Experiences with novel developed secondary conductivity sensors within the German Calibration Service (DKD)

Transcription

1 Experiences with novel developed secondary conductivity sensors within the German Calibration Service (DKD) Ulrich Breuel 1, Barbara Werner 2, Petra Spitzer 3, Hans D. Jensen 4 1,2 Zentrum für Messen und Kalibrieren -ANALYTIK- GmbH, D Wolfen, Germany 3 4 Physikalisch-Technische Bundesanstalt, D Braunschweig, Germany Danish Institute of Fundamental Metrology, DK-2800 Kgs. Lyngby, Denmark PTB Braunschweig, September 13/

2 Agenda Introduction Measurement quantity Electrolytic Conductivity Metrological hierarchy for Electrolytic Conductivity New ZMK development in detail Measurement of conductance G Determination of the cell constant The measuring system Temperature measurement Cause and effect diagram Validation by means of intercomparisons Summary and acknowledgements 2

3 The ZMK group with the calibration laboratory -K ZMK GmbH Sachsen-Anhalt ZMK -ANALYTIKGmbH Electricity Pressure Mass Balances Torque Time/frequency * Temperature Humidity Gauge blocks Length equipment * Not accredited yet Greatest number of quantities within a calibration laboratory Ortsteil Wolfen P-D ChemiePark Bitterfeld-Wolfen Areal A; Filmstr. 7 D Bitterfeld-Wolfen Germany Viscosity Electrolytic conductivity ph Liquid density Volume (Pipettes ) Phone: +49 (3494) Fax: +49 (3494) info@zmk-wolfen.de 3

4 The German Calibration Service (DKD) Deutscher Kalibrierdienst The DKD comprises calibration laboratories in industrial enterprises, research institutes, technical authorities, inspection and testing institutes. They are accredited and supervised by the Accreditation Body of the DKD and calibrate measuring instruments and material measures in the range and scope of accreditation. Location of the ZMK Group Source: 4

5 Quantity electrolytic conductivity within the NMI s Principle: Measurement of resistances in two different positions realized by micropositioner system changing of center sections Source: Primary methods for the measurement of electrolytic conductivity; Accred. Qual. Assur (2003) 8:

6 Quantity electrolytic conductivity within the DKD Typical situation in the DKD Measurement with commercial instruments and devices using 2- and 4-pole cells (same level as the users in the industry) Disadvantages: Non-linearity Temperature compensation Measuring uncertainties are too high Dependence from the manufacturers 6

7 New standard cells by ZMK 7

8 Metrological hierarchy for electrolytic conductivity Primary cells (of the national metrological institutes ) Transfer standards: Certified reference solutions for electrolytic conductivity Reference standards (Standard cells) Realized in the DKD by the results of the development project Commercial measuring instruments and devices for electrolytic conductivity Calibration objects 8

9 New ZMK development in detail Temperature independence Direct traceability to primary cells Low measuring uncertainties Manufacturer independence 9

10 New standard cell Schematic image of a standard cell 10

11 Several types of cells needed?! Deinionized water (appr. 1 µs/cm) 1.3 µs/cm 15 µs/cm 5 µs/cm lowest value with available reference solution in the DKD before finishing the development project Drinking water (500 µs/cm) 100 µs/cm Rainwater (50 µs/cm) 1 ms/cm Seawater (50 ms/cm) 20 ms/cm Industrial wastewater (5 ms/cm) Source of conductivity values: Principles of measuring technique, WTW GmbH 11

12 Extended measuring range by several cells 4 mm 6 mm 60 mm 20 mm 60 mm Platinization Cell A 1.3 µs/cm Cell B 15 µs/cm Cell E 100 µs/cm Cell C 1 ms/cm Cell D 20 ms/cm Measuring Range 12

13 Standard cells 5 standard cells for different ranges of electrolytic conductivity available (identified with letters A to E) D A 4 mm 60 mm 13

14 Measurement of conductance G Y = G + j B (1) Complex conductance Y in S Imaginary part not used Susceptance B in S Real part needed for determination of electrolytic conductivity Conductance G in S G = 1 / R (2) Ohmic resistance R in Ω 14

15 Example of G at different frequencies The conductance as a function of the reciprocal frequency Frequency range 0.5 to 5 khz 5,87 5,86 y = x R2 = ,85 G in ms 5,84 5,83 5,82 5,81 5,80 5,79 5,78 5,77 5,76 0,0000 0,0005 0,0010 0,0015 0,0020 0,0025 1/f in KHz-1 15

16 Determination of the cell constant Example: determination of the cell constant of cell B K = 0,1743 cm-1 Frequency range 20 to 200 Hz 28,67 28,66 y = x R2 = ,65 G in µs 28,64 28,63 28,62 28,61 28,60 28,59 28,58 Reference solution 5 µs/cm (nominal value), Hamilton Bonaduz AG, lot no. WO , certified by DFM (C0316) 28,57 0,0000 0,0100 0,0200 0,0300 0,0400 0,0500 0,0600 1/f in KHz-1 16

17 Complete set-up for electrolytic conductivity determination 5 standard measuring cells LCR-meter (Agilent 4284A) Precision thermostatic bath (oil bath, Lauda Proline PV 36) Temperature measuring device (temperature sensor Pt25 and temperature indication instrument TTI-2) 17

18 Temperature measurement Spatial inhomogenity: 2 mk Time stability: Measuring electrodes of cell C and cell D 3 mk Temperature sensor: Calibrated at temperature fixed points Positions of the temperature sensors for the determination of spatial inhomogenity 18

19 Cause and effect diagram L CR-Meter Cell constant Conductivity reference cell Drift of the reference cell Conductance (LCR-Meter) Repeatability Conductance (LCR-Meter) Extrapolation Extrapolation Temperature device Temperature coefficient Electrolytic conductivity Bath homogenity CO2 Equilibrium Bath stability CO2 Sensitivity coefficient Thermometer Temperature coefficient Temperature device CO2 Suppression factor CO2 influence 19

20 Validation by means of intercomparisons Intercomparison on electrolytic conductivity 2007 (5 µs/cm) EUROMET Electrochemical Analysis WG Project 918; Study on the traceability of salinity measurements in seawater Intercomparison on electrolytic conductivity 2005 (5 µs/cm) 20

21 Summary Development of several standard cells with accommodation to defined measuring ranges is an improvement of the metrological traceability of electrolytic conductivity The aim supply of reference solutions in the range from 1.3 µs/cm to > 100 ms/cm is solved; national New metrological procedure is validated and active applied by ZMK 21

22 Acknowledgements We thank the Landesförderinstitut Sachsen-Anhalt (Germany) for the financial support of the development project. The authors would like to acknowledge Dr. Reinhard Lange and Mr. Frank Seifert from Sensortechnik Meinsberg GmbH for their suggestions for the development of the standard measuring cells. 22

23 Thank you for your attention! ZMK GmbH Sachsen-Anhalt ZMK -ANALYTIK- GmbH

24 References 1 P. Spitzer, U. Sudmeier, U., Electrolytic conductivity a new subject field at PTB PTB-report PTB-ThEx-15, PTB, Braunschweig, 2000, pp K.W. Pratt, W.F. Koch, Y.C. Wu, P.A. Berezansky, Molality-based primary standards of electrolytic conductivity, Pure App. Chem., vol. 73, no. 11, pp , R.H. Shreiner, R.H., K.W. Pratt, Standard reference materials: Primary standards and standard reference materials for electrolytic conductivity, National Institute of Standards and Technology Special Publication, 2004, pp Y.C. Wu, W.F. Koch, K.W. Pratt, Proposed new electrolytic conductivity primary standards for KCl solutions, J. Res. Natl. Stand. Technol., vol 96, pp , H.D. Jensen, J. Sørensen, Electrolytic conductivity at DFM results and experiences PTB-Bericht PTB-ThEx-15, Braunschweig, 2000, pp H.D. Jensen, C. Verdier, Towards an improved primary standard for electrolytic conductivity, presentation of the Danish Institute of Fundamental Metrology at the NCSLI conference H.D. Jensen, N.-E. Dam, DFM measurement capability: Electrolytic conductivity January 2005, DFMreport DFM-04-R81, Lyngby, 2005, pp K. Rommel, Leitfähigkeitsmessungen in Elektrolyten Die Wahl der richtigen Frequenz, off print from the Fachzeitschrift für Labortechnik vol. 12, Guide to the Expression of Uncertainty in Measurement (GUM), 1st edition 1993, revision and restrike print 1995, International Organization for Standardization, Genf 24