A WIRELESS PASSIVE SENSOR FOR TEMPERATURE COMPENSATED REMOTE PH MONITORING IEEE SENSORS JOURNAL VOLUME 13, NO.6, JUNE 2013 WEN-TSAI SUNG, YAO-CHI HSU Ching-Hong Chang 2013/06/10

Outline Introduction Sensor operation Design and Fabrication Results Conclusion Personal Remark 1

Introduction(1/4) Background 2 Monitor and control pH Environmental Food spoilage Structural health industrial Chemical processing Biomedical Monitoring and controlling pH is important in numerous fields.

3 Introduction(2/4) Sensor Background The most common type of pH sensor is the pH combination electrode, which generally consists of a sensing and a reference electrode. Temperature in Kelvin (absolute temperature) Universal gas constant (8.314J/Kmol) Standard cell potential difference at T. Moles of electrons transferred

Combination electrode pH sensors typically with wired electrical connection directly to a potentiometer or pH meter is not suitable in embedded monitoring applications. Then the wireless passive sensor can measurements with no direct connection, but accurate measurement of pH using electrode based passive sensors is affected by temperature. Therefore, the wireless passive sensor employed temperature compensation that could be avoided to calibrate for the temperature changes. 4 Introduction(3/4) Goal

5 Introduction(4/4) A WIRELESS PASSIVE SENSOR FOR TEMPERATURE COMPENSATED REMOTE PH MONITORING Authors present an integrated wireless passive pH and temperature sensor for temperature compensated remote pH monitoring system. The sensor consists of a passive RLC resonator whose resonant frequency and quality factor change with the pH and temperature of the solution, respectively. The sensor's resonant frequency and quality factor are detected by measuring in the impedance of an external interrogator coil coupled to the sensor inductor coil. The pH and temperature measured the solution for employing temperature compensation in pH measurement. So this sensor overcomes the pH measurement error due to temperature dependence of the electrodes.

6 SENSOR OPERATION(1/4) EQUIVALENT CIRCUIT DIAGRAM OF THE WIRELESS PASSIVE COMBINED PH AND TEMPERATURE SENSOR.

SENSOR OPERATION(2/4) CONCEPTUAL BLOCK DIAGRAM OF THE COMBINED WIRELESS PASSIVE PH AND TEMPERATURE SENSOR. 7 Fig1. Conceptual block diagram of the combined wireless passive pH and temperature sensor.

Fig2. Equivalent circuit diagram of the wireless passive combined pH and temperature sensor. 8 SENSOR OPERATION(3/4) EQUIVALENT CIRCUIT DIAGRAM OF THE WIRELESS PASSIVE COMBINED PH AND TEMPERATURE SENSOR. Sensor coil Interrogator coil interrogator-sensor inductive coupling factor pH combination electrode Voltage sensing circuit Thermistor The value of the thermistor decreases with increasing temperature.

Fig3.Equivalent circuit diagram of the wireless passive combined pH and temperature sensor. 9 SENSOR OPERATION(4/4) EQUIVALENT CIRCUIT DIAGRAM OF THE WIRELESS PASSIVE COMBINED PH AND TEMPERATURE SENSOR.

Design and Fabrication(1/3) pH Combination Electrode 10

Fig4.18 MHz wireless passive temperature and pH sensor. 11 Design and Fabrication(2/3) Sensor and Interrogator There are resonant frequency near 18 MHz for this sensor. Negative Temperature Coefficient

12 Design and Fabrication(3/3) Sensor and Interrogator 5 turns 5.1cm 1.2mm diameter

13 Results(1/16) calibration tests solutions of different pH

14 Results(2/16) monitor commercial pH-meter thermometer

Fig5. Potential difference of the pH combination electrode for different solution temperature. 15 Results(3/16) Calibration of pH Combination Electrode High Impedance Digital Multimeter

adding 16 Test solution Results(4/16) Response Time of pH Combination Electrode Less than 1s Accuracy

Results(5/16) Stability of pH Combination Electrode Fig7. Stability of the pH combination electrode in pH solution at a temperature. 2 Days Thermometer Over 54h centered pH combination electrode has high stability without frequent Calibration. 17

Fig8. Experimental setup with the wireless passive pH/temperature sensor. 18 Results(6/16) Calibration of pH Sensor 25 o C~55 o C step 5°C. Ten different pH solutions for different temperature Sensor parameter Remotely monitored

19 Results(7/16) Calibration of pH Sensor Fig9.Frequency response of the sensor at different operating conditions. Resonant Frequency Quality factor

Results(8/16) Quality Factor Q Fig10. Quality factor as a function of solution temperature for different pH solutions. solution1 T=20 o C pH=5 solution2 T=20 o C pH=7 solution3 T=30 o C pH=7 20

21 Results(9/16) Resonant Frequency Fig11. Resonant frequency versus quality factor for pH 2.2 (isothermal point) solution.

22 Results(10/16) Q-adjusted resonant frequency Fig12. Resonant frequency (adjusted for change) versus pH of the contact solution for different solution temperatures. Junction capacitance Q will change

Results(11/16) Q-adjusted resonant frequency Fig13. Resonant frequency (adjusted for Q change) versus pH of the contact solution (as measured by commercial meter) for different solution temperatures. Fixed T Intercept=19.18MHz oCoC0.6612kHz pH 23

Fig14. Response of the temperature compensated pH sensor and commercial pH-meter as a function of the solution temperature. Both temperature- compensated and noncompensated results are shown. Results(12/16) pH of a solution from the quality factor pH=9.68 C=25 o C Solution The pH 0.1 accuracy 24

Results(13/16) pH of a solution from the quality factor Repeatedly immersing the sensor’s electrodes and thermistor into solution. 9kHz 1.5 Correspond pH Deviation is 0.05pH Correspond temperature Deviation is 3.9 o C Fig15. Resonant frequency and quality factor of the sensor when exposed to repeated cycles of pH 4, 7, and 10 solutions. 25

Results(14/16) Effect of Interrogator-Sensor Separation Distance Contact solution pH =10.48C =24.8 o C Peak Value and Vrms Variation less than 8 kHz Variation of 1.32 TABLE I. VARIATION OF RESONANT FREQUENCY, QUALITY FACTOR AND SIGNAL-TO-NOISE RATIOWITH INTERROGATOR-SENSOR DISTANC. 26

Results(15/16) Effect of Embedding Media on Sensor Response Sensor and interrogator with distance, d=4 maximum deviation 0.02% 0.61% 2.63% TABLE II. Variation of resonant frequency and quality factor for different embeddingmedia and interferers. 27

Results(16/16) Wireless Milk Spoilage Monitoring Bacteria group Contact solution Fig16. Milk pH and temperature over time. The inset shows the compensated and uncompensated pH as temperature increases from 6°C to room temperature. Contain 2% milk (initially at 6 o C) With a few yogurt 4 Days pH deviation >0.35 The reason is temperature increasing The temperature compensation sensor versus commercial temperature compensated pH-meter with maximum deviation of 0.1 pH 28

CONCLUSION(1/1) 29

PERSONAL REMARK Although this study can detect the ph by remote but the range of measure seem too short to detect. This study proposed method does not compare with others. Finally I think that this study can apply in many field such as air, gas, solution et al. 30

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