous Platinum“, Proc. Eurosensors XXIV,September 5-8,2010,Linz,Austria 2. R. Casanova,J.L. Merino, A. Dieguez,S.A. Bota,J. Samitier, “A Mixed-Mode Temperature Control Circuit For Gas Sensors”, Circuits and Systems, 2004. ISCAS '04. Proceedings of the 2004 International Symposium on. 3. D.Ibrahim, Department of Computer Science, Near East University, Lefkosa, Turkey, “Teaching Digital Control using a low cost microcontroller based temperature control kit”, International Journal of Electrical Engineering Education 40/3 4. Data Sheet of MSP430F149,Texus Instrument. http://eleceng.dit.ie/frank/msp430/Datasheets/msp430f149.pdf

5. IAR Embedded Workbench Version 3+ for MSP430, User‟s Guide. http://www.ti.com/lit/ug/slau138x/slau138x.pdf

6. MSP430 Hardware Tools ,User‟s Guide. http://www.ti.com/lit/ug/slau278h/slau278h.pdf

7. Texus Instrument. http://www.ti.com/ 8. Precision Operational Amplifier’s data sheet. http://cds.linear.com/docs/Datasheet/1001fb.pdf

51

Appendix Measuring station where the LABVIEW data has been taken(below)-

Gas Flow Controller(below)

52

LABVIEW connector to collect the data from the device(below)

First prototype(below)

53